[Surquhar]

Im just wondering what 3. 46 gears feels like on a DD. if you have upgraded to 3:46 let me know

[JamesM3M5]

I wouldn't do it. Turbos respond to load. Shorter gearing does the opposite. Increase torque output by the motor, not gearing down through the diff. If you had a naturally aspirated car, I'd say do it. Otherwise, no.

[rader1]

Originally Posted by JamesM3M5

I wouldn't do it. Turbos respond to load. Shorter gearing does the opposite. Increase torque output by the motor, not gearing down through the diff. If you had a naturally aspirated car, I'd say do it. Otherwise, no.

But the flip side to this is that when going from a 3.08 gear to a 3.46 your getting .38 increase in torque multiplication. Which can be pretty dang noticeable. I wouldn't swap to a 4.11 or 4.56 or anything crazy like that, but i think a 3.46 MIGHT be good median between torque multiplaction and retaining load on the turbos.
But, I haven't done a gear swap on this platform so i don't have any first hand experience to share and my comments have to be taken with a grain of salt.

[Bakeme521]

I am pretty sure HPautoworks does that swap for our cars with an LSD. I think I recall a while back someone saying they got it from them and they were running it. Try to contact HP and see.

[JamesM3M5]

Originally Posted by rader1

But the flip side to this is that when going from a 3.08 gear to a 3.46 your getting .38 increase in torque multiplication. Which can be pretty dang noticeable. I wouldn't swap to a 4.11 or 4.56 or anything crazy like that, but i think a 3.46 MIGHT be good median between torque multiplaction and retaining load on the turbos.
But, I haven't done a gear swap on this platform so i don't have any first hand experience to share and my comments have to be taken with a grain of salt.

Yes, you do get a 12% change in force applied at the rear wheels, but at the expense of revs. For a daily driver, I would definitely not do it on a car that only revs to 7k at best. I had a 3.46 in my Euro E36 M3, but it revved to 7800 and had power all the way to 7600.

[blisstik]

I didn't think it would multiply torque in any way. I thought you would be about 400-500 RPMs above any gear, which supposedly means you're in the torque range at all times but why do that when this car has a ton of low end torque.

Also, you're top speed will decrease. Not like we hit top speed anyways.

[JamesM3M5]

Originally Posted by blisstik

I didn't think it would multiply torque in any way. I thought you would be about 400-500 RPMs above any gear, which supposedly means you're in the torque range at all times but why do that when this car has a ton of low end torque.

Also, you're top speed will decrease. Not like we hit top speed anyways.

You increase torque applied at the wheels by the same percent as your ratio change. Acceleration is directly proportional to the force applied at the tire contact patch, ignoring wheelspin and aerodynamic drag.

So yes, you do accelerate faster in the same gear. But for the 335 daily driver, it would not be as noticeable as increasing boost. The torque band of a stock 335 is approximately between 2000 and 5000 RPMs due to the boost. Changing 12% in your diff ratio will mean 12% higher revs in all gears. As far as real world acceleration differences, I don't think you would end up with a measurable decrease in 1/4 mile or 60-130MPH time.

[R1000K3]

The change will give 12% more pulling power on the rear wheel, on all gears, which is a lot and very noticeable. Assuming there is sufficient grip, ET could be better with the lower gearing (3.46). There is no reason to believe the car will not be faster up to a certain speed, it as sure as the car pulls harder on e.g. 4th vs. 5th gear. But the final outcome also depends on how many gears you need to use to pass the quarter. In case the new final gearing of 3.46 requires on more gear change to pass the line than with 3.08 this higher gearing may win.

Generally speaking, the car will accelerate better on all gears within the effective RPM with 3.46. The 6th gear will pull about as strong as 5th gear did with 3.08 and 2nd gear will be brutal to say the least. The price is reduced speed on all gears, increased fuel consumption and more wheel spin (need for better tyres).

I think the stock gearing is well choosen for DD but from a performance perspective it is a waste of power to have a final gearing for a theoretical top speed of well above 300 km/h since most cars does not move that quick and you normally go OFF full throttle well before 300 km/h.

In the other end, if you look fo max top speed and really want to go 300 km/h with a MT stage 3 car, it is probably beneficial to get an even higher final gearing than 3.08 to keep the RPM at max power at 300 km/h. A MT with stock final gearing has normally lost many horses around 300 km/h (about 6500 RPM's) and it would help to lower the RPM with e.g. a 2.73 final gearing.

So, what do I personally want? I cant say for sure until a 3.46. gearing is tested on my car with my configuration and driving habits. But I think 3.46 would be better than the existing 3.08 because when I need to go as quick as possible from low to high speeds (about 280 km/h) the extra pulling power (increased TQ on rear wheels) will help.

