# compression



## deanhickey (Apr 6, 2015)

Wondering what compression i should be looking for in a 400 with a 68cam. i will be taking cold readings as the carb has been sent off for rebuild. any info will be greatly appreciated.


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## deanhickey (Apr 6, 2015)

*Readings*

1-150
2-150
3-160
4-180
5-150
6-150
7-155
8-60

Looks like #8 is bad. 3and 4 slightly higher.
any comments or observation? need all the help I can get.:confused


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## PontiacJim (Dec 29, 2012)

deanhickey said:


> Wondering what compression i should be looking for in a 400 with a 68cam. i will be taking cold readings as the carb has been sent off for rebuild. any info will be greatly appreciated.


From the 1968 Service Manual.

Compression test needs to be done warm engine and all spark plugs removed. Spin engine over through 5 compression cycles before doing test.

8.2 - 9.2 compression engines - regular fuel. 150-170 PSI @ 155-165 RPM's
10.5 - 10.75 compression engines - premium fuel. 185-210 PSI @ 155-165 RPM's

Note: Low compression pressures on HO 400, HO 428, & Ram Air engines are not a valid indication of engine condition. Due to the long valve overlap period with camshafts used in these engines, compression readings at cranking speeds as low as 120 PSI are considered normal.

No cylinder should be less than 80% of the highest cylinder reading.

_Number 8 does look bad.
_
:thumbsup:


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## deanhickey (Apr 6, 2015)

Thanks Jim, Just sent the Carb out to Cliff to be redone I guess i will be pulling the engine now, I hope its not the block.


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## PontiacJim (Dec 29, 2012)

deanhickey said:


> Thanks Jim, Just sent the Carb out to Cliff to be redone I guess i will be pulling the engine now, I hope its not the block.




Na, don't get so negative. Probably just worn out rings or even a bad valve. Good excuse to freshen up the engine and get it running like new again. Even IF you had a bad cylinder, they can be sleeved so it can be saved. Stay positive. :thumbsup:


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## deanhickey (Apr 6, 2015)

Thanks, I needed some positive news. having it refreshed is on the list, it just moved to the top.


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## PontiacJim (Dec 29, 2012)

deanhickey said:


> Thanks, I needed some positive news. having it refreshed is on the list, it just moved to the top.


You did not say how many miles on the engine or why you decided to do a compression check.

Was it burning oil or smoking out a tail pipe? Running poorly/missing?

You may want to also pull a valve cover to make sure the rockers have not loosened up on that bad cylinder. I am thinking if a valve is not opening fully, your readings may be affected. Once purchased a '68 GTO that the guy thought the engine was bad. It ran, but poorly. Pulled a valve cover and one of the rocker arms has loosened up and gone sideways off the valve. No damage, just put it back on and tightened it up and that car would catch rubber on a hard 1st to 2nd shift of the TH-400. Next time I saw him I told him about it and I could see the regret in his eyes 'cause he thought he was selling a car with a bad engine - cheap.

So, you may want to check a few things just to be sure, could even be a worn cam not opening the valves fully. Otherwise, you need to do the rebuild.


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## deanhickey (Apr 6, 2015)

She has been running good, getting second gear rubber on Saturday. Just had the time to do a test on her after i pulled the carb off. exhaust has been clean only smoke was from the tires.


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## deanhickey (Apr 6, 2015)

the milage is a bit of a mystery i would guess around 150,000. I will pull valve cover tomorrow and take a look and see what ti find. Have started to look for a good machine shop in Maine. I am actually looking forward to getting the running gear back up to spec. I will have to make my mid up on weather to put dished pistons in the engine so it will run on pump gas. Have you done this? How big of a reduction of power would there be?


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## Goat Roper (Oct 28, 2014)

deanhickey said:


> the milage is a bit of a mystery i would guess around 150,000. I will pull valve cover tomorrow and take a look and see what ti find. Have started to look for a good machine shop in Maine. I am actually looking forward to getting the running gear back up to spec. I will have to make my mid up on weather to put dished pistons in the engine so it will run on pump gas. Have you done this? How big of a reduction of power would there be?


