Dinan 4.10 LSD

[JEllis]

Originally Posted by bigjae1976

Anyone notice the $900 springs?

Wouldn't the 8400 rev limit be ideal for a shorter final drive?

Springs look interesting.... Hopefully they arent just renamed Eibachs!

Jason

[ChrisFastM3]

If you like a fast 0-60 & 0-100 times & can live with not being able to hit the very top speed the M3 is capable of (if you removed your limiter) then DO IT!!!! It is one of the best NA motor mods.

[lucid]

People are missing the point that you will need to shift at a lower vehicle speed with the shorter ratio. That means, after the shift, the stock car will still be on top of the gear the modified car just shifted from--hence, more torque at the wheels--at the same speed. In other words, you also need to consider where you'll land on the torque at the wheels curves after the shift.

The simplist way to consider all this is to look at power, which, by definition, takes all of this into account. The shorter diff does not give you more power. In a drag race, it does affect the effective power band though by shortening it, but at the cost of shifting more. I doubt that it will make a significant difference except for the start of the race, where the cars are far away from where they'd like to produce power. Meaning, the car with the shorter ratio will get to the power band quicker, and the rest will not matter all that much. But the start of a drag race is traction limited anyway, so I don't know that more torque would make much difference.

On the track, it might be a different story, but that would most likely be function of the track layout. And I don't see how shifting more often can help in that case either. I definitely would not want overall reduction in 2nd gear to be higher. I don't see how that would be useful on the track at all. 3rd gear, however, can be shorter IMO.

[JMD0977]

Originally Posted by lucid

People are missing the point that you will need to shift at a lower vehicle speed with the shorter ratio. That means, after the shift, the stock car will still be on top of the gear the modified car just shifted from--hence, more torque at the wheels--at the same speed. In other words, you also need to consider where you'll land on the torque at the wheels curves after the shift.

The simplist way to consider all this is to look at power, which, by definition, takes all of this into account. The shorter diff does not give you more power. In a drag race, it does affect the effective power band though by shortening it, but at the cost of shifting more. I doubt that it will make a significant difference except for the start of the race, where the cars are far away from where they'd like to produce power. Meaning, the car with the shorter ratio will get to the power band quicker, and the rest will not matter all that much. But the start of a drag race is traction limited anyway, so I don't know that more torque would make much difference.

On the track, it might be a different story, but that would most likely be function of the track layout. And I don't see how shifting more often can help in that case either. I definitely would not want overall reduction in 2nd gear to be higher. I don't see how that would be useful on the track at all. 3rd gear, however, can be shorter IMO.

I've seen some of your post in the past so I know you know alot about technical stuff, but as far as torque on the M3, it has a flat torque curve (from the low to high RPMs) always putting about the same torque throughout the torque band. Other car's torque curve are similar to HP curves were your statement makes alot of sense. With this upgrade, I would get to peak HP output faster every time and have 6%-13% more torque throughout the whole torque band anyways, right? Even if I got to shift earlier with the DCT, would be quick shift with no mistakes ever. I just been very interested in this upgrade for street and track use since I got the car.

[lucid]

Originally Posted by JMD0977

I've seen some of your post in the past so I know you know alot about technical stuff, but as far as torque on the M3, it has a flat torque curve (from the low to high RPMs) always putting about the same torque throughout the torque band. Other car's torque curve are similar to HP curves were your statement makes alot of sense. With this upgrade, I would get to peak HP output faster every time and have 6%-13% more torque throughout the whole torque band anyways, right? Even if I got to shift earlier with the DCT, would be quick shift with no mistakes ever. I just been very interested in this upgrade for street and track use since I got the car.

Note that I used the term torque curves, not curve, at the wheels. You are referencing "the" torque curve at the crank. In other words, you can generate a different torque at the wheel curve for each gear since gears act as torque multipliers. More specifically, when you go to the higher gear, you lose the higher torque multiplication of the lower gear.

EDIT: I caught an error in my previous reponse on this one. LSD does not change the width of the effective power band during a straight acceleration run as gear spacing is maintained. What I was really referring to is making the 3rd gear shorter, and hence dropping less rpms during the 2->3 shift, and staying more to the right of the power graph after the shift. The statement above, the first statement of this post is true though, which is the main point.

