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Discussion Starter #1
3.45 OR 3.64 FIFF? WHICH ONE AND WHY? WHICH ONE IS BETTER IN LOWER AND HIGHER GEARS? THANKS FOR THE INPUT?

EMPEROR
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EMPEROR said:
3.45 OR 3.64 FIFF? WHICH ONE AND WHY? WHICH ONE IS BETTER IN LOWER AND HIGHER GEARS? THANKS FOR THE INPUT?

EMPEROR
:M5rev: :viking:
Do a search...this has been a HUGE topic...search "3.45"

With that being said...one of the best sleeper mods to do (eventhough it is expensive)...IMHO...is to get the dynamic and static lock up changed on your stock rear end...I had Shadowman redo my rear end (OK no bad jokes!)and I really like it...

You can actually feel the rear end locking up, powering you out of corners with out the usual wheel spin/drifting...

After researching everything that I could...I kept the stock rear end ratio (3.15)...I cannot be happier...

3.64 would be way too steep...first will be even more useless...

Mark
 

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I agree that the 3:45 is the biggest bang for your buck. I had the Dinan 3:45 diff. installed an immediately noticed the difference in acceleration.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:eek:ffice:eek:ffice" /><o:p></o:p>

The only downside you lose some top end, but who ever pushes the envelope anyway?
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Keep the stock ratio and opt for the lockup option mentioned above. Without argument, the fastest times posted by M5s at the drags from this board have stock rear end ratios. The 3.45 may be quicker to respond from a roll, but I believe you lose a bit in standing start acceleration from a stop. Keep the stock ratio and add power.
 

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i think it depends on what you want to do with the car. If you want to drag race, take it to track days, high speeds etc. For me, the 3.45's made a huge difference on the track, i'm able to stay in 3rd and 4th gear at most tracks, no need to get into second. On the street, i'd agree that it feels much stronger. I saw an M5 for sale recently with the dinan 3.45 diff that says he ran 12.80 in the quarter mile, so i don't think the shorter gears really hurt anything.
Mike
 

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Discussion Starter #6
mostly canyon driving, doing a lot of down shifting and upshifting. some drag racing. just want to able to have a good take off and go fast.

emperor
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mottati said:
i think it depends on what you want to do with the car. If you want to drag race, take it to track days, high speeds etc. For me, the 3.45's made a huge difference on the track, i'm able to stay in 3rd and 4th gear at most tracks, no need to get into second. On the street, i'd agree that it feels much stronger. I saw an M5 for sale recently with the dinan 3.45 diff that says he ran 12.80 in the quarter mile, so i don't think the shorter gears really hurt anything.
Mike
 

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Sal

As was shared above it really depends on what kind of driving you do. Mark does a lot of Twisties and I know Mike tracks his so either the stock gearing or the 3.45 would probably suit you personally IMHO.

Either way it will make a huge differance in the feel of the car.



Sean

PS: Mark.. I’m tempted but I’ll just leave that comment alone LOL
 

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Mottati, I would agree that the 3.45 would be better for most tracks because it would allow you to be higher in the rev. band at a given speed. It may not be better for a track like the Nurburgring, but I do think it would be a plus for track stuff overall.

I wouldn't believe the 12.80 time without a time slip or credible reference. We have a couple of senior guys on this board that posted 12.6 -12.8 times with stock M5s. I trust them and have seen some of their time slips here. The 12.80 time may be the result of some other substantial mods. as well. The excess torque of the 3.45 would make 1st gear even harder to control from a launch and the 2nd gear shift point would needlessly be sooner. For track purposes or rolling races, I think the 3.45 would be better.

On the other hand, as you add power by various mods., the 3.45 will be a relative liability. As more power is added, torque is typically increased across the rev. band. The excess torque negates the need for steeper gearing. If you are going to do other substantial power increases, the 3.15 gearing will result in a faster car in every regard.
 

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Discussion Starter #9
SO THE REAL QUESTION IS 3.45 OR STOCK, AND WHAT IF I DO A LOT OF OTHER MODS?

EMPEROR


HBRAMSTEDT said:
Mottati, I would agree that the 3.45 would be better for most tracks because it would allow you to be higher in the rev. band at a given speed. It may not be better for a track like the Nurburgring, but I do think it would be a plus for track stuff overall.

I wouldn't believe the 12.80 time without a time slip or credible reference. We have a couple of senior guys on this board that posted 12.6 -12.8 times with stock M5s. I trust them and have seen some of their time slips here. The 12.80 time may be the result of some other substantial mods. as well. The excess torque of the 3.45 would make 1st gear even harder to control from a launch and the 2nd gear shift point would needlessly be sooner. For track purposes or rolling races, I think the 3.45 would be better.