I just did this, dished forged pistons and forged rods 30 over on the bore.
Compression ratio is 9.5-1 and the goat runs like a scalded ape on pump gas.
The old 335 HP was tired and now it is around 370 with the cam.
It will smoke the tire going into second with the TH-400 no problem in fact I really have to baby it so it doesn't chirp on the shift.
My experience with different engines is if you just do the top end it puts pressure on the old tired bottom end and you end up doing the whole engine anyway.
Go big or go home.
:grin2:


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## deanhickey (Apr 6, 2015)

Goat Roper said:


> I just did this, dished forged pistons and forged rods 30 over on the bore.
> Compression ratio is 9.5-1 and the goat runs like a scalded ape on pump gas.
> The old 335 HP was tired and now it is around 370 with the cam.
> It will smoke the tire going into second with the TH-400 no problem in fact I really have to baby it so it doesn't chirp on the shift.
> ...


What cam did you use? I have a 68cam (ys 1968 code engine) with a th400 and 3.36 gears (ZG code rear end) . this is all stock. would I need to change the cam and gears? I would like to keep it as stock as possible, but still smoke the tires.


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## Goat Roper (Oct 28, 2014)

I used these rockers.

COMP Cams: Magnum Roller Rocker Arms: Pontiac; 7/16" Stud, 1.52 Ratio

I used this cam and lifters.

COMP Cams: Xtreme Energy™, XE262H: Cam & Lifters

I used these pushrods.

COMP Cams: High Energy Pushrodsâ„¢: 5/16" Diameter, 9.146" Length

My rear end is a 2.93 ratio so you shouldn't have a problem with your 3.36 rear end.


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## RunninLeMans (Apr 3, 2014)

Dean - I have some experience with a couple shops in Maine, PM me and I'll email you some info.


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## deanhickey (Apr 6, 2015)

PontiacJim said:


> You did not say how many miles on the engine or why you decided to do a compression check.
> 
> Was it burning oil or smoking out a tail pipe? Running poorly/missing?
> 
> ...


Hi JIM, just a quick update, I poured some mystery oil in the cylinder and let it sit over night blew it out and tested it. the pressure came up to 180psi. There must have been a stuck ring. thanks for all the advise.


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## PontiacJim (Dec 29, 2012)

deanhickey said:


> Hi JIM, just a quick update, I poured some mystery oil in the cylinder and let it sit over night blew it out and tested it. the pressure came up to 180psi. There must have been a stuck ring. thanks for all the advise.



My Opinion. 150,000 original miles on an engine of the 1960's is much. They are not today's engines that have better fuel management which in turn gives longer mileage. With a carb engine, most of the ring/cylinder wear comes from the carb during the warm-up/idle time. The choke is closed and the carb runs rich which washes the cylinder walls down of lubricating oil.

When you add a squirt or two of oil into a cylinder and then re-test the compression, the oil acts as a ring seal and the compression WILL come up - so it is an indicator that your rings are worn or cylinders worn. Read this: Compression Wet Test Procedure: Results Easily Explained

That said, your engine mileage & the oil test would indicate to me that the engine is in need of a rebuild. And, at that mileage, if the oil/filter was not changed regularly and the engine saw any hard action, I would not trust the rod bearings at this point. Rod bearing failure are one of the killers of a high mileage Pontiac engine. :yesnod:


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## deanhickey (Apr 6, 2015)

I still plan on the rebuild, it just made me feel better knowing the block wasn't the cause. still have to deal with the high compression engine vs pump gas problem, so a rebuild is in the near future. will be going with dished pistons hope to drop the compression down to 9.5 and go .30 over on the bore.