[JMD0977]

I see what you mean. Dainan doesnt have it for DCT yet but I've been talking to some people to do this to mine by the time I get the car back from RdSport. Thanks for the info.

[b16r1ch]

Originally Posted by Sticky

People can do whatever they want with their car, and I WILL drag my car as well as track my car. I like that it is well rounded and can do everything well.

Cool...not saying dragging these cars is a bad thing - just not their nature. Not to mention, changing the gearing for ~3k (after install) seems a bit much.

Good luck!

-Rich

[b16r1ch]

Originally Posted by e46e92love

Tell me about it........so many punk kids buying this car for all the wrong reasons. What would posses a parent to buy their kid a 70k sports car. Its not even the money, its the common sense of putting a young kid behind the wheel of a sports car. Just blows my mind.........but I digress, sorry for going OT.

I agree, 1000%.

-Rich

[Sticky]

Originally Posted by lucid

People are missing the point that you will need to shift at a lower vehicle speed with the shorter ratio. That means, after the shift, the stock car will still be on top of the gear the modified car just shifted from--hence, more torque at the wheels--at the same speed. In other words, you also need to consider where you'll land on the torque at the wheels curves after the shift.

The simplist way to consider all this is to look at power, which, by definition, takes all of this into account. The shorter diff does not give you more power. In a drag race, it does affect the effective power band though by shortening it, but at the cost of shifting more. I doubt that it will make a significant difference except for the start of the race, where the cars are far away from where they'd like to produce power. Meaning, the car with the shorter ratio will get to the power band quicker, and the rest will not matter all that much. But the start of a drag race is traction limited anyway, so I don't know that more torque would make much difference.

On the track, it might be a different story, but that would most likely be function of the track layout. And I don't see how shifting more often can help in that case either. I definitely would not want overall reduction in 2nd gear to be higher. I don't see how that would be useful on the track at all. 3rd gear, however, can be shorter IMO.

The shift speed with DCT is so quick there really is no disadvantage. Not to mention, there is plenty of data out there supporting the advantage of shorter gears. Youtube has a nice vid of a stock m3 vs. a 3.91 and 4.10 car (e46).

Gearing is probably the biggest bang for the buck upgrade especially in how it makes the driver feel. Power is torque x rpm / 5250 anyway, more torque multiplication won't hurt.

[lucid]

Originally Posted by Sticky

The shift speed with DCT is so quick there really is no disadvantage. Not to mention, there is plenty of data out there supporting the advantage of shorter gears. Youtube has a nice vid of a stock m3 vs. a 3.91 and 4.10 car (e46).

As I said there might be a slight advantage on a drag race because you can get off the line faster if you can manage traction, but it won't be what most people think. Bruce, Swamp and I debated this a while back (I actually thought we were debating something else at that point--closer spacing of certain gears), and Bruce referenced an interesting analysis on this, but I don't remember where that is.

Originally Posted by Sticky

Gearing is probably the biggest bang for the buck upgrade especially in how it makes the driver feel. Power is torque x rpm / 5250 anyway, more torque multiplication won't hurt.

Again, shorter spacing can hurt you on the track as you might get stuck in between gears in the turns with 6MT. Also, the car has plenty of torque at the wheels in lower gears to the extent that you can't really put most of it down coming out of turns--even in 3rd gear. I thought I was personally having a problem with this, and then watched Turner go up the hill I was having trouble with in 2nd in the Turner E90 M3, which has a wide radius, and his rears weren't hooked up almost the entire incline either even with track rubber. I don't see what I would do with more torque at the wheels in 2nd on a track, especially if that means I would need to shift into 3rd even earlier.

On the other side of that incline, there is another incline with a radius which you go up in 3rd, and at the crest you are at about 80 mph. I spent the entire day trying to figure out how much throttle I can possibly use, and if I can go WOT there. Despite my best effort to apply the throttle really gradually, I lost and pulled in the back end once at 70 mph, which is not fun. Clearly, torque is not the limiting factor there either.

