Crazy question: Gear up the entire transmission?

[rinnamon]

I have the enviable opportunity to replace my clutch and thought I may take this opportunity to do something non-conventional with sports cars: get a little more gas mileage. I feel like all of the gears let the engine spin a little bit faster than I like.

Is it possible / is there a best practice for helping me stay at lower RPMs in my gears? I suppose that changing the gearing in the differential is a bad idea, given the highly lauded differential in this car. Does that mean that I would have to replace every gear in the 6-speed MT? Perhaps I could just shift my 5 and 6, but then I feel like there will be a big jump between 4 and 5. I'd rather just shift everything up.

Most of you probably think it's ridiculous, and maybe it is but tips/suggestions are welcomed.

[EAGLE5]

Change the differential. Changing gears would probably require many thousands of dollars.

[EAGLE5]

Oh, I think you can just put the longer auto differential in. Somebody might even want to swap.

[rinnamon]

Originally Posted by jsimon7777

Oh, I think you can just put the longer auto differential in. Somebody might even want to swap.

WAT? The auto has a longer differential and all I have to do is swap? Cool.


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[carbonBLUE]

Originally Posted by jsimon7777

Oh, I think you can just put the longer auto differential in. Somebody might even want to swap.

autos dont have a longer final drive ratio

[EAGLE5]

Originally Posted by carbonBLUE

autos dont have a longer final drive ratio

Yup, you're right. He just needs to swap with someone in another country with a BRZ manual.

http://www.subaru-global.com/13brz_spec.html

Sorry dude.

[wheelhaus]

Rhetorical- don't need to answer these.
Are you uneasy with the high revving nature of a small displacement sports car engine; do high revs make you anxious?
Could you simply shift earlier?
Do you spend a lot of time on the freeway, enough to trade a 1-2mpg gain for reduced acceleration?
Have you considered other options to improve mileage, such as underbody aero, tires, fluids, etc?
Do you ever drive at high rpm?
Do you ever drive the car aggressively or go on fun canyon drives or track days?
Are you trying to save money? i.e. Spending hundreds or thousands to change drivetrain parts to get 15-20 extra miles out of a tank is a little illogical, like buying a motorcycle to save money on gas.

If you're really after better mpg on the highway, honesty the best way to do this is a taller 6th gear, as it won't affect the other gears that would be used for performance driving. Unfortunately that's not a realistic solution, because I believe it doesn't exist (yet). Also, changing a clutch is relatively easy work, cracking the tranny open and replacing gear stacks is a whole different ballgame.

The next option, which is really your only option, is to change the ring and pinion gears in the diff to a taller ratio. Swapping these two gears will affect every gear, so the spacing will feel the same, just slower. It won't affect the diff operation as it doesn't require the diff itself to be changed. I believe our diff gears are compatible with some other Toyota/Lexus models, so there may be some easy options. Most people want a shorter final ratio for quicker acceleration, but you want a taller ratio... Our cars aren't exactly blessed with an abundance of power, so a taller final ratio will make the car feel slower overall.

[Turdinator]

I can't imagine why you would want to, but putting in a taller diff ratio would be your best option here. You will lose acceleration and may well not gain any mileage as you will have to use more throttle for the same acceleration in any given gear.

[rinnamon]

Originally Posted by wheelhaus

Rhetorical- don't need to answer these.
Are you uneasy with the high revving nature of a small displacement sports car engine; do high revs make you anxious?
Could you simply shift earlier?
Do you spend a lot of time on the freeway, enough to trade a 1-2mpg gain for reduced acceleration?
Have you considered other options to improve mileage, such as underbody aero, tires, fluids, etc?
Do you ever drive at high rpm?
Do you ever drive the car aggressively or go on fun canyon drives or track days?
Are you trying to save money? i.e. Spending hundreds or thousands to change drivetrain parts to get 15-20 extra miles out of a tank is a little illogical, like buying a motorcycle to save money on gas.

