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Old 02-24-2013, 07:56 AM
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1968 gto 400 build questions

hello, i'm new on here and looking to build up a 1968 gto convertible that i inherited when a good friend of mine passed away too soon. the car has a ys code block(400) in it that appears to match the car, along w/ #48 ram air 3 heads. the car has a 4 speed in it, and i am looking at taking the tremec 600 that is currently in my '69 camaro, and has a .6 overdrive, so i am considering 3.73 gears. i'd like the car to run mid 12's as most production cars these days do, and i want to keep the factory block and heads so it appears original. the car currently has headers, performer intake, demon 650, and hei ignition. any help to guide me in the rite direction in this build would be great, as i am not familiar w/ pontiacs! thanks!!

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Old 02-24-2013, 09:01 AM
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You are on the right track with your "looking factory" appearance theme. A car that nice with apparent numbers matching should stay that way.
What a fantastic sounding car.
You should get the PHS docs for it too.
To run the #48 heasd you will need a dish piston to lower the CR a tad.It will be too high for pump gas. Pistons with a "D" shape would be the best option .
Your build is totally within the bounds of reality.
Also with the 4 speed you have, It would be a plus to keep it. You should ID which one it is. If it is the close ratio trans, that would be best. Pontiacs make lots of torque. A low first gear will probably not benefit you in that respect.
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Old 02-24-2013, 09:12 AM
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i would like to build a car that gets decent mileage, thats why i was thinking about using the 5 speed, we go to the daytona turkey run every year and typically put 5-600 miles on in a weekend, and i'd like to try to go to more car shows. do i need to do a stroker kit to get to my goals or what would be required? i was going to get rid of the performer intake and go w/ the performer rpm. i don't mind the simple bolt on stuff(i'd probably grind the edelbrock off the intake and paint it). kinda my goal here is to put the car together as my friend would have done if he was still here. the engine in the car runs, but i don't trust the person who had done the machinework so i'd like to go thru the engine and improve it.
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Old 02-24-2013, 09:46 AM
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I would perform a simple engine health test before ripping into it.
Do a compression test
check the oil pressures, cold and fully warmed up.
Check engine vacuum at Idle .
Check the crankshaft end play to be sure nothing going on there.
You may want to degree the cam to determine what it is also.
Be sure to read up on how to do the tests. Crankshaft Coalition would be a good place to explore for a tutorial.
I would opt for a stroker if you need to rebuild it, just dont forget what i said about the compression ratio, as when stroking it, you will increase the cylinder volume and that will raise the CR higher.
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Old 02-24-2013, 10:05 AM
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If that car can be returned to factory original???
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Old 02-24-2013, 10:17 AM
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Sounds like a really nice goat. 12's with a factory 400 is a tall order. You can stroke those motors out to 467 or so and get some more torque and power. Butler Performance (Pontiac specialists) sells stroker kits for these engines. Good luck with the build.
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Old 02-25-2013, 04:41 AM
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I would leave the stock 400 alone and get another engine to modify. Look for a 455.

Take your time and build it up right, then drop it in over a long weekend.

Check the pontiac performance sites to get more specific advice.
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Old 02-25-2013, 07:24 AM
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A couple of the better Pontiac guys are right here, no need to go further. Between Bill (WDCreech), Lynn (LATECh) and myself, we gotcha "covered".

400 HP from a pump-gas 400 Pontiac is no problem at all. It takes a little port work, good induction/exhaust and a strong valve train. The factory Q-Jet intake will make more power than Performer (this is not a Chevy, and doesn't "act" like one).

48s are not "Ram Air" heads. This is a common area of confusion. 48s are '69 "large valve, small chamber" heads. Good ones, no doubt, but only a relative "handful" ended up on Ram Air engines (366 HP). Most were on manual trans 350HP 400s. Some were on 350HO engines, as well. The term "Ram Air head" should be reserved for "round port" (exhaust) heads with small (72 CC) chambers. This is to avoid confusion.

The Tremac is a decent transmission, but the Pontiac makes a WHOLE LOT more low-end torque than the more modern engines. We've seen success and failure using them. The Richmond 5-speed is KNOWN to be able to take the power. The TK-900 is pretty good, too, having driven a '79 T/A with one of our 461s in it.