On the other hand, as you add power by various mods., the 3.45 will be a relative liability. As more power is added, torque is typically increased across the rev. band. The excess torque negates the need for steeper gearing. If you are going to do other substantial power increases, the 3.15 gearing will result in a faster car in every regard.
 

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i think the 3.45 would be better because you still bring a high top speed you would make 290 easily but i suggest to open your rpm reverse limit so u won't lose power.

additional information:in 3.64 you need to change to the third gear around 80 Km but in 3.45 you could easily change around 100 km so in the 3.64 in my thought you will lose some accleration so i think the 3.45 would be better for 0-60 times and you won't have top speed in the 3.64 i think it will be around 275.

in my opinion the 3.45 would be better with opening your reverse limit and i think that your car will ran faster than before and u will see good numbers so go for the 3.45 ratio
:M5eyes: :) :) :) :M5eyes:
 

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Sal

The mod list for both mottati & drallen is similar to what we discussed on your package. So your set up when completed would end up being close to either of their cars.

Either of them would be a good way for you to judge the outcome.

Just check out Mikes car a little closer on Sunday and maybe go for a ride in it to compare.

Sean

PS: Mike I don't remember what diff is in your car?
 

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You can take my car for a drive on sunday to see what you think of the gearing.
Mike
 

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mottati said:
You can take my car for a drive on sunday to see what you think of the gearing.
Mike
I would really like to meet you guys on Sunday and compare gear ratios...especially with a similarly moded car...However a girlfriend and Carson Valley Days await...:grrrr:

Mark
 

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Here is something to consider. I have mentioned this before. Using a higher ratio, or gearing down as some say, does not necessarily mean you will accelerate faster. Simply because you have higher torque multiplication does not result in better acceleration. What if you extrapolate to 15 to 1? Does that result in better acceleration? Absolutely not. At some threshold, further increasing a gear ratio results in WORSE acceleration. That is not disputable.

My thinking is that the 3.15 is just about exactly optimal, especially for standing start racing. Therefore, increasing the numeric ratio by 10 to 15 percent will be a move further away from optimal. 10 to 15 percent is a lot.

From empirical results on this board, stock geared M5s have proven to be the fastest in the 1/4-mile, if that is important to you. A couple of near-stock 3.45 M5s actually showed disappointing 13.5-13.6 times.

At best the 3.45 is equal to the 3.15 in the 1/4-mile. Why modify something if there is no real gain? There is already an abundance of torque available in 1st and 2nd gears with the stock 3.15 rearend gear, so 0-60 times should be slower for the 3.45, not faster HARTGE M5. The 3.64 would be a huge mistake.

For rolling start or track events the 3.45 is probably real good. As I mentioned before, the benefit of future substantial power mods. will not be as fully realized with the 3.45 gearing. The 3.45 gearing will become a hinderance if you begin to make moderate torque (and power gains) across the rev. band.

I would stay with the 3.15 and do a full Superspint exhaust or even the Evosport stage II package.
 

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HBRAMSTEDT said:
Here is something to consider. I have mentioned this before. Using a higher ratio, or gearing down as some say, does not necessarily mean you will accelerate faster. Simply because you have higher torque multiplication does not result in better acceleration. What if you extrapolate to 15 to 1? Does that result in better acceleration? Absolutely not. At some threshold, further increasing a gear ratio results in WORSE acceleration. That is not disputable.

My thinking is that the 3.15 is just about exactly optimal, especially for standing start racing. Therefore, increasing the numeric ratio by 10 to 15 percent will be a move further away from optimal. 10 to 15 percent is a lot.

From empirical results on this board, stock geared M5s have proven to be the fastest in the 1/4-mile, if that is important to you. A couple of near-stock 3.45 M5s actually showed disappointing 13.5-13.6 times.

At best the 3.45 is equal to the 3.15 in the 1/4-mile. Why modify something if there is no real gain? There is already an abundance of torque available in 1st and 2nd gears with the stock 3.15 rearend gear, so 0-60 times should be slower for the 3.45, not faster HARTGE M5. The 3.64 would be a huge mistake.

For rolling start or track events the 3.45 is probably real good. As I mentioned before, the benefit of future substantial power mods. will not be as fully realized with the 3.45 gearing. The 3.45 gearing will become a hinderance if you begin to make moderate torque (and power gains) across the rev. band.

