6 speed is useless

[325bob]

I thought my z3 with a zhp/6speed swap was great for a thousand miles or so, but now don't see why they went to the trouble, 5th and 6th are so close its ridiculous,a downshift has to be to 4th to even notice.

[MauiM3Mania]

What works for some, does not for others. I appreciate the overdrive provided by the sixth gear in both my E36 M3 and E46 M3.

With a 3.91 in the E36, I need all the help I can get. Would I swap in a euro six speed and the 3.91 if I had to do it over, no. Consider where I live, there is no interstate. If I was on the mainland, yes I would have.

The E46 isn't as drastic and that's how it was fitted from the factory. It surely helps with fuel mileage and general wear and tear.

I wish my X5, with the 4.10, had a sixth gear/overdrive!

[325bob]

What works for some, does not for others. I appreciate the overdrive provided by the sixth gear in both my E36 M3 and E46 M3.

With a 3.91 in the E36, I need all the help I can get. Would I swap in a euro six speed and the 3.91 if I had to do it over, no. Consider where I live, there is no interstate. If I was on the mainland, yes I would have.

The E46 isn't as drastic and that's how it was fitted from the factory. It surely helps with fuel mileage and general wear and tear.

I wish my X5, with the 4.10, had a sixth gear/overdrive!

I had a 3.91 in my E36, actually put taller rear tires on it for a highway trip, O'fest in Carolina!, prolly gave me about what a 6 speed does, for cheap.

[MauiM3Mania]

I'm running the typical E36 M3 tire sizing of 245/40-17 (24.7" diameter) and the 3.91 final drive. Using an online gear ratio calculator, engine speeds at 60 mph are 2648 in 6th gear (.83OD), dropping down to 5th(1.00), engine speed rises to 3190 rpm. That seems significant.

A tire that is approaching five inches greater in diameter would be needed to provide the same rpm drop which the six speed's overdrive offers.

I'm not interested in running a 29.5" tall tire on my E36, if it were even possible.

[pbonsalb]

I am running a GS6-53, which has a 0.87 6th gear. The 420G has a 0.82.

[MauiM3Mania]

I am running a GS6-53, which has a 0.87 6th gear. The 420G has a 0.82.

Whats you take on the overdrive, worthwhile? I've read the ratio of sixth gear in the 420G is actually .828.

[pbonsalb]

To me it is a noticeable difference that I appreciate even with the 3.15 in my E36. I appreciate it even more with a short diff like the factory one in my E90.

I changed trans for strength since I had broken 2 ZF320. The 6th was a bonus. With the 3.15, I have no complaints about the 1:1 5th in the ZF320. I have run 3.23, 3.38 and 3.64 as well with the ZF320 and wanted a 6 speed for the overdrive. Some overdrive is better than none.

But honestly, since 6 to me is strictly for highway cruising, it is purely an overdrive and I would be happy if it was 0.75. A modified engine could still handle that. Top speed on a stock car might go down because of the reduced power that comes with the reduced rpm. If you underdrive enough, top speed could actually end up being in 5th gear. I like acceleration. I don’t really care about how far past 150 the car will go.

Anyway, I like the OD but if you are using a 3.15 or 3.23 you don’t really need it. It is an expensive conversion and might add 50 lbs.

The OP does not find the conversion to be worthwhile. I would guess he does not spend much time on the highway or he he does, he cruises at around 65-70. The rpm are not objectionable with a 5 speed and 3.23 at that rpm. But if you cruise at 80-85, they might be. Your exhaust could also be a factor since different rpm can bring different noises or vibrations.

[325bob]

To me it is a noticeable difference that I appreciate even with the 3.15 in my E36. I appreciate it even more with a short diff like the factory one in my E90.

I changed trans for strength since I had broken 2 ZF320. The 6th was a bonus. With the 3.15, I have no complaints about the 1:1 5th in the ZF320. I have run 3.23, 3.38 and 3.64 as well with the ZF320 and wanted a 6 speed for the overdrive. Some overdrive is better than none.

