Dinan 3.62 Limited Slip Differential

[Hujan]

Originally Posted by swamp2

The "wrong" (starting) gear for any contest is simply one for which the best time/speed/distance, whatever, is not achieved due to there being a (starting) gear which would have provided better performance.

Right. And 3rd in the 3.45 FD = 13.8 in the 60-130, whereas 2nd = 13.9. So why did you say above that starting in 3rd is the "wrong" gear if it offers superior performance to 2nd and you agree that the "correct" gear is the "gear which would have provided better performance"?

Originally Posted by swamp2

1. Different FDs will offer extremely minimal gains and minimal losses which can be somewhat arbitrary spread depending on the very minor details of the particular contest. Again, if an advantage is shown for 60-130, a disadvantage will almost certainly occur across another very similar contest, just for the sake of example, perhaps 50-120 or 70-140, etc.
2. Results for contests not requiring a single shift can show some significant differences for a FD mod. This relates directly to the gains being sensory in nature, real but only existing over a short time period. Gains across the board are simply impossible.
3. The results at the bottom of post #22 summarize this fairly well, which covers many power levels and many different contest. Don't we see red and green in every column and very small differences overall?

I actually agree with this and, with all due respect (I mean that sincerely), think this is what you've been overlooking. A higher FD may not be "faster" in absolute terms in every scenario. It will be quicker than the stock FD in some scenarios (particularly shorter distances) and slower in others (particularly longer ones).

The best analogy I can think of is track and field sprinting. There are two components to sprinting speed: Leg speed and stride length. To generalize a little bit, shorter sprinters (like myself) tend to have faster leg speed, but have less stride length. By contrast, the taller runners tend to have slower leg speed, but long stride length. So the shorter runners can take more steps than the taller ones, but don't go as far with each step.

As you might predict, the shorter runners tend to excel at the shorter events (e.g., 55 meter, 60 meter indoor events), whereas the taller runners tend to excel at the longer events (200 meters). At 100 meters, the two styles are fairly even. (Though Usain Bolt, at 6'5" is currently killing everyone at the 100 meter and, of course, at 200 meters).

To bring the analogy home, the higher FD like the 3.45 is probably analogous to the shorter sprinters whereas the lower FD like the 3.15 is probably analogous to the taller sprinters.

Thus, it's not fair to say that gear mods will not make the car "faster." That's far too imprecise. As we've seen, at certain events (particularly events with a slower starting speed such as the 0-60, 60-130) the 3.45 diff would be the tool of choice. At longer events, the 3.15 diff might have the advantage.

Ultimately, then, the question is where you want to skew your speed. For myself and others, we are willing to trade a little speed at longer sprint distances for more acceleration off the line and faster stoplight-to-stoplight movement. I know this sounds like heresy to a hardcore track rat, but it's rhetorical and hyperbolic to tell someone like me to "go get a 335i." As you yourself said, the differences are subtle. Thus, a higher FD is a way to get a bit more of the low-end torque feel of the 335i, without doing too much violence to the high-revving character of the S65.

It's not like trading a fine suit (M3) for a bathrobe (335i). Rather, it's like subtlety tailoring a fine suit to fit your body exactly.

Originally Posted by swamp2

I think I'm done repeating myself here. Many of the folks here on the thread now "get it". Without adding power (to weight ratio...) one can not add EITHER CONSISTENT nor SIGNIFICANT performance.

So I assume you'd be happy to trade your 7-speed DCT for a 4-speed manual? Or how about all things equal between a 6MT and a DCT car?

There's more than just power to weight. I actually think you and I agree on quite a bit but that fact is being obscured by a desire to speak in extreme absolutes that can be easily disproven.

[swamp2]

Originally Posted by Hujan

I actually agree with this and, with all due respect (I mean that sincerely), think this is what you've been overlooking. A higher FD may not be "faster" in absolute terms in every scenario. It will be quicker than the stock FD in some scenarios (particularly shorter distances) and slower in others (particularly longer ones).

Review the corrected simulations, there isn't any sort of short/long distance pattern and the results differences are in many cases in the hundredths of seconds. This is completely irrelevant in the real world.