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## PontiacJim (Dec 29, 2012)

deanhickey said:


> I still plan on the rebuild, it just made me feel better knowing the block wasn't the cause. still have to deal with the high compression engine vs pump gas problem, so a rebuild is in the near future. will be going with dished pistons hope to drop the compression down to 9.5 and go .30 over on the bore.


OK, good. Didn't want you to think the engine just became "good to go" and then something happened.

Lowered compression is the way to go. I will also suggest, as will most evryone here, that you purchase a set of forged connecing rods to replace your original rods. They are stronger and by the time you rebuild the stock rods & add the better ARP rod bolts, for a few dollars more you get a much better rod that you will not have to worry about and can take the upper RPM's if you choose to build a nice stout engine that'll spin a few RPM's. Don't know how current these prices are, but $298 is not bad. http://butlerperformance.com/c-1234...ternal-rods-5140-forged-replacement-rods.html

Plenty of info on the forum that should help in deciding on how you want to go with your engine with regards to performance level - stock, modified, or all out. :thumbsup:


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## bigD (Jul 21, 2016)

"...Don't know how current these prices are, but $298 is not bad..."


I think you can buy those rods directly from RPM for $288 shipped.

SAE 5140 STOCK ROD

But, at the time of this post their site is showing that they are out of stock.

They also sell H-beam rods which are lighter and stronger, for $400 shipped. They are showing to have some bushed H-beams, in stock--but are out of stock on the press-pin H-beams.

SAE 4340 STEEL H-BEAM

Eagle H-beams are a little higher.

http://www.cnc-motorsports.com/eagle-crs6625p3d-h-beam-connecting-rods.html

http://www.ebay.com/itm/Eagle-Speci...f48c8e8&pid=100005&rk=4&rkt=6&sd=161863242926

Icon makes a nice dish piston for a 400.

https://www.rpmmachine.com/shop/index.php?l=product_detail&p=6218

http://www.cnc-motorsports.com/icon-ic891-030-forged-dish-pistons-4-150-bore.html


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## deanhickey (Apr 6, 2015)

Thanks for all the info guys. Time to do my home work and get a package put together. I am leaning toward a sturdy stock like set up as it is a driver and i don't race but still like to smoke the tires. Once I have settled on a package i will post it and have the updates on the progression.


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## PontiacJim (Dec 29, 2012)

deanhickey said:


> Thanks for all the info guys. Time to do my home work and get a package put together. I am leaning toward a sturdy stock like set up as it is a driver and i don't race but still like to smoke the tires. Once I have settled on a package i will post it and have the updates on the progression.



Sounds like a plan. You'll want to go with the forged rods & forged pistons. However, the Hypereutectic pistons are also a good alternative for a street build - it is better than a cast piston and not quite as rugged as a forged. I used these on my brother's 360 Mopar build knowing how he drives and uses the car - cruises with it with the occasional light up the tires. Mid price range as well. Like anything else, lot of opinions on hypereutectic pistons.

Keith Black offers these: https://www.summitracing.com/parts/uem-kb346-030/overview/make/pontiac These have a 17 cc dish which with stock 72cc heads/.040 head gaskets, puts your compression about 9.4 which is a good number to shoot for on pump gas.

Here is the Wallace Compression Calculator which can be of help to you in figuring out the numbers to get your compression between 9.0-9.5 for iron heads & 91 octane pump gas. Deck height on most Pontiacs is .0200 down in the bore. Compression Ratio Calculator - Wallace Racing


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## bigD (Jul 21, 2016)

*"Hypercast" Pistons*

"...the Hypereutectic pistons are also a good alternative for a street build...lot of opinions on hypereutectic pistons..."

Yeah, that's right. There are lots of opinions on those pistons. Most everything I've read about the KB hypers, for a Pontiac, are bad. 

I've read that the SP hypers are OK, and work well in Chevy engines, and others. But SP don't make hypers for a Pontiac engine. Have read of lots of failures of the KB hypers, in Pontiac engines. And besides that, they are not cheap. For a few bucks more, you can go to the Icon dish.

