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      07-14-2012, 03:45 PM   #23
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Quote:
Originally Posted by DJDeez

4.06 - 1st gear
2.40 - 2nd gear
1.58 - 3rd gear
1.19 - 4th gear
1.00 - 5th gear
0.87 - 6th gear
3.68 - Reverse
3.85 - Final drive

The difference in readings between 4th and 5th gears would be marginal at best on a dyno. I can only assume safety comes into play hence the reason we dyno in 4th gear.
Good info. This platform is fairly new to me. Thanks.
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      07-14-2012, 04:57 PM   #24
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Quote:
Originally Posted by Stealth ///M View Post
Isn't the 1:1 gearing reached in 4th gear...?

Hence why we dyno the car is 4th..
The torque multiplication will not be reflected in any gear on the dyno. Otherwise, you would get something like maybe 1000 lbs torque in 2nd gear and 250 lbs torque in 5th gear. The dyno chart will reflect engine torque, not transmission and differential multiplied torque, but the dyno chart will show that engine torque reduced by the drivetrain drag losses.

You can dyno in any gear you want. I have dynoed in 3rd, 4th and 5th, without seeing any dramatic differences. The 1:1 gear is often chosen because it should be the most efficient gear since there is no step up or step down that consumes a little power.
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      07-14-2012, 10:47 PM   #25
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I always like to remind folks that there is no such thing as a free lunch with LSD mods.

You can increase wheel torque but you really need engine crank hp to make your car faster across a broad spectrum of different scenarios. Gains achieved with additional wheel torque are offset by the ability to stay in each gear for less time. In comparison to an unmodded competitor identical except you went for a aftermarket rear diff ratio in each and every gear, near redline, you will need to shift while the fellow running stock gearing will still be pulling. You'll be in gear n+1 while he'll be pulling MUCH harder in still in gear n. Repeat this across all gears and the loss from the effect is significant.
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      07-15-2012, 06:41 AM   #26
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Quote:
Originally Posted by swamp2 View Post
I always like to remind folks that there is no such thing as a free lunch with LSD mods.

You can increase wheel torque but you really need engine crank hp to make your car faster across a broad spectrum of different scenarios. Gains achieved with additional wheel torque are offset by the ability to stay in each gear for less time. In comparison to an unmodded competitor identical except you went for a aftermarket rear diff ratio in each and every gear, near redline, you will need to shift while the fellow running stock gearing will still be pulling. You'll be in gear n+1 while he'll be pulling MUCH harder in still in gear n. Repeat this across all gears and the loss from the effect is significant.
Intresting. Never thought of that.
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      07-15-2012, 09:20 AM   #27
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Keep it in the right gear and at the right rpms and you will be putting more tq to the wheels than a vette.......sorry, had to say it.

But the other suggestions work as well

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      07-15-2012, 09:21 AM   #28
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Quote:
Originally Posted by swamp2 View Post
I always like to remind folks that there is no such thing as a free lunch with LSD mods.

You can increase wheel torque but you really need engine crank hp to make your car faster across a broad spectrum of different scenarios. Gains achieved with additional wheel torque are offset by the ability to stay in each gear for less time. In comparison to an unmodded competitor identical except you went for a aftermarket rear diff ratio in each and every gear, near redline, you will need to shift while the fellow running stock gearing will still be pulling. You'll be in gear n+1 while he'll be pulling MUCH harder in still in gear n. Repeat this across all gears and the loss from the effect is significant.
Yeah, it blows my mind how many people don't always understand the "cost" of some mods. Sometimes they add one place but take away from another.

Duffs are perfect example.

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      07-15-2012, 12:19 PM   #29
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Quote:
Originally Posted by SehrSchnell View Post
The gearing just feels better to me, but number wise there is no real improvement. But considering that I never care for numbers, be it drag-strip, dyno, track, etc... it doesn't matter to me; the car feels better to me with that gearing, but you are absolutely correct.
I would hate the see the result of extrapolating this "philosophy" to the extreme... Personally I would not want a massively good feeling and exciting car that did 0-100 in one hour...
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      07-15-2012, 01:37 PM   #30
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Quote:
Originally Posted by SehrSchnell View Post
Totally agree. I was about to post your iconic saying "there is no free lunch". The gearing just feels better to me, but number wise there is no real improvement. But considering that I never care for numbers, be it drag-strip, dyno, track, etc... it doesn't matter to me; the car feels better to me with that gearing, but you are absolutely correct.
Really?? I bet any amount of money if you take to identical m3s to the drag strip and one has a 4: 10 rear, that it will be the faster car..