Originally Posted by Hujan

The best analogy I can think of is track and field sprinting. There are two components to sprinting speed: Leg speed and stride length. To generalize a little bit, shorter sprinters (like myself) tend to have faster leg speed, but have less stride length. By contrast, the taller runners tend to have slower leg speed, but long stride length. So the shorter runners can take more steps than the taller ones, but don't go as far with each step.

As you might predict, the shorter runners tend to excel at the shorter events (e.g., 55 meter, 60 meter indoor events), whereas the taller runners tend to excel at the longer events (200 meters). At 100 meters, the two styles are fairly even. (Though Usain Bolt, at 6'5" is currently killing everyone at the 100 meter and, of course, at 200 meters).

To bring the analogy home, the higher FD like the 3.45 is probably analogous to the shorter sprinters whereas the lower FD like the 3.15 is probably analogous to the taller sprinters.

This is nice analogy but doesn't correspond with the actual performance of the M3, stock or modded ones with FD mods. The problem with the analogy is that cars have gears and rpm is constantly in flux.

Originally Posted by Hujan

Thus, a higher FD is a way to get a bit more of the low-end torque feel of the 335i, without doing too much violence to the high-revving character of the S65.

It's not like trading a fine suit (M3) for a bathrobe (335i). Rather, it's like subtlety tailoring a fine suit to fit your body exactly.

Those that have wasted thousands of dollars for nothing but a bit of in gear "feel" (in a single gear at a time!) can continue to call FDs "fine tailoring" but again the analogy is broken. Are you constantly driving so close to redline that you couldn't just downshift to get a enormously better feel?

Originally Posted by Hujan

So I assume you'd be happy to trade your 7-speed DCT for a 4-speed manual? Or how about all things equal between a 6MT and a DCT car?

Not relevant, not in the least.

Originally Posted by Hujan

There's more than just power to weight. I actually think you and I agree on quite a bit but that fact is being obscured by a desire to speak in extreme absolutes that can be easily disproven.

Continue to interpret the data the way you wish.

FD mods offer a better in gear performance only on a single gear by gear basis and only when excluding the near redline sector. This does "feel" better and is better on a gear by gear basis. The rest is in the noise or related to a shift right before or right after a very particular contest.

[Hujan]

Originally Posted by swamp2

Not relevant, not in the least.

Oh, but it is. At least so long as you continue to insist that "[w]ithout adding power (to weight ratio...) one can not add EITHER CONSISTENT nor SIGNIFICANT performance."

We should be having a friendly debate about matters of degree, but first we've got to get you to stop taking indefensible absolute positions like the above.

Honestly, I've lost count of how many times you've contradicted yourself in this thread alone.

[CSBM5]

This whole "contest" is about what "significant" means. It reminds me of helping out my son trying to buy an E36 M3 many years ago...the seller claimed it had "absolutely ZERO rust", "mint condition" etc, but in person the car was a POS with rust in body seams and all underneath along with accident damage that was poorly repaired. . 10/10ths to one person is another person's 4/10ths. Some people think spending $4k for a 0.1 or 0.2 second gain at some speed interval is "destroying" the other diff. Others see it as a profound waste of money.

[Hujan]

Originally Posted by CSBM5

This whole "contest" is about what "significant" means. It reminds me of helping out my son trying to buy an E36 M3 many years ago...the seller claimed it had "absolutely ZERO rust", "mint condition" etc, but in person the car was a POS with rust in body seams and all underneath along with accident damage that was poorly repaired. . 10/10ths to one person is another person's 4/10ths. Some people think spending $4k for a 0.1 or 0.2 second gain at some speed interval is "destroying" the other diff. Others see it as a profound waste of money.

That supposedly minuscule difference assumes those simulations are accurate. Since they were prepared by people with an anti-diff-mod agenda, I'm taking them with a grain of salt.

[regular guy]

Originally Posted by Hujan

That supposedly minuscule difference assumes those simulations are accurate. Since they were prepared by people with an anti-diff-mod agenda, I'm taking them with a grain of salt.

