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THE BEAST THE BEAST is offline
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Default Theoretical question - 09-12-2016, 10:30 PM

If all variables are the same, like timing, mods, bolt ons, driver, etc. What would get down a 1/4 mile faster ? A n54 pushing 19psi across the board (if it in fact could hold 19psi through rpm range) OR a n54 with a max mid rpm boost of 21 or 22 psi and fast taper to say 15 psi by 6500 rpm?
Another question. Out of the 2 configurations only, what would the turbos like better ?
Stock turbos........, but same applies to upgraded turbos. Say 25 psi across the board, vs 28 peak in midrange and fast taper to 20 psi on top end.
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iminhell1 iminhell1 is offline
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Default 09-13-2016, 01:50 AM

More boost at higher RPM will be faster. This is due to how gears work. The faster the RPM the more work per rotation, which is translated into forward movement.


2010 135i auto, MHD E40 tune, Fuel-It stg 2 pump, best 1/4 mile 11.863 @ 119.17 mph
new mods this year, VRSF 5" stepped IC, RB EVO inlets, CP-e/Tial CP, 1320 **'s, xhp stg 3 trans tune, E-85 tune
Best 1/8 mile: 7.469 @ 98.56, 1.769 60'
Best 1/4 mile: 11.480 @ 121.79 1.802 60'
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Vorsprung_CJB Vorsprung_CJB is offline
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Default 09-13-2016, 08:31 AM

So imagine two imaginary dyno scenarios:

With the higher midrange boost that tapers up top, your average WHP is 400 between 4500 and 6000 RPM and then drops, so you upshift at 6k.

With the boost holding to redline, your average WHP is 400 between 5500 and 7000 RPM, you upshift at 7k.

You have the same power over the same number of revs, but when you shift sooner you spend less time in lower gear and more time in higher gear, meaning you average less multiplied torque over the time of the run. You would really have to know where the tradeoff would pay off one way or the other.

I know with cars that have a lot of taper up top, some have found shifting earlier resulted in better times and they are in a better power band, despite shifting to higher gears sooner. You would have to test and do the math, but generally I would think holding power to redline within a higher RPM range would do better in a pure 1/4 mile.

Also, turbos that can flow more CFM at lower boost pressure are generally happier at the same power level.

This is my understanding but someone else with more experience can feel free to correct me if I am off.
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THE BEAST THE BEAST is offline
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Default 09-13-2016, 09:41 AM

See, this is what i was looking for. Anyone else care to chime in ?
Yes, i understand shifting early, power band, etc. I shift at 5900/6k. Just wondering if higher midrange boost and shift at 5700 lets say, would be faster in a 1/4 mile. I know real world test is best, but this is just for theoretical purpose and discussion and get peoples brains working.
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THE BEAST THE BEAST is offline
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Default 09-13-2016, 09:42 AM

Oh, keep in mind , what keeps the turbos happiest out of the 2 scenarios as well.
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