Isuzu G-series Twin Cam

I forget who i was speaking to, or the exact details, but I remember being told using SOHC pistons in the DOHC block gives around a 7:1 or 7.5:1 compression ratio. Anyone know any more info about it?

Nick-

what about just cross referencing the sizes of the pistons or is it abit tricky to get that info?

If you use sohc flat top pistons (these normally raise the comp on a sohc) the compression ratio will be lowered. If you have the cc volume of the head then you can work out the ratio. I have the cc numbers at home somewhere. If you are thinking of turboing the engine then this is not a bad idea. Luckily the g180 and g200 have the same bore sizes as the twincams.

gem wrote:If you use sohc flat top pistons (these normally raise the comp on a sohc) the compression ratio will be lowered. If you have the cc volume of the head then you can work out the ratio. I have the cc numbers at home somewhere. If you are thinking of turboing the engine then this is not a bad idea. Luckily the g180 and g200 have the same bore sizes as the twincams.

Exactly what i was planning on doing If its around 7.5:1 ill definately do it. Reckon you could get those CC figures for me?

Nick-

hmm sounds interesting
just wondering how much life you could get out of the pistons though in a turbo application

A mate was using standard Isuzu cast pistons in a 4ZC1 Turbo, if tuned properly they will be fine. It took detonation at 20psi, 5th gear full noise [6500rpm, dont ask what speed he was doing] for it to happen. Wastegate creep was the cause. Even though ACL dont recommend it, their Hypereutectic cast pistons are pretty resiliant and work well in a Turbo setup.

Nick-

And if it really came to it, it's not like you couldn't get a group buy going on forgies, with that kind of demand...

If you wanted to, after fitting sohc pistons for lower comp, you could possibly even sell the twincam pistons as high comp sohc ones and get a bit for them? If valve clearance wouldn't be an issue.

DOHC pistons are very different. They are designed for a hemi type head and the piston crown is protruding in areas where the combustion camber is solid metal in a Z engine head. Might be ok in a G200Z head but no way would they clear the G161Z/G180Z heads. Apart from the ridiculous diesel type CR you'd end up eith. Besides, why bother with fitting big dollar W head pistons in a Z head? Waste of money.

If you want hi comp forged pistons, I still have a set of brand new high comp forged G161Z pistons. I have a TX standard bore block to fit them into as well.