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      11-12-2010, 09:00 AM   #1

Drives: M3 E92
Join Date: Sep 2010
Location: GREECE

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Send a message via MSN to stefanos-ktm
4.1 DIFF i am confused!!!

sorry opening again a topic for 4.1 diff.

The reason I open this topic is that I am really confused.

I have read this topics this topics this answers help me

Here's my real world experience with the 4.10 FD installed in my 2009 E92 M3 6MT. I've got around 14,000 miles on the 4.10 and well over 100 autocross laps. Other mods include the Active Autowerks exhaust, oiled air filter, Dinan springs, Dinan chip with 8600-rpm redline, UUC SSK and Dinan throttle bodies.

I don't do 1/4-mile races at tracks, I do occasional rolling start street races (but usually only up to around 100-mph) and I run BMWCCA sanctioned AX. AX is my main performance interest. It should be noted that I live at 5400-ft above sea level, so non-forced induction power adders are not near as effective as at sea level.

Around town the negatives of the 4.10 are poorer fuel economy and slight noise from the gears on the overrun. I expected these things going in and was only worried about the noise level. I can report that it's not bad at all and doesn't bother me, but I DO know it's there. My riders don't say, "What's that noise?", but it is more than stock. The advantages for street driving are in-gear responsiveness and acceleration in-gear. When I street race I hope to start at around 4000 rpm on the rolling start and use the full 8600 rpm redline and only shift once up to 100-mph. Squirting through traffic in 3d, 4th and 5th is clearly more responsive than stock.

If you look at those scientific charts, they're right. The gear ratios were not selected with this FD in mind, such that 1/4-mile time is actually worse, DUE TO THE TIME REQUIRED TO SHIFT. However, the in-gear acceleration can be better with the higher numerical ratio. Also, I'm able to space out my shifts a little more with the extra 200-rpm of redline that my car has.

AX is where the FD really pays off because, other than the 1-2 shift, the entire course is typically run in 2d gear. The 6MT has better acceleration than the DCT in 2d. The DCT will be faster on a road course, but the 6MT will be faster on an AX course.

Top priorities for AX speed are tires, then lightweight and wide wheels that reduce inertia and increase the contact patch and tracking width. Gearing and power come in distant thirds. I lean toward gearing, partly because my high altitude makes power VERY expensive to gain. Gearing is a known that won't be sapped by low oxygen density (my loss is around 16% vs. sea level). With my current setup (awaiting new, lighter 18" wheels and a switch to Dunlop Direzza tires) my car will spin its wheels anywhere on the course.

Anyway, I think that my case demonstrates there's no one absolute fastest answer. The answer is more like, "It depends on what you're doing." If you do standing start 1/4-mile races and that's important to you, then listen to the techno data. That is really, really true. Shifting time DOES cost speed. However, if you run events where shifitng is limited, you'll still want to minimize shifting time by either strategy or higher redline, or both, but it will not be as important to you as in a 1/4-mile event. A higher numeric gear ratio can be an advantage in events where there is little or no shifting.

I like the feel of the gearing with a 4.10 FD and I think it's quicker for AX.


Next topic
It's just a different ratio...should be the same LSD. Here's the pro's/con's

Accelerate faster
Great for drag racers.
Minor decreased gas mileage
Lower top speed. Dinan only claims that it doesn't change top speed because the cars are speed limited. If they were not speed limited, then it would reduce the top speed.
Need to shift gears more often (6.5% faster through the RPM range).
Possibly makes speedometer 6.5% less accurate. (Dinan says they don't change the speedo gear, and the speedo accuracy won't change...but I'm not so sure. Maybe somebody can explain how BMW can accomplish that feat.)
Wouldn't do it on a much more powerful (modded) motor because you'd be shifting gears much more often.
Now, even with all of those cons, I was going to do it on my stock E92. I've been talking to Dinan about this 4.10 ratio for six months. However, now that I'm building the stroker motor, I decided that I might want to go numerically lower, rather than higher, final drive ratio.

