# 72 GTO - Motor Rebuild / Questions



## stracener (Jul 27, 2010)

So I've got a '72 GTO-- not the most notorious or powerful machine, but I'm looking to ramp up the motor and especially the low end street performance. 

It's got the original (or at least original coded YS) 400 block and a Qjet 4bbl carb(A7059206 - 6575 CBF). Looks like the intake was modified, it says "Edlebrock" and "Pontinac Performer" on it. Looks like it's cast iron, same as the block. My best guess is it's a 2156.

Cylinder heads are stamped 7K3 which looks like stock '72. 

I'm looking at about a $3,000 rebuild budget. I think that the first step is pull it all apart, take it apart, have the block professionally inspected to see if it is cracked, needs to be overbored, cleaned, etc..., and then - aftermarket performance parts. 

Specifically looking at: Edelbrock 72 cc heads vs Kaufmann 74cc heads

Headers: Dougs vs Hedmann vs Hooker

Cams: tons of options, but leaning toward Lunati 60903LK	Voodoo Hyd Cam Kit - Pontiac V8 268/276 just because of the hot sounding idle (chicks dig that!??). Overall, I want something that sounds really cool, moves quickly on the street and works with a/c and power steering. Not too concerned about the top end. 

With the 72 or 74 cc heads; stock stroke and bore; and headers; will a 268/276 cam work, or is that too much?

Would like to keep the crank, rods and pistons, assuming they are okay after inspection. I think I MAY have a bad piston... assume I will have to change all rings. Not sure if it will need an overbore which would (I think) require new pistons and rings, but could still use same crank and rods (assuming no damage). 

If I can't keep the crank, would likely make it a stroker (but that will be a lot more $$). 

I've seen lots of articles about some pretty hot comp cams and KRE heads and intakes. I think my intake is okay, but not sure, think I have the Edelbrock 2156. In addition, think I should upgrade the ignition system. 

Any thoughts or inputs would be greatly appreciated. I'm about a month away from upgrading this motor, still welding, grinding, and busting rust at the time being. 

All the photos at:
MobileMe Gallery


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## 05GTO (Oct 6, 2004)

That awesome sounding idle will come from the 110 degree LSA, some of the problems you'll see is a need for a stall converter, low vacuum at low rpms and idle affecting the timing, tranny shift points and vacuum assisted brakes. 

I would bump it up to 112 or 113, maybe something like a RamAir IV cam which has a little higher RPM range.

Just my humble opinion,


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## jetstang (Nov 5, 2008)

Is this father or son talking??
Intake is Aluminum and is a really good intake for street duty.
I've heard a car with a comp cams 268, and it sounded real good. Lunatti voodoo cams have great cam profiles for good power, that would be my choice. Aluminum heads, sweet! 
Hell of a build, keep it up!


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## 66tempestGT (Nov 28, 2009)

comp 268 is a puss at least 280 for a 400. vac will suffer a little. power brakes may not like it. i wouldnt waste my money on fancy heads if a weak cam and intake are going to negate them. ponchos make bookoo torque but you dont need crazy cams and flow to get it. do you want radical sound or a tire melter? :cool


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## 66tempestGT (Nov 28, 2009)

let me be the first to say "068 cam". oops just kidding.


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## jetstang (Nov 5, 2008)

66tempestGT said:


> comp 268 is a puss at least 280 for a 400. vac will suffer a little. power brakes may not like it. i wouldnt waste my money on fancy heads if a weak cam and intake are going to negate them. ponchos make bookoo torque but you dont need crazy cams and flow to get it. do you want radical sound or a tire melter? :cool


You kind of contradict yourself Shane, hmm. 
Auto car needs a milder cam or big stall.
Check with Butler performance, they make huge power on pump gas.
7K3 heads are 96 CC, but only made 250 HP in that motor, so did they dish the pistons or just too big of ports on the heads? Need more compression. Or is 72 the year they switched from net to gross HP?
That Lunatti cam sounds perfect for a street build.
I'm sure your bottom end is a keeper, may need a bore and crank cleaned up. Pistons are cast, I would probably change them, and if you want to make a lot of power, go to forged pistons.
On a $3K budget, aluminum heads are going to eat most of that money, $4k should get it done.


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## stracener (Jul 27, 2010)

What's the tradeoff with the stall converter? I'm not sure what that does.


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## Jeff's Classics (Feb 24, 2010)

stracener said:


> What's the tradeoff with the stall converter? I'm not sure what that does.