You can Google up lots of info on the hypers. It seems that the SP's are OK, but not the KB's. 

https://www.google.com/webhp?source...ereutectic+piston+failures+in+Pontiac+engines


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## deanhickey (Apr 6, 2015)

Ok, I have been trying to figure out what piston, rods and cams to put in the rebuild. he problem is i don't have the the stock engine specs. could some one point me to where i can find the specs for a 68 400 YS with th400 and 336 reared? I have come across a lot of info and am reaching overload. Having dreams about cams and LSA.


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## bigD (Jul 21, 2016)

"...could some one point me to where i can find the specs for a 68 400 YS with th400 and 336 reared?..."

Well, not sure exactly what specs you need. But, here's a site which shows the numbers for the heads, block, & carb, hp & CR rating, cam used.

Wallace Racing's Pontiac Engine Search

All 400's had a 4.120" bore, 3.75" stroke, 6.625" rods, 3" mains, & 2.25" rod big end. The pistons had 4 valve reliefs, .980" pins, and a compression distance(pin height) of 1.70. I've read that most engines were built with at least .023" deck height.

http://www.crankshaftcoalition.com/wiki/Pontiac_V8_engine

The '68 YS engine came with #16 heads. These were said to have between 72 & 75cc chambers. They had screw-in studs, with 2.11/1.77 valves.

What other details do you need to know ?


"...I have been trying to figure out what piston, rods and cams to put in the rebuild..."

With the #16 heads, you'll need dish pistons, to reduce compression. The Icons are the best I'm aware of, without going to custom made pistons. The RPM 5140 rods are the cheapest decent rods. RPM H-beams are better, for about $100 more. The Summit 2801 cam is probably the cheapest decent cam, for your 400. But, if you'd prefer a smaller cam that is closer to the original cam in your engine, there are grinds that are real close to those specs.


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## deanhickey (Apr 6, 2015)

Thanks BIGD, i Have been using some of the online calculators to get the compression number i want (9.5). different ones ask for different things so it gets a little confusing.

I have decided this much. forged pistons (dished),rods, 1.5 on the rocker arms. bored out 30 over. I want to keep the cam fairly tame/close to stock. I am not on a tight budget so i don't mind overbuilding the engine. I only plan to do this once.
I would like the engine to have a little more oomph than stock if it can be done with a mild cam, I just don't want a slug.


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## PontiacJim (Dec 29, 2012)

Don't get your head in a tizzy! :lol: Pretty straight forward, but don't buy anything until you unbutton the engine and look inside.

If you wanted to eliminate a lot of the confusion, why not simply purchase a complete rotating assembly from Butler Pontiac? Go with the 455CI kit (.030" over 400CI & 4.21 stroke crank) as more cubes is more HP and you can get that at lower RPM's - plus it would be perfect for the TH-400 and 3.36 gears. Forged piston, rods, cast crank, rings, bearings, & balanced. $1600. Let them know your heads and what compression you desire and they will recommend it for you. http://butlerperformance.com/i-2445...stroker-kit-icon-for-400-block-4-210-str.html

You'll want a new harmonic balancer to go with the balanced assembly - which they sell.

Your cam selection will depend on several things. Compression, your heads; valve length, spring type/rate, any head work (assume you want to keep stock iron heads). The bigger cubes will need more air to RPM higher, so your heads/head flow will be what will limit this unless you get them to flow a little more. Not a bad thing because what you limit in RPM's you will make up in increased stump pulling torque of larger cubes, and torque is the name of the game. A good 3-angle valve job and a simple clean up of the intake ports will do you good.

