# Need help figuring what piston I need. (wallace calculator)



## RMTZ67 (Mar 12, 2011)

So I am having trouble figuring out how to use the comp calculator:confused. could use some help. I have a 67 gto original 400 has not been decked before and will be getting its 1st bore at 0.30. current 670 heads are 75cc.. if you need more info let me know. I did not know what the gasket bore is off hand. The machinist took the liberty of ordering some flat top pistons he mentioned in a prior conversation once I gave him the go ahead to do the bore.He believes it may have to be decked also removing #s off my block.The pistons below is what butler recommended with the info I gave them. And the book pic is what the machinist ordered. what do you guys think? he is aware of the 40-45 quench. by the way 068 cam.


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## PontiacJim (Dec 29, 2012)

RMTZ67 said:


> So I am having trouble figuring out how to use the comp calculator:confused. could use some help. I have a 67 gto original 400 has not been decked before and will be getting its 1st bore at 0.30. current 670 heads are 75cc.. if you need more info let me know. I did not know what the gasket bore is off hand. The machinist took the liberty of ordering some flat top pistons he mentioned in a prior conversation once I gave him the go ahead to do the bore.He believes it may have to be decked also removing #s off my block.The pistons below is what butler recommended with the info I gave them. And the book pic is what the machinist ordered. what do you guys think? he is aware of the 40-45 quench. by the way 068 cam.


Looks like the same type pistons - the "D" dish with 17 cc's. KB346 pistons, not the flat top at the top of the page - its for the 151 4-cyl engine.

Plugging in the numbers at the Wallace site, I come up with 9.17 compression and plugged in 4.30" for the head gasket. I also used the .041" head gasket thickness and 000 on the deck clearance as this would be the same as .041" quench distance. If you went for a .045" quench distance, compression on the calculator is then 9.09.

He may or may not measure for the .040" - .045" quench, but he also might. This is something you need to ask. Simply tell him you rather not cut the deck if possible and use the thinner Cometic head gaskets (which are as thin as .027" and also come in other thicknesses) if this would work instead. They can also be closer to the actual overbore of the cylinder which will add cc's compared to a larger bore size like the Felpro. Cometic gaskets are $100 each, but probably the best. So it may be cheaper to mill the deck and go with Felpro gaskets that come in the engine gasket rebuild kit. Again, this is something to discuss with your builder and voice your concerns and then listen to what he says - he may have a preference or none at all.

Here is what I have saved on head gaskets gathered from the web:

Fel-Pro introduced PN-8518 for the Pontiac V-8 during the 1970s. Containing a bore diameter of 4.3 inches and a preflattened thickness of .041 inch, it’s a stock-replacement design that’s compatible with most Pontiac blocks. an affordable choice for any stock rebuild, and even performance applications with a compression ratio up to 10.5:1, or slightly more.

A second Pontiac offering appeared in the Fel-Pro catalog during the early 1980s. PN-1016 is specially designed for high-performance applications with high compression and/or combustion pressure. Constructed of a Teflon-coated solid-steel core, it features stainlesssteel combustion armor and a wire ring combustion seal for maximum combustion containment. It contains a chamfered bore diameter or 4.3 inches and pre-compressed thickness of .039 inch. it’s a good choice for naturally aspirated engines with a maximum compression ratio of 12:1 and/ or mildly boosted applications.

Cometic is the only company that presently produces MLS cylinder head gaskets for the Pontiac V-8. Bore diameters range from 3.75 to more than 4.4 inches and standard compressed thickness measures .040 inch. Any other bore diameter and thickness from about .020 to .120 inch is available on a customorder basis. Suitable for stock rebuilds and max-performance applications.

Each .010-inch difference of head gasket thickness alters the static compression ratio by about .15:1.


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## bigD (Jul 21, 2016)

I would not use those "Hypercast" pistons under any circumstances. If they are used, you must have a really big top ring gap. There have been lots of wiped out engines because of using those pistons & a gap that was too small. 

Some guys use the cheaper SP L2262F forged pistons & have a dish machined into 'em. But if your budget will stand it, I'd recommend Auto Tec custom pistons. They can position the pins so that you can get zero deck height, without cutting extra material off the block. 

Other advantages are lighter weight & floating pins. Only negative I can think of is price. Will probably cost between $500 & $600.


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## RMTZ67 (Mar 12, 2011)

So Forgot to mention I am looking to run on pump gas 91-93 octane here. I would like to get the most compression that is safe. What do you guys think that would be? And is that possible w/o decking the block dont want to run no race gas no additives. It will be a cruiser and just get on it now and then. No track. I have only put 3000 miles in 10 yrs. May be less now that I got a travel trailer. BigD you still down on those pistons with that info?


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## PontiacJim (Dec 29, 2012)

*bigD*: "I would not use those "Hypercast" pistons under any circumstances. If they are used, you must have a really big top ring gap. There have been lots of wiped out engines because of using those pistons & a gap that was too small."

*PJ*: Hold on, don't throw the baby out with the bath water. You might not use them, but Butler did not have a problem recommending them and I'm sure they use them or they would not have recommended them. 

You are correct with regards to the ring gaps BUT, most piston manufacturers recommended ring gaps with their pistons based on piston material & use. Even the ring gaps used on the "better" forged pistons vary based on things like power adders. My machinist told me that some of these engines he builds for big shots of nitrous look like oil burners when running because the ring gaps have to be so wide. Once they hit the nitrous, the heat takes over and expands the pistons and closes the gaps to where they need to be - if not, they would but and break rings & pistons. 

The manufacturer of my forged pistons has a recommended gap when using nitrous. Why? Same as the hypereutectic pistons, heat. Nitrous generates more heat and if the rings gap is not spaced wider, they too will butt and bust the ring land or piston top off. So I don't think it fair, or justified, to slam the hypereutectic pistons and get *RMTZ67* all concerned when *the piston is actually not the problem, but rather the heat of expansion.* Ring gaps need to be set according to the piston manufacturer and not by the factory service manual unless you are using a like material piston.

This is from another forum and describes the problem to a "T":

"I've beat the snout outta hypereutectic pistons- massive nitrous hits, vicious over-revving, and now 2 supercharged engines.

