# Sealed Power piston #288P



## extinctmake (Feb 8, 2011)

This is a flat piston with valve reliefs for a 389. The manufacturer says the compression ratio with this piston is 10.1:1.

For a '65 GTO 389 with #77 65cc heads, the advertised compression ratio is 10.75:1.

If the block is bored .030 and fitted with these pistons, using the 65 cc heads, how could the compression ratio drop to 10.1:1 from 10.75:1 if this piston is not dished?


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## PontiacJim (Dec 29, 2012)

The manufacturer may be correct. Funny thing about the Pontiac factory compressions. It seems they advertised them higher than actual. 65cc heads may not be the true numbers unless you have verified them as they can differ. You will have to calculate the actual compression yourself by using a compression formula/calculator. Many factors will affect compression ratios. Dishing can lower compression, but also the cc's found in the valve reliefs on the piston crown can be used to adjust the compression. You want to know this number. There are several compression calculators online. Try the wallace racing site as they have several.


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## geeteeohguy (Feb 2, 2008)

I have been running forged Sealed Power +.030 flat tops in my '65 GTO's 389 for over 30 years. What Jim said on the CR...Pontiac over rated it by about a half point. That said, Sealed Power and TRW forged pistons sit a bit down in the hole, which lowers compresion a hair, but is not a good thing for quench and detonation. In my case, with my #77 heads which are 64cc, I must run race gas, even with a big camshaft, decent rear gear, and a 4 speed. It demands 98-100 octane, period. If I were building this engine today, I'd zero deck the block and use custom dished pistons, or I'd zero deck the block, use flat top pistons, and aluminum 65-72cc heads. You can do all the figuring you want, but the fact remains that even 10:1 on an iron headed 389 will need close to 100 octane fuel. I know. I've been driving mine for decades.


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## extinctmake (Feb 8, 2011)

Yeah that's what I was afraid of. I have had discussions on this site before regarding rebuilding my OEM 389 to my '65 GTO convertible to make it operate on today's lousy gas.

I had mentioned boring the 389 to fit dished standard-size 400 pistons and using my original #77 heads. I think the CR would be in the low 9:1 range. I didn't receive many favorable responses about rebuilding my engine that way.

I am no hurry to build this engine, but I am trying to map out a plan to rebuild this engine to retain the stock heads, intake, carb, etc., but operate on 87-91 octane fuel.

If the 98-100 octane race gas was still $4.00-$5.00 a gallon I could live with the high compression engine I currently have in my car because I don't drive the car a lot, but that high octane gas is over $8.00 a gallon now and I suspect it will only go up from there.


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## geeteeohguy (Feb 2, 2008)

I think I can help here. The .060/use 400 pistons I have done before. I would not do it again. I ended up with a hot running engine that could not be bored out again. Good way to 'use up' a block. Always bore as little as possible. Helped a friend of mine out with his '65 389 a few years back. He insisted on running the stock heads, too. He chose a Comp Cams XE268 cam, and went with custom Ross pistons for a CR of right at 9:1. The only expensive thing on the build was the pistons. It was a cheap build overall, under 3k. Well, the end result was that it pulls like a train and runs like a scalded cat......on 89 octane. Even 87 when it's not hot out. He has maybe 8-10,000 miles on it now, and it's a great combo. Running ram air cast iron manifolds and a Pypes exhaust. The car gets good mileage, runs as hard as my tripower, high compression 389, and does it on mid grade. So, if I were you, I'd get the block bored minimal, get the pistons made to match the bores ($500-$600), have the rest of the machine work done, and put it together. You can even zero-deck the block while you're at it. You'll end up with a solid, reliable, powerful, and blast-to-drive combo.


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## PontiacJim (Dec 29, 2012)

So many factors go into building an engine today. I have really been studying it all in trying to build my 455. You have to be very careful with what others say or what works. A lot of BS out there. Formulas and on-line calculators are cool, but these only provide an "on paper" best scenario and don't take into account real world use. I can build a huge HP & torque engine on paper, but once I couple it to the drive train, install it in the heavy car, and have to deal with gas selection, weather conditions, etc., all these factors will most likely throw out the window that "perfect" engine I just built on paper and tested on my McDyno computer program.

