# '67 GTO tuning question



## jak (May 9, 2006)

Hi there,
I am new to this forum. I got me a '67 GTO 400 ci 325 hp recently and I would like to tune it now. Performer RPM intake is already there. What would you recommend now? Is there an ideal combination of parts, carburetor / head / drive chain / camshaft ... if I want to bring bghp to around 500? Should I stay with Edelbrock or mix it with other producers?
Any advice would be greatly appreciated!
Thanks
Jak


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## 05GTO (Oct 6, 2004)

My opinion;

Keep the Edelbrock, find a set of #670 heads (port and polish), change the cam (236/244 degrees at .050 duration .489/.500 lift) bore the cylinders (.030,) TRW flat top pistons, hooker headers, rochester q-jet carb. 

Good luck!


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## jak (May 9, 2006)

Thanx for the advice! Didn't think that I have to bore the cylinders. 
J.


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## lars (Sep 28, 2004)

500 horse out of a 400 is a very ambitious project, and you're not getting there with stock heads unless you're going to be doing some serious rework of the flow characteristics. Recommend you do a little research on articles published by Ken Crocie, Hand, and Butler to see what you're up against... I've been building Pontiac engines for 30 years, and I've never had a street-able normally aspirated 400 hit 500 horse yet...


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## proformance1 (May 3, 2006)

lars said:


> 500 horse out of a 400 is a very ambitious project, and you're not getting there with stock heads unless you're going to be doing some serious rework of the flow characteristics. Recommend you do a little research on articles published by Ken Crocie, Hand, and Butler to see what you're up against... I've been building Pontiac engines for 30 years, and I've never had a street-able normally aspirated 400 hit 500 horse yet...



I'll second that! I used to own a automobile machine shop, and a lot of people talk horsepower, but the dyno is the only way to really make it happen!


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## jak (May 9, 2006)

Thank you for your opinions!
But what do you think is the max possible with standard techniques, I mean no rocket-science-stuff, you know.

J.


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## lars (Sep 28, 2004)

If you're looking for a streetable engine using conventional, affordable hop-up techniques and a well-built set of stock casting heads, you can get it into the 400-horse range (1 horse per cubic inch is a pretty good performance standard).


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## kerno (Apr 6, 2006)

Most Pontiac heads seem to exhibit better intake flow than exhaust flow. So you'll want to make sure the exhaust system is properly set up for the performance level you are trying to achieve. That means a good set of headers, an x pipe crossover (Bassani makes a good one) and at least 2 1/2 inch tubing all the way back. Remember that torque is what really makes the vehicle accelerate, so have the heads properly done, get a hydraulic roller (I'd like to see it no bigger than 230/240) and a set of the Comp Cams beehive springs and you'll have a good balance of performance and driveability. You have not mentioned the tranny. If it is a TH400, you're going to want at least 3.42's and a decent converter in there as well. If it is a 4 speed, we need a whole other discussion of how it ought to be geared based on which gear box you want to run. I'd also like to see an MSD 6AL and then we need to get Crane Cams to make a Pontiac version of their electronic distributor. You set the timing curve with dip switches on the distributor and it has a MAP sensor rather than an advance canister.


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## jak (May 9, 2006)

I guess the exhaust is alright. X-Pipe and 3'' tubing are on, and also an electronic ignition.
Tranny is a Hurst 4-Speed. 
I tried to dyno the car the other day at the local Porsche-dealer (writing from Germany). At about 270 hp, 4400 rpm and an impressive 445 Nm (325 ft-lbs) the wheels lost their grip. In the end there were four Porsche-technicians sitting in the car to exert the necessary pressure - but it wouldn't work. Very funny sight that.


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## 1969+37=2006 (Mar 30, 2006)

I had a 69 - 400. MAx rpms in a goat the were 5000. buidl your engine around that. I used a dual plane offenhauser manifold. It keeps you fuel velocity up until you punch or open the big carb up. Next headers are a must, polish and port your heads ( use a specialist)or get some made for the Judge which are tunnel port, you'llknow them when you see them they are round. I did a three angle cut on my valves to ensure quick seating. With 400 cubes lots of gas in ( 780 min ) and exhaust out gets quick revs. Lower end torque cams are better check their troque curves. 4:11 OLds gears were available for the street higher for the strip like 4:56. You'll top end before the end but that's what you want. Traction - Air bags inside the springs help stop wheel hop. Oh use a high voltage system and a good plug. With many of the above mods I did mid 13's in 60 series streeet tires.


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## jamesf (Apr 15, 2021)

_EDIT: I didn't realize this post was as old as it was until after I replied.....
Info is still valid.._
I'm new here although I had my 67 GTO for 35 years I also have a 75 Formula that I built.

I had Paul Carter at Koerner Racing rebuild my original 400 in the GTO about 5 years ago.
I had the original 670 heads ported by Dave Bischop at SD. A Voodoo HR cam picked by Paul.

With a Victor intake it made 500.1 HP on the Dyno with a 750 Prepped Holley.
With a stock intake at made over 480 HP. We did 5 Dyno runs If I recall with different intakes and carbs. None were less than 480 HP IIRC.

With the right Cam and Heads this can be done. Attached is the dyno sheet.
The car is perfect streetable. It sounds lumpy but it does not overheat, I have a TH400 with a basic rebuild, and 3:42 gears in the rear. It starts up easily like Mom's sedan.

Granted I am running Ram Air Manifolds, the original intake and the original Carb rebuilt by Cliff, and he used some headers I sent him for the dyno runs. So I'm not making 500 HP but somewhere around 480 I'd guess, But I could have run it like that and I doubt it would be a hassle to drive.

Ported Iron heads done right and the right cam can get you there.
And to do this, you have to open your wallet, as I spent north of 8K with Paul on this considering parts. labor, shipping and everything.


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## Rockinindian (Aug 5, 2021)

jak said:


> Hi there,
> I am new to this forum. I got me a '67 GTO 400 ci 325 hp recently and I would like to tune it now. Performer RPM intake is already there. What would you recommend now? Is there an ideal combination of parts, carburetor / head / drive chain / camshaft ... if I want to bring bghp to around 500? Should I stay with Edelbrock or mix it with other producers?
> Any advice would be greatly appreciated!
> Thanks
> Jak


Motors are nothing more than an air pump. The more and faster you move the air through it, the more power your making. Start with bigger heads. And spending on where you want your peak HP at what RPM depends on the camshaft grind. Also keep in mind once you hit the 5.00 in x 300 duration mark and higher it becomes not very street friendly as far as idling at a normal low rpm in gear unless it is manual trans. Port and polish your heads for higher rpm hp ranges. Cfm of carb/carbs to match can grind. Accessory fanBelt driven turbo's are available but in lower ppsi which still boost an easy 100hp nitrous on a hand switch instead of throttle switch can boost 100hp and higher depending on how much nitrous it is set for but nitrous use can shorten lifespan of your motor


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## Baaad65 (Aug 29, 2019)

How about a stroker kit? My Butler 461 hit 475hp on the dyno with a stock intake and reworked Quad, some head work and a good cam with almost 14 inches of vacuum for brakes, then I swapped in a Performer RPM, 850 QFT DP w/1/2" spacer, 1.65 rockers, 2.5 ram air exhaust manifolds, electric fan so I think I'm pretty close to 500hp....and yes call Butler they're super nice and will have all the answers 👍


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