If you're really after better mpg on the highway, honesty the best way to do this is a taller 6th gear, as it won't affect the other gears that would be used for performance driving. Unfortunately that's not a realistic solution, because I believe it doesn't exist (yet). Also, changing a clutch is relatively easy work, cracking the tranny open and replacing gear stacks is a whole different ballgame.

The next option, which is really your only option, is to change the ring and pinion gears in the diff to a taller ratio. Swapping these two gears will affect every gear, so the spacing will feel the same, just slower. It won't affect the diff operation as it doesn't require the diff itself to be changed. I believe our diff gears are compatible with some other Toyota/Lexus models, so there may be some easy options. Most people want a shorter final ratio for quicker acceleration, but you want a taller ratio... Our cars aren't exactly blessed with an abundance of power, so a taller final ratio will make the car feel slower overall.

All good points. I usually drive 1, 3, 5 in town and have more than adequate torque. I suppose a 6th gear swap would be good but again, opening up the tranny is probably not worth it. I end up getting about 27/29 in town and about 35 on the highway. Ohio isn't the hilliest of states.

I am indeed a little uneasy bringing my car to redline. I do on occasion but typically not.

If I can drop to 2500 rpm at 75 mpg, then I expect to get another 5 mpg.

It's not a money saving thing. It's less logical. It is like having the car I want and being able to hyper mile it at the same time.

I drive the car aggressively on occasion but don't race. I find that pulling off of the line isn't that important.

I think that I'd use 2 and 4 more often lid it was geared a little taller.

I am interested in other tips you have for mpg

Anyway, I'll probably leave it alone, given that it is still under warranty.

Thank you for clear honest answers.


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[sluflyer06]

They make cars for you buddy, but this platform isn't one of them, none of your goals align with the design philosophy of this car.

You want: gas mileage, lower revving engine, taller gears, hypermiling bs.

this car has: motor that doesn't make peak torque until 6,000, very short rear end gearing, boxer motor that historically are not great on gas

Seriously, your not going to get 5mpg with taller gearing, you MIGHT pickup 1 or 2 if your really lucky on the highway with taller gearing.


I'm sure theres a car and a forum that will happily be excited about soybean composted diesel hybrid hypermiling mobiles.

[jvincent]

Here's a simpler solution to change your gearing and improve your mileage.

Put some skinny tall tires on it. I know that 205/55/16 fit, so go even narrower/taller until you bump into the wheel well.

Thinking about it now, that will solve the fender gap issue at the same time.

Because hypermilingracecar!

[cdrazic93]

Change your final drive, lower it so 6th will drop rpm while crusing on the highway.

[Luis_GT]

Should have bought a prius

[wheelhaus]

Taller tires will have the same effect as taller gearing, that's a good point. Just remember that anything changed after the transmission will make the speedometer inaccurate.

Originally Posted by sluflyer06

They make cars for you buddy, but this platform isn't one of them, none of your goals align with the design philosophy of this car.

You want: gas mileage, lower revving engine, taller gears, hypermiling bs.

this car has: motor that doesn't make peak torque until 6,000, very short rear end gearing, boxer motor that historically are not great on gas

Seriously, your not going to get 5mpg with taller gearing, you MIGHT pickup 1 or 2 if your really lucky on the highway with taller gearing.


I'm sure theres a car and a forum that will happily be excited about soybean composted diesel hybrid hypermiling mobiles.

I think it's unreasonable to say to the OP this isn't the car for you, it's just against the grain, and I can appreciate that. Modern day engineering is an exercise in efficiency, we're constantly looking for ways to consume less and get more. No need to resort to using stereotypes as an insult.

Besides, taking a platform that's not designed specifically for efficiency and trying to make it a bit more efficient is, in fact, perfectly fine. Isn't that exactly the same as... Well, taking a platform that's is not designed to compete with faster, more powerful cars, and making it faster and more powerful? Hypocrisy at it's finest. I'm sure there's a car and a forum that will happily be excited about shit-talking and insulting anyone who thinks against the grain. Oh wait, we're already here...