A higher stall converter will slip up to a higher RPM/torque before delivering power to the driveshaft/diff. It's sort of luck slipping the clutch in a manual transmission car. It's needed if your engine/cam setup doesn't make much power in the lower RPM range, but it can be kind of a PITA if driving around at low speeds, such as parking lots, stop and go traffic, etc. And, depending on your rear gear ratio, can cause excessive heat in the transmission due to slippage at low/moderate speeds. Example of a bad application is a high stall converter in a car with an overdrive trans, which can cause the torque converter to slip constantly at lower highway speeds. A slightly higher stall speed can be fun and increase 60-ft times, too high can ruin the enjoyment of a car on the street IMHO.
Jeff


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## stracener (Jul 27, 2010)

Thanks guys. Father talking here, Dave. I know my son, Andrew, has posted in other areas. We're both rookie's at this, trying to find our way with a great project vehicle. 

I've e-mailed with Bruce from Rock n Roll Engineering about putting on 87cc Ebrock heads, improved cam, and headers. Think that's probably the way to go with this motor. It will also need new pistons. 

I don't think there is a need to "stroke" it out, think that with better heads, more aggressive cam, and better exhaust flow we can tweak enough hp out of it to make it work.


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## jetstang (Nov 5, 2008)

If you build enough motor,the trans, stall and rear dont' really match it, the car will still be fast. My buddy has a 63 Chevy II with a radical 355 circle track motor, and it scared the hell out of me, it may not produce great numbers on the strip, but was hell on the street. He didn't have a good, 3500 stall or 4.11 gears.


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## stracener (Jul 27, 2010)

So... adjusting the budget (upward), and doing some more research, we've found a machine shop locally that can do the block testing, boring and honing, then here's what we're looking at for this '72 400cu rebuild (at least one piston is shot, so absolutely have to swap pistons):

From Butler Performance:
New Forged Crank 4.500 Stroke 3" Main (this seems to make a BIG difference for low end tourque?!) 
Forged Ross Pistons and SCAT H-beam 6.800 Rods w/ARP 2000 bolts

From Rock n Roll Engineering: 
Eddlebrock 87cc ported heads
Hyd roller cam AND lifters

Summit racing: Doug's Headers
Fel Pro gaskets 

WE've got the Ebrock Performer intake and a Qjet 4bbl carb. Will we need new rocker arms? Suggestions? 

Still thinking about replacing the carb at some point, just want to get it driving. I'm assuming it will need distributor as well. 

Thoughts about this set-up?

What are we missing?

Dave <--- don't know much about engines !


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## freethinker (Nov 14, 2009)

stracener said:


> So... adjusting the budget (upward), and doing some more research, we've found a machine shop locally that can do the block testing, boring and honing, then here's what we're looking at for this '72 400cu rebuild (at least one piston is shot, so absolutely have to swap pistons):
> 
> From Butler Performance:
> New Forged Crank 4.500 Stroke 3" Main (this seems to make a BIG difference for low end tourque?!)
> ...


i would spend about 3000 less and get the same power. stock rebuild on the 400 with a mild comp cams cam. then put nos on it.
pontiac blocks dont need to be honed, waste of money. stock cranks are fine because pontiacs are low rpm engines. hell i used to circle track race pontiacs and we used a stock crank with no failures. that means you dont need fancy high dollar roller cams or rockers or forged pistons for pontiac for street engines. pontiacs seldom break parts if they are kept under 6000 rpm. the weakness in a pontiac is the oiling system. they are famous for spinning rod bearings.
i cant tell you how many people i have seen put big bucks in a street engine and the pos wont be driveable on the street. 
i advise keeping the engine close to stock and let the nos system give you your short bursts of power.


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## jetstang (Nov 5, 2008)

freethinker said:


> i would spend about 3000 less and get the same power. stock rebuild on the 400 with a mild comp cams cam. then put nos on it.
> pontiac blocks dont need to be honed, waste of money. .


Why wouldn't you hone the cylinders? 

Stacener, if you are just trying to get it running, do a stock rebuild .030 over pistons, and a cut crank. Then, later do the performance rebuild. Buy Jim Hands Hi-performance Pontiac book and read it, he is the man. I haven't read it yet, and just put a 350 in my 70 with a bigger cam, and I'm not happy with the performance, Pontiacs like cubic inches, big torque motors.
If you are going to run the aluminum heads, Forged Pistons and Roller cam, I would get the Tomahawk intake, Demon or Holley 750 and MSD ignition. Roller rockers for the big motor is good money spent, for a stock rebuild they're not really worth the expense. Don't forget the tranny and rear in your build, budget for it.