Compression is extremely important in that you get it right the first time. We ALL want to go big and brag of 10 or 11 to 1 compression, but it will give you more grief than good. Get a bad case of detonation woes because you chose the high compression, and you can seriously damage your engine quickly. Great for the track where all you will do is race a 1/8 or 1/4 mile at a time and can afford the racing gas, but not for the street. Don't think for a minute that a lower compression Pontiac engine won't perform. Build for torque & then gear the car for torque. If you want to go faster, use the driveline to do some of this. Don't go for 450+ HP and then use 3.23 gearing because you want to get good gas mileage. That's like claiming to be on a diet as you order 5 McCheese's and the "diet" Coke. Go 400 HP and 3.70 gearing. Best combination in my opinion is to purchase a complete stroker kit, ready to go, to get bigger cubes and more torque. Use the extra cubes to offset the use of a radical cam and you will probably be happier - and be able to use cheaper gas and get some kind of mileage. 

The next thing that is critical is cam choice. This is the brains and heart of your engine. This is what will dictate your torque and horsepower range & level. It will also affect cylinder pressure which directly relates back to detonation woes. Take note of what the factory cam specs have been, then look at what you are being offered in aftermarket grinds. Back to the "paper engine". Looks good and really has some impressive numbers. But then you hook it up to your drive train and that "paper engine" which had no load on the flywheel, now has 3800 pounds to pull it down. All of a sudden you have a different animal and the engine is pinging, has to be idled up to 1,000 or more to keep it from stalling, and you can't run on the local grade gas without mixing high octane "something." Study cam specs; duration, lobe separation, intake and exhaust valve closing, overlap. Bigger is not always better. The trend seems to be the 110 degree LSA, Factory cams were closer to 113-114 LSA. Why? The factory lift was fairly consistent around .406" to .413" with the Ram Air IV being .518" with 1.65 rockers. What Pontiac so often changed was not the lift, but the duration. Read a few road tests of the GTO's with the bigger cams -narrow power band and needed the 3.90 and 4.33 gearing to keep the car/engine in this band. Great for racing, not so much for the daily driver/car show circuit. And, if you go big cam, can your engine, or even drivetrain, handle it?

Take the time to learn as much as you can about camshaft terms and how each of these has a different effect on HP, torque, air flow, cylinder pressure, dynamic compression, static compression, back pressure, reversion, RPM range, power band, etc.. Just because someone shoots down your selection or suggests another doesn't always mean it will work for your combination. Remember, Pontiac did a lot of research into their cams and they worked pretty good - or the GTO would not have the reputation it has come to have now. My recommendation is to build your engine around your cam/piston compression selection, keeping in mind your drivetrain selection as matched up to this.

Don't be discouraged because you think you need 10 t0 1 compression, a 300 degree duration cam with .530" lift, on a 110 Lobe Separation Angle, and are shooting for an 11 second car. You want a compromise of streetability, some kind of gas mileage, able to use pump gas, and have a broad HP & torque band. Do a lot of reading and research, talk to people, check out some of those U-tube videos on Pontiacs.


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## geeteeohguy (Feb 2, 2008)

Well put, Jim, as usual. I think the OP wants a reliable, basically stock '65 ragtop that he can drive on pump gas while keeping the 389. He can easily do this on the cheap with the right custom pistons and camshaft, all else being equal. His car probably has a 3.23 rear end, which will work well with a stock-ish 9:1 build.


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## extinctmake (Feb 8, 2011)

You guys are on the same page I'm on in terms in what I'm looking for. I am not taking a $45,000 '65 GTO convertible to the drag strip. I'm not looking to brag about my compression ratio only to ping all the way home from the Wednesday night cruise-in.

What I'm looking for is to keep my '65 GTO convertible the way GM built it. I want to keep the #77 heads, intake, AFB carb, etc., but run on today's lousy gas.

It would be great if this car performed fantastic on the street while running on 87-92 octane gas. Geeteeohguy provided a blue print with what he helped a friend build. 

I want to think PontiacJim thinks running a Pontiac cam is the way to go and I have no problems doing that. I think the XE268 cam Geeteeohguy likes is snottier and if it is streetable, I am open to choosing that cam. 

