# 66 GTO engine



## Joe60 (Aug 1, 2020)

Hello,
preparing to send my engine out for rebuild. Before I do, I have a question on my engine choice. It's a non-original 400 with 62 heads and an 068 cam. Plan on running the original tri-power. It's a 4 speed car with AC,power brakes and a 3:23 rear end. Any issues with this combination before I spend the money?
Thank you,
Joe


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## PontiacJim (Dec 29, 2012)

No issues I see. Are you shooting for around 9.0 compression for pump gas? The 068 may be a little "soft" with the lower compression. The LSA shows to be 116 which may hurt the lowered compression - if going that route. If keeping stock high compression, 10+, then you are OK, but you may find you need a higher octane or octane additive - unless you live at higher elevations which can use higher compressions.


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## Joe60 (Aug 1, 2020)

Thank you sir! Going to stay with stock compression.
Regards,
Joe


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## LATECH (Jul 18, 2018)

Stock # 62 heads have 75 CC chambers. That will be 10.5 to one . That will be a problem on pump gas.

You need to get your Static CR down to 9.5 to 1 , then choose a decent cam ,so you dont lose all your low end by bleeding off compression with a large cam, just to get it to run without detonation.

Also decking the block, choosing pistons with the correct compression height, correct valve reliefs is para mount .

A Flat top piston works the best . AVOID the stupid looking 8 valve relief style pistons for any poncho motor.

Get a quality forged piston and a set of decent forged rods too.

The right cam and valve spring set is paramount to squeezing out the most power and RPM as possible as well.

Get the block squared.
Check / correct the line bore
Zero deck the block
You will no doubt want to bore your motor,to get a good ring seal. Plate boring/honing = way to go.
Use heads with a verified chamber size of 82 CCs.

82 CC heads with a 400 overbored to .030 = 9.45 to one Static. Perfect for pump gas.
Of course a distributor with the correct timing curve is paramount , and not a difficult task.
Carburetion / Fuel is also important. A quadrajet will work well, and I run one on mine , but I think it leaves somepower on the table , like at higher sustained rpms.I think it gets underfed at higher RPMs. Most likely due to the small float bowl chamber. A quickfuel would solve that becasu it has 2 chambers, one for the primary and one for the secondary. No ones going to bed hungry there.

I am thinking a quickfuel street slayer is in my future.

Later


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## LATECH (Jul 18, 2018)

Your cooling system also need to be up to snuff.

Champion makes an aluminum Rad for a good price. That, a shround, and a thermal fanclutch, 7 blade fan = done.
Running a 160 thermostat is a no win situation. Run a 180. Oil temps have to get warm enough to clean your engine and a cold engine builds moisture. Dont buy into the 160 thing


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## Lemans guy (Oct 14, 2014)

I am a Quick Fuel Tech fan as well.,,,,I run a 780 black with vac secondaries, the black coating is the same jet coat they put in headers, QFT say it reduces carb temps by 6%...

.and on Today’s gas everything helps....

you can curve every QFT carb circuit right in to your desired AFR....from idle and high speed bleeds to PVCR that change like jets...so I like them....

maw far as the thermostat, when I was down at Butler‘A which is near me I asked them about a thermostat. They said they put a 160 in every engine that they build...they build a lot and you should see this place.

now of course that is just when it opens and then it will run according to your set up and ambient temps etc. Hot engines cause detonation so keeping them cool to begin with is the reason I believe.

mine runs about 185 in summer on Highway
With a 160 thermostat...no wrong way, just variations on the range of cooling...

water in condensation and in oil does not have to be at a boiling point to evaporate, clouds in the sky are water vapor and not boiling, as is the evocation off ones arm on a hot day....it is not 212 degrees.


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## LATECH (Jul 18, 2018)

Your engine would still run 185 with a 180 thermostat in it. Theoretically. I could be wrong.
Once the thermostat opens , the temperature is dependant on ambient (outside) air temp, radiator efficiency , air flow across the radiator and coolant flow . The thermostat serves to get the engine up to operating temp quicker.
It also slows the coolant flow down enough in the engine for it to pick up the heat to be dispersed (restriction)
Its also nice on those cold autumn nights.

Of course Butler build some pretty heavy hitters, no doubt. With that much fuel, making that much horsepower, no doubt a lot of HEAT is a by product.Keeping a Butler street beast cooler makes sense. 700 hp on pump gas burns some fuel now, and the By product of all the fuel burning is heat

On a 375 horse pump gas motor it is not as critical.
However , a cooler engine will make more horsepower as the air/fuel charge will be denser , with underhood temps lower.
A cold air intake would solve much of that. Especially on a pontiac since the intake is an air gap, and one can block the heat crossovers in the heads to keep the air charge temp down on a hot day.
My 400 runs at 185-195 for the most part while cruising. On 90+ days it has hit 200-205. In heavy traffic it went to 215, and the fan clutch started pulling air, and it crept back down. Once i was out of traffic , back down to < 200.
Not hot really.
230 would be pretty hot and that is where I would be concerned about detonation, as well as cooling system pressure, and coolant loss.
Ideally for economy , and keeping the engine clean 190 -200 is best IMHO.


If the distributor is curved correctly , and the radiator is good , fan shroud, fan clutch, 7 blade , which is my exact setup, running a 180 thermostat is no issue.
The water pump divider plates are tweeked as well. 
I guess i can understand see running a 160. It avoids some issues here as far as engine temps, underhood temps. Makes it easier to avoid things like detonation when your tune isnt quite spot on. Gives some wiggle room to sort things out too.
Not saying yours isnt tuned right, just sayin. Getting a tune just right is quite a feat.
My 400 runs its best right at about 180.


