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Old 06-01-2012, 10:42 PM   #43
Mitch
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Quote:
Originally Posted by serialk11r View Post
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
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Old 06-01-2012, 11:02 PM   #44
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Quote:
Originally Posted by Mitch View Post
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.
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Old 06-03-2012, 07:01 AM   #45
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Originally Posted by azian_advanced View Post

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
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Old 06-03-2012, 12:32 PM   #46
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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.

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Old 06-03-2012, 03:24 PM   #47
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Originally Posted by earthsscum View Post
This

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

15% better in city and highway
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
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Old 06-03-2012, 03:43 PM   #48
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Didn't bother reading thread, but has the OP considered how much acceleration will be impacted?
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Old 06-04-2012, 12:51 AM   #49
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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).
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Old 06-04-2012, 01:27 AM   #50
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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.
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Old 06-04-2012, 12:17 PM   #51
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Originally Posted by serialk11r View Post
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.
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Old 06-22-2012, 12:49 AM   #52
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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
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Old 06-22-2012, 04:40 PM   #53
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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.....
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Old 06-22-2012, 04:47 PM   #54
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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.
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Old 06-22-2012, 05:41 PM   #55
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Originally Posted by icemang17 View Post
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?

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Old 06-23-2012, 05:20 AM   #56
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Quote:
Originally Posted by Mitch View Post
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.
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