I am runnning a 3.23 gear. A Muncie M20 4-speed. As a matter a fact, the rear axle in my car is a 3.23 open axle. I have a Safe-T-Track differential, but even if I swap out to a posi rear I plan on keeping the 3.23 gears. I want my car to perform like a good street GTO should only on the low octane swill.

If I wasn't so adamant about keeping my car numbers correct, I'd build a 1971 400 GTO engine for my car that will run on the 87 octane gas. 

You guys are helping me figure out a plan to rebuild my numbers matching 389 WT, #77 head, Carter AFB, GTO engine to run great on today's gas. 

I'm not looking to build a violent strip/street thumper. I want to keep my GTO factory looking, performing like a GTO should, and run on the 87-91 octane fuel that is the reality today.

You guys are a big help. Geeteeohguy, where can a guy get these Ross pistons that your friend put in his 389? It sounds to me that I would like to replicate what you helped your friend build for his '65 GTO. I think if I can get the right kind of pistons to get my compression down below 10:1, I'll have something to work with. 

I am open minded about camshaft suggestions.


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## PontiacJim (Dec 29, 2012)

My opinion. I don't care for the Comp XE cams on 110 LSA on a higher compression engine from what I have read. I had the XE274 in my 72 400 low compression engine. It did work great great. Power with the 110LSA cams seemed to fall off sharply around 5,600 RPM's, and you can feel it. Have read this same thing on many other blogs as well. I like to spin my engines, and I don't think you will be pushing it hard like I did to 5,800 RPM's. So probably not a factor for you. What I have read on many websites is that the 110LSA works good on low compression engines because it builds cylinder pressure based on the valve opening and closing cycle. Using this on an engine that already has a high compression, may compound an already high compression situation unless you go with high octane gas. For my build, I believe I am going with a 112LSA cam. This seems like so little in difference, but that's all it takes to make a good cam or one you regret. I want a little broader power range as the 110LSA is more aimed at a narrower power band. Factory cams were yet wider on their LSA. The Pontiac Factory "068" cam is always a good solid choice.

What I also think you want to do, and get, is a .040"-.045" quench tolerance- that air space between the piston and the bottom part of the head that is in the combustion chamber. This is supposed to squeeze the gas into the combustion chamber and minimize the tendency for detonation due to the small layer of gas/air that can ignite if that air gap is larger. This is why you may read the term "zero deck the block". The rotating assembly is mocked up in the block and the distance measured from the top of the block to the top of the piston. This amount of material is then milled off leaving your piston top even with the block surface. Then a head gasket that compresses to .040" or .045" is used to get the .040" - .045" quench speck. However, another way to do this, and what my machinist is doing, is use a Cometic gasket for the Pontiac that is .027" thick. He will then use the thinner gasket to determine how much he will have to deck my block, if nothing more than a clean up pass, to get me the .045" quench area. I am using open chamber heads, 1972 7K3's. So you may need some input from those who have the earlier closed chamber heads as you do. Getting a good quench tolerance is an operation that will help to minimize detonation.


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## geeteeohguy (Feb 2, 2008)

extinct, you'll have to contact Ross. Meantime, I'll try and get the amount of dish the pistons have. The reason the XE 268 cam works so well in my friend's 389 is because it's a low compression engine and theXE cams fill the cylinders early. His engine at 9:1 produces the same or more power than mine at 10.75:1, and he can do it on 89 octane. I must use 100 octane. Jim, this IS going to be a 'low' compression engine. An o68 cam will work (I'm using one in my 9.3 400) but an XE will work a bit better here. I need to get the numbers, though, as I suspect the actual CR of my friend's car might be as low as 8.7, as it will run on 87-89 octane. It runs _much_ harder than a stock '65 GTO. Extinct, with the right combo, you CAN have your cake and eat it, too.


