Ah the old compression for boosted motors discussion
For maximum effort max power builds using the biggest turbo the motor can spool low comp is great. It allows huge boost pressure and accompanying huge power. It will be peaky, slow to spool, and lazy when off boost. It will give a low potential for detonation and a wide tuning margin.
Conversely raising compression will liven up the motor and spool turbos faster. It will make more hp per pound of boost also. The ultimate max effort output will be lower though, because you’ll end up fighting detonation and can’t back timing off enough to compensate for the dynamic compression that will result. The margin for error is smaller, so you need to ensure you get good gas and keep timing conservative!
Those are generalities that are almost always right, fringe cases will of course prove them wrong.
For a street driven vehicle with the cylinder heads like the R3 pushing moderate boost (7-20 psi) in a properly sized turbo, 10:1 or 10.5:1 is fine. It will give good throttle response, rapid spooling, high MPG, and can be tamed with a boost dependent ignition retard.
So for example, you run 30 degrees timing at 100% throttle at 6500 rpm, then the device pulls a preset amount of timing for each pound of boost, so say it’s 14PSI and you have it set to pull 1 degree per PSI your timing would fall from 30 to 16. PC-V can do this.
This way, you’ll have aggressive timing off boost for mileage and fee of throttle and good part throttle power, but safe timing on boost.
Lots of factory turbo vehicles are running over 10:1 comp these days... like my mini. 10.5:1, stock overboost is 14 PSI when activated, but there are a ton running around in the wild at 18-20 psi safely on 92 octane. They do it for emissions mostly but it’s beneficial to tuners that want snappy responsive vehicles, not turbo dogs that take 3-5 second to spool (think 2JZ with 76mm pushing 900 hp).
The biggest benefit to aftermarket pistons will be the ring lands. They’ll be both thicker and better designed to accommodate the extra pressure in the cylinders.
In my own personal experience my car was 11:1 compression pushing 26PSI on a medium sized turbo using 91 octane CA swill gas. Crazy good throttle response, **** good mileage too. When I fed her E-85 the seas parted and oooh boy power!!
From everything I can find, the stock pistons will be fine to at least 265whp IF you keep detonation in check.
I can’t imagine most people want to go with something like a GT3076R turbo and push 30PSI and 400whp on their rocket.