My guess with the lowered compression might be near 380-400HP and 475-500 ft lbs of torque and might be able to stretch your usable RPM's around 5400-5500 RPMs with the right cam to match your heads. Don't use a 110 LSA cam as they work better on low compression engines, you probably want 112-114. The factory "068" might be a good choice, but I would want little higher lift with the 1.5's. I like the specs on the Crower # 60918 or #60916 http://www.crower.com/media/pdf/2008b/126-128.pdf Keep in mind that the bigger cubes will make a hot cam in a smaller engine a little more mild. I found this on the web, the Crower 60919: "I put together a + .030 overbore 455 Pontiac, 9.0 compression, stock 455 heads, Ram Air IV exhaust manifolds, factory cast intake, Q jet carb, and an 60919 cam, very similar to the Ram Air IV stock cam. This motor was built to be a very torquey street motor, 72 GTO four speed with 3.42 gears, built for highway cruising. The 60919 crower cam (finally got the number right!) is 231/240 @ .050, .470 lift, 112 LSA. The engine sat for a year before it got dynod just this week.
The numbers: Peak torque, 520 at 3600 rpm. Peak HP, 431 at 5200 rpm." 

The RA IV I feel would be too much as it gives up bottom end torque/power for upper RPM torque/power which your engine really won't be able to take advantage of unless you get your heads worked for improved flow. You would also need to get a higher stall converter. Keep in mind, if you use Butler, they or any other Pontiac builder like KRE, can recommend a cam for your needs as well. :thumbsup:


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## deanhickey (Apr 6, 2015)

Next question, does a 68 block need lifter bore bracing for a street engine or is this for racing or weaker late 70's blocks?


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## bigD (Jul 21, 2016)

deanhickey said:


> Next question, does a 68 block need lifter bore bracing for a street engine or is this for racing or weaker late 70's blocks?


No. Those are for big roller cams with really radical lobes.

http://www.pontiaczone.com/forum/showthread.php?t=26037

But, if you just wanna have it, it won't hurt anything. 

http://www.sdperformance.com/listProducts.php?categoryID=13

http://www.jbp-pontiac.com/products/valveTrain/LifterBoreBrace.html


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## PontiacJim (Dec 29, 2012)

It is said that you don't need it unless you go really big on the lift. My understanding is that the roller cams have a very steep ramp by design and thus opens your valve quicker, maintains the opening longer, and then drops down quickly to close. Roller cams/lifters have been around since the early aviation days. My concern, being a novice and not a cam scientist, is that the fast ramp opening would put a higher side load on the lifter bores during the opening phase of the valve - whether it is a stock lift or something really radical with really radical being an even greater increase of side loading of the lifter bore. So, although it is said you may not need the lifter braces, I think personally I would use them IF I decided to go with a roller cam in a Pontiac engine seeing the lifter galley was not designed for such a cam in mind. Just my opinion here. 

A roller cam is better than a flat tappet hydraulic cam (factory type), but the costs are much higher for a complete set-up. You will read that the rollers are better due in part to wear characteristics. Today's oil has less of the ZDDP needed for flat tappet cam break-in. So, don't rule out a stock type flat tappet cam - you just need to use the proper oil/ZDDP additives for initial/proper break-in. You can also get an additive to put in your oil after break-in or buy oil having the ZDDP in it. I am using a solid flat tappet cam and will use a ZDDP additive for initial break-in. Here is an article with info: https://www.amsoil.com/newsstand/classic-and-vintage/articles/reduced-zddp-and-wear-protection/

So a roller cam, lifters, possibly new pushrods, and I believe distributor gear will add more costs to any engine build. The lifters should also be clearanced for the lifter bore. Here is a little more on lifter choices: http://www.hotrod.com/articles/hppp-0811-pontiac-lifter-guide/

And here are some of the Crower lifter options just for reference: http://www.crower.com/media/pdf/lifters.pdf


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## bigD (Jul 21, 2016)

"...I would like the engine to have a little more oomph than stock if it can be done with a mild cam..."


