hi i have a 88 gta with the L98 engine with alluminum heads does anybody know what comp ratio should be and combustion chamber volume, is it 58 or 64 cc. I have a good set of pro action iron lightning heads fresh and ready minus the correct springs, they are 64cc with 220 int runners. i dont want to loose compression ! also changing the cam comps xfi xtremefi cams 260/270 -------560/555

 

The L98 aluminum heads are 58cc. Since aluminum transfers heat more readily than cast iron, and heat = energy, you need more static compression ratio with aluminum heads than with iron to make the same power. 58cc aluminum L98 heads = 64cc cast iron L98 heads.

So, if your new heads are cast iron and 64cc, you're fine.

 

I look at it as you can use more compression with aluminum heads to make more power, but if you want to say it your way, that's fine.

I think you have more of a problem going from 170cc aluminum heads to 220cc iron heads. That's a huge increase in intake runner volume and it will kill your low end power. 220cc's are for 400+ cubic inch race engines, in my opinion.