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      12-14-2013, 01:21 PM   #75
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Drives: BMW
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Originally Posted by solstice View Post
I searched for it and the highest boost I found for a Switzer tune on street gas was 20 psi. Do you have boost numbers for a 700 hp N54 on street fuel and stock turbos?

Again you can get more power with the same psi and CR but then you need to support full boost at higher rpms. I don't think the small mitsus can generate the volume needed for that. I could be wrong and that the turbos has more capacity and better intake and cat less DPs would allow for the flow needed at higher rpms, still this is more costly mods and this is an M car so I think BMW has pushed the limits quite well.

I'm suspecting that the S55 is close to max combustion pressure allowed by street gas and also generates that pressure as high up in the rev range it turbos can manage. There is likely a small gap left but this is no N55 or N63 where you can just double the boost with a flash tune and reap 100 hp.
Why? (To the last paragraph)

The S63 in the F10 M5 has a 10:1 CR and that engine has been tuned by Manhart to a proven 700-750hp. The S63 has a stock max boost of 1,5bar... The Manhart MHR 5/6S has a 30% increase in power over stock (560 vs 700-750). A 30% increase on the S55 is 560hp.

Why should the S55 not achieve the same gains seen on other similar engines?