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      11-19-2013, 11:48 PM   #23
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There has indeed been much discussion and debate on this topic here on the forum. Much of it I have been involved in. I suggest doing some reading of some of those threads before making a decision.

My overall recommendation is against such an upgrade.

Why? It is essentially down to the old adage, "there is no such thing as a free lunch". By that I mean such a mod obviously does not add power and additional power is what really makes a car faster overall (i.e. better accelerating). With this mod you trade more torque in each gear for less time operating at that torque (each shift must occur sooner). That tradeoff might make it seem like you do get something for nothing but you don't. In certain circumstances or to meet certain requirements the mod can be an "OK" one but it is hardly worth the cost in my opinion. Some of the cases where is might be worth it have already been mentioned:

-Very particular track requirements - explained well by post above. Be careful you can help yourself on one track and hurt yourself on another. Why bother with the risk unless you are always on the same track and pretty track obsessed.

-Some obsession/focus on contests in a single gear. These will show real performance improvements in many cases. This contributes to making the car feel faster overall but again as soon as you shift 1 or 2 times the advantage is basically lost. Also contributing to the feeling (although it is a completely misleading feeling) of being faster overall is the slight decrease in time spent in each gear. Heck if I am getting to redline so much faster and shifting more times in less total time the car must be faster, right? Wrong...

-Cars not so traction limited in first gear can obviously benefit more. In this case spinning even harder in 1st won't help much.

Going partially catless with or without a tune and with or without pulleys are all things that are less expensive and provide a real and significant amount of true overall performance gains.
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      11-20-2013, 11:59 PM   #24
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I think on the track that gears will in most cases result in faster lap times...especially for situations where you need to go into 2nd on a 6MT. Less shifting while staying in the power band. On an E46M3...its a huge advantage!

With that said I think there is less benefit with a DCT car because its so easy to downshift and stay in the power band. I also think that shorter gears will heat up the DCT a lot faster on the track. More shifting.
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      11-21-2013, 01:16 AM   #25
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Quote:
Originally Posted by swamp2 View Post
There has indeed been much discussion and debate on this topic here on the forum. Much of it I have been involved in. I suggest doing some reading of some of those threads before making a decision.

My overall recommendation is against such an upgrade.

Why? It is essentially down to the old adage, "there is no such thing as a free lunch". By that I mean such a mod obviously does not add power and additional power is what really makes a car faster overall (i.e. better accelerating). With this mod you trade more torque in each gear for less time operating at that torque (each shift must occur sooner). That tradeoff might make it seem like you do get something for nothing but you don't. In certain circumstances or to meet certain requirements the mod can be an "OK" one but it is hardly worth the cost in my opinion.
It seems like this would only be a downside if you were revving all the way to 8400 RPM before shifting. Maybe I'm in the minority, but only when I'm going balls out do I get up into the 8000 RPM range. In daily driving, I'm shifting in the 4-5k range. Thus, in daily driving, it seems like there would only be an advantage.

Also, even going balls out, would not the "downsides" of the 3.45 be mitigated by raising the rev limit to 8600 RPM, giving me 200 more RPM to stay in the same gear if I wanted?
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      11-21-2013, 03:25 AM   #26
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It seems like this would only be a downside if you were revving all the way to 8400 RPM before shifting. Maybe I'm in the minority, but only when I'm going balls out do I get up into the 8000 RPM range. In daily driving, I'm shifting in the 4-5k range. Thus, in daily driving, it seems like there would only be an advantage.

Also, even going balls out, would not the "downsides" of the 3.45 be mitigated by raising the rev limit to 8600 RPM, giving me 200 more RPM to stay in the same gear if I wanted?
Are you "worried" about the lack of performance in your car when daily driving and consistently staying below 5000 rpm? Why do you need a diff to make a car "faster" when you are not interested in extracting the maximum available performance already available in the car? I guess if you just want "results" in a single gear and only in a specific (low) rpm range then sure, go for a altered differential gear ratio. The car should feel and be a bit faster (better acceleration) under such very limited conditions.

I guess I just don't really understand this desire. I also don't really understand folks hesitation to redline their car. I also don't do not buy the whole "lack of torque in the M3" nor the lazy driver phenomena (again not wanting to downshift and not wanting to redline even when wanting maximum go). Thus the FD mod or not debate is very closely related to the torque vs hp, "lazy driver" and FI vs NA debates. They are facets of the same basic phenomena.

