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Improve Low End Torque, E92 M3?

Discussion in 'E90/E92/E93 M3 (2008-2013)' started by wanesso, Apr 4, 2010.

    wanesso guest

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    Has anyone had Dinan improve their low end torque without replacing the engine; is it possible? My husband's 335xi is noticeably more spirited from 0-40 than my M3 and that just doesn't seem right.....
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    bcweir

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    The 2008 M3 and the 335xi have completely different powertrains.

    The 2008 M3 uses a 414-hp V8 engine driven through the rear wheels with 295 pound feet of torque. The 335xi uses a twin turbocharged inline six putting out 300 hp and 300 pound feet of torque.

    These are two totally different engines and have little in common with one another other than both being BMW engines.

    Due to the vastly different powertrains between the two, it's hardly a fair comparison, and the weight differences between the two are negligible at best. The M3 V8 makes 5 pound feet less torque than the 335's twin turbo i-6, almost unnoticeable difference. The two engines also make their optimum horsepower and torque levels at completely different RPMs.

    Some other variables than can affect acceleration are driving styles, rear end ratios on the differential, as well as the type of transmission used (manual, SMG paddle shifters, DCT transmission, or the automatic).

    I should also remind you that the 335xi has all wheel drive, giving it a traction advantage at the front wheels. While you could swap to a numerically higher differential, I think that's an excessively expensive and unnecessary swap just to try and overcome a 5 pound torque difference and all wheel drive.

    wanesso guest

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    hadn't considered the better front wheel traction on the 335xi , makes sense--I will stop whining and enjoy the high-end torque I have....

    ForcedInduction guest

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    The torque difference is due primarily to the turbo vs. the NA high-rpm M3 engine design. Street turbo engines typically make more torque at a low rpm and over a broader operating range than an NA engine. The AWD isn't a factor in acceleration except on slippery surfaces unless you have lots of torque.

    Many people would prefer more low end torque in the M3 engine but it's always a trade-off when looking for top end HP. A turbo M3 V8 would fix the problem. ;)
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    az3579

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    This doesn't make logical sense. What's better; 4 drive wheels or 2? Are you telling me you can get the same amount of acceleration from, say, a 600hp RWD car as opposed to the same car with an AWD configuration? The RWD car will just sit there spinning its tires while the AWD will at least try to launch the car, since it has twice as many tires that power goes to.
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    tiFreak

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    I think he was thinking about a rolling start when he said that

    ForcedInduction guest

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    You missed the important part about LOTS OF TORQUE... ;) The discussion is about the 335xi vs. the M3.

    Street turbos have lots of torque down low compared to an NA engine, especially a high-winding M3 engine. In the case between the M3 and 335xi, traction isn't usually an issue unless you are on slippery surfaces. Last I checked the '10 335i vs. 335xi, the xi was .1 of a second faster is 0-60 mph. Unless the OP is in the habit of drag racing from every stop light, I don't think that traction was her concern or the difference in acceleration sensation.
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    bcweir

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    Another point that's getting missed...

    Despite the wider disparity in horsepower (414 for the M3 vs 300 for the 335xi), there's less than a 5 lb ft torque difference between the two engines (advantage 335xi).

    This by itself would not account for the perceived wide disparity in acceleration between the two cars.

    My belief is that it's likely either the rear end differential being disparately different ratios, or it might be a difference in driving styles, or even transmissions. Or, it could be that these two disparately different engines simply make their optimum torque values at radically different areas of the rpm band.

    ForcedInduction guest

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    The 335xi makes it's 300 lbs. of torque from 1300-5000 rpm where as the M3 makes it's peak of 295 lb/ft at 3900 rpm and is relatively weak on the bottom end to make more top end HP. So yes the torque curves are much different as is the case with virtually all NA vs. turbo engines. See page 8 & 9 of the first BMW PDF doc for the 335xi torque curve info. It doesn't make any difference if the torque is derived via gearing or an engine with more torque, torque is what accelerates the vehicle from a stop. More is better. :D That's why a turbo M3 V-8 would eliminate any issues with a lack of acceleration off the line...

    http://www.e90post.com/forums/showthread.php?t=38856 - click on "Engine Intro"

    http://www.kenrockwell.com/bmw/m3/2007/engine.htm
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    CRKrieger

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    BINGO! This is what matters between these two cars.

