going from 3-layer to a 4-layer h.g.

[awdcsm]

ok ive been doing research on my 4g67 head + 4g63t/evo8 pistons combo, and ive calculated my compression ratio to be 9.2:1, is this to high for daily boosting, iam aiming at 9.1-9.0 to 1 ratio and maybe if i trade out my 3-layer headgasket for a 4-layer headgasket can that bring down my c.r. a little?

f.y.i. if your not familar with the dohc 4g67 head please dont dawg me out about it again, go do your research about this head before you say something ignorant.

 

[BogusSVO]

yes the thicker hg will help lower your cr.

did you cc the head or just going off of published info?

 

[My1GLaser]

I wouldn't worry about dropping the CR .1:1 and it making much of a difference. If you pm me your email addy, I will email you a CR calculator that I have in an excel spreadsheet.

I was worried about the same thing when I built my motor since I was shooting for no more that 9:1 CR. I went way overboard and cc'd the head, put in non-projected plugs and dropped it by .3cc blah, blah, blah.

In the end 9.2 and 9.0 CR are so similar it won't matter. I'd be more worried about setting up the critical engine elements.

Get the quench pad so it is as close to .040 as possible. You don't want your pistons to be .010 down into the cyl and then add a .054 or .060 thick HG. Your motor will be more prone to detonation.

Also make sure that the CC is polished and there are no sharp edges.

Make sure the HG you have is the correct overbore size and matches your head and bore size properly. If you use a std bore HG on an overbored block and the valves are unshrouded then the HG could protrude into the CC which is not good. I don't know anything about the 4G67 head CC size and shape though.

Bogus will chime in if this is good info since he does it for a living.

 

[donniekak]

He is not going to get a quench with the evo pistons, they sit down in the bore to far. I wouldn't worry about it, i would make sure everything is smooth and seal it up. The tune will be the most important part of making the build work.

 

[awdcsm]

Make sure the HG you have is the correct overbore size and matches your head and bore size properly. If you use a std bore HG on an overbored block and the valves are unshrouded then the HG could protrude into the CC which is not good. I don't know anything about the 4G67 head CC size and shape though.QUOTE]


the4g63 and 4g67 have different bores so which gasket would be best a 4g67 or 4g63?

 

[My1GLaser]

Sorry I can't really comment on that since I don't know. It might not even be a problem with your setup, but you don't want the HG sticking into the CC so I wanted to mention it. I would guess that the head CC circumference is actually smaller than a 4g63 head and you would probably be fine. Someone has surely done it before and will hopefully comment, or you could search the topic.

My block was .020 over and there was a good amount of CC work done to the head including unshrouding the valves. My HG was VERY close to the edge of the CC and I wished that I had gotten an overbore HG instead of the Std.