If you want a car that you don't need to redline and don't need to choose the best gear possible to get her to go, you'd definitely be better of with a 335i. You'll also probably like the new M3/M4 better than I will.
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      11-21-2013, 09:46 AM   #27
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Are you "worried" about the lack of performance in your car when daily driving and consistently staying below 5000 rpm? Why do you need a diff to make a car "faster" when you are not interested in extracting the maximum available performance already available in the car? I guess if you just want "results" in a single gear and only in a specific (low) rpm range then sure, go for a altered differential gear ratio. The car should feel and be a bit faster (better acceleration) under such very limited conditions.

I guess I just don't really understand this desire. I also don't really understand folks hesitation to redline their car. I also don't do not buy the whole "lack of torque in the M3" nor the lazy driver phenomena (again not wanting to downshift and not wanting to redline even when wanting maximum go). Thus the FD mod or not debate is very closely related to the torque vs hp, "lazy driver" and FI vs NA debates. They are facets of the same basic phenomena.

If you want a car that you don't need to redline and don't need to choose the best gear possible to get her to go, you'd definitely be better of with a 335i. You'll also probably like the new M3/M4 better than I will.
Apparently you don't drive your M3 much in San Diego traffic if you are constantly redlining your car. The M3 is my daily driver and it's not practical to redline the car from stoplight to stoplight everyday on my way to work. Most of my commute is spent in the 2k to 5k range. Sure, there are occasional opportunities to stretch the legs up to 7k or 8k, but those are rare on my daily commute. Do you suggest that instead of cruising at 75-80 mph in 7th gear on the highway, I should drop it down and cruise in 3rd just so I can say I'm redlining it?

Of course, things change when I'm out for a group run or, soon enough, a track day. In that case, it's all about the upper RPMs. But in daily driving scenarios, low RPMs are the nature of the beast more often than not. So, frankly speaking, I would not mind a little more 335 character in the M3 for my daily drive provided I can maintain the high revving NA M3 character for the fun times.
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      11-22-2013, 12:46 AM   #28
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Apparently you don't drive your M3 much in San Diego traffic if you are constantly redlining your car. The M3 is my daily driver and it's not practical to redline the car from stoplight to stoplight everyday on my way to work. Most of my commute is spent in the 2k to 5k range. Sure, there are occasional opportunities to stretch the legs up to 7k or 8k, but those are rare on my daily commute. Do you suggest that instead of cruising at 75-80 mph in 7th gear on the highway, I should drop it down and cruise in 3rd just so I can say I'm redlining it?

Of course, things change when I'm out for a group run or, soon enough, a track day. In that case, it's all about the upper RPMs. But in daily driving scenarios, low RPMs are the nature of the beast more often than not. So, frankly speaking, I would not mind a little more 335 character in the M3 for my daily drive provided I can maintain the high revving NA M3 character for the fun times.
We are not seeing eye to eye here (on top of a basic disagreement...)

I do not commute, but that is irrelevant. I do drive a fair amount both in heavy, light and no traffic, all around So Cal. I also track my car a bit at various tracks around So Cal. Personally I try to balance my driving to respect a natural/reasonable balance between the law and common sense. I get close to or at redline at least a few times during most of my drives when any significant amount of time is spent in the car. As an aside, for this diversity of driving and for the large increase in performance, I chose the M-DCT. The ease and speed of the shifting with M-DCT even further bolsters my claims against "lazy driving".

Your comment above about cruising is simply absurd. Cruising and accelerating hard and obviously entirely different driving styles, purposes and generally require an entirely different driving approach.

From your post it seems you are still missing my point. Again, why bother to FD mod your car to get improved acceleration from it (that is the primary point, whether you redline or not, correct) when you either don't want to or are unwilling to extract the existing available performance?

For me I use the right gear and right rpms (same thing really) to extract the level of performance I want. Obviously the right combination can be both for the purpose of maximum acceleration, but can also be for maximum experiential enjoyment that comes from the acoustics, vibration and frenetic nature of the S65 at very high rpms. Simply either what I "need" or more simply stated what I want in any given situation.

The idea of many (who I claim fall into the "lazy driver" camp, which appears to be you since you don't want to shift to get increased acceleration) that high rpms are inherently unsafe or are always aggressive is nonsense. I know you did not specifically state this, but it is common motif in such discussions and you have hinted at this.