You don't need to "stroke" the engine to make power. A 400 Pontiac is no punk. In fact, that's the engine that made GTO's "reputation" (which is NOT getting beat). With a good set of connecting rods,the Pontiac is tough and powerful. However, stroking it makes for the performance of a 455 without the weakness of the 455 (block). 400 blocks are physically stronger than 455s simply because the "hole" (main tunnel) down the middle is smaller, leaving more material in the bulkheads where it's needed.

Butler Performance is a good shop. But Pontiac "stroker kits" are available form every parts warehouse in the country where Eagle products are sold. Nothing 'rare" about Pontiac performance parts, and for the most part, fall in between BBC and SBC for "price" (like the CID and power levels).

Have fun! Cool car, a GTO ragtop!

Jim
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Old 02-26-2013, 05:11 AM
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would this package get me to my goals- the car currently has a crane solid lifter cam, not sure of specs(never got them) but i know it is .500 lift at the valve,harland sharp 1.5 roller rockers, crane pushrods, clean up the bowls and port match the intake to the heads, performer rpm intake, aftermarket forged rods, 9.5:1 compression, the stock crank(400) or do i need to stroke it? hei ignition, headers and 2.5" exhaust, holley 650. do i need to go further w/ the heads?
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Old 02-26-2013, 05:41 AM
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Just my thoughts...as Mr. P-Body mentioned, there are several guys on this forum that have you covered but, they can correct me if I'm wrong. I love the Demon Carbs but wouldn't you get more out of your engine if you upped the CFM to 750 or even a bit larger? I built a 428 Pontiac a few years ago and ran a Demon Carb even larger with great results...If I remember correctly it was an 850 CFM.

Like I said...just my thoughts.

Ray
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Old 02-26-2013, 08:43 AM
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what widetrack said,plus

Quote:
Originally Posted by 69 widetrack View Post
Just my thoughts...as Mr. P-Body mentioned, there are several guys on this forum that have you covered but, they can correct me if I'm wrong. I love the Demon Carbs but wouldn't you get more out of your engine if you upped the CFM to 750 or even a bit larger? I built a 428 Pontiac a few years ago and ran a Demon Carb even larger with great results...If I remember correctly it was an 850 CFM.

Like I said...just my thoughts.

Ray
the HEI needs to be upgraded,the stock HEI needs a better external coil.Im not sure what the 400 heads flow so get them tested and make sure the cam matches the heads.It sounds to me like a 13 second combination not 12.
Still not enough information.Are you using slicks or drag radials?
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Old 02-26-2013, 08:54 AM
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Quote:
Originally Posted by vinniekq2 View Post
the HEI needs to be upgraded,the stock HEI needs a better external coil.Im not sure what the 400 heads flow so get them tested and make sure the cam matches the heads.It sounds to me like a 13 second combination not 12.
Still not enough information.Are you using slicks or drag radials?
I agree with you Vinnie...but if I'm correct, these cars came out with a 750 CFM Quadrajet right from the factory and I felt that if he's done a few up grades already, he may be under carburated with his 650 Holley.

And yes, more information is always good.

Ray
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Old 02-26-2013, 09:02 AM
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To add to my last post. back in the mid 70's, I had a 326 Firebird...I put on a 650 CFM Holley and it worked great...Well as great as a 326 can work...LOL...I dropped in a 400 with a bit of head work, cam, lifters, Offenhauser duel port intake and a set of Appliance headers (has anyone else ever heard of Appliance Headers?), a few other minor mods and kept the 650 Holley...When I walked on it, I think I had more power with my little 326. I went to a 850 Holley double pumper and it woke everything up.

That's why I thought he may be under carburated.

Ray
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Old 02-26-2013, 11:41 AM
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"Demon" carbs are no longer available. They were genuine imitation Holleys, anyway. An AED Holley will make more power than an equal sized Demon.

Rule of thumb, a 400 CID engine needs at LEAST a 750 CFM carb. With the 650, it will run out of "breath" right around 5,000. In olden times, the 800 CFM "spread bore" Holley (list # 6213) was the hot lick on a GTO.

What exactly ARE your goals for power? BTW, it was the Offenhauser Dual Port that kept your 400 from making good power. It's a door stop.

Jim
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Old 02-26-2013, 12:17 PM
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I did not know that Demon carb weren't available anymore...thanks for that. The Offenhauser may be a door stop...and I'm in no position to argue but, all I was saying was that going up in CFM on the Carb woke the 400 up...and in 1976, 77 we didn't have all of the offerings in regards to speed parts for Pontiacs that they do now.

Thanks for the information Jim

Ray
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