Would be nice to have more when all is hooked up though on the straights, and that's why I'm saying I would rather have the 3rd gear slightly shorter. And for fuel economy reasons, I don't see why 6th can't be longer (the new LSD decreases total reduction in 6th even further). Who uses that on the track or in a drag race anyway?

[bigjae1976]

I was just reading that the M-DCT doesn't have an overdrive gear. That sucks for highway cruising although this car was not really built for that.

I did the gear calculations using the stock 18" rear tire size.

4.10 - 33; 54; 73; 94; 113; 131; 158; 4250rpm @ 80mph
3.62 - 37; 61; 83; 106; 129; 149; 179; 3750rpm @ 80mph
3.15 - 43; 70; 95; 122; 148; 171; 205; 3250rpm @ 80mph

I think the 3.62 would be a good compromise for most of us as far as cost, daily utility, and performance.

Originally Posted by b16r1ch

Cool...not saying dragging these cars is a bad thing - just not their nature. Not to mention, changing the gearing for ~3k (after install) seems a bit much.

Good luck!

-Rich

Why not get a Z06 or even a Z51 if you really want a car that will kick @ss out of the box in a drag race?

[bigjae1976]

Originally Posted by Sticky

I was thinking some more about this and I bet the hot upgrade for the DCT's will be going to 3.62 gearing which is the E46 M3, M5, and M6 final drive.

Is the E46 M3 diff a direct swap for the E9x M3?

[Sticky]

Originally Posted by bigjae1976

Is the E46 M3 diff a direct swap for the E9x M3?

Wish I knew... maybe the M6 diff will be?

[Sticky]

Originally Posted by bigjae1976

I was just reading that the M-DCT doesn't have an overdrive gear. That sucks for highway cruising although this car was not really built for that.

I did the gear calculations using the stock 18" rear tire size.

4.10 - 33; 54; 73; 94; 113; 131; 158; 4250rpm @ 80mph
3.62 - 37; 61; 83; 106; 129; 149; 179; 3750rpm @ 80mph
3.15 - 43; 70; 95; 122; 148; 171; 205; 3250rpm @ 80mph

I think the 3.62 would be a good compromise for most of us as far as cost, daily utility, and performance.



Why not get a Z06 or even a Z51 if you really want a car that will kick @ss out of the box in a drag race?

Maybe some people like doing things differently and LIKE BMW's? Why be like the rest of the sheep?

[Sticky]

Originally Posted by lucid

As I said there might be a slight advantage on a drag race because you can get off the line faster if you can manage traction, and your effective power band is narrowed, but it won't be what most people think. Bruce, Swamp and I debated this a while back (I actually thought we were debating something else at that point--closer spacing of certain gears), and Bruce referenced an interesting analysis on this, but I don't remember where that is.



Again, shorter spacing can hurt you on the track as you might get stuck in between gears in the turns with 6MT. Also, the car has plenty of torque at the wheels in lower gears to the extent that you can't really put most of it down coming out of turns--even in 3rd gear. I thought I was personally having a problem with this, and then watched Turner go up the hill I was having trouble with in 2nd in the Turner E90 M3, which has a wide radius, and his rears weren't hooked up almost the entire incline either even with track rubber. I don't see what I would do with more torque at the wheels in 2nd on a track, especially if that means I would need to shift into 3rd even earlier.

On the other side of that incline, there is another incline with a radius which you go up in 3rd, and at the crest you are at about 80 mph. I spent the entire day trying to figure out how much throttle I can possibly use, and if I can go WOT there. Despite my best effort to apply the throttle really gradually, I lost and pulled in the back end once at 70 mph, which is not fun. Clearly, torque is not the limiting factor there either.

Would be nice to have more when all is hooked up though on the straights, and that's why I'm saying I would rather have the 3rd gear slightly shorter. And for fuel economy reasons, I don't see why 6th can't be longer (the new LSD decreases total reduction in 6th even further). Who uses that on the track or in a drag race anyway?

No, there will be a big advantage at all times as you are ALWAYS putting down 13% more torque (DCT 3.62).

I don't have an issue with traction, especially when moving, but if these cars do than what do the people with much larger, torquier RWD cars do?

The car will enter its powerband more quickly with these gears, and I think the advantage would be greatest on the racetrack.

