z28mccrory

iTrader: (7)

Hey guys,

Im trying to figure out how much i could get my compression to drop by simply changing heads.

I had my 418 motor built with nitrous in mind. It ended up being 10.8:1 with unmilled 5.3 heads. Im curious if i were to go with a set of 6.0 heads, or possibly another large chambered head, how much i could get it to drop.

Sales2@Texas-speed

iTrader: (5)

What size valve relief or dished pistons are you running? Also which head gasket to get to that 10.8:1. A few more specifics about the short-block will be needed to do the calculations correctly. From a 61cc to a 71cc will drop a 418 around 1 full point in static compression...but again, that's an estimate.

z28mccrory

iTrader: (7)

I dont know the exact specifics on it.

The pistons have a very small dish to them, probably 2mm or so.

Im running the cometic gaskets, i think .051... been a while.

Im just trying to get a ballpark idea of what it would drop me to.

The idea of a big turbo is starting to get thrown around, and just curious if i would have to change pistons, or if a head change would get me by. The 418 only has like 500 miles on it so i hate to have to dig back into it, would seem like such a waste. My current 5.3 heads would be great on my TA.

Sales2@Texas-speed

iTrader: (5)

For a .051" gasket, 4.065" bore and 4" stroke and 61cc chamber, you'd have to have about 16cc worth of relief/dish for 10.8:1 SCR. Does that sound right to you??

If so, a 71cc chamber with another .051" gasket would net you about 9.8:1 SCR.

z28mccrory

iTrader: (7)

I dont think it changes anything, but the car is a 4.03" bore and a 4.1" stroke

I have no idea on the pistons dish, the engine shop ordered them for me from Ross, i was never involved in the specs.

Sales2@Texas-speed

iTrader: (5)

Same results from 4.03"x4.1"

z28mccrory

iTrader: (7)

Lol, i figured but just in case i was missing some magic number.

So is 9.8:1 reasonable for a big turbo build, or am i going to need to go lower?