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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > Looking at all the dynos, can someone please explain...



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      12-19-2006, 10:51 AM   #1
sdiver68
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Looking at all the dynos, can someone please explain...

...the torque curve drop-off > ~6K RPM?

It's rather steep, and I can't help but wonder what this car will do with a more normal looking TQ curve at higher RPM's?
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      12-19-2006, 11:19 AM   #2
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Quote:
Originally Posted by sdiver68
...the torque curve drop-off > ~6K RPM?

It's rather steep, and I can't help but wonder what this car will do with a more normal looking TQ curve at higher RPM's?
Turbo engines will always have a bell shaped looking torque curve. Sounds unfortunate until you realize that the bell shape occurs from having having heaps more midrange torque than an equivalently powered naturally aspirated or supercharged powerplant, and not from having less torque above 6000rpm. It's nice to drive a car that makes peak power 1200rpm short of redline

-shiv
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      12-19-2006, 11:20 AM   #3
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you just have to shift a bit earlier than the redline

it's actually pretty nice
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      12-19-2006, 11:52 AM   #4
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Quote:
Originally Posted by shiv@vishnu
Turbo engines will always have a bell shaped looking torque curve. Sounds unfortunate until you realize that the bell shape occurs from having having heaps more midrange torque than an equivalently powered naturally aspirated or supercharged powerplant, and not from having less torque above 6000rpm. It's nice to drive a car that makes peak power 1200rpm short of redline

-shiv
I agree that bell shaped is normal, but this seems like more of a lop-sided bell than most I'm used to seeing. Like almost flat from way down low until ~5.8K or so, then steep drop. To your point, though, I AM way more experienced with NA engines than FI. Thanks for the clarification.
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      12-19-2006, 12:01 PM   #5
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please post pic of dyno plot ur referring to
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      12-19-2006, 12:04 PM   #6
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Quote:
Originally Posted by hemi to e90
please post pic of dyno plot ur referring to
Here you go
http://www.e90post.com/forums/showpo...01&postcount=1
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      12-19-2006, 12:07 PM   #7
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thanks i wouldnt worry about it. its correct for what it is and the HP picks up nicely to compensate
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      12-19-2006, 12:26 PM   #8
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Well torque is going to drop after 5252 rpm and horsepower will increase. So there is no need to worry and you can shift all the way into redline if you want... atleast with the xede the hp isn't being reduced, so let her rip.
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      12-19-2006, 12:47 PM   #9
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Quote:
Originally Posted by Bravo1
Well torque is going to drop after 5252 rpm and horsepower will increase. So there is no need to worry and you can shift all the way into redline if you want... atleast with the xede the hp isn't being reduced, so let her rip.
While I know what you're trying to say, there's no relationship between torque and 5252 RPM. Torque could easily increase after 5252 RPM. Maybe not on this engine but certainly possible on others.

At 5252 RPM torque and HP will have the same numerical value. Above 5252, HP will ALWAYS be greater than torque and below 5252 HP will always be less. No exceptions.

However there is no law or formula to stop an engine making more torque at say 5500 RPM than it does at 5252. A Formula 1 engine for example has it's peak torque around 10000 RPM.
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      12-19-2006, 02:06 PM   #10
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Manufacturers will sometimes artifically tune the car so that it makes less power on the top end than is actually possible. This is to protect the engines...

A question regarding XEDE here - how does Xede adjust boost in the car? is it a constant % above factory, or do you aim to hit a target number? Assuming the factory tune drops boost on the top end, can Xede be programmed to compensate?

thx,
-S
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      12-19-2006, 02:30 PM   #11
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Quote:
Originally Posted by SteveMD
While I know what you're trying to say, there's no relationship between torque and 5252 RPM. Torque could easily increase after 5252 RPM. Maybe not on this engine but certainly possible on others.

At 5252 RPM torque and HP will have the same numerical value. Above 5252, HP will ALWAYS be greater than torque and below 5252 HP will always be less. No exceptions.

However there is no law or formula to stop an engine making more torque at say 5500 RPM than it does at 5252. A Formula 1 engine for example has it's peak torque around 10000 RPM.
Or the new M5. Which has peak torque at 6,200 I believe.
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      12-19-2006, 02:53 PM   #12
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are you asking WHY the torque drops off so much compared to NA cars or what>?
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      12-19-2006, 03:03 PM   #13
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Quote:
Originally Posted by teknochild
are you asking WHY the torque drops off so much compared to NA cars or what>?
I'm asking why the TQ curve looks so strange and drops so suddenly. Shiv said it was because of FI. I think there are gains to be made in reshaping the curve, but Shiv does that for a living and I'm just a racer so take my opinion fwiw, which in engineering is not even $.02!
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