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      11-19-2010, 03:19 AM   #66
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Drives: 1999 528iT, E53 X5, E46 325xi
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Originally Posted by shiv@vishnu View Post
The restriction is from the high density catalysts, not from pipe diameter. And since we are talking about a turbo that flows a maximum of 360-370whp on a good day, extra inlet large ID isn't required.

As for n54 (dual) downpipes, the notion that 3" pipes will outperform 2.5"pipes is funny considering each downpipe only needs to channel half the exhaust flow. But the idea of "bigger is always better" sells to those who don't know any better.

Have you taken the N55 downpipe off yet? If so you will notice that the backside of the hot housing is nice and open much like a turbo on an N54...the stock downpipe crams down to a little over 2" across the you are telling me that it's not beneficial for a turbo to open up into the turbine housing, the neck back down at the v band to get out into the open expanse of the downpipe.

And why did mr. 5 gain hp using 3" dps over 2.5s?

I'm not trying to hijack anything, I deal with HP Autowerks all the time and Harold is one of the best people I've ever had the pleasure of talking to and doing business with. I can't knock the fitment of it or the gains of it (18hp is nice), the only thing I'm criticizing is the use of an oem size flange which from the factory is a bottleneck to begin with.

And 360/370 hp is it? Are you so sure about that? 3 years ago you said you were uncertain if we could break 400hp in an N54, and look where we are at now.

Last edited by itsbrokeagain; 11-19-2010 at 03:49 AM.