    As for the difference between AWD and RWD, it doesn't take a slick surface to make a difference. Back in the days when I was autocrossing my 110-hp Audi 4000 Quattro, we stuck a g-Analyst in it for a few runs. Milwaukee autocross guru Bob Clark was amazed when he saw my starting forces. His best in an E30 325is was 0.67 g with a little wheelspin. My 4000-rpm launch generated 0.88g - nearly as much traction as the car could muster on those tires. Of course, after the first 100 feet, I was toast, but off the line, AWD gave me a hole shot advantage.

    Here's the thing: while both of our cars could generate about 0.9g braking or cornering, that was because we were using all four tires and all the weight of the car on the tires for those functions. Accelerating with only two wheels, you have only the proportion of the traction that half your tires and the percentage of the weight of the car on those tires will give you. Bob's car was well balanced, which would suggest about 50% of that 0.9g would be available, but the weight transfer of acceleration added the extra downforce on the rear tires that he used to get nearly 0.7g out of them - while the front tires (and the weight on them) added nothing. The Audi, OTOH, got to use all of its weight and traction patches to accelerate.

    Some of this didn't occur to me until years later when I crashed my BMW. Driving along in a light rain, I had to brake for stopped traffic ahead of me. Unfortunately, that was the precise brake application that broke a rusty brake line above my rear axle. That took out my left front and right rear brakes, leaving me with the other two. As I braked harder (not understanding why the car wasn't slowing as it should), I heard the tires lock up and slide, which surprised me because my reasonably well-tuned 'butt dyno' told me I was only generating something like 0.25g, not the 0.45-0.50g that I knew I could do on wet pavement. At the same time, I noted that the car was sliding straight, not getting 'squirrely' as I would expect with locked wheels. [I knocked an old Oldsmobile into a Wisconsin State Trooper stopped at a light.] As they lifted Da (suicidal) Red Dog to haul it away, the tow operators pointed out the pool of brake fluid under the rear axle, which was the final clue to put the debacle together. Of course! I only had two wheel brakes! Half the usual traction - two wheels not losing traction (or braking) so I went straight instead of spinning - double the usual stopping distance! :mad:

    The moral of these stories is, if you've got only two wheels doing something, expect it to get done only half as well.

    ForcedInduction guest

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    The specifics here are the 335xi and M3. In that regards the AWD wasn't the difference in perceived acceleration from 0-40 as BMW's 0-60 times confirm. I agree AWD has advantages in both the wet and dry but my AWD comment was specific to the OP's question and the follow-up replies regarding low end torque and acceleration.
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    bcweir

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    Can the 335xi make that much of a difference with just a 5 pound ft. advantage?

    Talk about making some major hay out of a very small advantage?
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    Zeichen311

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    Nothing small about it

    You're confusing a torque peak with a torque curve. The N54 engine produces 300 lb-ft over a ridiculously wide portion of its operating range: 1300-5800 rpm. At 1300 rpm an S65 produces barely 200 lb-ft: a full 50% torque advantage to the 335xi, albeit one that steadily dwindles to 5 lb-ft at 3500 rpm. When you couple that with four wheels laying down the power you get quite a hole shot.

    The M3 quickly regains the advantage for several reasons. Neither engine drops out of its high-torque band on upshifts, but the S65 stays near its peak torque through higher RPM than the N54 and the S65 also has a higher rev limit. This translates to greater physical work (torque x angular displacement [revolutions]) done in each gear. Also, once the cars put on some speed the tires' grip isn't as easily overwhelmed by the torque, eliminating that benefit of AWD.

    ForcedInduction guest

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    If you compare the area under the torque curves you can see how the N54 turbo has much more usable torque over the low rev operating range which is why it pulls better off the line at normal revs. If you stuck a ton of gear in the M3 or launched at high rpm then the two would accelerate similar but with a lot more drama from the M3 due to higher revs and clutch or tire slippage, etc.
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    epbrown01

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    I know where you're coming from on this. My other car is a Solstice GXP chipped by GM to 290hp/340lb-ft, so acceleration is much stronger than my M Coupe's S54 making 262lb-ft at 3900rpm or so.

    Rather than engine work, you might consider swapping your final drive for a 4.10 ratio, which will move your torque curve down the rpm range. It won't eliminate the advantage the N54 has at low rpms, but will close the gap a bit.
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    Zeichen311

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    ...at the expense of a small hit to fuel economy and increased cruising RPM at all speeds.

    Just pointing this out in case she's not aware of the tradeoff. This is an excellent suggestion and may be the least expensive, most reliable way to improve low-end grunt.

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