I would stay with the 3.15 and do a full Superspint exhaust or even the Evosport stage II package.
I am with HBRAMSTEDT on this one...I cannot believe the need for a lower ratio, with engine mods...

Last week end I was merging from I-80 to I-5 and the car accelerated so hard that I was in full anti-lock to stop from almost rear ending a car doing 85. This was starting from about 35 and crossing three lanes of traffic in about a hundred yards...I really like this car...If the 3.45 makes me faster...I would of hit that car...

Example two...I was on some backroad twisties in the Sierra Nevadas...Heading towards Shadowman's territory... I was on this rural, two lane, country road and I was going around this corner, hot, and on the gas...(yes I know, I should be on a track, and yes, I was lucky there was no oncoming traffic)...there was snow melt (water) on the road...as I hit the water, the backend started to come around...I thought for a split second, clutch in and brake and hope that I do not fall off the side of the road or hit the gas...well, I hit the gas...with the car sideways, I applied power...you could actually feel the rear end locking in a slide...I got power to the ground and the car straightened out...with my heart racing twice its resting rate, I thanked Shadowman for the recommendation of fooling with my rear end...I thought that it was too expensive for this type of mod...but I was wrong...

So, what I am trying to say is, what ever ratio you decide on, get your static and dynamic lock up changed...

I am having fun with it,

Mark
 

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I like the lower gearing because it enhances the best part of the car, which is that awesome responsiveness when you suddenly floor it in any gear at any rpm, which also can be enhanced with augmented throttle response (new software) and good traction (tires).. I agree 1st gear is a rubber burner but so it is on the stock setup too.

I think though with the 3.64 cruising at 80 mph would have your rpms around 3300 in 6th which might be a little loud (esp with modded exhaust) and concerning for engine longevity..

I think alot of folks assume BMW knew best when they went 3.15, but there may have been highway gas mileage concerns (tax) entering the equation...

My buddy put lower gears in his 77' monte carlo, it really throws you into the seat now but couldn't go above 55 mph (so had to add another gear)..
 

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drallen said:
I am with HBRAMSTEDT on this one...I cannot believe the need for a lower ratio, with engine mods...

Last week end I was merging from I-80 to I-5 and the car accelerated so hard that I was in full anti-lock to stop from almost rear ending a car doing 85. This was starting from about 35 and crossing three lanes of traffic in about a hundred yards...I really like this car...If the 3.45 makes me faster...I would of hit that car...

Example two...I was on some backroad twisties in the Sierra Nevadas...Heading towards Shadowman's territory... I was on this rural, two lane, country road and I was going around this corner, hot, and on the gas...(yes I know, I should be on a track, and yes, I was lucky there was no oncoming traffic)...there was snow melt (water) on the road...as I hit the water, the backend started to come around...I thought for a split second, clutch in and brake and hope that I do not fall off the side of the road or hit the gas...well, I hit the gas...with the car sideways, I applied power...you could actually feel the rear end locking in a slide...I got power to the ground and the car straightened out...with my heart racing twice its resting rate, I thanked Shadowman for the recommendation of fooling with my rear end...I thought that it was too expensive for this type of mod...but I was wrong...

So, what I am trying to say is, what ever ratio you decide on, get your static and dynamic lock up changed...

I am having fun with it,

Mark
if you have higer ratio you will have more accleration in the gears but you may increase your reverse limit to gain the saame power before with better accleration for example: in 3.15 you may have 400hp in 6900 rpm with 3.45 ratio you will have it maybe in 7100 rpm so you may open your revrse limit to have the same power with better accleration.


as you know ther's a peak rpm which have the total power of the car, going after that will decrease your hp so if you open the reverse limit in the 3.45 you won't lose power and you will have better accelration with the same power.


inserting the 3.45 ratio without opening the reverse limit i think it will have the same times for quarter mile because it's losing power but if u open your reverse limit you will have for absolute, a very good numbers with the same or near speed for each gear and the same top speed and the same power.
 

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HARTGE M5 said:
if you have higer ratio you will have more accleration in the gears but you may increase your reverse limit to gain the saame power before with better accleration for example: in 3.15 you may have 400hp in 6900 rpm with 3.45 ratio you will have it maybe in 7100 rpm so you may open your revrse limit to have the same power with better accleration.
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Maybe i'm not understanding this correctly, but changing he gear ratio will have no effect of the hp/torque at a given rpm, though it will happen at a different road speed.

I think you also mean increasing the rev limiter.
Mike
 

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Hartge M5: I agree with you: another shorter differential with a raised rev limiter is the way to go if you change differential.
 
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