99% of the complaints about hypereutectic pistons "shattering", in my opinion, come from improper setup/machining. Hypereutectis want tolerances that are very different from either a forged or a standard cast piston. Recommended ring gaps are usually much wider on a hypereutectic because the material and the design of the piston throws a LOT of heat at the rings. If you don't follow recommendations you'll butt the ring ends together (especially if you encounter detonation), instantly "shattering" the piston. Usually involving ripping the ringland above the top ring off the piston, and instantly destroying the engine.

Also, Hypereutectis want a bore-to-piston clearance much tighter than a typical forged piston- much more like a regular cast piston. In the range of .0015-.0020 for a N/A application, .0020-.0025 for a nitroused or blower application. Anything wider and you're just beating up the piston by letting it rock in it's bore too much.

I am currently using KB Hypereutectic pistons in my 383 blower motor. Top ring gap is a MASSIVE .032". Almost TWICE what a typical cast or forged piston would require. And exactly what KB recommends for my application. Works fantastic. I have personally, in the past, made the mistake of gapping too tight thinking I knew better than the manufacturer (did them at .025). I was wrong. First time I hit detonation I butted the ring ends and ripped the top ringlands off the pistons, destroying the engine.

Now that I've got the gaps set right I have encountered similar situations with detonation but the pistons held up just fine this time. Do it EXACTLY like they tell you to and you can push Hypereutectics a LONG LONG way. They aren't made of glass. They're tough little suckers.

I am NOT recommending that you throw hypereutectic pistons into your next boosted/nitroused motor. Forged pistons will still take more punishment, in my opinion. _But ANY piston will eventually fail if you run it in detonation. Some just take longer to fail than others_."

Followed by: "I agree with everything that you said, but remember that you're running KB hyper... pistons, which are much better then most."

*PJ*: Forged have their place, cast has their place, and hypereutectic has its place. Each choice requires that the manufacturers specs be followed by the machinist and/or the engine assembler/builder. Used the hypereutectic in my brother's engine and still going strong. I would not have a problem using them in one of my engines as a replacement for cast pistons and if costs were a factor. I don't think I would use them with nitrous either. But otherwise, I would not have a problem. As stated above, detonation will kill them or any piston if not checked. With the lower 9.0 compression, I don't think detonation should be a problem unless the wrong cam is selected that builds more cylinder pressure & thus more dynamic compression that could lead to detonation.


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## bigD (Jul 21, 2016)

To each, his own.

My opinion is: Why take a chance, when there are plenty of stronger, lighter forged pistons available ? 

Only reason I can think of is if using them will save you hundreds of dollars, and you're on a very tight budget. 

We all have our opinions. This is mine, about hypercast pistons. 

http://www.pontiaczone.com/forum/showpost.php?p=228820&postcount=6


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## PontiacJim (Dec 29, 2012)

bigD said:


> To each, his own.
> 
> My opinion is: Why take a chance, when there are plenty of stronger, lighter forged pistons available ?
> 
> ...



Agreed, we all have our opinions - and diverse opinions can only help some in asking more questions, doing more research, or making better informed choices. You would not run with the hyper's whereas I would and I would not run a roller cam without the lifter brace whereas you would.

The post you linked to was put up in 2005. It is now 13 years later. Improvements, or even better awareness, of setting up these pistons can only have evolved since 2005. 

From what I gathered, since these pistons are a casting, many were setting ring tolerances according to what they were familiar with and would have used for the factory or replacement cast piston - not the hypereutectic pistons. They are of a different composition just as forged pistons can be made of different materials & mixtures of alloys and ring placement was made higher putting them into more heat.

In my opinion, they have features that are better than cast WHEN used in a stock or mild performance engine not using nitrous or supercharging.

Hypereutectic pistons are simply a stronger type of alloy with a higher silicon content. Silicon doesn't expand so you can run tighter clearances with these pistons than with others, which helps seal-in the combustion pressure, plus the alloy used in these types of pistons is better than what other cast pistons have so they are stronger than any typical cast piston, but they are still cast pistons, which have limitations to what kinds of stresses and such they can be put through. 

KB Pistons can be installed tighter than other performance pistons. A close fitting piston rocks less, supports the rings better, and seals the engine for maximum power.

The Keith Black pistons unique thermal conductivity, ring location and varied end use requires special attention be paid to top ring end gap. *KB pistons make more HP by reflecting heat energy back into the combustion process and, as a result, the top ring runs hotter and requires additional end clearance*. Increasing ring end gap does not affect performance or oil control because normal end gaps are realized at operating temperatures. Failure to provide sufficient top ring end gap will cause a portion of the top ring land to break as the ring ends butt and lock tight in the cylinder. The broken piece may cause further piston or engine damage.

Hypereutectic piston engines will require 2-4 degrees less total ignition timing. One key to top performance is to have all cylinders igniting and producing a like flame travel that produces the same timing numbers. Equal air flow, fuel mix, quench, chamber temperature, swirl, and compression at each cylinder work to this end.

HYper's had some set-backs when they first hit the market and from what I have read all over the net is it came from improper ring gaps and taking into account that they were said to be stronger than cast and guys running power adders which further aggravated the ring gap problem - suffice to say that the pistons were not the true problem, but the expansion found in the rings at the higher temps due to the higher location of the top ring land which required wider ring gaps. Once the hyper's, like any engine product, gets tarnished or is given a bad review, the stigma of a bad product seems to hang over them like a cloud even though it is a good product when used as intended and manufacturer specs are adhered to. Finding blogs, threads, & forums that are current and not 15 years old seem to put hypereutectic pistons in a more favorable light. :yesnod:


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## RMTZ67 (Mar 12, 2011)

*Hypercast pistons*



bigD said:


> I would not use those "Hypercast" pistons under any circumstances. If they are used, you must have a really big top ring gap. There have been lots of wiped out engines because of using those pistons & a gap that was too small.
> 
> Some guys use the cheaper SP L2262F forged pistons & have a dish machined into 'em. But if your budget will stand it, I'd recommend Auto Tec custom pistons. They can position the pins so that you can get zero deck height, without cutting extra material off the block.
> 
> Other advantages are lighter weight & floating pins. Only negative I can think of is price. Will probably cost between $500 & $600.





RMTZ67 said:


> So I am having trouble figuring out how to use the comp calculator:confused. could use some help. I have a 67 gto original 400 has not been decked before and will be getting its 1st bore at 0.30. current 670 heads are 75cc.. if you need more info let me know. I did not know what the gasket bore is off hand. The machinist took the liberty of ordering some flat top pistons he mentioned in a prior conversation once I gave him the go ahead to do the bore.He believes it may have to be decked also removing #s off my block.The pistons below is what butler recommended with the info I gave them. And the book pic is what the machinist ordered. what do you guys think? he is aware of the 40-45 quench. by the way 068 cam.





