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Engine, Exhaust, Transmission Discuss the FR-S | 86 | BRZ engine, exhaust and drivetrain.


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Old 05-30-2012, 01:09 AM   #1
HotLavaMan
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Considering going to 3.727 gear/pinion in 6MT

Has anyone heard definitively that the rear diff is the same one as a Lexus IS250? I'm very interested in going from the 4.10 to the 3.727 gearing but don't want to waste money on a special order part that I probably would have a hard time returning if it isn't the correct one.

I'm trying to get lower RPM in 6th for highway cruising. Sure, I could just replace the gearing on 6th but that seems very expensive route to go. I don't think I'll mind making the other gears a bit taller.

Anyone know for sure one way or another? Other option is to try to order the JDM part from Japan as the GT86 has the 3.727 is an option.

Also : anyone know how if it's easy to adjust speedo for different ratio? Hopefully just a firmware setting?

Thanks

Last edited by HotLavaMan; 05-30-2012 at 01:10 AM. Reason: Added speedo question
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Old 05-30-2012, 01:24 AM   #2
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sorry for thread jacking but may i ask why? is the gas saving that significant or is there other reasons that I miss? I'm surprised at the high gear in 6th myself but slowly getting used to being able to quickly pass car in cruise control without downshifting, i think they made this conscious decision to make it feels like a sport car.
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Old 05-30-2012, 01:26 AM   #3
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All of the reviews say this car is a hair under-powered as it is. Do you have your car yet? Have you driven it much on the highway? I thought my Civic Si revved absurdly high on the highway, but I got used to it quickly and the fuel economy was acceptable. That's another consideration: what's the payback period for the cost of swapping a differential vs the actual fuel savings you'd see?
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Old 05-30-2012, 01:40 AM   #4
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It's a fair question and one that I reckon many who go forced induction will be asking.
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Old 05-30-2012, 02:07 AM   #5
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I've got about 650 miles on mine. I find the current pickup adequate and don't mind down shifting to pass. My goal is simply to cruise at a slightly lower RPM (increase in gas mileage and decrease in noise). It's not bad as it is now and as you say, it's probably a long payback for gas savings to pay for it. I find the gearing a bit short from what I'm used to so that's why I'm looking into it.
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Old 05-30-2012, 12:10 PM   #6
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subscribed. im interested in this too
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Old 05-30-2012, 12:57 PM   #7
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I can confirm the differential is the exact same as the IS300 and IS250.



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Old 05-30-2012, 01:19 PM   #8
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I can confirm the differential is the exact same as the IS300 and IS250.



Jeff
Awesome. Thanks much Jeff.
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Old 05-30-2012, 01:36 PM   #9
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3.727 would have been a much better compromise for the manual for street use. 4.1 appears to have been selected more for the track than the street.

With the 4.1, on the manual I believe you will be doing a lot of shifting in city driving in the 1-4 gears, while on the AT I believe you will be doing more shifting between 4-6 on the highway.

How big of an investment is an IS250 diff?
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Old 05-30-2012, 02:12 PM   #10
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If you want to get a complete differential, you'll want one from the IS300 with optional LSD. IS250's do not have LSD.

IS300/250's come with 3.73 (MT) or 3.91 (AT) gearing, but only the IS300 has the optional Torsen T2 LSD that the FR-S/BRZ has.

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Old 05-30-2012, 02:28 PM   #11
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I reckon a lot of IS guys will switch to the 4.1 ratio.

I'm interested in this but was hoping to go the opposite on the AT. I'd like to go to a 4.4 or somewhere in the ballpark. If anyone has any info please share. Thank you!
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Old 05-30-2012, 02:45 PM   #12
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I reckon a lot of IS guys will switch to the 4.1 ratio.

I'm interested in this but was hoping to go the opposite on the AT. I'd like to go to a 4.4 or somewhere in the ballpark. If anyone has any info please share. Thank you!
ya the auto could use lower gearing for better acceleration. I would do this in a second.
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Old 05-30-2012, 02:48 PM   #13
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I spoke with my local Lexus dealer parts department. It's either a 41039-22010 or 41039-35010 and he's not sure which one would be the correct one. Price is either $172 or $197 and will take about a week to get here from central Lexus parts depot. So more research required.

Jeff Lange, do you have any suggestions on finding out which Lexus part number it would be?
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Old 05-30-2012, 02:54 PM   #14
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ya the auto could use lower gearing for better acceleration. I would do this in a second.
5th & 6th could be lower on th AT
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