n/a 2.5 with g head compression

[cky]

i really don't like the 7.8 comp ratio of the turbos so i was thinking of ways to get it to like 8.5 or so. what would the comp be on a tbi 2.5 if you put on a g head or a g head with bowl work or a swirl with lots of bowl work. i know this gets discussed alot but i feel strongly on slightly higher compression and everyone usually rags on it. but with the right tuning and mild boost like up to 18 lbs max it would definetly be benificial for a street car.

[Una]

What's the compression ratio of an N/A 2.5? The G head usually drops compression ratio's by .5 and makes the engine far more knock resistant. I'd bet it'd work great for ya. Stick to 2.5 electronics..

[cky]

an n/a 2.5's comp ratio is 8.9:1. if it drops it .5 that would be soooo sweet. right where i want it. man anyone else have any input.

[cky]

wait don't all g heads have 10mm head bolts. so i would need the holes bored out to 11. anything else im missing.

[mwinkle353]

I just put a G head on my 89 2.5L CB for my shadow. I didn't notice any problems with the larger bolts.

[Una]

I had a minor amount of trouble getting 11mm headbolts into my G head.. But they all fit in, just a couple were very snug.

[RSTURBO]

they will fit like una said some will be tight the ones that where tight for me was the inner bolts

[rfb6435]

Quote:

Originally Posted by RSTURBO they will fit like una said some will be tight the ones that where tight for me was the inner bolts

Some G heads fit 11mm head bolts and some don't. On mine some bolts would fit and some wouldn't. I fixed this by running a 7/16 (pretty sure it was 7/16) drill bit down each hole to take just a little material off and make it fit. It really didn't take much and can be done with the average cheapo drill.

-Rich

[moparzrule]

I think it's the 287 G head castings that fit the 11mm bolts (thats what mine is and I don't think it was drilled out) easily but the 445 casting G head doesn't or are very tight.

[cky]

so what does anyone think of the higher compression setup.

[moparzrule]

Not worth it, the little you gain on the low end is not worth sacrificing not being about to run more boost. I went with a G head so I could safely run 22 PSI on pump gas VS sticking with a swirl and being stuck with 18ish. Thats about 30 HP difference minus maybe 5 for the lower compression but a G head also flows more air so even more HP up top, I figure about 40 HP gain overall.