High compression? 11.5:1?

[clean87sedan]

Went to my local tuning shop and was talking about what I'd like to do. I'm thinking about going with some 84mm CP 11.5:1 compression pistons. Only concerns are; will that be too much for this engine and cause piston to valve clearance issues? Does having only 1 big exhaust valve change it because of the size of the reliefs vs. The 1 exhaust valve? Will the reliefs even be in the right spot? What rods do I have to get? Ls? Gsr? So many questions lol that's why I'm asking here. Also have a 272 cam and .020mm milled off the head. Any help helps!

[lostforawhile]

just remember you will have to run premium, and with that high of a compression you want want to look into methanol injection, I like the systems from devils own, you have lots of options to set up your system, you set up the methanol to spray at higher rpm, this helps prevent detonation

[Tdurr]

ohh baby, get to searching. you can can find most of the the info you need. Look for rjudgey post. hes all about head flow.

[Hauntd ca3]

11.5:1 isnt really all that high for a jap motor.
depending on the engine management you plan on running, or carb and distributor , it can all be got around by careful tuning if you run good gas.
if you are carbed, you will need the distributor re-graphed to suit the high comp ratio.
generally the vac advance is biffed and the weights and springs are changed to slow down the rate of advance so it wont ping its head off at low revs.
with efi, you can change the advance and fuel to eliminate pinging by retarding the spark or adding more fuel, but you need to run a knock sensor to do this properly.
but then again, static comp ratios and dynamic are 2 completely different beasts.

[clean87sedan]

Forgot to say I was fuel injected. Also am obd1 so tuning should be easier. I think 92 will be good for this compression. I know people running 12 and higher and are using shell 92. That's what I use and what I'm tuned on.

[cygnus x-1]

In order to get that high you will pretty much have to run domed pistons of some sort. It's possible to get there by milling the head and welding up the combustion chambers, but that's a pretty labor intensive modification, and you will want forged pistons for that CR anyway. You might be able to use off the shelf B series pistons, but the valve reliefs won't be exactly right, and for the money you might as well just get some custom pistons made. Figure somewhere around $150/ea for custom forged pistons. The big name piston mfgrs do this all the time.

B series rods would be a good idea too since they use a larger wrist pin. A series rods are ok if you aren't going to rev the piss out of it.


C|

[clean87sedan]

Yea my head is milled .020mm so I think I'm gonna either go 11:1 or 11.5:1. Gotta do more research and pricing and read reviews on brands. Either je or cp.