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      08-27-2021, 08:37 AM   #1
b58_drew_f22
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B58 Optimal Shift RPM For Best Performance

Hello everyone,

First post and new M240i owner. My car is 6MT and MHD stage 2.

I am curious what's the best RPM to shift for roll-racing/highest performance especially in 2nd and 3rd gear. As for now I've been shifting shortly before redline.

I would like to hear some feedback on what everyone else prefers and hopefully get this narrowed down as I have yet to see a forum that answers this question.

Thanks.

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      08-27-2021, 09:18 AM   #2
Ron Jeffries
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Well, let's see. Since you can exceed most Ohio speed limits in second, and every speed limit on the continent in third ...

What you wanna do, I suspect, is turn on the HP / Torque display and see if you can detect where the torque starts to drop, which is shortly before redline. There may be a torque graph somewhere on line but I don't have one at hand.

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      08-27-2021, 11:51 AM   #3
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Quote:
Originally Posted by b58_drew_f22 View Post
I am curious what's the best RPM to shift for roll-racing/highest performance especially in 2nd and 3rd gear.
The charts below may be of use to you. Then there's Glenn Messersmith's Optimal Shift Point Calculator: https://glennmessersmith.com/shiftpt.html.

Dinan's B58 Stock HP & Torque Dyno Results


MT Speed-in-Gears 2-6 (2)


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Last edited by dradernh; 08-27-2021 at 11:56 AM..
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      08-27-2021, 11:53 AM   #4
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Quote:
Originally Posted by Ron Jeffries View Post
What you wanna do, I suspect, is turn on the HP / Torque display and see if you can detect where the torque starts to drop, which is shortly before redline. There may be a torque graph somewhere on line but I don't have one at hand.
It's a little more complicated than that. You want to upshift at the point where the rear wheel torque is the same in the two gears. So you need to recalculate the torque curve for the overall gear ratio in each gear - then you can read off the best shift point.

Or you can use the horsepower curve to find the point at which the rev drop between gears gives you the same power.

Both methods should give the same answer, but the horsepower approach is a bit simpler.
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      08-27-2021, 03:02 PM   #5
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Redline in 1st
Redline in 2nd
~6700 rpm in 3rd and 4th
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      08-31-2021, 11:16 AM   #6
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Quote:
Originally Posted by XutvJet View Post
Redline in 1st
Redline in 2nd
~6700 rpm in 3rd and 4th
Interesting. I also had someone very knowledgeable who races the B58 say 6200 is when he likes to shift as that's when the turbo starts to fall off. I almost feel you can't go wrong shifting between 6k and 7k depending on the situation.
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      08-31-2021, 12:28 PM   #7
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Quote:
Originally Posted by b58_drew_f22 View Post
Interesting. I also had someone very knowledgeable who races the B58 say 6200 is when he likes to shift as that's when the turbo starts to fall off. I almost feel you can't go wrong shifting between 6k and 7k depending on the situation.
Contrary to popular belief, ideal shift points aren't based on the moment where peak power starts to drop off. With the B58, nearly all peak power is sustained to fuel cut. Even with my N55 where power drops fairly significantly after 6200 rpms, the ideal shift points are 6700-7000rpms depending on gear.

Take note of the shift rpms BMW implements for the 8ATs in the N55 and B58. That will give you a clue into the ideal shift points assuming you're running the stock turbo. If you make changes to the turbo, all bets are off.
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      08-31-2021, 04:03 PM   #8
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Would you happen to have the same charts for the B48?

Quote:
Originally Posted by dradernh View Post
The charts below may be of use to you. Then there's Glenn Messersmith's Optimal Shift Point Calculator: https://glennmessersmith.com/shiftpt.html.

Dinan's B58 Stock HP & Torque Dyno Results


MT Speed-in-Gears 2-6 (2)


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      08-31-2021, 05:44 PM   #9
dradernh
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Quote:
Originally Posted by abraxas613 View Post
Would you happen to have the same charts for the B48?
For the Dinan chart, I don't, and I don't see an HP/torque chart for the B48 on Dinan's site: (https://www.dinancars.com/). They must have one; I recommend contacting them to see if it's one they will share with you.

For the first of the speed-in-gears charts, you can download an Excel sheet from DiffsOnline that will enable you to create your own chart. This is the download link: http://diffsonline.com/images/GearingCalculator.xls. If you want the Bob Tunnell calculator shown in the first speed-in-gears chart, it's at this link: http://www.tunnellracing.com/gearcalc.xls. My malware software didn't like that link, but I'm guessing that it's really okay. Note that if you have an AT, both of these calculators only allow for six speeds (FWIW, if I had an AT, I'd likely choose to chart gears 2-7).

The second of the speed-in-gears charts is one I created for myself in Excel using the data produced by the Bob Tunnell Excel sheet's output. If that chart is of interest, it's something you'll have to do for yourself 'cause I can't begin to remember how to create an Excel chart like that one!
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TC Kline Coilovers; H&R Front Bar; Wavetrac; Al Subframe Bushings; 18X9/9 ARC-8s; 255/35-18 PS4S (4); Dinan Elite V2 & CAI; MPerf Orange BBK; Schroth Quick Fit Pro;
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      09-01-2021, 09:22 AM   #10
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Id say every car is different, Id look at your own dyno graph to really zero-in on it. Otherwise itll be a little more vague.. 6-7000rpms. Looking at the torque output of the next gear will help also, not just when the car starts to trail off.
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