But honestly, since 6 to me is strictly for highway cruising, it is purely an overdrive and I would be happy if it was 0.75. A modified engine could still handle that. Top speed on a stock car might go down because of the reduced power that comes with the reduced rpm. If you underdrive enough, top speed could actually end up being in 5th gear. I like acceleration. I don’t really care about how far past 150 the car will go.

Anyway, I like the OD but if you are using a 3.15 or 3.23 you don’t really need it. It is an expensive conversion and might add 50 lbs.

The OP does not find the conversion to be worthwhile. I would guess he does not spend much time on the highway or he he does, he cruises at around 65-70. The rpm are not objectionable with a 5 speed and 3.23 at that rpm. But if you cruise at 80-85, they might be. Your exhaust could also be a factor since different rpm can bring different noises or vibrations.

You've gotten my point, the OD ratio is so close to 5th,its a joke, I'd love a .75 for the interstate trips, which are now usually averaging 75/80 mph., I do have a stainless header and big exhaust system, but drone isn't objectionable, I'm thinking of going back to my 3.46, for autocross acceleration..

[pbonsalb]

When I had the 3.23 then 3.38 then 3.64 with 5 speed, I found the highway rpm to be more and more objectionable. At the end with the 3.64, which I loved, I was unhappy enough with highway driving that I was shopping for a 6 speed conversion. Just about any rpm reduction would be welcome.

Download the rpm calculator from the technical tab at the diffs online website. Plug in tires and diff ratio and 6th gear and have fun.

I use to run 255/40/17, which made my 3.64 into maybe a 3.58. Still, it was more than I wanted on the highway. Ultimately instead of the 6 speed conversion back then, I removed the supercharger and 3.64 and installed a turbo and a 3.15. Bliss. Massive turbo torque made the car way faster with the 3.15 than with the 3.64 and supercharger. The $2k in 6 speed conversion costs covered much of the difference between the supercharger proceeds and the turbo system costs. Honestly, I’d be happy with a 2.93 now, but it’s not a priority.

[325bob]

When I had the 3.23 then 3.38 then 3.64 with 5 speed, I found the highway rpm to be more and more objectionable. At the end with the 3.64, which I loved, I was unhappy enough with highway driving that I was shopping for a 6 speed conversion. Just about any rpm reduction would be welcome.

Download the rpm calculator from the technical tab at the diffs online website. Plug in tires and diff ratio and 6th gear and have fun.

I use to run 255/40/17, which made my 3.64 into maybe a 3.58. Still, it was more than I wanted on the highway. Ultimately instead of the 6 speed conversion back then, I removed the supercharger and 3.64 and installed a turbo and a 3.15. Bliss. Massive turbo torque made the car way faster with the 3.15 than with the 3.64 and supercharger. The $2k in 6 speed conversion costs covered much of the difference between the supercharger proceeds and the turbo system costs. Honestly, I’d be happy with a 2.93 now, but it’s not a priority.

My 3.91 was like a cheap supercharger, 1st was useless, and interstate travel was at 4k, I've always thought turbo was the answer, with that 2.93, lol, newer vettes get better MPG than I did.they are running 65 mph at just above idle speed.

[MauiM3Mania]

My 3.91 was like a cheap supercharger, 1st was useless, and interstate travel was at 4k, I've always thought turbo was the answer, with that 2.93, lol, newer vettes get better MPG than I did.they are running 65 mph at just above idle speed.

I believe the C6 Corvette had a 0.50 overdrive. My brother had a C6 and it cruised the interstate with amazing fuel mileage. Those cars also had the torque to pull it off with the gearing.

[MarcoZandrini]

Hey, swap in a 2 speed GM powerglide transmission!

[325bob]

Hey, swap in a 2 speed GM powerglide transmission!

or the 1 speed "Turboglide", still not sure what that was.