04-05-2018, 09:39 AM
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#16 (permalink)
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A True Z Fanatic
Join Date: Aug 2012
Location: NW, AZ
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Quote:
Originally Posted by Jayhovah
I disagree with this. There is no benefit to downsizing the exhaust for scavenging on a turbo motor, and it will only harm spool speed. You want to maximize the pressure differential across the the turbo to speed up the spool.. back pressure behind the turbo will only reduce spool, flow, and require more boost to make power.
For the 2.5" vs 3" exhaust question, its really just a question of diminishing returns.... It doesn't appear to me (and I haven't really looked at it with much scrutiny so I could certainly be wrong) that the 3" is going to do a whole lot more for you in a modest 500whp type of build.
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I don't disagree with what you are saying as I think we are saying the same thing but you provided the long and more detailed answer. Ultimately the 3" will out perform the 2.5" due to scavenging and the reasons you pointed out, however I have not seen much difference on power, spool or any other performance points on a non-built motor. The 2.5" will produce good numbers up until about 635whp or so before the tq becomes to much and as you stated it will be a question of diminishing returns on a 2.5" if you want big power. As far my comment on spooling faster or more aggressively, that is due to back pressure if I am mistaken then I have been edumicated! 
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