So again what purpose will a FD mod serve for you on your daily commute both at low or at high rpm? Do you desire a slightly stronger "kick" in the back when flooring the car but then will almost immediately be letting off the throttle (again, do be wary/scared of those high rpms...(sarcasm))? Do you want to feel that stronger "kick" but are unwilling to get a stronger or even the strongest kick possible by using a better or the best gear? If that is what you want, its not unreasonable to go for a FD mod. However, if you want that, but are unwilling to simply leave your diff alone and shift to a lower or the lowest possible gear, with a higher or the highest possible torque multiplication, then this is fairly contradictory behavior.

The only condition I can argue for a FD change is when you want this increased "kick", mainly in a single gear but are unwilling to shift to a better or the best gear to accomplish the same (of course even a single shift will typically accomplish much more of what you actually wanted, not to mention what 2,3 or 4 gears lower will do). Again in this case I call this "lazy driving". If the shoe fits put it on, if I'm off in left field please explain carefully how and why.

P.S. No offense is meant by the term "lazy".
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      11-23-2013, 07:00 AM   #29
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Here's why I'm going for the gears- Years ago I used to drive trucks for a roofing company, making material deliveries to job sites. They had a fleet of Chevy trucks for this purpose, almost identical with straight 6 motors and manual transmissions, probably running 3.55 or 3.73 gears. There was one truck however that the fleet mechanic had changed the rearend gears in down to a 4.10. Truck #77 used to take off like a rocket and if you got on it too quick you'd smoke the tires. Whenever I could snag the keys to that one it was always a good day.

The M3 is great in the 6-8K rpm range, where a rearend gear change won't even produce a noticeable result. However since most of us, as the OP stated, live in 2-5K reality, there is no substitute (minus a supercharger) for torque applied to the road.
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      11-23-2013, 11:20 AM   #30
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We are not seeing eye to eye here (on top of a basic disagreement...)

I do not commute, but that is irrelevant. I do drive a fair amount both in heavy, light and no traffic, all around So Cal. I also track my car a bit at various tracks around So Cal. Personally I try to balance my driving to respect a natural/reasonable balance between the law and common sense. I get close to or at redline at least a few times during most of my drives when any significant amount of time is spent in the car. As an aside, for this diversity of driving and for the large increase in performance, I chose the M-DCT. The ease and speed of the shifting with M-DCT even further bolsters my claims against "lazy driving".

Your comment above about cruising is simply absurd. Cruising and accelerating hard and obviously entirely different driving styles, purposes and generally require an entirely different driving approach.

From your post it seems you are still missing my point. Again, why bother to FD mod your car to get improved acceleration from it (that is the primary point, whether you redline or not, correct) when you either don't want to or are unwilling to extract the existing available performance?

For me I use the right gear and right rpms (same thing really) to extract the level of performance I want. Obviously the right combination can be both for the purpose of maximum acceleration, but can also be for maximum experiential enjoyment that comes from the acoustics, vibration and frenetic nature of the S65 at very high rpms. Simply either what I "need" or more simply stated what I want in any given situation.

The idea of many (who I claim fall into the "lazy driver" camp, which appears to be you since you don't want to shift to get increased acceleration) that high rpms are inherently unsafe or are always aggressive is nonsense. I know you did not specifically state this, but it is common motif in such discussions and you have hinted at this.

So again what purpose will a FD mod serve for you on your daily commute both at low or at high rpm? Do you desire a slightly stronger "kick" in the back when flooring the car but then will almost immediately be letting off the throttle (again, do be wary/scared of those high rpms...(sarcasm))? Do you want to feel that stronger "kick" but are unwilling to get a stronger or even the strongest kick possible by using a better or the best gear? If that is what you want, its not unreasonable to go for a FD mod. However, if you want that, but are unwilling to simply leave your diff alone and shift to a lower or the lowest possible gear, with a higher or the highest possible torque multiplication, then this is fairly contradictory behavior.

The only condition I can argue for a FD change is when you want this increased "kick", mainly in a single gear but are unwilling to shift to a better or the best gear to accomplish the same (of course even a single shift will typically accomplish much more of what you actually wanted, not to mention what 2,3 or 4 gears lower will do). Again in this case I call this "lazy driving". If the shoe fits put it on, if I'm off in left field please explain carefully how and why.

P.S. No offense is meant by the term "lazy".
It seems there's a lot of controversy about a diff change, though the people against -- of whom you are probably the most prominent -- are in the minority.

I get the sense that the few of you who are against diff changes (1) have no real-world experience with them and are mostly going off theory, and (2) are perhaps not understanding what they do. (No offense on either account.)

