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it actually does both... members here on the board swear by it.

the butt o meter says that things are going a bit faster but times really are a bit quicker...

Are you looking for a dinan 3.45 because i have a completely unused diff that im swapping out for a koala motorsports quaiffe. It was installed on my car sometime in april but the car has not moved in nearly 10 months due to my supercharger install.
 

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I have the Dinan 3.45 gears and love 'em. Acceleration is very quick and some of the stress is taken off of the running gear. However we all know about the weak stock clutch. I do not track my car so I can't say if times are improved. My guess is that the times would not improve because you will most likely need to shift one more time in the run and that would cost you a bit. ouich Stop light to stop light, the 3.45 gears are the way to go! :1:
 

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I think the diff is great for any situation but you bring a good point Mr Bock. The extra shift that might be required in the quarter might negate some of the gained speed.

If you are not timing the car you will certainly notice an improvement.
 

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An extra shift might be likely under many conditions, such as on the street or certain autocross or roadrace courses, but I doubt that an extra shift would be needed in the 1/4 mile. With the factory gears, the car has just been shifted into 4th gear when you hit the traps. It's so close, I actually tried to make it through the traps in third gear. With my car's redline at 7450, I came within 50 yards or so of the finish line in 3rd before hitting the rev limiter. So I'd be surprised if the 3.45 would require yet another shift (into 5th). This is easily predicted (calculated) if someone with a 3.45 cares enough to run the numbers.

But the real question - that STILL remains unsubstantiated - is will the 3.45 gears actually improve 1/4 times? Many think that with the S62's torque curve, there would be no benefit. I just don't know.
 

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Thank you to all of those who saw that i had the dinan diff availible. I would like to say that currently it is spoken for. Thank you.


The diff creates a higher multiplication of torque to reach the ground...it really doesnt make any more power, it just forces the wheels to spin faster, as if there was more power.
 

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Re: 345 Diff or 3.64 ?

What about going to a 3.64 ratio?

Has anyone done this? My shop says I might not be satisfied with the 3.45 and the 3.64 will give me even more (15% more revs. over the stock 3.15).

The Quaife sounds like the way to go with 40% LSD and fresh clutchs.
 

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I have a custom made 3.45 by Evosport with 30% static lockup and 2x dynamic lockup...I love it. Definitely woth the bucks.
 

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If I'm not mistaken hasnt the 3.64 pretty much been dismissed as a viable option for the M5. In the 3.45, first is pretty darn short , and with a 3.64 would be even worse? Kind of an unacceptable trade off in driveability? At least that's what I remember from the thread.
 

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Re: 345 Diff or 3.64 ?

Carbo said:
What about going to a 3.64 ratio?

Has anyone done this? My shop says I might not be satisfied with the 3.45 and the 3.64 will give me even more (15% more revs. over the stock 3.15).

The Quaife sounds like the way to go with 40% LSD and fresh clutchs.
Your shop is giving you bad info. The 3.64 is too steep, unless you have serious race rubber & spend your time trying to beat $10K Camaros in 0-60 sprints from stoplights. Significant gains will not be realized over 30 MPH with deeper gears. You will not be able to hook up with such deep gears combined with the Getrag 4.xx first gear ratio. If you want to play stoplight drags, the M5 is the wrong car. Such duty can break the tubular aluminum rear subframe due to wheelhop.

The Quaife has no clutches and it is not a 40% LSD. It is no longer manufactured for the M5. Call Evosport and order a 3.45 clutch-type LSD, if your first gear is too high.
 

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MEnthusiast said:
Doesnt the higher gearing create more power at the rear wheels? If so, why wouldn't it improve times (shifts excluded)?
It creates more torque multiplication, but basic Physics say that torque does not do work! The power at the wheels is the same. This is why a chassis dyno does not care what gear you are in or what diff ratio you have. With gears that are numerically higher, the engine applies more force to the pavement at a LOWER VELOCITY. What this means is the car will accelerate harder, but you'll be going SLOWER at the same RPM. Basically...the car feels like it's stronger when your going slower. The sensation of acceleration in the same gear is remarkable.

Seat of the pants does not equate to real performance gains. The stopwatch will identify any gains and they will be modest. Ponycars and some sports cars see big gains in acceleration with deeper gears. These cars typically have transmissions with a first gear ratio between 2.50 to 3.00. For example, some early Camaro & Mustang 5L cars have overdrive transmissions with a 2.95 first gear ratio. First gear in a Viper & Z06 is below 3.50. The first gear ratio in the M5 Getrag is over 4.00, so torque multiplication is generous it does not need deeper axle gearing to launch hard.