To the other guy, yes, everything has it's drawbacks and you speak as to how to other guy will be shifting more. But what you didn't state is that the car with gears (driven right) will be much quicker out of the hole and should hold that gap
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      07-15-2012, 01:40 PM   #31
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take a mountain bike (for illustrative purposes) .
One guys leaves it in a lower gear and the other guy starts in the highest. The highest gear will leave the line first, but yes will have to shift each gears as they max out. The other guy with the low gear will be struggling to get going and inevitably be behind (even though he will shift less)
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      07-15-2012, 03:35 PM   #32
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You can get other minor torque improvements from a pulley (at the wheels) and a tune.
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      07-15-2012, 04:21 PM   #33
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Quote:
Originally Posted by SehrSchnell View Post
No idea about the drag-strip, I wondered many times how my car would do. I guess it will depend on the length of the strip, by putting those gears in I sacrificed top speed.
right, for absolute top speed, dead gears are preferable. Race tracks are only 1/4 mile so the gears would def be very beneficial and great for around town city/highway driving. Maybe others can chime in, but I would guess @ 3k around 80 mph cruising in 6th
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      07-15-2012, 05:57 PM   #34
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      07-15-2012, 07:17 PM   #35
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Quote:
Originally Posted by Stealth ///M View Post
Had 4:10s in my old supercharged car(s). Took them out as went to a
3:73. That tall of gearing is useless in the first two gears. Also, that gearing doesn't increase torque, only multiples the feeling of it in the first three gears.
Who sells the 3.73 gears?
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      07-15-2012, 07:41 PM   #36
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Who sells the 3.73 gears?
I'm guessing he had a Mustang?
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      07-15-2012, 07:56 PM   #37
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Quote:
Originally Posted by talontid View Post
I'm guessing he had a Mustang?
My '08 Bullitt Mustang had 3.73 gears stock.
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      07-15-2012, 08:23 PM   #38
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Quote:
Originally Posted by talontid
Quote:
Originally Posted by I M STIG View Post
Who sells the 3.73 gears?
I'm guessing he had a Mustang?
Yep. Three mustangs, now in a M3.
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      07-16-2012, 12:57 AM   #39
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Quote:
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You can easily calculate who will be faster at the quarter in terms of the effect of gearing. Since both will have to shift into 3rd, the effects probably are minimal.
...
Yes, correct. There is virtually no difference. Here is an apples to apples comparison done with CarTest (physics based software for vehicle simulation). This software has been nicely validated for accuracy by me and a couple other forum members as well. THE ONLY change between the runs is the gearing. Traction, launch, weight, power and all other factors are IDENTICAL, thus removed from the comparison. As you can see, in almost all time to distance contests the vehicles can be considered identical. In some speed X to speed Y runs one car OR THE OTHER can have an advantage. Of course for a more "lazy" (i.e I don't want to downshift) style of driving the geared car will most often be superior.

This is a pretty useless mod IMHO...

(Note: 18" wheels and 6MT with a very fast shift time of 0.3 seconds used in this simulation)
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      07-16-2012, 06:48 AM   #40
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Interesting that an E9X M3 will be equally fast with a 3.15 or a 4.10, or any other contrast in gear ratios for that matter. We have now debunked the "performance axle ratios" offered by the factory for many cars as a fraud. And Dinan must not have been using the right simulation software when testing its aftermarket differentials. Maybe it was actually testing them in the real world instead.

With the DCT, the shift speed factor is nearly eliminated. However, an extra shift adding time is only an issue when the race ends at a speed that requires the lower geared car to do an extra shift and the higher geared car not to do one.

You can choose a target speed that will favor the higher geared car, but you can also choose a target speed that will favor the lower geared car. Or you can choose a speed range in one gear or in a couple of gears that favors one car or the other.

Bottom line is that BMW choose the gearing as a compromise. It could have easily gone up or down one size. It needed to hit certain fuel economy targets and it needed to hit certain performance targets.

I do agree that diff ratio changes come with compromises. Highway rpm may be higher, MPG may be less, traction may be worse off the line, acceleration will be slower or faster to certain arbitrary target speeds or through certain arbitrary speed ranges. The factory's compromise is usually good for the average driver.

But having done diff ratio changes in the real world (3.15, 3.23, 3.38 and 3.64 on my 99M3), I like them and believe that reasonable ones make a performance improvement that the performance driver appreciates. When my 99M3 was centrifugal supercharged and relatively torqueless, making only 368 lbs rwtq, I liked the 3.64. Now that it is turbocharged and making 517 lbs rwtq, I like the 3.15 and for traction reasons, I may go to a 2.93. However, I am not basing my like or dislike on arbitrary target speeds or arbitrary speed ranges, because I have found based on experience that there is much more to the real world than computer simulations with limited inputs.
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      07-16-2012, 11:39 AM   #41
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WOW! You guys are debunking "the myth" of gears on the internet based on an app that shows you who's faster... Where are all the real world tests?? I would bet alot of $$ that says the car w/ gears if faster in the 1/4. Your app is also missing 60ft times as well. I dunno, if you guys wanna believe it ok, but I have had 3:27, 3:73 and 4:10 (although diff cars, the results are independent of each other and proved gearing makes a big diff).. Now to the OP original question, yes gears will make city driving feel that much better, and will keep the car in its' powerband
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      07-16-2012, 11:41 AM   #42
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Oh and BTW based on the app screen shot you posted, that et does not correlate to the trap speed; that's a LOW 12 sec pass easily.
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      07-16-2012, 07:20 PM   #43
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If you want more torque you bought the wrong car. The S65 begs you to wring it's neck and shift gears. It is an NA sports car engine with a high redline and a nice progressive power band to match, big lazy torquey engines are boring and don't force the driver to work and therefore are unrewarding in my opinion.
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      07-16-2012, 07:37 PM   #44
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If you want more torque you bought the wrong car. The S65 begs you to wring it's neck and shift gears. It is an NA sports car engine with a high redline and a nice progressive power band to match, big lazy torquey engines are boring and don't force the driver to work and therefore are unrewarding in my opinion.
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