Hey guys gave the Formula to my gf being i just bought me a new lt1 car :-P... Anywho I gotta put the thing back together... I just finished porting the heck out of my aluminum l98, and I was doing a bit of reading and it seems I should mill em... I want to retain the stock gasket thickness .039-.041 I will be using 1003 headgasket so there about .039... Anyway to the question at hand how much should i have milled on them things... The car needs to be completely dependable for her now, since i wont be driving it I need it to be reliable... LoL..... So how much you think i should have taken off .020????

 

They already have a 58 cc chamber but you still want to take them down a bit to raise the compression since they are aluminum. You could get away with them as is on a 305 but I would take them down a bit to get aroubnd 9.7 or higher. However I am not sure what that number would be. If you call a mcahine shop that would do the work they should be able to help you out.

 

Dang dont anyone wanna chime in on this one?

 

I had mine milled .02 on my 350 but my compression ratio is now around 10.3 on pump gas and that is with a .051 gasket. I would mill them the least amount possible if you are running a 350. If you put them on a 305 you can get away with taking a lot more off.

 

there going on my 305, i ditched the entire 350 thing completely, i bought a 94z instead, lol... so this is my gfs new toy, along with my weekend worrior :-D

 

TTT, there going to machine shop on tuesday guys.

 

.03 is about the limit before you run in to fitment problems with the intake.

 

ok so milling em .03 will bring my compression up to what? i am using stock compression headgaskets also... so my compresion will be @ 9:3.1 milling .03 off em would bring it up like what 9:7.1?

 

No no no!

You only mill your heads for flatness, whatever the machine shop discovers they NEED. You don't pick an arbitrary number.

Mine needed .007 shaved off for trueing up. So I didn't have them milled any more than that.

Why do you want to burn such expensive gas? I'd be shooting for 87 octane. Got better things to spend money on than over-priced gas!

 

He should still be able to use 89 octane or so. Since these are going to be used on a 305 he needs about another point in compression to get the most out of those heads. Hence the milling. Even with around 9.7 or 9.8 CR he should be able to use 89 since these are aluminum. I can run 89 in my LT1 that has 10.5:1.

 

yep i run 89 in my lt1 also with no problems... im gonna take em the the shop see what they say, but im mostly likely getting .020 taken off of em

 

Formula, Sitting Bull is right. I think your getting a little crazy with these heads considering they're for street use and dependability.
.020 is a lot. If your running 9.3:1 stock on 58cc then .020 might get you deep 10s not high 9s(compression). Just because your using aluminum heads and can get away some things doesnt mean to go overboard. I mean if you did a lil porting or vavle job then yeah you'll lose a 1cc or 2. But, to keep it around 58cc you'll need minimum grind on the head. Just get the heads milled flat with the least amount of alum taken off.

 

hehehe there wasnt a little porting done, there was alot of porting done to it. the machine shop is just milling em flat and nothing more, he said use the .028 composite gm gasket and ill be fine

 

Good to hear! They'll be excellent on a 305

 

Ya they should be fun on it... Now to get the TBI tuned for it, thats the next nitemare....