Do a search...this has been a HUGE topic...search "3.45"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?
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.
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.
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:mottati said:You can take my car for a drive on sunday to see what you think of the gearing.
I am with HBRAMSTEDT on this one...I cannot believe the need for a lower ratio, with engine mods...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.
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.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,
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.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.