I have an anti-diff-mod agenda? I have no dog in any fight on this forum. But I did notice that guy who said he'd race for pinks high-tailed it outta here pretty fast after I told him I would accept if I had a DCT.

But based on your experience with that specific simulation program, can you describe how you think the results were intentionally skewed with an agenda in mind? Especially after I told you my methodology?

[swamp2]

Originally Posted by Hujan

Oh, but it is. At least so long as you continue to insist that "[w]ithout adding power (to weight ratio...) one can not add EITHER CONSISTENT nor SIGNIFICANT performance."

Well I guess I think/thought it should be obvious that shifting in essentially zero time is better than shifting in mulitple tenths of second is way better and is more or less equivalent to having more power...

And yes, I still firmly believe and believe 99% of folks here would agree that the differences shown in the simulations are INSIGNIFICANT. I've also used CarTest enough and seen enough validation to know that it is making a very realistic A vs. B comparison here. You on the other hand are in the 1%.

Lastly, a prerequisite for the claim that "nothing makes a car faster except improving its power to weight ratio" isn't really flawed when thinking about the difference between 4 gears and 7. 7 gears will produce a decidedly higher average power than 4 gears. Thus this statement is predicated on the fact that a reasonable spread in gears is already achieved that spans the full range of traction and top speed. The reason this does not (or I guess should not) have to be explicitly stated is because it is pretty well always achieved in any remotely sporty car. If you also don't get this, time for even more home work on your end.

Originally Posted by Hujan

We should be having a friendly debate about matters of degree, but first we've got to get you to stop taking indefensible absolute positions like the above.

Look, I'm sorry you blew you money on a mod that doesn't make your car faster. Get over it. Live and learn. My position is fully defensible, it's you who is desperately grasping and straws and claiming basically that noise is significant or that there are some patterns where those you describe clearly don't exist.

It also appears you also can't keep on a single topic through it's completion. You don't care to continue your incorrect sprinter vs. distance runner analogy?

Originally Posted by Hujan

Honestly, I've lost count of how many times you've contradicted yourself in this thread alone.

Go ahead, count em and list em....

And lastly, neither me nor regular guy have any agenda here other than helping folks learn about mods with the help of a little bit of science. You've really got to be awfully paranoid to think that an "anti-diff-mod agenda" is even remotely a possibility.

However, perhaps, just perhaps, a lot of folks argue until they are blue in the face about the benefits of an overpriced mod when it really has none. Nah, I've never seen that on the internet before...

Just stick to the results in a single gear and the good old butt dyno. This mod does feel better, you can have that point and I won't argue it.

Again, who below thousands of dollars and is now in rationalization mode? It ain't me and ain't regular guy either.

[swamp2]

Originally Posted by Hujan

That supposedly minuscule difference assumes those simulations are accurate. Since they were prepared by people with an anti-diff-mod agenda, I'm taking them with a grain of salt.

Let's also try common sense 101 if you don't like physics...

1. A final drive mod increases the wheel torque in each gear by a fixed ratio?
2. Redline in each gear is arrived sooner and at a lower speed in each gear?
3. These effects will counteract each other. One adds some performance benefit and the other hurts performance?

If you disagree with any of these, the conversation can really fully end right there.

If you would like to see this graphically, look at these acceleration plots from CarTest. Turquoise is 3.45 with M-DCT and purple is stock 3.154 FD, again with M-DCT. The amount of time during each shift while the stock car stays in the lower gear accelerating much harder than the "improved" acceleration in the modded car is quite significant. Again the reason for quotes around improved is because even a 3.45 vs. 3.15 difference pales in comparison to the differences between gears and there is plenty of time when they are in different gears. Even just by the second shift there is almost a second where the stock cars is still in second gear while the modded car has initiated a shift.

I don't know how much more clear I can be here providing both the basic irrefutable observations and the physical concepts of this mod, as well as an actual objective plot of the results.

Refute away...

[CSBM5]

Originally Posted by Hujan

That supposedly minuscule difference assumes those simulations are accurate. Since they were prepared by people with an anti-diff-mod agenda, I'm taking them with a grain of salt.

