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      12-14-2013, 01:08 PM   #74
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Drives: 2015 M3 6MT
Join Date: May 2013
Location: Seattle

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Originally Posted by Boss330 View Post
No I don't know the boost levels, but a rule of thumb is that a boost of 0,5bar is a 50% increase in power. At 0,5 bar a 2l engine is as powerful as a 3l engine (at a similar state of tune). So a 100hp engine makes 150hp at 0,5bar boost (less in the real world as compressing air creates heat which makes the air less dense, hence intercoolers).

But I don't get your logic on the N54 vs S55 comparison.
The N54 makes 300hp at 0,5 bar Fboost
The S55 makes 430hp at a undisclosed boost level (assuming both engines have stated hp according to DIN/ISO/EU standards)

Both have the same CR.

My guess would be that the S55 makes 430hp at 0,9-1bar of boost. A tuned N54 will also be at those boost levels if tuned to 400+hp.

If the N54 can make 6-700hp at the same CR as the S55, I don't understand why the S55 shouldnt also be able to do the same?
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.

Last edited by solstice; 12-14-2013 at 01:23 PM..