PontiacJim said:


> Agreed, we all have our opinions - and diverse opinions can only help some in asking more questions, doing more research, or making better informed choices. You would not run with the hyper's whereas I would and I would not run a roller cam without the lifter brace whereas you would.
> 
> The post you linked to was put up in 2005. It is now 13 years later. Improvements, or even better awareness, of setting up these pistons can only have evolved since 2005.
> 
> ...


 Well thanks BigD and pontiacJim for your input. Varying opinions is expected in most any question brought to the table. That being said everyone should do there research and take in to account others opinions. When I started out this venture I was expecting to replace a cam and has grown to a entirely different scope. So to say it was unexpected would not be the truth. But its been a long time since I have been this deep into a engine so trying to refresh myself and learn a few things along the way.This forum is indeed a life saver. So thanks to all those who help the least of us out. If the plan was to completely go thru this engine I would have saved up a fortune. But since this build was unexpected I have to make due. Hyper pistons, use my current rods with arp bolts.Refresh my 067 heads. Well you get the picture. Like you said PontiacJim Butler recommending them is saying something. I doubt they would sell them if they did'nt have there place. The machine shop and owner that recommended the pistons has been in business here for over 40 years. "BUT" they need to know your needs and wants for your engine. With what I will use my car for I could probably use coffee cans for pistons lol. Car shows and the occasional sunday cruise. Dont get me wrong I like spinning those wheels like everyone else but only on occasion. So thanks for your input guys. And I am sure this will not be the last question I ask. RMTZ67


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## BearGFR (Aug 25, 2008)

You're taking the right approach by taking your time and doing the research. Like every other topic on the internet you'll find opinions and ideas all over the map. It's a great source of information but one must dig deeper into all of it and consider background and the logic behind what people have to say in order to arrive at the real truth. Personal experience and even personal biases do play a part. I ran a solid roller on the street and on some long distances for more than 5 years with no lifter bore brace and it wasn't an issue. However the cam profile was not super aggressive and didn't need monster springs to keep it under control. It was a rocker arm failure that sidelined it, and to be truthful that was partially my fault for failing to recognize some warning signs. I'm going with a more aggressive cam this time that yields more lift and about 20 degrees more duration even after 'dropping back' to 1.5 rockers - and using a lifter bore brace. I'm also using stainless steel full roller rockers in place of aluminum ones. I went through one of those long "multiple opinion" challenges with regard to the lifters and oiling not too far back. I'm using Crower "HIPPO" (high pressure pin oiling option) lifters and during mockup realized that they would not be getting oil whenever they were at zero lift on the cam base circle. The question was, "will that be an issue"? Opinions were everywhere, even from different people I talked to at Crower over a period of several weeks. Ultimately I opted to provide full time oiling, and my first 'solution' of modifying the lifters themselves left me with a brand new set of $800 lifters that I had essentially ruined. (My solution 'worked' at zero lift, but also caused oil leakage at max lift - doh!). I have a second set of new lifters and a solution now that will work as intended, but it was scary because it involved modifying the lifter bores in my original to the car numbers matching and therefore irreplaceable at any price block. Gulp. I used a small rotary tool to cut some grooves at the bottom of the lifter bore oil feed holes to extend them 'downward' so that they now feed oil to the lifter oil bands at zero lift, but also don't leak pressure 'anywhere'. I had to really think about that one long and hard before I picked up that tool, let me tell you! 
Anyway, you're doing the right thing. Take your time and understand not only what you're doing but why you're doing it, and everything that can logically result from the choices you make. It all eventually makes sense. 

Bear


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## geeteeohguy (Feb 2, 2008)

The thing that concerns me the most is that the machinist said that decking will remove the numbers on the block. Only Chevrolets have that issue, due to engine number and VIN number location on the pad on top of the deck. Pontiacs have the number on the front of the block, below the passenger cylinder head, next to the timing cover. In an area that would never get machined or milled in any way. In my experience, Chevy-savvy machinists are NOT then ones to use when doing a Pontiac Strato-Streak V8!! YMMV.........but you've been warned.


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## RMTZ67 (Mar 12, 2011)

*Deck #s*



geeteeohguy said:


> The thing that concerns me the most is that the machinist said that decking will remove the numbers on the block. Only Chevrolets have that issue, due to engine number and VIN number location on the pad on top of the deck. Pontiacs have the number on the front of the block, below the passenger cylinder head, next to the timing cover. In an area that would never get machined or milled in any way. In my experience, Chevy-savvy machinists are NOT then ones to use when doing a Pontiac Strato-Streak V8!! YMMV.........but you've been warned.


 Well on there behalf he did tell me the #'s there were not important. It's me that needs a refresher course:blush: where the important #'s are.:blush:


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## RMTZ67 (Mar 12, 2011)

*pontiac builders*



geeteeohguy said:


> The thing that concerns me the most is that the machinist said that decking will remove the numbers on the block. Only Chevrolets have that issue, due to engine number and VIN number location on the pad on top of the deck. Pontiacs have the number on the front of the block, below the passenger cylinder head, next to the timing cover. In an area that would never get machined or milled in any way. In my experience, Chevy-savvy machinists are NOT then ones to use when doing a Pontiac Strato-Streak V8!! YMMV.........but you've been warned.


 Well there are not many if any pontiac only builders around anymore. And some like CVMS Also don't know what they are doing. I am sure you are aware of Goat Ropers story. So looks like its a gamble no matter who or where you take it . I had another builder build my 350 4 bolt on my Z28 and when I did the break in it went to s#!*. Was it my fault? I have broke several motors without issues. I took it to another builder to diagnose why I could not get it to run smooth before I knew there was a problem. He stated he believed the lifters were probably set too tight. Maybe you could just offer some tips as what to look for. They are doing the machining and I will be putting it together. A refresher course of sorts. Along with rockys how to book. I could buy several blocks and try 3-4 times for a good one and still have thousands left over for what Butler or any of the others charge.