Anything but that was true in my case years ago on the M5board when a member (actually a well-known public figure) was confused about not gaining any performance in the 1/4 when changing from a 3.15 to a 3.64 diff (car was actually slower). I decided to run some simulations to see just what that effect was, and I evaluated the popular 3.45 diff change at the same time. I found the same as has been presented here which actually surprised me at the time (~8 years ago) as I had not thought deeply about it before.

If you can show where there is a fault in the physics model of Cartest, please provide the information. I'm sure the developer would like to know also.

[Yaw]

Originally Posted by regular guy

But I did notice that guy who said he'd race for pinks high-tailed it outta here pretty fast after I told him I would accept if I had a DCT

Nope still here and finding this a very informative discussion. I see the data as showing a 3.45 car faster than stock, while not by much in the 1/4 mile times, many racers would kill for a bumper length in a race. Also noticed the 5-60 mph delta which is indication of performance from a flubbed start is not insignificant. Where I see the big differences in the data is the in gear times which shows how the car would pull out of a corner on a track or exit/on ramp.

While ^^ just adds to the discussion, what I am reminded of here is how many variables need to be looked at when making a (successful) performance increase and how well the car is setup from BMW.

[Hujan]

Originally Posted by swamp2

Well I guess I think/thought it should be obvious that shifting in essentially zero time is better than shifting in mulitple tenths of second is way better and is more or less equivalent to having more power...

And yes, I still firmly believe and believe 99% of folks here would agree that the differences shown in the simulations are INSIGNIFICANT. I've also used CarTest enough and seen enough validation to know that it is making a very realistic A vs. B comparison here. You on the other hand are in the 1%.

Lastly, a prerequisite for the claim that "nothing makes a car faster except improving its power to weight ratio" isn't really flawed when thinking about the difference between 4 gears and 7. 7 gears will produce a decidedly higher average power than 4 gears. Thus this statement is predicated on the fact that a reasonable spread in gears is already achieved that spans the full range of traction and top speed. The reason this does not (or I guess should not) have to be explicitly stated is because it is pretty well always achieved in any remotely sporty car. If you also don't get this, time for even more home work on your end.



Look, I'm sorry you blew you money on a mod that doesn't make your car faster. Get over it. Live and learn. My position is fully defensible, it's you who is desperately grasping and straws and claiming basically that noise is significant or that there are some patterns where those you describe clearly don't exist.

It also appears you also can't keep on a single topic through it's completion. You don't care to continue your incorrect sprinter vs. distance runner analogy?



Go ahead, count em and list em....

And lastly, neither me nor regular guy have any agenda here other than helping folks learn about mods with the help of a little bit of science. You've really got to be awfully paranoid to think that an "anti-diff-mod agenda" is even remotely a possibility.

However, perhaps, just perhaps, a lot of folks argue until they are blue in the face about the benefits of an overpriced mod when it really has none. Nah, I've never seen that on the internet before...

Just stick to the results in a single gear and the good old butt dyno. This mod does feel better, you can have that point and I won't argue it.

Again, who below thousands of dollars and is now in rationalization mode? It ain't me and ain't regular guy either.

You're a clown. I don't have an FD mod on my car.

But please, keep preaching to me about how you like to avoid blowing money on mods that don't increase performance with that bloated mod sig of yours.

[Hujan]

Originally Posted by swamp2

1. A final drive mod increases the wheel torque in each gear by a fixed ratio?
2. Redline in each gear is arrived sooner and at a lower speed in each gear?
3. These effects will counteract each other. One adds some performance benefit and the other hurts performance?

If you disagree with any of these, the conversation can really fully end right there.

I don't disagree with any of those points.

What I fail to see, and what you've yet to explain, is why--on a car that shifts in milliseconds--running through each gear faster is a problem. You seem to prefer a diff setup that allows you to stay in each gear for longer, and yet get angry when I suggest you get a transmission with fewer gears. If the need to shift less and stay in each gear longer is better, why not do it?

Speaking of physics, do you agree that for every action, there is an equal and opposite reaction? If so, then since an FD mod lowers top end speed by some amount, can we assume it is also increasing low-end speed by a similar amount? The question then is how often you're driving your car at 198 mph.

