Quote:
Originally Posted by 86TOYO2k17
So it looks like most people are saying lowering compression isn't recommended. what about increasing comp to 13.5:1 ?
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I don't know if the FA20 uses any types of trickery to alter its compression/expansion ratio. My belief is that they are always a 1/1 and that there is just alterations in the cams and injector profiles to compensate for engine knock risks at lower rpms in varying conditions. I have no idea if Delicious Tuning, who tuned my BRZ, makes changes to modify compression/expansion ratio.
With that said, an increase to 13.5:1 would increase the risk of knock, especially at lower rpms. This risk of knock would raise with higher AITs or other factors, and the fear would be that the motor would reach some limit where it couldn't adjust timing or alter cam profiles enough to compensate on those hot days or whatever. This is where a tuner could institute an Atkinson cycle to the motor, altering the compression/expansion ratio, but I don't know if this is done; I'm not a tuner.
If higher compression was used then I would limit the car to E85 for safety.
[ame]https://www.youtube.com/watch?v=9Wc_q_4blyw[/ame]