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## PontiacJim (Dec 29, 2012)

RMTZ67 said:


> Well there are not many if any pontiac only builders around anymore. And some like CVMS Also don't know what they are doing. I am sure you are aware of Goat Ropers story. So looks like its a gamble no matter who or where you take it . I had another builder build my 350 4 bolt on my Z28 and when I did the break in it went to s#!*. Was it my fault? I have broke several motors without issues. I took it to another builder to diagnose why I could not get it to run smooth before I knew there was a problem. He stated he believed the lifters were probably set too tight. Maybe you could just offer some tips as what to look for. They are doing the machining and I will be putting it together. A refresher course of sorts. Along with rockys how to book. I could buy several blocks and try 3-4 times for a good one and still have thousands left over for what Butler or any of the others charge.


It is not very difficult if you take your time and understand what it is you are doing. Rocky's book is pretty good with detailed pics. You will need tools, and the cost of purchase might not be as cost effective as having your machine shop assemble the shortblock (piston, rings, rods, crank, cam bearings, main & rod bearings, rear main seal) and you install the oil pump, oil pump rod, pan, cam/lifters, timing items, top end, etc.. 

A budget build is fine and you know what to expect and don't plan on racing it.

Hyper's would be my choice as has been suggested. Having the cast rods magnafluxed, resized, and ARP rod bolts installed should be fine for a street engine. I see Spotts Performance offers reconditioning/resizing of cast rods with the ARP rod bolts for $200. A set of 8 used rods is $50 more. So your shop should be close to the $200 ballpark in reconditioning your rods with the ARP rod bolts - unless they add polishing the side beams and shot peening, and then you would probably be in the territory of new I-beam rods. The forged I-beam rods look to be about $319.00 plus shipping.

With new pistons, you will generally get the engine balanced. On averaged this seems to run about $200. This will include pistons/pins, rings, rods, crank, harmonic balancer, and flywheel. You will want to get a NEW balancer. I would not use the old original as the rubber typically deteriorates and timing can be off or catastrophic failure can occur. Yours is a "2 piece" on the 1967 and they go for around $170 vs $50 for the one piece 1968 and up balancer. They cannot be swapped as your timing chain cover is set-up for the '67 2-pc and the balancer diameter is a different size and your timing cover degree scale is designed for that balancer. Not saying you cannot use yours, but I don't know as I would trust it if it is the original.

Additional block work would be the installation of threaded plugs in the front of the block's oil galley holes. These are freeze/cup plugs that get staked. They can work loose and it is best to simply tap the hole and install threaded plugs. Many shops do this automatically. Should not be a big charge to do this. I would let them install the freeze plugs as well because they have the tools that make it much easier & quicker for them to install.

So just a few things to think about. I always write up a "plan" or "outline" on what parts I need and what the shop will do/assemble and what I am going to do. :thumbsup:


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## RMTZ67 (Mar 12, 2011)

*Engine build*



PontiacJim said:


> It is not very difficult if you take your time and understand what it is you are doing. Rocky's book is pretty good with detailed pics. You will need tools, and the cost of purchase might not be as cost effective as having your machine shop assemble the shortblock (piston, rings, rods, crank, cam bearings, main & rod bearings, rear main seal) and you install the oil pump, oil pump rod, pan, cam/lifters, timing items, top end, etc..
> 
> A budget build is fine and you know what to expect and don't plan on racing it.
> 
> ...


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## geeteeohguy (Feb 2, 2008)

Paul Carter of Koerner Racing Engines in Tuscon, AZ has been around a long time, and is a Pontiac specialist. He gets nothing but rave reviews on the PY/AMES Pontiac forums. That said, I have not used his services, so cannot give you a first-person review. But if I were in your shoes, and as close as you are to AZ, I would at least call him and have a talk. He's a great guy and a huge help on the other forum. His modest 389-400 builds have produced very respectable power AND reliability. FWIW....

AS a P.S: and disclaimer, I recommended CVMS to Goat Roper, when their rep was still stellar before Jim had vision issues. I still feel crappy about it.


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## PontiacJim (Dec 29, 2012)

The shop will tap the oil plugs. They will most likely just wipe down/clean or blow out any small particles. What you do want to check for is that the plug is not screwed in all the way. If it goes in too far, it can restrict or close off the oil supply to the lifters. Also make sure the hidden plug behind the freeze plug was installed at the back of the engine. You should be able to shine a flashlight down the distributor hole and see it, but you could inquire by asking if the pipe plug at the rear of the oil galley was the same size as the ones they installed in front - put it in a question like that and it should not insult them because you are just curious. :thumbsup:

I would not use the 80 lb oil pump - *my opinion is* it is really too much unless you open up the bearing clearances or were spinning your engine up past 6,000 RPM on a regular basis. The 60 psi pump would be better. The Mellings pump is good, but if you can afford it, the Butler blueprinted 60 psi pump is the way to go. https://butlerperformance.com/i-244...i-oil-pump-w-pickup-screen-bpi-m54ds-pro.html 

Now if you feel this too much, _buy the Mellings 60PSI pump and add the heavier oil pump plate with anti-cavitation grooves._ It comes with the longer bolts for installation. I purchased this one for $30, but then decided to go with the Butler 60 PSI pump which they did not have at the time and only offered in the 80 PSI. I did inquire about using the blueprinted 80 PSI pump in my 455 build at the time and Butler said the Mellings 60 PSI pump would work just fine. So check this out: https://www.tinindianperformance.com/pontiac-oil-pump-plate/ 

You also want a new hardened oil pump shaft like this one: https://www.summitracing.com/parts/mel-is-54a/applications/make/pontiac?prefilter=1

I don't know if they make an early balancer with the timing marks on it like the '68 and later balancer that is available. Can't say as I have seen one. Adding a timing tape may be your only option on that one.


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## geeteeohguy (Feb 2, 2008)

What Jim said on the oil pump. And pretty much everything else. 80 PSI pumps are good for spun bearings and oil leaks on stock clearanced engines, IME.


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## tjta (Jul 24, 2020)

Hello everyone! I'm new to this forum. 

I'm in the middle of a rebuild but not on a GTO but a Trans Am. Hopefully, I could share and receive some advice as well on the drive train side.

The engine is a 400 manufactured in 73. 

I'm in the aftermarket selection process with replacing the old pistons ( which were forged from a previous rebuild about 25 years ago or so ) and replacing them with possibly 4032 forged JE SRP Pistons. Also changing out the rods from the stock to 4340 Forged Eagle H-beam.

My intended use is street/strip with some hard driving and once in a blue moon at the drag street. 

