Is it possible to money shift a DCT if you've changed the differential gear ratio?

Stainless 45 · 08-24-2012, 09:54 PM

Normally the car won't let you select a gear that overrevs the engine when downshifting with DCT, but what if you've gone with aftermarket gears, say Dinan or some other, and the car's ECU still "thinks" you're running stock? Is there a possibility of overrev?

C|3R1C · 08-24-2012, 11:00 PM

I've read that has happened with the 3.62 but have yet to see an issue with the 3.45.

C|3R1C · 08-25-2012, 01:37 AM

Quote:

Originally Posted by m3alabama

That is why I believe dinan compensates by increasing rev limiter to 8600 to allow 200 extra rpms to be available to work with so you are "over revving" the 8400 but to a safe and programmed 8600. Whether you can go past that, I am sure its possible with short enough gears.

I think they give the extra 200 RPM intentionally to increase the power band (quoted from them), not as a fail safe for the short gears, considering only the 3.62 has a known issue. I don't believe protecting against an overrev was their intention, considering so few compared to those who get software actually buy the gears.

Stainless 45 · 08-25-2012, 07:36 AM

I would have thought that whatever input the computer uses to account for engine rpm would be affected by the shorter gears, say for instance the speed the driveshaft is turning already when you go to downshift. Wonder how it calculates this since overrev is not possible with stock gears.

bm11 · 08-25-2012, 08:02 AM

Increasing the redline and rev limiter doesn't make the engine safer to over rev. An engine fails when the valve springs cease to return the valves in time for the piston to clear in top dead center, causing the piston to impact the valves. This is why F1 cars run pneumatic valves.

You could increase the rev limit to 10,000 but it doesn't mean the engine will handle it.

klammer · 08-25-2012, 10:56 AM

No overev, 3.45 gears, and believe me, have had plenty of opportunities

CanAutM3 · 08-25-2012, 04:53 PM

Quote:

Originally Posted by Stainless 45

Normally the car won't let you select a gear that overrevs the engine when downshifting with DCT, but what if you've gone with aftermarket gears, say Dinan or some other, and the car's ECU still "thinks" you're running stock? Is there a possibility of overrev?

I am just guessing, but I seriously doubt that the ECU uses road speed to calculate if it can downshift or not. Most likely it only uses engine RPM. So no, IMO, a different rear end would not cause a "money shift" issue with DCT.

08-24-2012, 09:54 PM	#1
Stainless 45 First Lieutenant Drives: Last of the V-8 Interceptors Join Date: Oct 2010 Location: Long Island, NY Posts: 383 iTrader: (0)	Is it possible to money shift a DCT if you've changed the differential gear ratio? Normally the car won't let you select a gear that overrevs the engine when downshifting with DCT, but what if you've gone with aftermarket gears, say Dinan or some other, and the car's ECU still "thinks" you're running stock? Is there a possibility of overrev? __________________ 2011.5 LeMans Blue e92 DCT, ZCP, European Delivery. Black Edition Grilles, No Keyhole or Reflectors, Rear Fogs Enabled, Encore Innovation Exhaust, LUX Angel Eyes. "Last of the V-8 Interceptors, a real piece of history..."
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08-24-2012, 11:00 PM	#2
C\|3R1C So Kewl Guy Drives: 2010 E93 M3 DCT Join Date: Sep 2011 Location: Los Angeles Posts: 407 iTrader: (0)	I've read that has happened with the 3.62 but have yet to see an issue with the 3.45. __________________ 2010 E93 M3 / AA Catless X-Pipe / AA Catback / Vorsteiner Vented Hood and Bootlid E93 Trunk / ADV1 7.1 Wheels GB / LS3 LED Lights / AFE Stage 2 / Velos Designwerks Tune In progress: AA Pulley

08-25-2012, 07:36 AM	#4
Stainless 45 First Lieutenant Drives: Last of the V-8 Interceptors Join Date: Oct 2010 Location: Long Island, NY Posts: 383 iTrader: (0)	I would have thought that whatever input the computer uses to account for engine rpm would be affected by the shorter gears, say for instance the speed the driveshaft is turning already when you go to downshift. Wonder how it calculates this since overrev is not possible with stock gears. __________________ 2011.5 LeMans Blue e92 DCT, ZCP, European Delivery. Black Edition Grilles, No Keyhole or Reflectors, Rear Fogs Enabled, Encore Innovation Exhaust, LUX Angel Eyes. "Last of the V-8 Interceptors, a real piece of history..."

08-25-2012, 10:56 AM	#6
klammer Colonel Drives: 11 spc gry m3 e90, 07 X5 Join Date: Jan 2010 Location: chicago Posts: 2,723 iTrader: (0)	No overev, 3.45 gears, and believe me, have had plenty of opportunities __________________ mods: akra evo, dinan 3.45 diff, ess akra tune, dinan stg.3, Alcon bbk, HRE P40

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08-25-2012, 08:02 AM	#5
bm11 Enlisted Member Drives: 2012 E92 M3 DCT Join Date: Aug 2012 Location: Waterville, ME Posts: 48 iTrader: (1)	Increasing the redline and rev limiter doesn't make the engine safer to over rev. An engine fails when the valve springs cease to return the valves in time for the piston to clear in top dead center, causing the piston to impact the valves. This is why F1 cars run pneumatic valves. You could increase the rev limit to 10,000 but it doesn't mean the engine will handle it.