[86TOYO2k17]

Originally Posted by Irace86.2.0

I should rephrase: if you expect to get to 350whp on pump then you will need to use e85 or lower compression. High compression is good for fuel economy and NA power and even for getting low end power for a turbo to spool faster, but boost raises the effective compression ratio, so that is a problem. Boost on low compression gives the power of having high compression, while having low compression at low rpms where knock risk is higher. The other solution is the Atkinson Cycle in modern engines that reduces the effective ratio while maintaining the expansion ratio, or there are these new variable compression motors like what GM and Nissan have introduced. With such a motor, it could be possible to run a static compression ratio that was variable from 12:1 to 20:1 without a turbo, but on to you.

Evo has a static compression ratio of 9:1 with 19psi of peak boost making the effective compression ratio is 20:1. The BRZ has a static compression ratio of 12.5:1 with 9psi of boost on a basic kit making the effective compression ratio is 20:1 and both cars will dyno around 250whp +/-, but which is better? Our cars will have more power, and it will come on sooner, but the Evo can add more boost without dramatically raising the effective compression ratio or without raising much of the effective compression ratio down low, which is why it is easier to run on pump gas.

So, how to get around this? Bleed off boost with a variable boost controller, so you institute a progressive boost pattern by rpm and boost by gear, so that you can run a lower effective boost ratio at low rpms and at higher loads (lower gears) when knock is at a higher risk. If you do this, you will be able to have a static compression of 12.5:1 as a minimum, so spool time is decent, gas milage might be better and pickup will be better for putting around town. Then you will have the benefits of higher compression when you add E85.

Or you can lower static compression.

So it looks like most people are saying lowering compression isn't recommended. what about increasing comp to 13.5:1 ?