Let's get a couple of things out of the way first. Our transmissions need torque multiplication to magnify the torque produced by the engine. 300 lb/ft. of torque is not going to get a 3,800 lbs. car moving without torque multiplication.

My goal with the diff is to slide the torque curve down so that I have more torque on tap at any given gear than I would otherwise have on the factory diff. This is especially attractive in slow-speed activities where I'm already in 1st or 2nd, such as when taking off from a stoplight or trying to slip past a bus in slow-and-go city driving. To get any kind of torque in those scenarios, I would have to floor it. A diff will give me more torque on tap and will let the car rev without me having to jam the throttle. It gives you a little more "touch" on throttle selection. I can be more surgical.

Your arguments against a diff change have their logical limits. If downshifting were the cure-all that you claim, one could change to a 2.95 diff or a 2.85 diff and get all the benefits of long gears for cruising, and just drive around town in 1st to 3rd to build torque. No one does this. Why? Because you're car would feel like it had flat tires when taking off in 1st and 2nd. Until you got some momentum, the car would feel like a lead balloon.

I want the exact opposite of that sensation. I want the car to have more spring off the line and more torque on tap in 1st and 2nd.

The only downside is that, whereas the factory diff might get me to X speed by the time I reach the redline, the 3.45 diff will only get me to X-n speed by the time I reach the redline.

My response is to point out that (1) you can mitigate that by raising the redline (as I intend to do) and (2) at least in daily driving, I am not constantly stretching each gear to the redline before shifting anyway, so I'm already leaving some in-gear speed on the table as it is. Maybe this makes me "lazy" (no offense taken) or a "pussy" (not your words), but that's how I drive day to day. There's only a couple of spots on my daily commute where it's safe and practical to hit the redline in 3rd or higher gear.

One other motivation worth mentioning: When my PS2 tires wear out, I plan to swap them for 255/35 front and 275/35 rear PSS tires. The larger overall wheel diameter will effectively reduce my rear-wheel torque by a small percentage. The 3.45 diff will mitigate that and leave me with a small, single-digit increase in effective wheel torque relative to that same gear on the 3.15 factory diff on factory tires.
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      12-21-2013, 04:41 PM   #31
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my dinan 3.45 diff blew up will report back with whats gone wrong
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      12-21-2013, 11:19 PM   #32
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Quote:
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my dinan 3.45 diff blew up will report back with whats gone wrong
Please do! I'm still going strong and no issues
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      12-30-2013, 05:45 PM   #33
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my dinan 3.45 diff blew up will report back with whats gone wrong
Any updates on this? I have a 3.45 Dinan diff on order. They are severely backordered from Germany and won't be here until "summer," so now's the time to change my mind if I want to.
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      12-30-2013, 06:58 PM   #34
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It seems there's a lot of controversy about a diff change, though the people against -- of whom you are probably the most prominent -- are in the minority.

I get the sense that the few of you who are against diff changes (1) have no real-world experience with them and are mostly going off theory, and (2) are perhaps not understanding what they do. (No offense on either account.)
I'm late to the thread (sorry) but before my M3, I used to own a C6 LS3 powered Corvette which had some light mods, including a diff change. In my case, I changed from 3.42:1 to 3.91:1, which is about a 15% change. When I made that change, I understood that the car wouldn't actually become faster in the 1/4 mile. It would pull 15% harder than it did before, in each gear, and it would require shifting out of each gear 15% sooner, in mph. Overall, not much difference in 1/4 mile times or traps.

Even so, I was extremely happy with the change because even though the car *wasn't* actually faster, it *felt* a lot stronger, which I personally enjoyed. BTW, if that seems like a nonsensical statement, consider the reverse example of the 1996 Mustang. The standard Mustang V8 with the modular 4.6 liter V8 had 260 hp. The Cobra had 305 hp but they had identical transmission and diff ratios. The difference was that the Cobra revved higher. So when you drove the two cars, you were presented with the scenario that the 260 HP Mustang felt exactly as fast as the 305 HP cobra yet the Cobra had significantly faster 1/4 mile times. How could that be? Because it revved higher, it stayed in lower gears for longer. So the base V8 pulled as hard as the Cobra, just not for as long.

Anyway, my perspective is that such a change is a positive one and a great mod to make, and, unlike a tune, you see a significant difference in how hard the car pulls in each gear while not endangering your engine.

Pat

P.S. You are crazy for raising your redline (no offense btw

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      01-20-2014, 11:01 PM   #35
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3.45 diff.