Every point you make in support of the 3.15 relative to the 3.45 could also be made about, say, a 2.8 FD. Where does it end? Should we start strapping on 2.1 FDs?

If your point is that the 3.15 gives the best balance, then go ahead and run some simulations using a 2.8, 2.6, or some other stupid low FD. If those numbers still look good to you, perhaps it's your analysis that is the problem.

[swamp2]

Originally Posted by Yaw

Where I see the big differences in the data is the in gear times which shows how the car would pull out of a corner on a track or exit/on ramp.

Until it's time to shift and the gains are lost...

[swamp2]

Originally Posted by Hujan

You're a clown. I don't have an FD mod on my car.

But please, keep preaching to me about how you like to avoid blowing money on mods that don't increase performance with that bloated mod sig of yours.

I apologize if you do not have a FD, from the discussion, it sounded quite clear to me that you did.

When did I ever say cosmetic mods are bad? Just take them for what they are and that is basically what a FD mod is.

My single most significant performance modification to my car is THE decidedly biggest bang for the buck bolt on possible with this car. That is not listed in my signature for what should be obvious reasons... I've got pulleys as well but haven't bothered updating my sig in ages.

[swamp2]

Originally Posted by Hujan

What I fail to see, and what you've yet to explain, is why--on a car that shifts in milliseconds--running through each gear faster is a problem.

This represents a fundamental lack of misunderstanding about performance on your behalf. You really need to think about this more and a lot harder. I stated the reason and showed it both qualitatively and quantitatively. It appears in fact that you do not agree with my prior item #3, that is the essense of your misunderstanding here on this particular point.

Originally Posted by Hujan

You seem to prefer a diff setup that allows you to stay in each gear for longer, and yet get angry when I suggest you get a transmission with fewer gears. If the need to shift less and stay in each gear longer is better, why not do it?

Redline, redline, this is the reason why we can't always stay in a lower and better gear. However, in any contest where the car in the total effective gear (final drive ratio x gear ratio) trades off between a smaller and larger value the advantages come and go. It's really fairly simple. You lack of an understanding of the fundamentals is really clear here.

Originally Posted by Hujan

Speaking of physics, do you agree that for every action, there is an equal and opposite reaction? If so, then since an FD mod lowers top end speed by some amount, can we assume it is also increasing low-end speed by a similar amount? The question then is how often you're driving your car at 198 mph.

Again, total lack of basics. Top speed is governed by, pretty well in this order:

Peak hp
Drag and frontal area
Losses (primarily drive train and tires)

Cars can however, be geared for a "gear limited top speed" or a "drag limited top speed", in the case of gear limited the above does not apply. The above is for the more typical case of a drag limited top speed. I've posted extensively on these calculations and the relevant physics prior.

Don't start with Netwon's Laws BS here. It is not relevant in the least as to the way you are explaining it. Just like the broken runner analogy... It does however apply well to the case of drag limited top speeds. The car does not accelerate (any more) since it is in a state of total force balance. A reduction of top speed has pretty well nothing to do with an increase in low speed acceleration.

Keep jamming your foot further and further in your mouth...

Originally Posted by Hujan

Every point you make in support of the 3.15 relative to the 3.45 could also be made about, say, a 2.8 FD. Where does it end? Should we start strapping on 2.1 FDs?

I really can't believe the blatant misunderstanding here. I am not arguing that 3.15 is better than 3.45. I am arguing that they are so close that it is a waste of money to spend to change it. If the car came with a 3.45 I would argue it makes no sense to move to either 3.15 or 3.62. Really, PLEASE, READ.

Originally Posted by Hujan

If your point is that the 3.15 gives the best balance, then go ahead and run some simulations using a 2.8, 2.6, or some other stupid low FD. If those numbers still look good to you, perhaps it's your analysis that is the problem.

