5MT vs 6MT

[mbtoloczko]

I had an interesting discussion today about Subaru transmissions with Ali Afshar at Easy Street Motorsports (builders of the world's fastest street driven WRX in the 1/4 mile). One topic that came up was the strength of their upgraded (synchro) 5MT vs the STi 6MT. Apparently, the Easy Street synchro 5MT is actually a little bit stronger than the STi 6MT. They state that their synchro 5MT can handle up to 500 HP, it uses helical cut gears so it is not more noisy than a standard 5MT, and it costs about $5800. Yeah, that's a ton of money, but its less than what it would cost to try to fit a 6MT into an SVX. For those of you wanting the 6MT for its strength, I just thought I would mention this.

[Chicane]

I want a 6 spd for the following reasons:

1. More gears. More gears= better.
2. Shifting is fun.
3. I want top end. And off the line.
4. 6 spds are sweet. Having that extra 6th gear would just be... gah... I can envision pulling it into 6th at 130mph. HehehEHhhe.
5. Supposedly stronger than regular 5spds
6. Better MPG on the highway
7. It's an STi part, and STi= cool.

- Rob

[mbtoloczko]

Originally posted by Chicane
I want a 6 spd for the following reasons:

1. More gears. More gears= better.
2. Shifting is fun.
3. I want top end. And off the line.
4. 6 spds are sweet. Having that extra 6th gear would just be... gah... I can envision pulling it into 6th at 130mph. HehehEHhhe.
5. Supposedly stronger than regular 5spds
6. Better MPG on the highway
7. It's an STi part, and STi= cool.

- Rob

Re: point 3 and 4: The 5MT and 6MT utilize the same 3.9 final drive ratio. And the tranny gear ratios are more similar that you might expect:

6MT 5MT
4th: 1.346 3rd: 1.366
5th: 0.971 4th: 0.972
6th: 0.756 5th: 0.738

You'll be shifting into 6th gear in the 6MT before you shift into 5th in the 5MT. The only real difference you'll notice with the 6MT is that you'll be shifting more often at lower speeds. As far as off-the-line performance, the 6MT STi first gear ratio is nearly the same as the 5MT first gear ratio. The 6MT is essentially a 5MT with an extra gear stuffed in between 1st and 2nd. This gear addresses the uselessness of the 5MT first gear on the track.

Re: point 5: Yes, the 6MT is stronger than standard 5MTs. It isn't stronger than a beefed up 5MT. That was my original point.

Re: point 6: In light of the gear ratios, I don't understand why you think you'll get better gas mileage with the 6MT.

[svxsubaru1]

I like the 6spd alot, but having more gears is not always better with more gears you have to shift more and shifting takes time. The 6spd also has lower gear ratios over all compared to the wrx 5spd. Ive heard that the subaru SCCA rally team uses stock 6spds for there rally cars, the rally cars have like 400-450 horse, and there are betting the crap out of the trannies. The 6pd weighs considerably more than the 5spd, I think about 90 pounds, and if you switch to the r180 rear diff so you can use the stock drive shaft the rear diff ways another 20 pounds more than the r160 diff.

[Chicane]

Hrm. Well crap. I was under the impression that the 6spd was like the 5spd only it had an extra gear on top, for mad top end.

:\

ARGH. Maybe I can live with a 5spd then.

- Rob

[drivemusicnow]

I'm not sure what the differentials are, but that makes a huge difference.,.. if the diffs are higher in the 6MT, than that DOES have a higher top end, what are the differential gear ratios of the two??

[mbtoloczko]

Final drive ratio is just another word for differential ratio. The diff ratios are the same on the 6MT and 5MT (3.90).

I still contend the best transmission for our car would be one out of an '04 Turbo Forester.

Gear ratios:

1st : 3.454
2nd: 1.947
3rd: 1.366
4th: 0.972
5th: 0.738

Final Drive: 4.444


It has a high "whee" factor.

[mbtoloczko]

Originally posted by Porter
I still contend the best transmission for our car would be one out of an '04 Turbo Forester.

Gear ratios:

1st : 3.454
2nd: 1.947
3rd: 1.366
4th: 0.972
5th: 0.738

Final Drive: 4.444


It has a high "whee" factor.

One interesting thing I read about manual tranny durability is that because the pinion gear is smaller, there is less contact area between the ring and pinion, and as a result, the high final drive ratio diffs are more prone to breakage. But yes, the "whee" factor would be good. :-)

[Chicane]

Originally posted by Porter
It has a high "whee" factor.

It would also have a high 'whine' factor while on roadtrips. And another 'whine' factor when you have to pay for gas on said roadtrips. :P

- Rob

[oab_au]

Originally posted by mbtoloczko
Final drive ratio is just another word for differential ratio. The diff ratios are the same on the 6MT and 5MT (3.90).

No, the final drive ratio, is the ratio of the ring gear and the pinion gear. The differential ratio is the ratio of the sun and planet gears. This is normally 2:1 but can be different, as in the European transmissions center differential.

Harvey.

You'd be very hard pressed to "break" a Subaru differential. They're quite strong. That's why Subaru uses 4.444 differentials on the overseas STis... more mechanical advantage at the differential and less torque load at the gears makes for less gear breakage.

[Subafreak]

If I could remember what I can't remember ( Who was it that did the 6speed conversion and then never really mentioned how it went when he was done?) Anyway he had a Euro 6speed and it had much higher gears than the JDM and U.S. spec 6 speeds. So it was more like a 5 speed with another overdrive gear.

[Chicane]

AlexUmn or something like that.

He is my hero (6spd SVX done)

- Rob

[svxsubaru1]

The US 6speed has the same gear ratios off the euro 6speed. I am sure on that one I have heard this from like 5 diffrent magazines, and a couple of techs.