Change gear ratio?

[Afdad120108]

So im not an expert but a buddy of mine has a mustang ppl are know for changeing out the stock gears to 3.73 or 4.10's. Now im not sure what the FR-S final drive is but could we change it for quicker 0-60 times like the mustangs?

[Dimman]

Originally Posted by Afdad120108

So im not an expert but a buddy of mine has a mustang ppl are know for changeing out the stock gears to 3.73 or 4.10's. Now im not sure what the FR-S final drive is but could we change it for quicker 0-60 times like the mustangs?

It's 4.10 here. The only lower ratio I can think of that may have chance is the 4.30 from a NA Mk3 Supra. But that's pretty much ancient history. Japan gets 3.73s on their base model.

[Afdad120108]

So could we change the to 4.30 and would it make a difference? Im sure some company will pick up makeing some aftermarket gears i there is enough demand for it

[Dimman]

Originally Posted by Afdad120108

So could we change the to 4.30 and would it make a difference? Im sure some company will pick up makeing some aftermarket gears i there is enough demand for it

We don't know yet. The diff may be an evolution of the Mk3's but that is 25 years of evolution, so they could be too far changed.

4.30 wouldn't make enough of a difference for the work, unless there are engine mods that increase the rev limit and the power up top, I think.

[Afdad120108]

Oh i see and anything shorter would most likely hurt fuel economy and such so wouldnt really be worth it

[arghx7]

If it were shorter, people would bitch about fuel economy and possibly noise/vibration from turning higher rpm. You can't please everyone. If there is enough demand, the aftermarket could supply a new final drive ratio.

[serialk11r]

Has the aftermarket ever provided a single different gearset? 0.61 6th gear would be a milder rpm drop going 5-6 than the 1-2 shift, and would save a crapload of fuel on the highway especially if you're going under 70mph.

[Sleeperz]

For a small change you could use smaller diameter tires.

[arghx7]

Originally Posted by Sleeperz

For a small change you could use smaller diameter tires.

and throw off the speedometer if you don't have a way to change its calibration... The vehicle speed should be calculated by the wheel speed sensors through the stability control system. So if the final tire diameter doesn't change it the speedometer would remain accurate.

I would think that changing the final drive ratio would be the easiest solution to turn higher revs without other drawbacks.

[GMU-BRZ]

I was wondering about this. I'm not planning on tracking my car, just having it as a daily driver. I was wondering if I could make 5th and 6th, or maybe even just 6th, a little longer to make it about even with the AT. Probably get 35mpg highway vs 30 currently. I guess I'd have to consider cost, potential warranty issues, etc.

[Dimman]

Originally Posted by serialk11r

Has the aftermarket ever provided a single different gearset? 0.61 6th gear would be a milder rpm drop going 5-6 than the 1-2 shift, and would save a crapload of fuel on the highway especially if you're going under 70mph.

For Subaru there are a few options, PPG is one company. For Toyota, Marlin Crawler has offered gearsets for the old R series transmission (Mk3 Supra and trucks).

But these were performance and strength oriented rather than economy.

[arghx7]

Originally Posted by GMU-BRZ

I was wondering about this. I'm not planning on tracking my car, just having it as a daily driver. I was wondering if I could make 5th and 6th, or maybe even just 6th, a little longer to make it about even with the AT. Probably get 35mpg highway vs 30 currently. I guess I'd have to consider cost, potential warranty issues, etc.

On the surface, it certainly seems like turning fewer rpms would yield fuel economy benefits on the highway. And it might in certain situations. But I'm not sure where you get an additional 5mpg from--where did you get that number? Do you really think that, if 5 highway mpg (even 2) were achievable with no drawbacks from something as simple as a gear ratio change, that Toyota wouldn't have done it?

Here's what you have to keep in mind. It's a relatively high revving 2 liter engine with limited part throttle, low rpm torque. It's not a GM LSx V8 engine. If you put the thing in top gear and accelerate at Interstate speeds like on the US06 drive cycle used for certification, you are going to load the engine down further.



Not only could the vehicle feel more sluggish than if it had shorter gearing, the exhaust temperatures are going to increase from the additional load. Then the stock ECU would probably enrich the mixture to reduce exhaust temperatures so the cat, exhaust manifolds, exhaust valves, etc will be protected. So there goes part of your fuel economy benefit. From Toyota's perspective they could have trouble meeting CO emissions standards from the enrichment that results from lugging a high revving, small displacement engine.

Remember that due to taxation the manufacturer already has an incentive to get higher fuel economy for the vehicle as long as that doesn't cause other problems.

[Allch Chcar]

Originally Posted by Dimman

It's 4.10 here. The only lower ratio I can think of that may have chance is the 4.30 from a NA Mk3 Supra. But that's pretty much ancient history. Japan gets 3.73s on their base model.

Why would they use the huge rear end from a Supra? More likely it's the same size as the RX-8. Those have 4.444 and 4.777 gears.

Originally Posted by arghx7

If it were shorter, people would bitch about fuel economy and possibly noise/vibration from turning higher rpm. You can't please everyone. If there is enough demand, the aftermarket could supply a new final drive ratio.

Options would still be nice. The 4.1 is a compromise.

Originally Posted by GMU-BRZ

I was wondering about this. I'm not planning on tracking my car, just having it as a daily driver. I was wondering if I could make 5th and 6th, or maybe even just 6th, a little longer to make it about even with the AT. Probably get 35mpg highway vs 30 currently. I guess I'd have to consider cost, potential warranty issues, etc.

I believe the 3.727 gears only improved MPG by 2-3 but I'd have to check again to be sure. Since the OD gear is the tallest one available in the transmission. You'd have to get a custom Overdrive gear which is $$$.

Originally Posted by arghx7

Not only could the vehicle feel more sluggish than if it had shorter gearing, the exhaust temperatures are going to increase from the additional load. Then the stock ECU would probably enrich the mixture to reduce exhaust temperatures so the cat, exhaust manifolds, exhaust valves, etc will be protected. So there goes part of your fuel economy benefit. From Toyota's perspective they could have trouble meeting CO emissions standards from the enrichment that results from lugging a high revving, small displacement engine.

Taller gears do improve MPG to a point. But you will lose some low end acceleration. What arghx7 is saying is that if you increase the load to the open loop enrichment part of the map you will eat up any MPG benefit. It's the same way if you shorten the gear ratio so that you're cruising on the highway in open loop, your MPG will be atrocious.

[Dimman]

Originally Posted by Allch Chcar

Why would they use the huge rear end from a Supra? More likely it's the same size as the RX-8. Those have 4.444 and 4.777 gears.



Options would still be nice. The 4.1 is a compromise.



I believe the 3.727 gears only improved MPG by 2-3 but I'd have to check again to be sure. Since the OD gear is the tallest one available in the transmission. You'd have to get a custom Overdrive gear which is $$$.



Taller gears do improve MPG to a point. But you will lose some low end acceleration. What arghx7 is saying is that if you increase the load to the open loop enrichment part of the map you will eat up any MPG benefit. It's the same way if you shorten the gear ratio so that you're cruising on the highway in open loop, your MPG will be atrocious.

I believe it's the same diff as the IS which has its roots with the old Supra and that's the only lower diff ratio I could remember off the top of my head. Trans is related to the RX-8, but not sure the diff is.