67 400 Rebuild - Pontiac GTO Forum
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post #1 of 5 (permalink) Old 08-24-2019, 01:03 PM Thread Starter
 
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67 400 Rebuild

New to the forum and need some advice. I'm having my 67 400 335 hp engine rebuilt. I want to lower the compression (around 9.2-9.5)to run pump gas. I'm putting in the h.o. "068" cam will be installing the factory h.o. exhaust manifolds w/2.25 pipes. I have read other post about the 8 eyebrow pistons available and looks like these should not be used. Can anyone recommend the best piston to use? Any other comments or recommendations is most appreciated. This is a TH400 auto, A/C, power brake car with 2.93 non-posi rear. Just want a good pump gas motor with with the h.0. upgrade.
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post #2 of 5 (permalink) Old 08-24-2019, 04:45 PM
 
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Originally Posted by mpru View Post
New to the forum and need some advice. I'm having my 67 400 335 hp engine rebuilt. I want to lower the compression (around 9.2-9.5)to run pump gas. I'm putting in the h.o. "068" cam will be installing the factory h.o. exhaust manifolds w/2.25 pipes. I have read other post about the 8 eyebrow pistons available and looks like these should not be used. Can anyone recommend the best piston to use? Any other comments or recommendations is most appreciated. This is a TH400 auto, A/C, power brake car with 2.93 non-posi rear. Just want a good pump gas motor with with the h.0. upgrade.
You might try reading thru my 400 engine rebuild post. " Crack open my 400, this is what I found" Asked pretty much all the questions your asking. 068 included and more. Breakin on mine coming soon.
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post #3 of 5 (permalink) Old 08-24-2019, 06:37 PM Thread Starter
 
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Wow! Thanks for information. I'm going thru the same situation you did and this is a great help. I've got a lot of work to do. Thanks again.
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post #4 of 5 (permalink) Old 08-24-2019, 10:58 PM
 
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"...Can anyone recommend the best piston to use?..."

Wouldn't recommend the 8-eyebrow pistons for any build.

I'd consider Auto Tec customs the best. But will probably cost $550-$600.

But, the Speed Pro forged pistons are cheaper & are plenty strong. They're just heavier & use the thicker factory spec rings. The tops are thick enuff so that you can have a dish machined into them, to reduce CR, for pump gas. Lots of guys have done this.

https://www.ebay.com/itm/Speed-Pro-T...YAAOSw-xVaFdO8

Another higher cost option is icon pistons, which have a 14cc dish.

https://www.summitracing.com/parts/u...w/make/pontiac

For rods, you can either have the stock cast rods resized, using ARP bolts, or you can buy stronger forged rods. I recommend RPM H-beams. Will probably cost well over $200 to have the cast rods resized. The RPM rods cost $400.

http://www.racingpartsmaximum.com/sa...elhbeam-2.html

Last edited by bigD; 08-24-2019 at 11:18 PM.
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post #5 of 5 (permalink) Old Today, 06:23 PM
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What Big D said you can take to the bank. Ross makes great dished pistons for our engines as well. Not cheap. But they work very, very well. Helped a friend build a '65 389 with Ross pistons for a CR of about 8.5:1, and with stock heads and a Comp Cams 268 cam, it runs like a scalded dog on 89 octane. Now that the engine is apart is the perfect time to go ahead and install the correct dished pistons. You will never regret it. I built my '65 389 back in 1981 with forged flat topped pistons, and these days, can't get the fuel to run the car at the pump. It's a race gas situation, and it keeps me from enjoying the car. Do it once and do it right. You are asking the right questions here!!
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