Different FDs will offer very slight advantages and disadvantages based on the (fine) specifics of various types of contests (my god I am blue in the face from repeating this). There is simply no global optimized value. Bringing the values down so numerically low will not result in enough wheel torque for good acceleration at low speeds and will also result in having a gear limited top speed in perhaps 5th gear. It will also negatively affect in gear results in a significant fashion. Most of the differences though will be established in 1st and 2nd gear. But guess what 1/4 mi traps won't be much affected. Times to speeds will based on the off the line performance. Overall the differences are probably less than you might expect. Again, why?, power to weight is by far the most important factor.

[Yaw]

Originally Posted by swamp2

Until it's time to shift and the gains are lost...

I would rather have a gain to lose than have no gain at all. You're assuming I am not lifting after a few seconds of enjoying increased acceleration exiting an off ramp and could care less about what happens after I shift. Or that my gain out of a corner gets me that little bit closer to the car ahead on track to get a point-by and secure a podium spot in my next HPDE. Another analogy would be downforce. I add aero to my car which increases my speed exiting corners but hurts me down the straight. Would you rather be dropped on corner exit and have to look for your overtake into a braking zone as your non aero car patiently waits as "gains are lost" at the end of the straight?

[swamp2]

Originally Posted by Yaw

I would rather have a gain to lose than have no gain at all. You're assuming I am not lifting after a few seconds of enjoying increased acceleration exiting an off ramp and could care less about what happens after I shift. Or that my gain out of a corner gets me that little bit closer to the car ahead on track to get a point-by and secure a podium spot in my next HPDE.

If all one did is exclusively stay in a single gear a FD mod would very much make sense. I see your point but you have to admit that at other times you will be in gear n, for some fractions of a second, while the non FD modded car will still be in gear n-1, out accelerating you, thereby gaining back the gains you achieved. It's a near continual give and take, just like any closely matched cars who do not have simultaneous shift speeds. Now again, as mentioned prior, for some corners and corner combinations, a final drive mod may be overall beneficial if perhaps it consistently avoids an extra upshift. But again this is due to the specificity of the condition. It is with such specificity that a FD mod may offer a small but concrete advantage.

[regular guy]

Originally Posted by Yaw

Nope still here and finding this a very informative discussion. I see the data as showing a 3.45 car faster than stock, while not by much in the 1/4 mile times, many racers would kill for a bumper length in a race. Also noticed the 5-60 mph delta which is indication of performance from a flubbed start is not insignificant. Where I see the big differences in the data is the in gear times which shows how the car would pull out of a corner on a track or exit/on ramp.

While ^^ just adds to the discussion, what I am reminded of here is how many variables need to be looked at when making a (successful) performance increase and how well the car is setup from BMW.

Good to know the discussion is helpful. I'll add this, whoever said you want to choose the correct FD for the track you're on...definitely true!

[eeeboy]

I bought the 3.62...without it, I would have sold my M3...because I like torque
It is amazing....

[Mr.Slow]

Originally Posted by swamp2

Entirely not worth the money. It does not add power thus doesn't make the car faster. The tradeoff for more torque multiplication (feels good, certainly) is less time in each gear. This makes contests across mulitple gears pretty much a wash. Lot's of discussion and debate on this mod here on the forum.

not fast but It can make car quick

[SneakyDeeky]

Originally Posted by C|3R1C

Those with the 3.45 really like it based on reviews I've read and have had no issues. They say the car should have came like that from the factory.

I'll second that , as I changed the gearing in my 335i when I installed my Wavetrac diff and it definitely should have come from the factory like this.
For the non-Ms, 6MT = 3.08 and Auto = 3.46. I had my diff built with an Auto ratio in it and it's probably my favorite mod.

[coloradoe92m3]

This data makes sense, especially less time in each gear negating more in gear acceleration but how does it work where for example people talk about M3 low torque at engine is nor relative because its able to use shorter gearingto multiply torque to tthe wheels in comparison to a c63 let's say. If shorter gears don't add HP, which I get than why do people talk about M3 ability to use shorter gearing? I get its a different comparison and different cars but I don't know that saying since gearing doesn't change power that there is no improvement in acceleration. M3 would never keep up with a c63 ( non pp) if gearing were llinger. I just am trying to fully grasp concept.