The shorter spacing may be a chore with the manual, with the DCT it will be faster and a non-issue.

[lucid]

Originally Posted by Sticky

No, there will be a big advantage at all times as you are ALWAYS putting down 13% more torque (DCT 3.62).

You are incorrect here. Always 13% more torque as compared to what? At what vehicle speed? You are still missing the point that you will shift earlier than the stock car, and right after you shift, the stock car will have more torque at the wheels since it is in the lower gear, so you simply are NOT always putting down 13% more torque than the stock car. This is all taken into acount by the power rating of the motor. Torque multiplication does not give you more power. It will allow you to accelerate faster momentarily, but if you are concerned about the whole picture, things are not going to be as different as you seem to make it. Changing the final drive by 13% does not mean the car will accelerate 13% faster in the 1/4 mile.

Originally Posted by Sticky

I don't have an issue with traction, especially when moving, but if these cars do than what do the people with much larger, torquier RWD cars do?

Have you tracked your car, and if you have, are you on WOT coming out of corners? If you are, either there is something wrong with you motor or you've already spun out many times. People with much larger engines which generate more power (crankshaft torque is irrelevant as if you have the power you can gear it to get the torque at the wheels), are even more careful with the throttle coming out of corners. If you are not aware of this, I can see how you are not getting the rest of what I am saying.

Originally Posted by Sticky

The car will enter its powerband more quickly with these gears

There is not such thing as "the" powerband for a car. However, as I said earlier, the new LSD will narrow the effective powerband between gears, so there will be a slight benefit from this.

Originally Posted by Sticky

The car will enter its powerband more quickly with these gears

There is no such thing as "the" powerband. However, as I said earlier, the new LSD will narrow the effective powerband, which will provide a slight advantage. As I also said earlier, if you can manage traction, it will help you get to that rpm range quicker as well, but that's just from a dead stop, 0 rpms, which doesn't happen more than once on a track.

Originally Posted by Sticky

The shorter spacing may be a chore with the manual, with the DCT it will be faster and a non-issue.

If you read what I wrote earlier, you'll see that we agree on this one.

[Sticky]

Originally Posted by lucid

You are incorrect here. Always 13% more torque as compared to what? At what vehicle speed? You are still missing the point that you will shift earlier than the stock car, and right after you shift, the stock car will have more torque at the wheels since it is in the lower gear, so you simply are NOT always putting down 13% more torque than the stock car. This is all taken into acount by the power rating of the motor. Torque multiplication does not give you more power. It will allow you to accelerate faster momentarily, but if you are concerned about the whole picture, things are not going to be as different as you seem to make it. Changing the final drive by 13% does not mean the car will accelerate 13% faster in the 1/4 mile.



Have you tracked your car, and if you have, are you on WOT coming out of corners? If you are, either there is something wrong with you motor or you've already spun out many times. People with much larger engines which generate more power (crankshaft torque is irrelevant as if you have the power you can gear it to get the torque at the wheels), are even more careful with the throttle coming out of corners. If you are not aware of this, I can see how you are not getting the rest of what I am saying.



There is not such thing as "the" powerband for a car. However, as I said earlier, the new LSD will narrow the effective powerband between gears, so there will be a slight benefit from this.



There is no such thing as "the" powerband. However, as I said earlier, the new LSD will narrow the effective powerband, which will provide a slight advantage. As I also said earlier, if you can manage traction, it will help you get to that rpm range quicker as well, but that's just from a dead stop, 0 rpms, which doesn't happen more than once on a track.



If you read what I wrote earlier, you'll see that we agree on this one.

Argue with this (camera car stock m3, middle 4.10. far right 3.91):

I never said you would have 13% more power, but power is a function of torque.

There is such thing as the powerband, to be specific since you seem to not want to use your common sense, the area where the car makes its power (high revs). With shorter gears you get to this area quicker, rather simple.

I am WOT as soon as it won't upset the balance of the car, I think you need to attend a performance driving school if you are having issues applying this level of power. I'll be inquiring about the 3.62 shortly, it will blow a car with stock gearing away and the car will feel livelier and torquier, best bang for the buck upgrade.

