My final gear swap project

[Jeff Lange]

They are not different between A/T and M/T in Canada and USA.

41110-30A03 - A/T without LSD (Not used in Canada or USA only in Japan and other overseas markets on low-spec cars)
41110-18021 - A/T and M/T with LSD (Used for Canada and USA)

Both are 4.10:1 and externally look the same, but that LSD makes a difference. .

Jeff

[PantsDants]

Originally Posted by Jeff Lange

They are not different between A/T and M/T in Canada and USA.

41110-30A03 - A/T without LSD (Not used in Canada or USA only in Japan and other overseas markets on low-spec cars)
41110-18021 - A/T and M/T with LSD (Used for Canada and USA)

Both are 4.10:1 and externally look the same, but that LSD makes a difference. .

Jeff

It's odd that 41110-30A03 is even listed as a part for the FR-S; I saw it on a few different sites. All I was really getting at was this is further evidence of cross-compatibility between the cars.

[ReThink]

Killer build good sir. Interest is piqued!!

[ft_sjo]

This might be useful:




Apparently they're all slippers. The first one is about 40% more expensive than the others though. Not sure why, perhaps they're not all slippers!

[PantsDants]

Sooo I noticed Weir Performance also offers a 5.71. Naturally, I had to investigate.

M/T, 6th gear, 4.556 final drive: 62.88 mph @ 3000 rpm
A/T, 6th gear, 5.29 final drive: 71.36 mph @ 3000 rpm
A/T, 6th gear, 5.71 final drive: 66.12 mph @ 3000 rpm

Even with the shortest gear ratio they offer, the A/T still cruises at a lower rpm than the M/T with 4.556. Now I'm even more conflicted as to what ratio I want. Can any of you guys with the manual and a 4.556 comment on the noise or loss in mpg? Are there any differential integrity concerns that come with such a short final drive? Other than burning through my tires at an alarming rate?

I'm leaving for my trip tomorrow so I probably won't be on the boards much (that's a lie, I'll probably be lurking the whole time) so don't think I just disappeared without following through on the project. As soon as I get back and make up my mind on the gearing, I'll update with my progress.

[PantsDants]

Originally Posted by ft_sjo

That last one pulls up on www.lexuspartsnow.com as an IS250 carrier but I don't know if that's a LSD or not. Good info either way.

[37]

Originally Posted by PantsDants

Now I'm even more conflicted as to what ratio I want.

The only true fix there is a manual gearbox.

Originally Posted by PantsDants

Can any of you guys with the manual and a 4.556 comment on the noise or loss in mpg? Are there any differential integrity concerns that come with such a short final drive? Other than burning through my tires at an alarming rate?

No noise. Proper alignment is key.

Haven't noticed a considerable loss in MPG on the highway. Maybe -0.5 to -1 MPG? Shorter gears will certainly impact city mileage unless you short shift (but that's no fun).

Differential integrity? No. The 4.556 is a factory ratio and this is a low-torque platform. You won't put down enough torque NA for it to be a concern.

Tires will let loose more easily. Your rate of alarm here is an unknown as the result will vary with your right foot and tire adhesion.

[PantsDants]

Originally Posted by 37

No noise. Proper alignment is key.

Haven't noticed a considerable loss in MPG on the highway. Maybe 1 MPG? Shorter gears will certainly impact city mileage unless you short shift (but that's no fun).

Differential integrity? No. The 4.556 is a factory ratio and this is a low-torque platform. You won't put down enough torque NA for it to be a concern.

Tires will let loose more easily. Your rate of alarm here is an unknown as the result will vary with your right foot.

Ah, I should clarify. What I meant by noise was exhaust drone on the highway due to the higher revs. I was just asking about the MT with 4.556 as a point of comparison because it should be very similar to what I'm looking at doing if I get the shortest final drive possible, 5.71.

My concerns about diff problems stem from the fact that I'm planning on going suuuper short. I'm fairly certain the 5.29 and 5.71 were made by Toyota for use in the Suzuki Samurai, of all things, and I don't think that had a Torsen.

[the.big.kahoona]

Originally Posted by PantsDants

Sooo I noticed Weir Performance also offers a 5.71. Naturally, I had to investigate.

Linky? Couldn't find it on their website

[PantsDants]

Originally Posted by the.big.kahoona

Linky? Couldn't find it on their website

http://weirperformance.com/finaldrivegears.html
Look under Supra 1986.5-92- ALL.

[Captain Insano]

Oh my goodness this thread is full of win. OP I can't wait to see your results since I'm really wanting to do a FD modification at some point and I also have an AT - I have same conundrum you face, I keep wondering how aggressive I want it to be.

[37]

Originally Posted by PantsDants

Ah, I should clarify. What I meant by noise was exhaust drone on the highway due to the higher revs. I was just asking about the MT with 4.556 as a point of comparison because it should be very similar to what I'm looking at doing if I get the shortest final drive possible, 5.71.

Drone can be judged by downshifting to 5th on the highway. Unless you've removed your cats or installed a cheap, obnoxious exhaust then you should be fine.

Have you plotted out the 5.71? It looks WAY too short, even with an auto trans. To closely match a 6MT with 4.67 in gears 1-2-3 you'd need a 4.9. You might only be focused on gears 4-5-6 and missing how short the first three will become. Don't overlook that as it's a major place where a final drive matters.

Realize that the 6AT in this car will have tall 4-5-6 gears no matter what you do. You either need a 6MT if you want all 6 gears spaced shorter or different auto gears. Shortening the first three too much just to shorten the last three means could mean you'll end up with a street car that's undriveable. You truly would be roasting tires and alarming yourself with a 5.71.

Here is a direct comparison of a 6AT + 4.9 (red) with a 6MT + 4.67 (blue): http://www.teammfactory.com/gearcalc...ission+1+%26+2

Take note of what happens at 4th gear. You can't fix that plot with a final drive. You need different transmission gears.

Originally Posted by Captain Insano

...I also have an AT - I have same conundrum you face, I keep wondering how aggressive I want it to be.

See above. Despite your username, don't go too insane.

[PantsDants]

Thanks again @37. I didn't realize there was such a gap between 1-2-3 and 4-5-6 on the auto. I definitely don't want to go that short after all. I'll play around with the gear calculator some more, but looks like my original idea of 4.88 or 5.29 might be the way to go, as you suggested.

[TouchMyHonda]

Originally Posted by 37

Drone can be judged by downshifting to 5th on the highway. Unless you've removed your cats or installed a cheap, obnoxious exhaust then you should be fine.

Have you plotted out the 5.71? It looks WAY too short, even with an auto trans. To closely match a 6MT with 4.67 in gears 1-2-3 you'd need a 4.9. You might only be focused on gears 4-5-6 and missing how short the first three will become. Don't overlook that as it's a major place where a final drive matters.

Realize that the 6AT in this car will have tall 4-5-6 gears no matter what you do. You either need a 6MT if you want all 6 gears spaced shorter or different auto gears. Shortening the first three too much just to shorten the last three means could mean you'll end up with a street car that's undriveable. You truly would be roasting tires and alarming yourself with a 5.71.

Here is a direct comparison of a 6AT + 4.9 (red) with a 6MT + 4.67 (blue): http://www.teammfactory.com/gearcalc...ission+1+%26+2

Take note of what happens at 4th gear. You can't fix that plot with a final drive. You need different transmission gears.

See above. Despite your username, don't go too insane.

WOW! the 5.71 would literally kill drivability 1-3.... it would be SOOO annoying.