Also in this topic the member LUCID gives a lot of details

Originally Posted by lucid
OK guys, I took the time to plot wheel torque vs vehicle speed as some folks really do think that switching final drives ALWAYS gives you more torque at the wheels, which is not true, and which has been my minor contribution to this discussion. I don't know how else to illustrate that fact apart from plotting the numbers.

Your car simply will NOT accelerate faster on a, say, 0-200 km/h run by 6.5% simply because your final drive has been changed by 6.5%, and this graph illustrates why. As can be clearly seen in the graph, you are NOT always putting down 6.5% more torque at the wheels during the run. After the shifts, the modified car actually has significantly LESS torque at the wheels for a vehicle speed range (see blue line about 30% higher than the red line after the 2->3 shift).

The net result is that you will end up accelerating somewhat faster, but not by 6.5%, so it won't be what some people think. The difference is especially pronounced in the 1st gear since both cars need to go through the entire rpm range during that interval.

There are also some finer points such as when the race ends. If it were the end at 170 km/h, the stock car would have an advantage for instance since it can still stay in 3rd gear whereas the modified car needs to shift into 4th and lose its torque multiplication advantage.

This is all aside from the point that on a track, 2nd gear is used coming out of turns (never mind the fact that 1st gear is used once), and there are traction limitations which bring up the issue of how much of that torque you can actually put down without completely losing the back end. Sticky thinks I should take yet another performance driving class. I should perhaps relay that suggestion to Will Turner whose E90 M3 also seemed to be traction limited turning in second gear going up the hill I had issues with so that he can benefit from Sticky's advice as well (never mind the fact that his car had track rubber).

Attachment 195882

EDIT: The 4.01 on graph title and legend are typos. The calculations used the 4.10 ratio. I will fix that text and upload the new graph.
Not applicable to DCT and 4.10 is almost half the reduction that 3.62 for the DCT would be.

The car is faster with the shorter gears, especially the DCT which would absolutely destroy a manual with 4.10's.

This gearing discussion has happened many times over on M5board, I suggest you educate yourself on the real world difference (this is going to 3.91 which is about the same as the manual M3 would be going to 4.10):

"There is a substantial difference in the acelleration. Here are the results, using average numbers:

------------------------Stock -----------------------Dinan ----------------------Difference

60 ft. time ---------2.229 sec------------------2.225 sec----------------0.004 sec

0-60 mph ---------4.56 sec---------------------4.40 sec------------------0.16 sec

Quarter Mile -----12.78 @ 115.59 ---------12.54 @ 118.24 -------0.24 sec, 2.65 mph

50 - 110 mph-----7.86 sec---------------------7.31sec-------------------0.55 sec"

The difference on the road course is great as well, spending more time at higher revs and GETTING there faster.

i was reading all this topics and details and there were usefull but??

i want to take this part for my car but i have some worries!!

the car i want it more for street racing.
all the racing is rolling second gear!!

offcourse if you will race someone with 3-or 4 year your car will be faster but if you race your car rollin 1 gear are you sure you will be faster or not!!!

the reason i am saying all this is because
in my s2000 i have but shorter the diff and i saw

rolling 1 gear
stock s2000 VS s2000 shorter diff faster the stock untill 4 gear limited
rolling 2 gear
stock s2000 VS s2000 shorter diff faster the shorter but the stoch s2000 was coming faster behind

1/4 mile faster the stock

rolling 3 faster the shorter

i know that you cannot compare s2000 with m3 2000cc with 4200 cc
but i am wondering because this mopdification because is expensive you destory tour deff lot of noise is not the same like stock after and before and lot of money 4000 dollars.

sorry but is there any proof tha two m3 e92 one stock and one with 4.1 diff are racing this

1/4 mile
rolling 1 gear untill 5 gear revlimited
rolling 2 gear untill 5 gear revlimited

whichone is faster
youtube maybe??

sorry for my english i am trying my best!!