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## PontiacJim (Dec 29, 2012)

Geeteeohguy, Yep, I'm on board IF you go with the lower compression to take advantage of the XE cam, that's why I pointed this out using it in my '72 400 build. I used those aftermarket/generic inexpensive (comes in a kit rebuild) cast pistons with 4 valve reliefs, that look like they are doubled up and make 8. I suspect my compression was not very high on that engine. The XE worked great up to about 5,600 RPM's. It sounded like extinctmake was still looking a the 10:1 compression which in my opinion makes the XE cam a poor choice. Many guys rebuilding their engines seem to shy away from lower compression when in fact it is the better way to go in the long run and the XE takes advantage of this and still makes the lower compression work.

So, if the compression is dropped as you state, then the XE is a good choice and will perform well, my engine pulled real hard to 5.600 RPM, I could hit 100 MPH from a dead stop right quick with 3.23's, and no detonation issues. I always used the cheapest gas at the pump which around here is 87 octane.


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## geeteeohguy (Feb 2, 2008)

Jim, as you know, the 8 relief jobber pistons are not optimal. They sit way down 'in the hole' and are champhered at the edges, too. Terrible quench tendencies and more likely to ping even with less compression. I'm glad they worked out for you. My buddy verified that his cam is an XE268H, and is looking for his piston specs. I installed the pistons, and they sat near flush with the block, are light forgings, with a nice dish in the center. Not cheap, but as I said, his low compression engine runs as hard or harder than mine, and I have at least 2 compression points on him. With today's camshaft choices, high compression is indeed over- rated.


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## extinctmake (Feb 8, 2011)

Geeteeohguy, how does your friend's 389 idle with that XE268H cam? It sounds like I can get the Ross pistons you've mentioned and then have the machine shop zero deck the block. Did your friend do anything to his heads beyond hardened valve seats and a normal valve job, or did he have some port work done as well?

Everything PontiacJim mentions in his last post is how I'd like my car to perform. I sounds like what I need to achieve that goal is to replicate what GeeteeOhguy's friend did with his 389.


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## geeteeohguy (Feb 2, 2008)

Extinct, I couldn't talk my friend into doing anything with the heads. Not even hardened seats. Hardened seats aren't really needed on a Pontiac unless you pull a trailer or operate for extended periods over 3,000 rpm. His car idles very well, with a slight lope that does not affect good low speed operation. It's responsive as heck right off idle up to redline (5200 rpm) and gets decent fuel mileage. He is running a 3.36 gear and an M20 4 speed. I can't believe how well his engine runs for such a low cost, throw-toghether build. It is putting out more power than it did originally with high compression, and it runs all day on non-premium pump gas. Win-win. He is running the cast iron HO exhaust manifolds with a Pypes 2.5 inch exhaust system. The car drives _very_ nicely.


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## PontiacJim (Dec 29, 2012)

Geeteeohguy, yep, I think I read one of your posts speaking of these pistons. I know now they are not a good selection, but I had faith in the machine shop I was using at the time. I was also on a budget and wanted inexpensive cast, but thought I was at least getting some kind of quality like factory. When I watched him remove my manifold-to-exhaust pipe stud with the torch and blow it out, and my manifold, I knew then I was in trouble. Thought as a machinist he would have cut the stud flush, chuck it in a drill press, and drilled it out. Hell, I could have done that myself. Needless to say, that was the shop that my engine with the bad oil pressure was done at. Oh, well, live and learn.

Extinctmake, you should not need the hardened seats as Geeteeohguy states. What you do want to do is use stainless steel valves. This seems the way to go instead of hardened seats. They are fairly reasonable to buy. I think I got my set at PAW if they still exist. Geeteeohguy might have some recommendations on this. I would not invest too much, if anything, on porting for a street car. Maybe port matching. You can do more harm than good sometimes if you don't know what you are doing. The best thing will be a good performance 3-angle valve job on the heads. One of my older Pontiac build booklets states that your 389 heads have 3/8" press-in rocker studs and to replace these with the 7/16" screw-in studs. Install the factory push rod guide plates. You can replace the intake valves with 1961-62 Chevy Hi-Po valves which are 1.94" in diameter, having a slightly longer 4.915 vs. 4.870 length. They are tuliped and swirl polished. (If nothing else, I would go with the larger 1.94" valves if you are buying valves anyway. I don't think you really need "tuliped" valves - talk to your machinist on this option before you buy your valves). Any larger may shroud the valve and not be beneficial. 

