I'm putting Vortec heads on my 305 and I've been playing around with a compression calculating program. My 305 has been bored .030 and has Sterling 12 cc dish pistons, so that limits me a bit as far as higher compression. Assuming the deck height on my block is .030 and I'm using a .041" gasket with a 4.190" bore and with the heads milled to 55 cc I'll get 8.7:1. However if I use an .015" gasket it jumps to 9.3:1...I've heard bad things about .015's, so is it worth it? I mean having 9.3:1 would be nice, but I don't want to be retorquing my head bolts every other day.

TIA,

Matthew C. Hall

 

The other important consideration is Quench (piston to head distance). You want to the piston .040-.050" away from the head at TDC. More than that and resistance to detonation goes down.

If the piston is .030" in the hole at TDC then the thickest gasket you want is .020".

I'd suggest talking to your local engine builder about which gaskets he uses. More than likely he knows which ones are junk and which ones work.

 

agreement from me.

 

Matt, where did you get your bore dia from? With a 305 the stock bore is 3.750" and 30over would put you at 3.780. With the rest of the equasion being the same a .020" head gasket would put you at 9.4/1cr. Hope this helps.

Steve