The easiest way to accomplish this is with a longer stroke. So, I'll agree with PontiacJim on this one. I'd go with a Butler stroker assembly. 

http://butlerperformance.com/i-2459...-400-block-4-250str.html?ref=category:1234863

Or, if you don't have a good Pontiac savvy machine shop, in your area, you can buy the stroker assembly, along with the machined block, ready to assembly. 

http://butlerperformance.com/i-2445...ck-kits-unassembled.html?ref=category:1234783 


"...I am not on a tight budget so i don't mind overbuilding the engine. I only plan to do this once..."

With this in mind, I'd either buy a crate shortblock, or even a complete crate engine, unless you wanna use only your heads and block.

Len Williams can supply either a shortblock or longblock. He can build these with a forged crank, dish pistons, & other options.

455 Short Block

455 Long Block

Sandoval also sells a stroker shortblock, for around $4000. I suggest using flat top pistons and going with 6x-8 heads. These heads are easy to find, for a reasonable price, have hardened valve seats, and will give you a pump gas friendly CR. Even with the "mild cam" that you want, one of these engines will make around 400hp & near 500ft lbs of torque, and will have plenty of vac & a smooth idle. :smile3:

pontiac crate engines


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## BearGFR (Aug 25, 2008)

I agree - don't freak out just yet. Next time you do a compression test, make sure you do it on a warm engine, all the plugs removed, throttle blocked wide open, etc. If you still have a 'low' cylinder, try a few squirts of clean engine oil into the spark plug hole and immediately test that cylinder again. If the readings improve significantly, that's a clue that the pressure is leaking past the rings. If they don't change, then the most likely cause is a leaking valve or possibly a head gasket.

Cam shaft and cam timing has a big influence on the actual readings so don't obsess about the values. An engine with a 'hot' cam with lots of duration will have low cranking compression readings. It's more important for them all to be consistent with each other.

Bear


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## geeteeohguy (Feb 2, 2008)

I recently did a compression test on my '65 and had a low hole....the schrader valve in the compression tester had gone bad. A new valve from NAPA ($2) and I had 170-175 on all 8. I have run into this a lot. Verify with another gauge. When an engine has 60PSI in one cylinder and 100+ in all the others, you can hear the bad cylinder when you crank the engine with the engine disabled. You can verify with a vacuum gauge if you want. The engine will crank and speed up when the weak hole hits compression stroke, so it will sound like: na na na na NEAH na na na na......instead of na na na na na na na na na, etc. Usually, a weak hole in a Pontiac is a burnt exhaust valve, at least in my experiences. 
On Pistons: I've always used the old fashioned forged Sealed Power pistons with great results. I get decades of service out of them with no blowby or ring issues. I have two friends who have built Pontiacs recently with the high tech, low friction ring pack short pistons, and both of them have serious blowby and oil control issues with basically new engines. In my opinion, for longevity, closer to stock is best. I've got 90,000 miles on the 400 in my '67 that I overhauled in 1988, and it still doesn't use oil. Forged Sealed Power pistons and a Melling (068) cam.....


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## deanhickey (Apr 6, 2015)

Hi Scott, Just got in touch with Jason and will be dropping the engine off first week in may! He seems like a really nice guy and a straight shooter. thanks again for the info.


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## deanhickey (Apr 6, 2015)

Update on the engine. After disassembly we discovered the engine was bored .030 over and had a mix of rods and various other cost saving measures . The cam was a Melling SPC-3 cam. So much for a stock rebuild. Have decided to with a 0.040 4.25 stroke with dished pistons and an 068 cam. compression will be in the mid 9"s. will also redo the timing, oil pump, carb has been rebuilt, rods and pistons forged. hope to gain a "little" on the performance side, at least that's what I told my better half. > will post photos when complete.


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## BearGFR (Aug 25, 2008)

deanhickey said:


> ... hope to gain a "little" on the performance side...


Yeah, that ought to wake it up just a tiny bit.... >

Bear


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## deanhickey (Apr 6, 2015)

engine finally in, only took three years.(lol) I think it was worth it. watch a short YouTube video is the only way I could load it.


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