Your exhaust system needs to be good as well. As mentioned, the 2 1/2" pipes, and add a crossover pipe. Appears the "X" crossover style pipe performs better than an "H" crossover pipe. Pontiacs need to breathe.


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## BearGFR (Aug 25, 2008)

Also be aware that Pontiac published those numbers that were "blueprint" specs. Engines built to exactly those tolerances would have the stated compression ratios. However, factory engines weren't ever built to those tolerances. It was a game that allowed racers to build engines to race in NHRA Stock classes (built to "factory blueprint" specs) but were still race engines that made a lot more power than their street counterparts.

I have an Excel spreadsheet I wrote, linked inside of a word document, that will calculate actual compression ratios from the needed measurements. I've posted it on here several times so it'll probably turn up in a search.

Bear


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## extinctmake (Feb 8, 2011)

Yeah, I have a stock set up when it comes to exhaust. I also have the OEM Carter AFB. I am under the assumption that GeeteeOhguy's friend also runs more fuel through his scalded cat.

Would the stock cast rods work ok or should I try to find a set of old forged rods? 

I am surprised about the lack of need for hardened valve seats. Nobody is concerned about valve recession? I do like the idea of using larger valves and I am fine without not having to port the heads.

I am trying to come up with a recipe for a numbers correct '65 GTO 389 that will run well for the street on 87-91 octane fuel. I am thinking if I can closely replicate Geeteeohguy's friends' 389 in his GTO, I should be pleased.

I can get by with the current engine in my car, but I would like to start collecting as many of the parts I know I will need to rebuild my OEM engine. I've discussed this project in the past with Bear and Geeteeohguy, but it was about boring the cylinders to fit standard size 400 dished pistons (this idea got shot down) and then I found some Sealed Power pistons that yield 10.1:1 compression (this also got shot down).

I really appreciate everybody's input. I want to make sure I get this engine built right and it will operate on today's fuel.

I think you all have put me on the proper trajectory.


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## geeteeohguy (Feb 2, 2008)

No, my buddy is running a Holley 750 4bbl. Not much better than a stock carter AFB. He is using the stock original rods. As I said, he didn't want to spend any money. I would not recommend 'old forged rods'. Buy a brand new set for less than $300 and you'll be bulletproof. I don't think you'll be able to run larger valves in your stock heads...there is simply no real room to do so. (I could be wrong here). Anyway, there is no need to run bigger valves for your build. Big valves make top end horsepower, which needs revs and lots of breathing (headers and big carburation). You are after a stock or better performing GTO on today's gas. 9:1 CR with dished pistons and a the cam I described will give you very nice performance that's drivable every day.


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## PontiacJim (Dec 29, 2012)

The heads seem to be the limiting factor on the 389, but they still make great power. The factory valves are 1.92". The Chevy 1.94" intakes were spoken of as they were also much cheaper than the Pontiac replacements. It is not much of an increase per say, not like the late 400 2.11" intakes - which would not fit.

I second the use of aftermarket forged rods. You can get a set of rods that look like the factory type very reasonable as cheap insurance. Cost effective when compared to rebuilding the cast rods to make them reliable, but they are still going to be old.

Another performance cam that came up in my search is a step up from the "068" cam, the "744" factory cam. This is listed as a "street/strip" cam and is said to work on the 8.5-9.0 compression engines. I would also suggest to email or talk with one of the many Pontiac engine builders who would most likely steer you in a good direction on cam selection. A cam can be designed 100 ways, you just want the one that fits your choice and engine build. Just remember that more duration pushes the torque range higher up the RPM scale and you don't want to go too big on a cam that does not match the RPM you plan on using.


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## RunninLeMans (Apr 3, 2014)

I made a similar mistake on my engine build, bought the Sealed Power pistons and installed them with a stock head gasket without decking the block at all. Many new pistons are made with a shorter compression distance length than stock assuming you'll deck the block when you rebuild (mine were 1.71", the 288's are 1.70", wrist pin center to piston top). I didn't deck the block as it looked good, and my static compression was lousy (~8.3:1) although dynamic compression/cylinder pressure was adequate with a Lunati Voodoo cam and it's fast closing intake angle. I had to pull it apart and measure everything, discovered my quench height was 0.080" to 0.085" (0.030"-0.035" deck plus 0.049" gasket). Since I'd already had too much time and money into a 326 (another learning story) and was shopping for a block with bigger holes, I decided to re-assemble with 0.027" head gaskets for this year and make the best of it. 

