Could use some help selecting a new set of heads

[Seymor Butts]

Hey gentlemen!

I could use a little help or advice selecting some heads for my motor.. Some background here.

Engine is a Pontiac 400ci out of a 1975 Trans Am. The engine has been rebuilt in the past, however the heads etc are original. As you may know, the heads on it aren't the best for compression. I am looking at getting a set of heads to increase some CR. I also want to swap the cam shaft at the same time, so I want to be sure I am selecting the correct heads and cams. I've done a bunch of reading on this and my head is exploding with numbers and terms.

I realize that in order to run on pump gas I can't go over 9 CR. For that reason I am planning to go with a set of heads with 87cc combustion chamber. That should get me to about 8.5-8.6 CR.

Where I got stumped is how do I select the right cc volume for my intake runner and exhaust runner?

Also, since I want to get a set of cams (mild/med), how do I make my decision on what's the best max valve lift for me?

Thanks to you all for any and all feedback : )



Happy upcoming new year!

[astroracer]

Talk to Jeff Kaufman http://www.krepower.com/
When I get around to building the 455 for my 'Bird I will be using his heads and cam.
Mark

[72blackbird]

dup

[72blackbird]

You can run about 9.0- 9.2:1 static compression with iron heads on 91 octane (closer to 9.4-9.5:1 with a razor-sharp tune), and 10.0-10.25:1 with aluminum heads- this is because aluminum doesn't retain heat like cast iron and you can run more compression to make more power. Most builders achieve 9:1+ with iron heads on a 400 by starting with 6x-4 heads and milling them after the combustion chamber volume is verified. It's a little easier on a 455 or 461- a set of 6x-8's typically yield around 98-102cc and put you right at 9-9.2:1 SCR.

Aluminum 72cc Edelbrock round port or 74cc KRE D-port heads will put you at around 10.25-10.4:1 on a 400, and will make more power (around 450 hp) out of the box, more than any ported 6x head. Cam choice depends on many factors, but usually boils down to idle quality choice. I would also consider upgrading to forged pistons and rods, if this hasn't already been done, especially if you upgrade to aluminum heads and greatly raise the power level over stock.

Geno

[Seymor Butts]

Great info, thanks so much for that!

Happy New Year to everyone reading this as well : )