I believe this is a strong enough set up, but I would like know if there are any disadvantages running this combo in daily driving. My daily driving consists of going to weekly car shows. I have a lot of country roads and highways with some city driving. 

I have read somewhere that these pistons are noisy??

Reusing my original cast crank and the builder is beefing up my heads. He produced a sheet which shows our intended CR is in the 9.1 or bit higher. Cam is 216/228 @ 50, .454/.480, 112 LSA . .


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## PontiacJim (Dec 29, 2012)

tjta said:


> Hello everyone! I'm new to this forum.
> 
> I'm in the middle of a rebuild but not on a GTO but a Trans Am. Hopefully, I could share and receive some advice as well on the drive train side.
> 
> ...


We welcome anyone with a Pontiac and like it best when it still is powered by a Pontiac engine.  

Your combo is fine for a street build. Build the engine for torque not HP. The forged pistons should be ordered once your engine builder knows what the bore size is, ie needs to be bored .030", .040", or .060". Then once he has pistons in hand, he will bore the cylinders close to the needed bore size and then finish the cylinders by honing to get the manufacturer's recommended clearances. These would be based on an engine using gas, and no power adders like nitrous. Power adders can increase heat, which increases piston expansion, which then requires additional piston-to-cylinder wall clearances. If you do not clearance for such power adders, then when the piston expands you can scour the cylinder walls, butt piston rings at the gap and break rings/pistons, or lock up a piston in the cylinder. BUT, I assume you are not using a power adder, but wanted to cover this incase you were thinking of it.

Forged pistons generally need more piston-to-cylinder wall clearances because they expand more than a cast or hypereutectic piston will. So you hear the stories of forged pistons that will "rattle" a little when cold and goes away when the engine warms up. It also depends on the type of forging as some expand less and this is why your machine shop will follow the manufacturer's clearances for that piston type. I would not be too concerned. Forged pistons are the way to go as they can also better handle any detonation should you encounter any.

With 9.1, or slightly higher, you should not have any issues with detonation and pump gas. 9.0 is the target number, but the range can be as high as 9.5 if the engine is built well with matched parts.

Key point here is quench distance. Your machine shop should be very familiar with this. You want to have a quench ( that little space between the top of the piston and flat area on the bottom of the head around the combustion chamber) distance between .040"-.045". This really helps with preventing detonation by forcing the gas mixture into the chamber for a more complete burn, and cools (thus the word "quench") the gas mixture. Your machinist can measure the deck height and order a custom pin height for the piston to get the top of the piston even with the deck, called zero deck, or just slightly lower down in the hole like .005". Then you can use a Felpro head gasket having a compressed height of .040" to give you the .040"-.045" quench.

The deck can also be milled down to get the piston height you need, but I personally rather not while others will have this done to get the needed deck height, square up the block, or clean up the deck surface.

Most Pontiac pistons are .015"-.020" down in the bore. So option #2, what I did, was purchase a set of Cometic brand head gaskets .027" thick. My .020" down in the hole pistons with the .027" head gaskets gives me .047" of quench - close enough to .045". Cometic's are not inexpensive. They also come in other thicknesses and different bore sizes.

Forged rods are what you want to replace the factory cast rods. Your options are the H-beam or the I-beam, bith have the better 7/16" bolts. The I-beam is more like factory in look, but is forged and has the better rod bolts Seen here - https://butlerperformance.com/i-316...lts-press-fit-set-8.html?ref=category:1234812 The H-beam comes in 2 flavors, a press-fit piston pin or bushed for floating piston pins. So you want to match the rod pin style to the forged piston recommendation - press fit or bushed fit for floating pins. Press fit is fine for a street engine. They are more money and not sure any real advantage for a street engine. Here is the H-Beam bushed as an example - https://butlerperformance.com/i-316...0-pontiac-rj-bushed.html?ref=category:1234853

You will need to have the crank assembly balanced. Get a new harmonic balancer to replace the old original - cheap enough, cheap insurance.

The Pontiac crank has small serrations at the rear main seal area to help lubricate the old style rope rear main seals. If you use a Viton seal, this needs to be polished so the serrations do not dig into the Viton seal and damage it over time. Many suggest the Best brand graphite rope seal and seem to have less problems with rear main leaks. I have used the BOP brand Viton on my last 400 build with no issues after 25,000 miles. But other have issues from day 1. So the rope seal may be a better choice, but that is between you and your machinist. https://butlerperformance.com/i-244...r-326-400-bga-6380x.html?ref=category:1234758

Cam looks to be a good choice for street/daily driver with the 112 LSA. Get a good 3-angle valve job.


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## Old Man Taylor (May 9, 2011)

They should not be noisy. They recommend a fairly tight clearance for that forged piston.


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## tjta (Jul 24, 2020)

Thank you, Thank you, and Thank you. 

I appreciate your response.

I have 2 other thoughts......Would there be any reliability issues with the stock Pontiac crankshaft up to my intended level of 400hp? 

Also, my builder will be installing new valves ( intake and exhaust ) along with the changing the rockers to roller tips and increasing the ratio from 1.5 to 1.65 on the intake valves and 1.5 on the exhaust side. According to him it will give more of a lift and change the duration a little as well. Any disadvantages or reliability issues with this scenario? Any noticeable Hp increase? The heads are the 4x heads that came with the engine. He is also putting in bronze valve guides and putting in exhaust seats I think he said.


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## Old Man Taylor (May 9, 2011)

If the stock crank is checked OK for cracks, then it should be fine. As to the 1.65 rockers, I would have to know the cam specs, but it is unusual to look for more lift on the intake alone.


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## tjta (Jul 24, 2020)

Cam is Crane 216/228 @ 50, .454/.480, 112 LSA . .
Crane number is Cr283942


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## Old Man Taylor (May 9, 2011)

You don't need or want anymore lift unless you have made other modifications to the heads and/or valves.


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## Montreux (Mar 8, 2009)

tjta said:


> Hello everyone! I'm new to this forum.
> 
> I'm in the middle of a rebuild but not on a GTO but a Trans Am. Hopefully, I could share and receive some advice as well on the drive train side.
> 
> ...


How does your builder plan to raise the compression to 9+? If memory serves, '73 motors were low 8's for compression.


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## PontiacJim (Dec 29, 2012)

Montreux said:


> How does your builder plan to raise the compression to 9+? If memory serves, '73 motors were low 8's for compression.


