It is well known that raising the compression ratio of the pistons
sharply increases performance
For NA engines, the standard compression ratio is between 9.5:1 and 10:1

TWE sells 11:1 pistons for 91 octane
And I think pistons of 12.5:1 are available for race gas

The downside to the high compression pistons is risk of detonation
In the forced induction world, JS safeguard is used to prevent detonation

Has anyone tried a combination of say 12.5:1 pistons and JS to get high performance without detonation ?

additives are NOT a substitute for a mechanically sound system.



ever.

at most, try the 11.0:1 pistons with JS. it's a safeguard... not a magic fairy dust that will allow you to do things beyond the capabilities of the gas you have.

i say this not to smash your hopes and dreams, but to prevent a costly and dangerous engine failure.

I have discussed this at length with a number of people and the general consensus is that 11 or 11.5:1 is the max CR you would want to run on pump gas without some sort of engine management. And I have a friend here in Colorado who is currently successfully doing that on an EJ25 on nothing but stock ECU with a bumped redline. The stock ECU is actually quite good at protecting the engine from detonation and self destructing.

I will be using 12:1 pistons on my coming build. But I will not be doing that without engine management. I actually plan on running that on pump gas of 92 octane on a daily basis. But I will also have it tuned such that it will run properly, but there will be a performance compromise and the timing will not be as advanced nor the HP as high as the engine will be capable of. But I also plan on having a separate map for race gas that will let me maximize the performance of the engine for racing purposes.

That's the long answer. The short answer is I know of noone who has run something like 12.5:1 on something as simple as a JS. It is probably possible, but without real engine management to set the timing and fuel delivery at the appropriate levels you are not going to see anything near the true performance that such an engine would be capable of delivering...