[lucid]

Originally Posted by Sticky

Argue with this (camera car stock m3, middle 4.10. far right 3.91):

And what does that say exactly? That the modified final drive is slightly faster? Isn't that what I've been saying all along? Was the stock car blown away? No. And it was a short race. Let them go at it longer so that the gear change issues kick in. Not that these street racing videos ever prove anything one way or the other.

Originally Posted by Sticky

I never said you would have 13% more power, but power is a function of torque.

What does the above statement supposed to mean exactly? What is your point?

Originally Posted by Sticky

There is such thing as the powerband, to be specific since you seem to not want to use your common sense, the area where the car makes its power (high revs). With shorter gears you get to this area quicker, rather simple.

So, tell me where "the" power band, as you state it, starts and ends exactly? Give me specific rpm values and tell me why those numbers and not others. (as if the engine is not making power elsewhere)

Originally Posted by Sticky

I am WOT as soon as it won't upset the balance of the car, I think you need to attend a performance driving school if you are having issues applying this level of power. I'll be inquiring about the 3.62 shortly, it will blow a car with stock gearing away and the car will feel livelier and torquier, best bang for the buck upgrade.

What is "not upsetting the balance of the car" if not what I said by losing traction and the back end because of getting on the throttle too early out of a turn? This is the first that is taught at any driving school. Of course you can go WOT after you feel its safe to do so, but that usually means you've straightened out considerably after a tight turn. It's a different story if you are in a miata though. Then you can mash it all you want since the thing has very high traction/power ratio on track rubber.

What I am saying is 13% change in final drive will not result in 13% average acceleration during the 1/4 mile, as calculated by trap speed/1/4 time (delta velocity/delta time). If what you are saying about "always 13% more torque at the wheels" was true, it would have to lead to 13% higher average acceleration, but it won't. I told you why, but you are avoiding the issue.

I agree the car will feel liverlier during regular driving though. In that case, one is operating the engine in a limited vehicle speed range, and what happens after you shift is not a major consideration.

[bigjae1976]

Originally Posted by Sticky

Maybe some people like doing things differently and LIKE BMW's? Why be like the rest of the sheep?

Agreed.

Originally Posted by Sticky

Wish I knew... maybe the M6 diff will be?

Yes, it would be great if someone knew...bump.

Originally Posted by PencilGeek

"Overdrive gears" are just marketing buzzwords. All gears still go through the final drive (differential). You only care about speed-per-RPM. So with a the 1:1 7th gear in the DCT with its 3.154 FDR , that's very close to the 0.872 "overdrive" 6th gear in the 6MT with its 3.846 FDR -- as the speed-per-RPM is similar. The gear multipliers for top gears in the DCT are 3.154 and 3.356 for the 6MT. And this makes the DCT actually have a taller "overdrive" than the 6MT (since it's gear reduction is numerically lower).

I also looked at the speeds/gear ratios. I'd say with anything other than the stock 3.154 FDR in the DCT, you'd have to shift to 5th gear for the 1/4 mile. So if you did decide to change the FDR, 3.62 looks like it would be the best compromise because you'd still be in 2nd gear for 0-60...and 5th gear for 1/4 mile. Now, if you did the stroker motor, you're probably have to shift to 6th gear for the 1/4 mile because I'm assuming you'd be above 128 MPH in 5th gear.

Thanks for clarifying that. I agree, the 3.62 seems like the best of both worlds.

[b16r1ch]

Hmmm...

You are not gaining any more power with gearing, you are simply 'moving' the RPM band to the left (referring to a dyno graph).

So, in a drag race moving to a 4.10 should will improve your 60' but reduce your trap speed. On a road course, you will be able to accelerate 'quicker' out of slow/throwaway turns but ultimately 'slower' in an extended straight. Of course, this depends on the track...i.e. short gearing should help in shorter technical courses between and hurt in longer high-speed courses.

Again, to each their own. I still think there are better ways to spend $3k to reduce lap/track times...i.e. reducing rotational unsprung weight and increasing overall grip.

-Rich

[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).



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.

[BarryC]

Subscribed. I'm interested in any info regarding a numerically higher FDR for DCT.

Thx,
BC