He is using aftermarket pistons - the pin height can be moved to raise the piston higher in the bore. Or, you can mill the block/deck to get a "zero deck" height which can increase compression.


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## tjta (Jul 24, 2020)

Thanks Jim for stepping in to explain. I saw my builder today and we are going to try and clean and mag another used 6x-4 from 1977 and apparently from a Trans am as well. This should get us closer to 9.5.1. The heads will be worked over with 30 degree valve job and a very minimal amount of porting ( around the intake and exhaust areas ) My builder has a machine that spits out this info after knowing the numbers including the heads flow numbers. Hopefully, it checks out cause I’m paying the machine shop another charge to have them check it out. I will have to sell the other 4x heads to try to recoup some of my losses. On the brighter side, some of my shiny new part came in. Stainless steel Ferrea valves, 4340 Forged Eagle h beam rods( they felt very light but look sturdy, Jp performance Billet gear set ( made in Australia! ) Hasting performance rings, top will be 1/16 th instead of the thinker 5/64 normally used. This will reduce friction and more ductile then the thicker one ( more hp to a degree ). The pistons are 4032 forged flat top with only 2 relief valves as opposed to 4 reliefs for more compression. They are being made so made another week or so before arrival. Hopefully.


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## tjta (Jul 24, 2020)

Not sure where to post this question.......I have a question regarding the exhaust valve size. We were first going to use the 2.11/ 1.77 new stainless steel valves from Ferrea on the #62 heads We have decided not to use the #62 heads due to the missing alternator accessory bolt hole. 

We are going forward with a 6X-4 head from 1977 that apparently has 93.74cc. As long as it cleans up and maged ok I think it could be a candidate. This head has the 2.11/1.66 valve size.

If we were to use the 1.66 exhaust valves vs the 1.77 exhaust valves.......what advantages/disadvantages are there one over the other. 

Thanks


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## PontiacJim (Dec 29, 2012)

tjta said:


> Not sure where to post this question.......I have a question regarding the exhaust valve size. We were first going to use the 2.11/ 1.77 new stainless steel valves from Ferrea on the #62 heads We have decided not to use the #62 heads due to the missing alternator accessory bolt hole.
> 
> We are going forward with a 6X-4 head from 1977 that apparently has 93.74cc. As long as it cleans up and maged ok I think it could be a candidate. This head has the 2.11/1.66 valve size.
> 
> ...


Basically none. As I recall, the later heads used a slightly improved exhaust port. The 1.77's won't gain you much. Just select a cam having a little more duration or lift on the exhaust which most Pontiac cams already have.


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## tjta (Jul 24, 2020)

Thanks Jim. My cam is the Crane H 272-2 which has 216/228 int/exh @50, 272/284 advertised, 112 lobe, Gross lift 454/480,
My builder is installing 1.65 roller rockers on the intake and 1.5 roller rockers on the exhaust side. My converter stall is 2500 and my rear end is 3.08. What is your opinion on that?

btw...the 6x-4 heads checked out ok and are now being built up.


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## PontiacJim (Dec 29, 2012)

tjta said:


> Thanks Jim. My cam is the Crane H 272-2 which has 216/228 int/exh @50, 272/284 advertised, 112 lobe, Gross lift 454/480,
> My builder is installing 1.65 roller rockers on the intake and 1.5 roller rockers on the exhaust side. My converter stall is 2500 and my rear end is 3.08. What is your opinion on that?
> 
> btw...the 6x-4 heads checked out ok and are now being built up.


Hmmm. Getting close to 9.5 compression might be better with a little more LSA. 112 will work, but may build a little more cylinder pressure -meaning you may be using an octane additive. The long duration may just work fine with the 112 LSA. The cam shows to have 55 degrees of overlap which is a good street cam.

The 1.65's will work and lift the valves faster, so you want to make sure you have enough spring pressure to keep valve train stability. Then you want to know that you have no valve spring binding and enough clearance between the spring retainer and valve guide. Intake lift will be near .500". But, your machinist seems to know what he is doing.

The 2,500 stall with 3.08 gears should be fine.


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## tjta (Jul 24, 2020)

Thanks Jim. There a couple of figures on the interest regarding spring pressures. I have read spec for Pontiac with flat tappet cams need around 120-130 lbs closed to enable good seating sealing and just over 300 lbs when open at max lift to prevent valve float. Otherwise you won't be able to get your cam's max rev range.

I have also seen a spec from a retailer selling my camshaft of 93 lbs @1.550 closed, and 284 lbs @1.090 open. So there is some discrepancy.

Also, the builder is looking at putting in a bearing set ( classified as performance/race from what I have read ) from Sealed Power SEA113M20 for the main bearing set and SEA8-7050CH20 for the rod bearing set. He also mentioned that you will have to keep your oil clean for these type of bearings, I guess to prevent debris from getting in contact with the bearing. What are the advantages and disadvantages of this type of bearing set compared to regular bearings. Will these bearings fail sooner than regular bearings? I'm not planning on going to the track on a regular bases. I would like the bearings to last at least 100K without having to worry about debris finding it way to the bearings and destroying the engine anytime sooner than 100K.

I do regular oil changes anyways. So I don't skimp out on that part.


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## PontiacJim (Dec 29, 2012)

tjta said:


> Thanks Jim. There a couple of figures on the interest regarding spring pressures. I have read spec for Pontiac with flat tappet cams need around 120-130 lbs closed to enable good seating sealing and just over 300 lbs when open at max lift to prevent valve float. Otherwise you won't be able to get your cam's max rev range.
> 
> I have also seen a spec from a retailer selling my camshaft of 93 lbs @1.550 closed, and 284 lbs @1.090 open. So there is some discrepancy.
> 
> ...


On the valve springs. Keep in mind that the springs will lose some tension as they get use on them. The XE cam has what is considered a "fast" ramp, ie it is "steeper" and opens the valve quicker - sorta like a roller cam lobe profile would do, but nowhere near as aggressive being a flat tappet cam. Now think of the speed that the lobe is spinning and raising the lifter up and pushing on the pushrod and rocker arm. At high rpm with insufficient over-the-nose (open) spring pressure, this can allow the lifter to ski-jump off of the cam lobe just after max lift. *This is called lofting.* When lofting occurs valve spring pressure on the lifter is momentarily very low, less than engine oil pressure in the lifter. Thus allowing the lifter to “grow” to take up the slack. In a very short time, measured in nanoseconds, the preload is gone and the pumped-up lifter holds the valves open - not a good thing for power.