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## Jeff's Classics (Feb 24, 2010)

freethinker said:


> i would spend about 3000 less and get the same power. stock rebuild on the 400 with a mild comp cams cam. then put nos on it.
> pontiac blocks dont need to be honed, waste of money. stock cranks are fine because pontiacs are low rpm engines. hell i used to circle track race pontiacs and we used a stock crank with no failures. that means you dont need fancy high dollar roller cams or rockers or forged pistons for pontiac for street engines. pontiacs seldom break parts if they are kept under 6000 rpm. the weakness in a pontiac is the oiling system. they are famous for spinning rod bearings.
> i cant tell you how many people i have seen put big bucks in a street engine and the pos wont be driveable on the street.
> i advise keeping the engine close to stock and let the nos system give you your short bursts of power.


If you don't hone the cylinders the new rings won't seat and you'll be tearing it back apart due to excessive blow-by and low cylinder pressure.
If you want to run NOS you will HAVE to run forged pistons. Cast or hypereutectic pistons will quickly break when using NOS, especially if you don't have your fuel system and ignition timing properly setup.
I do agree that a stock based engine with a nice cam, good flowing heads and intake, propertly setup ignition and carb will be a LOT of fun on the street without breaking the bank.
I've also heard very good things about Butler Performance, and Kaufman heads, which I plan to use on my '68 GTO eventually.
Jeff


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## Rukee (Feb 8, 2007)

:agree forged pistons with NOS is a must! Also balance the rotating assembly.


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## freethinker (Nov 14, 2009)

jetstang said:


> Why wouldn't you hone the cylinders?
> 
> 
> .


i was talking about honing the main bores. we dont hone cylinders. we rebore them.


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## Rukee (Feb 8, 2007)

Main bores? You mean the main crank journals? That would be line boring the block. You could hone the cylinders even if you don't overbore. I have a honing stone tool fits into a drill and would never replace rings without honing the cylinders. You don't want to overbore unless you HAVE to, IMO anyway.


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## freethinker (Nov 14, 2009)

Rukee said:


> :agree forged pistons with NOS is a must! Also balance the rotating assembly.


no they arent. but its probably a measure of safety if money is no object. the most stress on a piston is not the power stroke. the most stress on a piston is the upstroke. centrifugal force tries to pull the piston and rod apart at the top of the stroke. this is also a function of rpm and pontiacs being a low rpm engine you dont need forged pistons. 
i personally would not use forged pistons in a street car. forged pistons require at least 3 thousands clearance. this creates a noisy engine that will wear out rings sooner that stock cast pistions. but to each his own i guess.


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## Rukee (Feb 8, 2007)

Noisy engine? What? 
Run an early stock GTO with cast pistons and you will/can break them with pump gas with just a timing issue. I know, I have a broke one here was in the car when I bought it 16 years ago. A forged piston will withstand far more abuse then a cast one will, and let's face it, NOS is abusive to a piston. I installed forged pistons back then and have never looked back. And I drive hard and often. Engine does not burn oil or is it noisy, it sounds awesome, check my videos, but like you said, to each his own. :cheers


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## jetstang (Nov 5, 2008)

:agree Forged piston engines do burn more oil than a cast piston due to the additional cylinder wall clearance. But, the additional clearance is because a forged piston grows more at operating temperature, thus reducing the excessive clearance. So, as long as you let the engine warm up the forged piston wears the same or less than a cast piston. 87-92 Mustang 5.0s had forged pistons, 93s used hyperetech, that is why all the stock motors are living on the strip and run fast, but they use about a quart of oil every 1500 miles, at least the 6 I owned did.
Forged pistons are a must in Nitrous/blower/turbo motors, unless you are building a hand grenade motor. If the budget doesn't allow pistons, keep it off the bottle for everyones safety.
Freethinker, have you ever seen spark plugs with the electrode burnt off because of a lean condition on a nitrous motor? Happens all the time, imagine the piston taking the same heat?


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## stracener (Jul 27, 2010)

WoW... a lot of great advice and excellent discussion on the motor rebuild. We're gonna start the disassembly this weekend, or next, but it will take us a while! Thanks again for all the insights, I'll ask more questions as we go along.


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## stracener (Jul 27, 2010)

JETSTANG: great advice on the Jim Hand Book - Building High Performance Pontiac V8's. That book is loaded with practical information by a proven professional. Thanks for the recommendation.
Dave


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## jetstang (Nov 5, 2008)

No problem. He is also on the Pontiac Years forum, so you can ask him questions directly.


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