I have it and love it. I am running 20" BBS LMR, so for me I was just looking to re-coup some of the torque I lost with these bigger wheels.

Gears are definitely a win-win for acceleration, especially with a DCT and a motor that has so little torque. There is a reason that at every race track in professional racing, gears are always changed to match the top end speed available at that particular track. I have never seen the top revs in my M3 in 7th gear, ever, so it"s a no brainer IMO.

The 3.62 can cause issues with the dct and downshifts, rev matching, clutch release timing, etc...I had this and went ot the 3.45 where it is perfect.
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      01-20-2014, 11:07 PM   #36
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Quote:
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I have it and love it. I am running 20" BBS LMR, so for me I was just looking to re-coup some of the torque I lost with these bigger wheels.

Gears are definitely a win-win for acceleration, especially with a DCT and a motor that has so little torque. There is a reason that at every race track in professional racing, gears are always changed to match the top end speed available at that particular track. I have never seen the top revs in my M3 in 7th gear, ever, so it"s a no brainer IMO.

The 3.62 can cause issues with the dct and downshifts, rev matching, clutch release timing, etc...I had this and went ot the 3.45 where it is perfect.
Cort! You're alive. I remember the issues that the 3.62 diff was causing..

How's the tune/car? Come say hi sometime, we've got some goodies for your TT V8
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      01-20-2014, 11:19 PM   #37
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3.45-Benvo

Hi Mike,

Thank you for all the diagnostics with the 3.62, you were spot on and as usual, took a lot of tine out of your day to go above and beyond in helping me find out the issue.

Still loving your tune...the best, and as you know, with the full Dinan catless system and Dinan intake, you were VERY impressed with how well this car ran, it is still the best sounding car I have ever owned (short of my Carrera GT), which is saying a lot as I drive a 458 many days a week and my M3 is better sounding and actually has a better throttle and shift program.
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      01-21-2014, 08:36 AM   #38
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Quote:
Originally Posted by cortwagner View Post
I have it and love it. I am running 20" BBS LMR, so for me I was just looking to re-coup some of the torque I lost with these bigger wheels.

Gears are definitely a win-win for acceleration, especially with a DCT and a motor that has so little torque. There is a reason that at every race track in professional racing, gears are always changed to match the top end speed available at that particular track. I have never seen the top revs in my M3 in 7th gear, ever, so it"s a no brainer IMO.

The 3.62 can cause issues with the dct and downshifts, rev matching, clutch release timing, etc...I had this and went ot the 3.45 where it is perfect.
+1.

A higher final drive will pretty much always be quicker in acceleration and lap time on track (assuming not overly geared where it significantly affects the attainable top speed. On a track you pretty much always shift the same amount for each straight, and changing the gears might add or reduce 1 shift per straight which is more than offset by the improved acceleration. For the seamless power delivery of DCT, no real time is lost in an additional shift.

On the street, you're rarely in the cars power and and are in the mid range 95% of the time. With such little torque in the S65, gears will greatly improve the response and acceleration at low and mid rpm -which you'll feel at all times and will greatly help in traffic.
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      01-22-2014, 08:41 AM   #39
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Billy, I believe you mean lower final drive (which is higher numerically). You also managed to sum this up best so far in the thread. ^^^^ Also note this is from someone in the very rare position of actually being paid to drive.

If you want more of something you can add to it by multiplying. This is what the final drive does. The trade off is potentially lower top speed if the car revs out before hitting its aerodynamic wall and lower fuel economy as you are turning more RPMs in top gear on the highway at any given speed. If you want a very clear example of this, get on your mt bike and pedal away in the small crank ring. Fast acceleration, lots of torque but top speed is limited by how quickly you can spin your legs. Now switch to the big ring and you will get the idea of what the lower final drive provided.
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      01-23-2014, 07:33 PM   #40
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Quote:
Originally Posted by cortwagner
Hi Mike,

Thank you for all the diagnostics with the 3.62, you were spot on and as usual, took a lot of tine out of your day to go above and beyond in helping me find out the issue.b

Still loving your tune...the best, and as you know, with the full Dinan catless system and Dinan intake, you were VERY impressed with how well this car ran, it is still the best sounding car I have ever owned (short of my Carrera GT), which is saying a lot as I drive a 458 many days a week and my M3 is better sounding and actually has a better throttle and shift program.
Anytime! Glad you're enjoying it

I wish the 6MT had a seventh gear. With the manual trans churning close to 3,500 at freeway speeds, this is definitely more viable for DCT vehicles. Torque multiplication is your friend!
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