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## PontiacJim (Dec 29, 2012)

Joe60 said:


> Thank you sir! Going to stay with stock compression.
> Regards,
> Joe



OK, looks like your combo should have no issues. Something that will help - see if your rebuilder can achieve a .040"-.045" squish/quench area between the top of the piston and the flat area of the head that shrouds the piston top. This can be beneficial and help keep detonation in check. The tight clearance forces the air/fuel mixture into the combustion chamber and can help in slightly cooling (thus the term "quench") the mixture.

Have fun!


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## Lemans guy (Oct 14, 2014)

Well said LA tech, the cooling is a range and proper tune is the answer. I keep my distributors curved in, I have two Sun distributor machines. So I can dial it in easy.

I also run Daytona dual band digital AFR gauges on the dash. With vacumn gauge and fuel pressure gauge.

I run my quick fuel with 13.8 AFR on the idle circuit, 13.2 on the main jets for light throttle cruise,When I engage my accelerator pump I go to my desired 12.2 AFR for power.,...my Power valve is dialed in with an 8.5 valve where I like it and it delivers that 12.2 as well.

I have a proximity control switch on my vacumn secondaries that light an LED on the dash when they open. So that let’s me dial in the secondary jets to optimal 12.2 as well.

I use the idle and high speed bleeds to drop when my primary jets come on. They usually come on about 2500 RPM, I dropped mine to 1800 Rpm, because I like it there.

So yes tuning and curving the distributor and carb make a difference in how the engine runs. Smoot, strong with no detonation is what you want.


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## LATECH (Jul 18, 2018)

Wow, Lemans Guy .Impressive. 

Do you set up distributors for others on the Sun machine?


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## Lemans guy (Oct 14, 2014)

Yes I do a lot, have done stacks of them, not for money,. I do them for all The Hot Rodders around here, curved a 1970 GTO judge the other day. Recently I did 5 gen 2 corvette distributors for a corvette builder all in one day,....jeesh, ....

in a day I usually just do one or two. HEI’s, Original Points, Petronix, MSD’s crane conversions, new Petronix dists, rebuilt ones etc. They almost always even, when new have way too much timing...

you have to set it right for today’s gas....


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## LATECH (Jul 18, 2018)

Cool. I will keep you in mind for my next build.


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## LATECH (Jul 18, 2018)

Have you ever modded an old pontiac points dizzy to run a gm pickup coil and reluctor, to use as HEI?

Of course the module wont fit inside, but how about the reluctor/pickup coil?


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## Lemans guy (Oct 14, 2014)

Sure, but with your knowledge and abilities I have no doubt that you are already set up on that GTO!.......


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## Lemans guy (Oct 14, 2014)

No, I have not. But there a guy Dave Ray who specializes in that, making the original HEI inside a Points distributor. He has a website, “ Dave’s small body HEI’s“...

Mr. Ray is an extremely knowledgeable guy on these. I would try him if you want to do that. I believe he worked for GM developing HEI’s.

Now HEI and Petronix are different,...but most guys just use a Petronix module and keep the original points dizzy. Since Petronix modules now have variable dwell they actually are pretty good.

HEI’s did have an emissions purpose and could support hotter spark, that is why they had to make the distributor body a larger diameter so the spark would not jump between terminals.

on a street car I am not sure that there is a great benefit to HEI, especially since these aftermarket modules have variable dwell.

and really they provide no more horsepower than points despite what many believe.Google this story....”Ignition Shootout, Points vs HEI“...skip the articles salesman talk and go to the back the dyno test......and you will not see a couple of HP difference points vs HEI and sometimes points are better.

But HEI does have great features and the GM product is very good,...if you want to do that Dave Ray is your man.


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## LATECH (Jul 18, 2018)

Thanks Bud. I do like the ease of the pertronix conversion. My dizzy is all set up , mechanical and vacuum advance etc,and it is in good shape all the way around. 
I have thought about the pertronix many times , but the points are working fine and it runs good. 
Not gonna fix it , it aint broken. 
I have a reguler large cap HEI (GM) and it too is in good shape.It will need setup before it is run.
I just like the factory look of the points dizzy under the hood.Plus it is as simple as a stone axe ,so...


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## Lemans guy (Oct 14, 2014)

Points run great, as long as you keep the dwell set. I like the snappy action on points, the way they run and start up. Very reliable if one pays attention. I see them float on my machine about 6,000 Rpm at the crank, and they do reduce dwell time as RPM’s rise. That is why variable dwell is so good. But this does not matter on a street car unless you drive around at 6,000 RPM.


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## Old Man Taylor (May 9, 2011)

The Corvette points will go well past 6000.


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## Lemans guy (Oct 14, 2014)

Yes and tension on the points matters. I use a points tension gauge to check it, tighter will reduce float but increase wear...and looser will improve wear but allow more float as the points ride on the cam lobe tops.

It is why they developed dual points, to increase dwell time at higher RPM. But that was quickly eclipsed by HEI.....with a Hall effect magnetic switch these, magnetic switches don’t float because they are not mechanical, it is not really a worry unless you are a racer or operate at high RPM’s a lot then you have to check it. Because it will misfire when it floats


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## Montreux (Mar 8, 2009)

Yeah, it either lights the fire, or it doesn't! Points performance will degrade over time; that's why you do periodic tune-ups. And electronic either works or it doesn't. So if your points let you down, you can usually get it running with a nail file and a screw driver. If your electronics let you down, it's time for a tow.


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