Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community - FT86CLUB
Page 4 of 6 123 4 56
Show 40 post(s) from this thread on one page

Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community - FT86CLUB (https://www.ft86club.com/forums/index.php)
-   Engine, Exhaust, Transmission (https://www.ft86club.com/forums/forumdisplay.php?f=8)
-   -   Considering going to 3.727 gear/pinion in 6MT (https://www.ft86club.com/forums/showthread.php?t=7190)

Mitch 06-01-2012 11:42 PM
Quote:
Originally Posted by serialk11r (Post 231754)
Only problem is, you still have the crappy ginormous gap between the ratios, so you will only get marginally better 1st gear acceleration :/

Apparently on some Japanese site the 3.727 gets about 5% better fuel economy on their test cycle, which is probably around what you can expect cruising on the highway. If you drive a lot the savings could add up quickly.
Base mpg: 30.0 mile / gal
New diff: 5% improvement
New mpg: 31.5 mile / gal

Premium fuel cost: $4.00 / gal

Base gas cost: $0.133 / mile
New gas cost: $0.127 / mile
Savings: $0.00635 / mile

Payback mileage (miles to break even, every mile after is actual savings): 157.5 miles per $1 spent modifying the gear ratio.
In other words, if you spend the $1106 mentioned earlier, it would take 174,195 miles before you broke even on the cost of the differential.

And for a little sensitivity study...
Payback mileage as premium fuel cost changes:

$3.00 / gal : 210.0 miles per $1 spent modifying the gear ratio
$3.50 / gal : 180.0 miles per $1 spent modifying the gear ratio
$4.00 / gal : 157.5 miles per $1 spent modifying the gear ratio
$4.50 / gal : 140.0 miles per $1 spent modifying the gear ratio
$5.00 / gal : 126.6 miles per $1 spent modifying the gear ratio

serialk11r 06-02-2012 12:02 AM
Quote:
Originally Posted by Mitch (Post 236398)
Base mpg: 30.0 mile / gal
New diff: 5% improvement
New mpg: 31.5 mile / gal

Premium fuel cost: $4.00 / gal

Base gas cost: $0.133 / mile
New gas cost: $0.127 / mile
Savings: $0.00635 / mile

Payback mileage (miles to break even, every mile after is actual savings): 157.5 miles per $1 spent modifying the gear ratio.
In other words, if you spend the $1106 mentioned earlier, it would take 174,195 miles before you broke even on the cost of the differential.
Yes, which is why the cost needs to be taken into account obviously. If it weren't so expensive to get custom gearsets made then a 6th gear swap that drops revs say 15-20% rather than just 10 would make a lot more sense.

earthsscum 06-03-2012 08:01 AM
Quote:
Originally Posted by azian_advanced (Post 235057)

but if the transmission gear shafts between the AT & MT are swappable, then you're looking at a much better difference.
This

When in history has an a/t got better mileage than a m/t?

15% better in city and highway :mad0260:

Jeff Lange 06-03-2012 01:32 PM
Quote:
Originally Posted by earthsscum (Post 238070)
When in history has an a/t got better mileage than a m/t?
Currently most A/T models get better mileage than their M/T equivalents. The computer has more control of what the transmission is doing and they are much more efficient than they used to be.

Jeff

serialk11r 06-03-2012 04:24 PM
Quote:
Originally Posted by earthsscum (Post 238070)
This

When in history has an a/t got better mileage than a m/t?

15% better in city and highway :mad0260:
Again, as has been said before, the programming on ATs has gotten to the point where the typical AT understands how to get good fuel economy on the EPA cycle, and probably most MT drivers. The EPA test cycle completely murders MT because you're not allowed to shift depending on power demand, only speed.

However, hypermilers all drive stick, even though the ratios are usually shorter :)

OrbitalEllipses 06-03-2012 04:43 PM
Didn't bother reading thread, but has the OP considered how much acceleration will be impacted?

HotLavaMann 06-04-2012 01:51 AM
Quote:
Originally Posted by OrbitalEllipses (Post 238579)
Didn't bother reading thread, but has the OP considered how much acceleration will be impacted?
Yeah, I'm giving that consideration. I'm happy right now with acceleration and think a small drop will be acceptable. Still considering high cost of this route.

I like the idea of a sixth gear that drops RPMs down to AT level and for the type of money we're talking about here (perhaps ~$1200 installed) then maybe waiting for a third party to come out with a different sixth gear is an option. Sure, install of a different sixth gear should be more expensive but the actual gear itself should be relatively reasonable (although that is a wild ass guess).

serialk11r 06-04-2012 02:27 AM
Quote:
Originally Posted by HotLavaMan (Post 239511)
I like the idea of a sixth gear that drops RPMs down to AT level and for the type of money we're talking about here (perhaps ~$1200 installed) then maybe waiting for a third party to come out with a different sixth gear is an option. Sure, install of a different sixth gear should be more expensive but the actual gear itself should be relatively reasonable (although that is a wild ass guess).
The actual gears are what I'm afraid of! Diffs come in different ratios that are compatible, and typically have quite a few ratios to choose from, but transmissions are much more vehicle specific and this 6th gear is the longest 6th gear you can find out of all similar transmissions. So getting a better highway cruising gear would require it to be custom made, and I think the costs for that would be frighteningly high. Even if you get some company to make a few hundred sets, they can't get the cost as low as a differential which is already in mass production.