An easy way to cure lifter pump up is to reduce the preload by "zero lashing" the lifter and adding something like a one quarter turn on the poly-lock & 7/16" BB rocker arm stud (this will not work on the factory set-up). This way, the lifter is virtually pumped up all the time and acts more like a solid lifter and the lifter does not "grow" taking up the slack and pumping up.

_Valve springs with higher spring rates _go a long way toward reducing lofting and lifter pump-up. Light weight components such as hollow stem and smaller stem valves, lightweight rockers, and spring retainers and springs can also help, but moreso for higher RPM's than most street engines will see.

So the higher spring rates should be used with the XE cams because of their fast ramp speed opening the valves quicker and could produce "lofting" of the lifter on the cam lobe at higher RPM's - even in a street engine because the springs will lose some of their initial spring rated pressures due to use/time.

On the bearings, looks like your journals have been turned down .020" to clean them up. The most important thing when going undersized on the journals is to have a nice fillet (radius) area where the crank/rod journals meet up with the sides. I could not find the first Sealed Power number as supplied. The second number did pull up as a Tri-Metal bearing - typical "old school" bearing and no issues.

I prefer and use the 3/4 groove Speed Pro main bearings - you can ask your builder about these. Provides more oiling than the 1/2 groove and you do not lose the needed lower bearing support which you do not get when you use a fully grooved bearing set.

I don't know why he told you to keep the oil clean, but I would not worry too much and they should last a long life. I used the tri-metal bearings in my brother's 360CI rebuild and 3/4 groove mains - still going strong after 8 years. I know I have the 3/4 groove mains for my 455. Not sure what brand, but probably Speed Pro as well.









PONTIAC Speed Pro 113M Speed-Pro Competition Series Main Bearings | Summit Racing


Free Shipping - Speed-Pro Competition Series Main Bearings with qualifying orders of $99. Shop Main Bearings at Summit Racing.




www.summitracing.com


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## PontiacPollo (6 d ago)

Hi JIM, hope you’re doing great and having a great holiday I’ve been following some of your posts and would like your opinion based on your great experience and knowledge, it will be much appreciated if you could help me I’ve recently started to work on a 1974 pontiac formula 400 which has been in my family since brand new it was stored for about 20 years and decided to getting it back to work so towed it to a garage shop and fixed many components to get it on the road Some of the work already done is: - [ ] Rebuilt Rochester Quadra jet carburetor - [ ] New valve seals and guides along with head refresh service at machine shop. I have the 4x heads. - [ ] New camshaft, the Crower 60240 (Cliff Rugles suggestion) - [ ] New electronic distributor, cables and spark plugs - [ ] New cooling system, and more upgrades…. Engine block and internals didn’t got disassembled nor checked and now that all engine has been put together and running, oil pressure gauge drops very quickly even with a thicker oil grade New oil show very small particles or worn metal and mechanic says it’s probably coming from crankshaft or connecting rods bearings So now engine is coming out again for complete rebuild and also would like to get a bit of more performance out of this engine. This engine seems that hasn’t been rebuilt before but still don’t have any measurements until it gets to the machinists As of what I’ve read, this engine was manufactured with 8.0:1 compression ratio, Do you think it would be a good opportunity to get some different pistons to get a bit more compression for performance? If so, please if you could suggest which parts to look for. Sent from my iPhone


PontiacJim said:


> Agreed, we all have our opinions - and diverse opinions can only help some in asking more questions, doing more research, or making better informed choices. You would not run with the hyper's whereas I would and I would not run a roller cam without the lifter brace whereas you would. The post you linked to was put up in 2005. It is now 13 years later. Improvements, or even better awareness, of setting up these pistons can only have evolved since 2005. From what I gathered, since these pistons are a casting, many were setting ring tolerances according to what they were familiar with and would have used for the factory or replacement cast piston - not the hypereutectic pistons. They are of a different composition just as forged pistons can be made of different materials & mixtures of alloys and ring placement was made higher putting them into more heat. In my opinion, they have features that are better than cast WHEN used in a stock or mild performance engine not using nitrous or supercharging. Hypereutectic pistons are simply a stronger type of alloy with a higher silicon content. Silicon doesn't expand so you can run tighter clearances with these pistons than with others, which helps seal-in the combustion pressure, plus the alloy used in these types of pistons is better than what other cast pistons have so they are stronger than any typical cast piston, but they are still cast pistons, which have limitations to what kinds of stresses and such they can be put through. KB Pistons can be installed tighter than other performance pistons. A close fitting piston rocks less, supports the rings better, and seals the engine for maximum power. The Keith Black pistons unique thermal conductivity, ring location and varied end use requires special attention be paid to top ring end gap. *KB pistons make more HP by reflecting heat energy back into the combustion process and, as a result, the top ring runs hotter and requires additional end clearance*. Increasing ring end gap does not affect performance or oil control because normal end gaps are realized at operating temperatures. Failure to provide sufficient top ring end gap will cause a portion of the top ring land to break as the ring ends butt and lock tight in the cylinder. The broken piece may cause further piston or engine damage. Hypereutectic piston engines will require 2-4 degrees less total ignition timing. One key to top performance is to have all cylinders igniting and producing a like flame travel that produces the same timing numbers. Equal air flow, fuel mix, quench, chamber temperature, swirl, and compression at each cylinder work to this end. HYper's had some set-backs when they first hit the market and from what I have read all over the net is it came from improper ring gaps and taking into account that they were said to be stronger than cast and guys running power adders which further aggravated the ring gap problem - suffice to say that the pistons were not the true problem, but the expansion found in the rings at the higher temps due to the higher location of the top ring land which required wider ring gaps. Once the hyper's, like any engine product, gets tarnished or is given a bad review, the stigma of a bad product seems to hang over them like a cloud even though it is a good product when used as intended and manufacturer specs are adhered to. Finding blogs, threads, & forums that are current and not 15 years old seem to put hypereutectic pistons in a more favorable light. :yesnod:


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## PontiacJim (Dec 29, 2012)

PontiacPollo said:


> Hi JIM, hope you’re doing great and having a great holiday I’ve been following some of your posts and would like your opinion based on your great experience and knowledge, it will be much appreciated if you could help me I’ve recently started to work on a 1974 pontiac formula 400 which has been in my family since brand new it was stored for about 20 years and decided to getting it back to work so towed it to a garage shop and fixed many components to get it on the road Some of the work already done is: - [ ] Rebuilt Rochester Quadra jet carburetor - [ ] New valve seals and guides along with head refresh service at machine shop. I have the 4x heads. - [ ] New camshaft, the Crower 60240 (Cliff Rugles suggestion) - [ ] New electronic distributor, cables and spark plugs - [ ] New cooling system, and more upgrades…. Engine block and internals didn’t got disassembled nor checked and now that all engine has been put together and running, oil pressure gauge drops very quickly even with a thicker oil grade New oil show very small particles or worn metal and mechanic says it’s probably coming from crankshaft or connecting rods bearings So now engine is coming out again for complete rebuild and also would like to get a bit of more performance out of this engine. This engine seems that hasn’t been rebuilt before but still don’t have any measurements until it gets to the machinists As of what I’ve read, this engine was manufactured with 8.0:1 compression ratio, Do you think it would be a good opportunity to get some different pistons to get a bit more compression for performance? If so, please if you could suggest which parts to look for. Sent from my iPhone


Hi PontiacPollo,

Your 4X heads should be with the larger 2.11" intake valves and they are said to be a 98CC combustion chamber (some claim they are closer to 100 CC's). To be sure of the chamber size, you want to CC one chamber after the valve job and all work is done.

The pistons won't raise compression as the factory pistons are all flat-top. It is the heads that give you compression on a Pontiac engine - so raising compression is done with the head selection.

To get to a 9.0 compression ratio on a 400CI bored .030" over, you will need a combustion chamber of 83 CC's. Milling a Pontiac head .005" gives you 1 CC. You would have to cut/mill the heads about .080" to get to 83 CC's and that is not practical.

The Pontiac piston is typically .020" below the block deck surface. If you "zero deck" mill the block or get custom pistons that move the piston pin down .020" so it raises the piston up, your compression would be 8.2 with your 98 CC heads. This would also leave you with a squish area (the small space between the top of the piston and head surface) the same distance as your head gasket used - typically .040". This is a good number, you don't want anything less.

With this "zero deck" clearance, you could mill the head surface .030" which would reduce your 4X chambers from 98 to 92 CC's. Engine compression would now be 8.7. Not bad.

You could raise compression by "zero decking" the block or ordering pistons moved up higher in the block - depends on what your engine shop wants to do - and your budget. Then mill your 4X heads .030" to get 92 CC's, use the .040" thick head gasket for the good "squish area," and have 8.7 compression, if the chambers will CC out to 92.

You did not say what cam you have. With the lower compression, you could take advantage of it with a cam that builds cylinder pressure. With the lower compression engines, I like the Cams that use an 110 LSA (Lobe Separation Angle). 

MY OPINION here. The Crower 60240 would not be my cam of choice ONLY because it is ground on the 112 LSA. If you look at the cam specs, it recommends 9.5 compression for max power. The rest of the specs look good on duration and lift. I like the Comp Cams XE line of cams. They have the 110 LSA which builds cylinder pressure - which acts as if adding more compression. They will have a good hard pull and wake up a low compression engine, but typically run out of steam around 5,000 - 5,500 RPM's. The XE 262 could be a good choice. I used the XE 274 on a low compression 8.2 (which was probably 8.0 or less with the 8-valve relief pistons) and I had a manual trans so did not need a higher stall converter, and the engine pulled very hard up to 5,500 RPM and then the power dropped off.

In my opinion, using a cam above would be a better choice than the Crower cam with low compression.

You could use a standard piston with factory pin height putting the piston .020" below the deck, mill the heads .030" (you can go more, but then you may need new pushrod lengths), and to get a good "squish" distance use the .027" Cometic head gaskets (.020" + .027" = .047" squish) to give you a compression of 8.5. Fel Pro head gaskets at .040" will lower compression to 8.4, but the "squish area" will become .020" + .040" = .060" - which is probably OK as that would be stock, but .047" would be a little better. Cometic head gaskets are more money, so that is a consideration.

When choosing a piston, you want to look at piston pin height. The factory piston pin height is 1.710". So I would look for a piston having the factory pin height. I would get the hypereutectic pistons for your build unless you want forged pistons. Most new cars use this type of pistons BUT, you have to follow the recommendations as to ring gap - they are typically wider that cast pistons. There are of course other pistons available from other makers and you can get cast or forged, stock or custom made.

Here is the specs from Butler, but you can also get them from other sources like Summit or Jegs.



https://butlerperformance.com/i-30158600-hypereutecticcast-6cc-flat-top-pistons-400-3-750-str.html?ref=category:1394344



You have a few options as to what you can do to get a little more power out of your engine. I am not engine expert, so the above is just some of my opinions as to what I might do. I would not let low compression worry me too much and you can use pump gas. Cliff Ruggles has far more experience than I do and his recommendation on the Crower cam is probably good, but I have had my experience with the low compression 400 and the XE cam, so that is where I am coming from. On my 455 build, I have a Crower cam on the 112 LSA and a 9.2 compression. If it had been below 9.0, then I would have gone with a 110 LSA cam as my pick over the 112 LSA.

Things to think about! Let me know if you have more questions and I will do my best to answer them.

Jim


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## PontiacPollo (6 d ago)

PontiacJim said:


> Hi PontiacPollo,
> 
> Your 4X heads should be with the larger 2.11" intake valves and they are said to be a 98CC combustion chamber (some claim they are closer to 100 CC's). To be sure of the chamber size, you want to CC one chamber after the valve job and all work is done.
> 
> ...


Hi Pontiac Jim

Thank you very much for your valuable support, I see that you are very knowledgeable about these engines. It's the first pontiac engine I've ever worked with and your advice has taught me a lot. I have passed this data on to my machinists to see which path they suggest taking according to the measurements and data you gave me. Really very grateful for your time and knowledge. I'll tell you how it goes.

Regards


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## PontiacPollo (6 d ago)

Hi Pontiac Jim

Thank you very much for your valuable support, I see that you are very knowledgeable about these engines. It's the first pontiac engine I've ever worked with and your advice has taught me a lot. I have passed this data on to my machinists to see which path they suggest taking according to the measurements and data you gave me. Really very grateful for your time and knowledge. I'll tell you how it goes.


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