If you install 25% steeper rear axle gear, all it will do is move each gear down one number. What I mean is 6th becomes same as old 5th, 5th becomes same as old 4th etc. Ignoring speeds under 20 MPH and speeds over 150 MPH, a race between two cars (one with stock gearing and one with 25% deeper gears) will show the driver simply uses a different gear position at any moment in time. The RPM & acceleration at the same speed will be very similar. The 25% deeper differential gearing effectively disables overdrive and turns 1st gear into a creeper gear for pulling boats out of the water or pulling out tree stumps at 2 MPH. In this scenerio, the car will "accelerate & behave identically", except for times when you need 6th gear or when you are trying to perform John Deere duties in slow motion. Again, the operator will simply use a different gear position. Most drivers will start out in 2nd gear because it will feel like stock first gear. In my case, I regularly use 6th gear at speeds over 45 MPH and I seldom have a need for a creeper first gear. This is why I'm satisfied with stock gearing.

Hope this makes sense.
 

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LSCMAN:
Makes sense to me. Thanks for the explanation.

The 3.64 is definitely out. Now I need to rethink the whole idea. It is a lot of money.
 

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Lscman:

I was waiting for you to jump in here and set the record straight. This 3.45 gears question comes up so much that your thoughts oughta be engraved somewhere in stone.

It's interesting how folks with 3.45 gears all seem to love them. I'm with you though, the stock 1st gear is already (almost too) low, and I'm not about to give up 6th gear, that's for sure... unless of course, the 3.45's were proven to improve 1/4-mile times significantly.

Do guys with 3.45's really start out in 2nd routinely?
 

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Carbo said:
LSCMAN:
Makes sense to me. Thanks for the explanation.

The 3.64 is definitely out. Now I need to rethink the whole idea. It is a lot of money.
Maybe reading Eleven's recent drag racing thread would help. He ran mid 12's with 3.15's and a couple minor mods. I read another thread here where an M5 owner ran high 13's with Dinan 3.45's. I'm not suggesting your car will slow down with deeper gears, but I have yet to see a 3.45 car with repeatable track data showing improvements that go beyond a buttometer.
 

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MEnthusiast said:
Doesnt the higher gearing create more power at the rear wheels?
I know this has been answered already (and correctly, by the way), but here's another perspective.

Theory says changing the diff ratio just trades speed for torque, resulting in exactly the same power. The relationship between torque and speed is that they are the two factors of power. In other words, torque * speed = power.

Those who believe that torque accelerates a car are tempted to shift the balance of the above equation towards increased torque at the expense of speed. However, acceleration absolutely does require power (both torque and speed), not torque alone. No amount of experience, hearsay or borrowed authority can change this fundamental fact of physics.

At any speed, your car is fastest when your engine is making maximum power. Since the power output from the engine is dependent on the speed (rpm, as shown by the power curve), it is important to keep the engine at the rpm where the most power is made. To get the maximum acceleration, you need to make sure your gearing allows you to keep the engine running at the rpm where it makes the most power.

The purpose of the transmission is to force the engine to operate at the desired rpm range. Unfortunately, we don't have enough gear selections in the transmission to always keep our gearing optimal. For example, from a stop, first gear is not good enough to raise the engine rpm up to where the power is until you reach about 30 mph. This is where gearing might improve your acceleration. If you have abundant traction at speeds under 30 mph, then the 3.45 diff will surely help you get up to 30 mph more quickly. If your traction is not so good, the 3.45 diff probably won’t help.
 

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I love to hear good technical gospel. Lscman is right on target. Nice analysis. This is pretty much what I have been saying all along.
Elevens is an experienced drag racer. It is good to hear sound advice.

Take the empirical evidence. I have been watching and gathering info. on this board a long time. Sometimes the results of many others here begins to show a pattern and you can deduce what mods. are worthwhile.

Without argument, the fastest 1/4-mile E39 M5s on this board have come from stock-geared (3.15) M5s. Many posts of time slips have resulted in high 12 seconds runs, and not one of them, to my recollection, was with 3.45 gears. I have seen posts of members with sub-par 1/4-mile times and 3.45 gears, a bunch of them. One member here also voiced his disappointment when he found his 3.45-geared M5 to be slower than his friend's stock one. I know there are a lot of other variables to be considered in that one.

The 3.45 may be better during in-gear rolling encounters, but the trade-off is not worth it. I would rather add power to the engine, maintain the stock gears, and have the best of both worlds.

The best mods. for a stock E39 M5 are Michelin PS2 tires, Supersprint header, and a well-chosen modified clutch. Roy Hopkins cut 7/10ths of a second off all of his 1/4-mile times with these mods. in his One Lap of America outing in 2004. Philly M5 turned impressive 12.7 or 12.8 times with similar upgrades. There are many more who did the same, but they all had stock gearing.
 
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