If you can find Jim Hand's chapters on camshafts, advertised duration versus 0.050", dynamic compression versus static, it'll clear up a lot of mysteries. Did for me, wish I'd done all the reading beforehand instead of as I went along...


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## geeteeohguy (Feb 2, 2008)

How does the old saying go? Something like "If you think education is expensive, try ignorance." Great advice, Runnin'!


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## extinctmake (Feb 8, 2011)

So I should replace the rods with forged aftermarket rods (est. $300), use Ross reverse dome forged pistons (est. $600), zero deck the block, give the cylinder heads a three-angle valve job and don't worry about hardened valve seats (use stainless steel valves?), install screw in rocker arm studs, and I should consider using a Comp Cams XE268H cam and use guide plates.

Speaking of Comp Cams, I checked the specs for this cam and upon doing so, noticed there is a complete kit recommended for this cam. It has the cam, lifters, timing set, valve springs, and valve keepers & retainers. I also saw the recommended push rods and the guide plates. Something else I would consider is the 1.52 ratio roller rocker arms they listed. Would these rocker arms fit under my stock valve covers? 

I really appeciate the input in this thread. I plan on collecting parts for this project soon. I know I will have to do something about getting my GTO to operate on low octane gas and operate on it well.


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## geeteeohguy (Feb 2, 2008)

Your heads will need to be modified for the guideplates. A machine shop can do it. My buddy didn't use screw in studs or guideplates on his, and it's fine. I have the stock press-in studs on the original #77 heads on my '65 GTO with a .490 lift cam, and have been running it hard for over 30 years with no problems. What I'm saying is; screw in studs and guideplates are great, but not necessary with a build like this. If you want to do it, it's peace of mind. But not a deal breaker if you don't. Using the matched 'kit' from Comp cams is what I'd probably do, though. Stock rockers are 1.5, so 1.52 would be pretty close. A lot of guys run the 1.65 rockers, but that would make your optimal cam more 'radical' and as a daily driver, not really practical. Keep is simple with good quality parts and you should be happy. You are on the right track.


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## extinctmake (Feb 8, 2011)

What do you think of these rods from Butler Performance:
Part # Description Price Per Set 
RPM-LG5-6625I Pontiac 6.625 I-Beam 5140 Forged Replacement Rods 980 Pins Press Fit - 7/16 ARP Fasteners $288.95 

I am fine without using screw-in rocker arm studs and guide plates if my engine is suitable as is for the street use I am intending.


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## the65gto (Oct 9, 2008)

Many years ago? late 60's, had my heads in the machine shop for a general check up and asked the machinist to just pin my press in studs


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## geeteeohguy (Feb 2, 2008)

extinct, call Butler and tell them what you are planning and what you have. I don't know the part numbers and applications of the forged rods, as I've never used any of them. You'll need to do the same thing with the pistons....my advice would be to get a good machine shop picked out and work with them, most definitely a Pontiac-oriented shop. There are several good ones, Jim Lehert of Central Virginia Machine Service is one of the very best. If you have not done this before, it would be very wise to enlist the help of an expert who can help you choose the right piston/cylinder clearance, ring pack, crosshatch, rods, etc. and possibly assmble the short block for you. It's pretty simple, but everything has to complement everything else, or it will turn out less than perfect. Get it right the first time. Again, you are doing all the right things, asking questions, forming ideas, etc. You have a firm grasp on what you need/how to get it, and haven't spent any money yet. Well done....and how to get the most for your $$$.


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## RunninLeMans (Apr 3, 2014)

You might also look into the Lunati cam kits, especially the Voodoo series, they are gaining a following lately. I have the relatively mild 901 Voodoo in my 326, 213/219 0.050" duration, I'll post a review in a couple weeks when it's on the road. I believe the 903 would be comparable to the XE268...


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