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      09-28-2013, 10:08 AM   #93
Boss330
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Quote:
Originally Posted by NISFAN View Post
Not an easy comparison, but consider the F30 Alpina B3 produces 443lb.ft with the long stroke N55
The Alpina B3 is a very interesting comparison in this regard.

It has a N55 with long stroke/small bore and is equipped with two turbochargers and delivers 410hp and a maximum torque of 600Nm.

The S55 has a short stroke/large bore twin turbo engine that delivers 430hp and "substantially more" than 500Nm (but likely not above 550Nm).

N55 B3: 410HP/600Nm
S55 M3: 430HP/500Nm (550Nm)



N55 B3: 410hp (301kW) between 5500 and 6250rpm
N55 B3: 550Nm between 2200 and 5200rpm (600Nm max at 3000rpm)

S55 M3: 430HP between 5700-7200rpm
S55 M3: 500+Nm between 1800-5700rpm


These two engines I suspect will feel quite different in their power delivery and willingness to rev. The S55 should be more agile, perhaps especially when not "on boost", due to it's short stroke that means less rotating mass and hence less inertia. That aids response when not on boost and makes it easier (I would imagine) to get a engine that responds better and looses some of the lagginess of the N55. Especially considering larger valves possible with larger bore, which means better flow. Better flow means more air and fuel. Which again leads to more exhaust volume and better spool up of turbo's, and less lag...

Also interesting, and in line with what I believe is generally true of oversquare vs undersquare engines, is that the N55 Alpina B3 produces substantially more torque but less HP than the S55 that has more HP but less torque.

(We don't know boost pressure of the B3, and the S55 has a function where maximum boost is only applied under high temperatures/altitude etc. So hard to get a realistic comparison on boost levels anyway. But state of tune seems quite close, so the B3 N55 and S55 should still make a valid point re long vs short stroke).

Certainly going to be interesting to read comparisons of these two engines


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Last edited by Boss330; 09-28-2013 at 11:49 AM..
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