On ecomodder.com someone swapped their last gear and apparently it wasn't too bad to install, but it might be different on this transmission. That person's gear was I think made by taking 2nd gear from another transmission and flipping the cogs around to get a really low ratio, and since they had to TIG weld something on the gears I think the parts were weakened and so they failed after about 15k miles.

HotLavaMann 06-04-2012 01:17 PM
Quote:
Originally Posted by serialk11r (Post 239565)
The actual gears are what I'm afraid of! Diffs come in different ratios that are compatible, and typically have quite a few ratios to choose from, but transmissions are much more vehicle specific and this 6th gear is the longest 6th gear you can find out of all similar transmissions. So getting a better highway cruising gear would require it to be custom made, and I think the costs for that would be frighteningly high. Even if you get some company to make a few hundred sets, they can't get the cost as low as a differential which is already in mass production.

On ecomodder.com someone swapped their last gear and apparently it wasn't too bad to install, but it might be different on this transmission. That person's gear was I think made by taking 2nd gear from another transmission and flipping the cogs around to get a really low ratio, and since they had to TIG weld something on the gears I think the parts were weakened and so they failed after about 15k miles.
Ouch. Certainly not going that route. Best that can be hoped for is that this same transmission housing is used in several different iterations and a different iteration has a taller sixth. I'm certainly not going to plug in a welded part into something as key as a transmission. Thanks for the info.

ill86 06-22-2012 01:49 AM
Anyone source anything higher than 4.3? AutoFactory is using a 5.11.. That's what I'm after for the circuit.

Edit- nevermind.. Found it :)

icemang17 06-22-2012 05:40 PM
The 6MT is geared quite low.....but the spacing between the gears, even overdrive 6th is actually quite tight..... for more relaxed cruising the AT rear end or the lexus rear end would drop rpms a bit, at a cost of acceleration down low..... My suggestion..buy the TOYOTA or Subaru part....literally the same part as Lexus, but without the premium price markup......assuming the lexus part is $1100, it wouldn't surprise me if the Scion part was 1/2 that.....

serialk11r 06-22-2012 05:47 PM
Quote:
Originally Posted by icemang17 (Post 273319)
The 6MT is geared quite low.....but the spacing between the gears, even overdrive 6th is actually quite tight..... for more relaxed cruising the AT rear end or the lexus rear end would drop rpms a bit, at a cost of acceleration down low..... My suggestion..buy the TOYOTA or Subaru part....literally the same part as Lexus, but without the premium price markup......assuming the lexus part is $1100, it wouldn't surprise me if the Scion part was 1/2 that.....
As has already been said, the AT rear end is exactly the same.
I imagine getting a Lexus IS diff is the cheapest way to change final drive. Might be able to sell the 4.1 to some unhappy IS250 owners too lol.

Jeff Lange 06-22-2012 06:41 PM
Quote:
Originally Posted by icemang17 (Post 273319)
The 6MT is geared quite low.....but the spacing between the gears, even overdrive 6th is actually quite tight..... for more relaxed cruising the AT rear end or the lexus rear end would drop rpms a bit, at a cost of acceleration down low..... My suggestion..buy the TOYOTA or Subaru part....literally the same part as Lexus, but without the premium price markup......assuming the lexus part is $1100, it wouldn't surprise me if the Scion part was 1/2 that.....
Lexus and Toyota parts come from the same place. When they have the same part number, they have the same MSRP price (in North America). Of course dealers are free to set their own pricing, and local Lexus dealers may sell parts for more money I guess.

I'd actually be most interested in what Subaru sells the diff for. Anyone have the Subaru part number for the LSD and complete pumpkin on a BRZ?

Jeff

JC 06-23-2012 06:20 AM
Quote:
Originally Posted by Mitch (Post 236398)
Base mpg: 30.0 mile / gal
New diff: 5% improvement
New mpg: 31.5 mile / gal

Premium fuel cost: $4.00 / gal

Base gas cost: $0.133 / mile
New gas cost: $0.127 / mile
Savings: $0.00635 / mile

Payback mileage (miles to break even, every mile after is actual savings): 157.5 miles per $1 spent modifying the gear ratio.
In other words, if you spend the $1106 mentioned earlier, it would take 174,195 miles before you broke even on the cost of the differential.

And for a little sensitivity study...
Payback mileage as premium fuel cost changes:

$3.00 / gal : 210.0 miles per $1 spent modifying the gear ratio
$3.50 / gal : 180.0 miles per $1 spent modifying the gear ratio
$4.00 / gal : 157.5 miles per $1 spent modifying the gear ratio
$4.50 / gal : 140.0 miles per $1 spent modifying the gear ratio
$5.00 / gal : 126.6 miles per $1 spent modifying the gear ratio
That's assuming you drive all highway and doesn't include installation. The payback period is probably 250k miles plus in reality. I applaud thinking outside the box but this is an asinine idea. Not only will it never pay back financially but you are voiding the drivetrain warranty on your brand new car. If you all you want is a quieter car take off the sound tube and add some sound insulation. It will save you $500+ and actually make your car noticeably quieter.


All times are GMT -4. The time now is 08:07 AM.
Page 4 of 6 123 4 56
Show 40 post(s) from this thread on one page

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2025, vBulletin Solutions Inc.
User Alert System provided by Advanced User Tagging v3.3.0 (Lite) - vBulletin Mods & Addons Copyright © 2025 DragonByte Technologies Ltd.


Garage vBulletin Plugins by Drive Thru Online, Inc.