Just some quick thoughts

[Brey335i]

The AT is a 3.46 right? Feels pretty beast lol

[R1000K3]

I'm not sure about the exact number for AT's but the higher number (lower final gearing) is for AT.

[Wedge1967]

I've played with gearing on other cars I've owned, even bikes. If you go with an LSD to gain traction and opt to change gear ratio, you better do you're homework before you jump to conclusions. You may feel an increase in torque on a lower torque car, but you have to remember it's a fine line you'll be walking with an N54. You could actually make the car slower. 1st gear in a E9x MT is 4.06 with a final drive of 3.08. 1st gear in a E9x AT is 4.17 with a final drive of 3.46. 335d has a final drive of 2.81.

You also have to take into consideration the mods you're running. A FBO AT car making 450ft lbs of torque at the wheel would actually be better off running 2.81 final drive drag racing. I trap my AT @ 110 to 115. I'm shifting at 103 into 4th gear, but redline in 4th isn't until 137.46, so I'm losing time due to an extra shift. Also, if I torque up on the line too hard I smoke the tires in 1st, but launching in 2nd is too hard on the trans considering redline in 2nd is 67mph so it lugs the engine off the line.

So, with a 2.81, my shift point into second gear would be 46 mph vs 37, third at 82 mph vs 67 and I would redline 3rd gear at 126.94 mph vs 103. I wouldn't need to shift into 4th gear saving time with only 3 shifts throughout the 1/4.

Think I'm crazy? Shiv ran the 1/4 in 11.5 @ 126mph. You watch videos of races, what happens to a car when it shifts? In Shiv's video, from launch 1st gear 2 seconds @ 40 mph, 2nd gear 2 seconds @ 65mph, 3rd gear 3.5 seconds @ 100 mph and 4th gear 4 sec @ 126 around 6300 rpm.

I don't think the 2.81 or the 3.46 would work well in the MT. 2.81 wouldn't be enough to drop a gear in the 1/4, and 3.46 would actually cause you to reach for 5th by the end of the 1/4.

You can also play around with tire sizes to see what would work best for what you want the car to do.

Check out http://www.bokchoys.com/differential/GearRatios.htm to see a list of gear ratios.

Then plug in the numbers to see how it will effect your ride on this page: http://www.bokchoys.com/differential...calculator.htm

[R1000K3]

You are not crazy and the selection of final gear is not trivial.

There is no optimal final gear for all configurations and applications. To make it simple; in case you need the car to accelerate as fast as possible to medium speeds like e.g. 200 km/h and a bit well above a 3.46 gearing is better than the stock gearing on MT's. These cars drops noticeable in pulling power on 4th gear and up and 12% more pulling power will help a lot. If the goal is to make the car as fast as possible in terms of speed, a 2.81 final gear it is better, but the acceleration will decrease on all gears (within the same RPM segment).

My own experience with different gear set-ups on motorcycles and cars is to use the lowest gearing you can without getting annoying high RPM on highway speeds. Then I don't mean the announced speed but the actual speed. Another important factor is how fast do you want the vehicle to be when you drive the fastest you do from time to time. If you need the possibility to drive 280 km/h from time to time there is no reason to have it geared for 315 km/h (theoretical) and a brutal pulling force gearing like getting a top speed of only 250 km/h is out of the question in this example.

We need to remember though that there is a lot of much quicker cars from 0-130 mph on streets and people who wants to beat them with 335's, and this is quite possible, needs to change the final gear and get better grip to fix this.

[turb0mik3]

I have a 3.46 and I love it. I find the extra torque is really helpful around the track. But if you want DD then I say it isn't worth it.

[The Ghost]

These cars drops noticeable in pulling power on 4th gear and up and 12% more pulling power will help a lot.

Odd, my car pulls noticeably harder in 4th gear (higher load, more boost). I need to get a VBOX to log, but my second 1/8 is faster and quicker (proportionately) than he first.

Good topic here. I wonder about gears myself, but the tq is so wide, I don't know how much it will matter in the 1/4.

[VegasM2]

I made the change to a 3.46 when I did my LSD upgrade and I love it! This is my daily driver as well and I barely notice the higher revs. I thought I would dread it but it's not that bad. Love being able to step on it and always have the available torque. Great upgrade IMO.

[Motorsport.Nick]

Good info in here!

I've been investigating an LSD upgrade for my manual 335. In the past I've enjoyed higher final drive ratios in NA cars but I dont have much experience with building turbo cars until now. Im torn because my gut tells me to upgrade the final drive...