Im going to be running 6.6:1 compression ratio in my rb30 setup. Just wondering how low people have gone in rb's? The idea is to run 30psi on straight pump lol. Cheers

Or.... you could use E85 - problem solved.

Agree^^^^ i would go more comp and e85 low comp motor are old news now days they are doughy lazy things off boost x

Yeah I would run E85 but the closest pump is 40mins from me so its not really viable. Dont get me wrong I agree with both of you. Ive been using pump and water/meth on an n/a bottem end but still getting detonation. I think it may be piston to bore clearance related as its getting abit of oil in the chambers ( new moly rings on hones std bore ). Getting new std hypatecs and a 3mm cometic to see if that helps. Obviously the lower comp should. Hoping the piston to bore will be tighter. Has anyone had a similar problem, 8 degrees timing 22psi 9:1 compression chinese gt45 etc, with 1100cc water/meth and still rattling? Cheers

If you cant get E85, the answer is Water/meth injection. 8.5:1, advanced timing, 30psi, pump fuel. winner.

Looks like low comp it is for me lol. Its got low compression height hypatec pistons in it with a 3mm cometic so I'd say its got around 6.5:1 going by calculations. Drives near identical off boost, no more lag than before. Probably drives so well because of the extra 2mm lifting the head and advancing the cam. Its got 30psi and 20 degrees timing on 95ron, 33-34/ 24 degrees timing with water/meth, no knock, just way under tyred at any speed lol. Cheers

mines 8.5:1 28psi pulp no water/meth injection, loves it all day everyday. 6.6 would be a pig to drive :O

what turbo setup is on it?

Why not run a thinner head gasket?

I wanted a bigger tuning window and I got it by also opening the quench area up. Its honestly SFA different from how it used to drive with 9:1. I am going to check the cam timing to see how far advanced it is which I'll probably have to retard it abit. Its got an ebay manifold, wastegate and ebay gt45 in a UC torana. Low compression is the way to make lots of power on an octane limited setup. I could probably run 35psi on straight 98, try doing that with higher compression . Sure theres less squeeze happening but by the time its got an extra 10psi boost aswell as the extra fuel to go with the extra boost its got to push the piston down harder lol. Psi_wagon, I understand your running 28psi with 8.5:1, thats 24.69:1 ( boost compression ratio ), to get the same I'd have to put 41-42psi in mine. I guarantee more air and fuel will be passing through the engine . How much timing have you got on 28psi? Cheers ---------- Post added 26-01-14 at 17:37 ---------- Checked cam timing today and was spot on with the cam card so I'd say it was a little retarded before the head gasket change. After a little more tuning today its surprising how well it goes with straight 95, feels virtually the same as with the water/meth, its now on 33psi - 15 degrees timing at 5500rpm ramping to 18 degrees by 6500rpm. So theres a little more timing up my sleeve with 98 octane . Cheers Some original photos have not been recovered yet.