1991 RS 305

I'm hoping to get my vortec heads to the machine shop tomorrow. I'm having them milled and back cutting the valves. I've done searches on this and .030 seems to be the magical number to have shaved off. I thought it would be neat to be able to keep the heads CC stock and just run a thinner gasket. In all my searches it seems the best compression I'll get doing this will be like 9.2:1. This is ok, but I might as well kick her up to 10:1 since compression is free power. Is it agreed that this will be a safe ratio? Will .030" do the trick? I think for 10:1 I'll need about 56cc chambers? Any opinoins appreciated on the above info!! Second thing is the head gasket. Which ones are best. Since I'm milling the heads I'm assuming I don't need to go with an ultra thin gasket. Anyone know what thickness I'm shooting for?

Thanks for any input. Matt

Dewey316

For the gasket, you want the stock style which IIRC is .015" If you go with a thicker head gasket, you will mess up the qwench. If you go to a 56cc chamber, with a stock head gasket, you should be golden.

1991 RS 305

Excellent!! Thanks for the quick reply!

I should also ask... With this much removal from the heads, will I have problems with the angle of the intake meeting the heads? Edelbrock performer RPM Vortec is the intake I have if it matters.

Thanks..

DM91RS

The angles are one reason I left mine stock with no milling and used a GM composite head gasket .028" thick. Runs on 87 all the time also.

Sorry it doesn't answer your question though

DM

1991 RS 305

So I was at the machine shop and the guy there wants to make sure we hit the compression I'm looking for without going too far. So I'm looking to find out what kind of pistons came in the LO3. Are they a dish, flattop? Id they are a dish or if they have valve reliefs, does anyone know the CC of the piston? Thanks!!!

ShiftyCapone

iTrader: (7)

The intake you choose should seal. Board member Chuck! runs milled vortecs (.030 removed) and he runs the performer vortec carb intake with an adpater plate.



They have four vavle reliefs with a slight dish. I believe the switch to this style was in '87 when they reduced the CR on the 305 from 9.5:1 to 9.3:1.

1991 RS 305

Thanks for all the above info. Not to be a pain, but do you think it's safe to mill my heads to 56cc. Should I play it safe and go to like 57cc? I am worried about detonation issues mainly. But at the same time compression is free power. I will burn premium of coarse. I have to call the machine shop in the morning ant tell them what cc's I want. Any more input is appreciated!!

Thanks, Matt