Change gear ratio?

[Allch Chcar]

Originally Posted by Dimman

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.

Just to get this straight, the Beams powered IS/Altezza also had the AZ6. But did they all share the same rear differential?

[AJ PwR]

I wouldn't go longer gear as well. It will hurt the acceleration which I don't want. I am thinking 4.5 or 4.6 would be nice, it will be a 10% noticeable difference by math.

So the BRZ diff is a Toyota diff ? Or a Subaru diff ?

[Dimman]

Originally Posted by Allch Chcar

Just to get this straight, the Beams powered IS/Altezza also had the AZ6. But did they all share the same rear differential?

I'm not 100% certain but given Toyota's past models the diff pumpkin and axles will be universal for the model but with internal ratio and open/lsd options to suit the car's performance.

I think Jeff Lange on here could clarify.

[Dimman]

Originally Posted by AJ PwR

I wouldn't go longer gear as well. It will hurt the acceleration which I don't want. I am thinking 4.5 or 4.6 would be nice, it will be a 10% noticeable difference by math.

So the BRZ diff is a Toyota diff ? Or a Subaru diff ?

Toyota.

[serialk11r]

arghx7 IIRC the EPA test doesn't even spend much time in 6th gear does it?
If the AT cruises along at super low rpm, and it does fine on emissions, what's the problem with having MT do the same? I guess the AT automatically kicks down a gear for acceleration which would reduce CO/HC and stuff, but last time I checked higher load in closed loop decreases CO/HC, so it's not clear to me that this is an emissions related thing.

I did a few rough extrapolations and the AT gearing allows the car to be near the BSFC-optimal load point at 80mph, so I think fuel enrichment is only an issue if you're trying to floor the gas in 6th while at 2000rpm or if you're going like 100mph, which you shouldn't be doing on the highway.

That's why I think something like a 15% decrease in 6th gear rpm would be nice, you maintain more passing power than the AT, it'll drop 75mph rpm to ~2600rpm and reduce noise, and will improve fuel economy by a little, which matters a lot to people who commute long distances. I used the BSFC chart for a 1NZ-FXE and specific torque, so it's going to be a little bit different, but the fuel consumption difference was ~15% at 60mph, ~10% at 70, ~8% at 80. If the FA20 is better at being efficient in low BMEP range then the difference is smaller, but the EPA test is coming back as 34 vs 30 which is a massive difference :/

Part of the reason why I think this is a good idea is because the moment people start trying to rev this engine higher, people will start dropping higher final drives in to increase acceleration, and it would be particularly nice if that didn't mean cruising along the highway at S2000 like rpm.

[arghx7]

Originally Posted by serialk11r

arghx7 IIRC the EPA test doesn't even spend much time in 6th gear does it?

The US06 does. See attached standard shift schedule from the EPA website--scroll all the way down to the bottom for US06, 6 speed manual (it's in some weird ass format). You will notice that it is ~1200 seconds long. That's because the US06 certification test actually repeats the same drive cycle; the first ~600 seconds is a warmup and doen't actually sample from the tailpipe.


in the standard EPA shift schedule, you are in 6th gear from seconds 62-122 and from seconds 147-488.

If the AT cruises along at super low rpm, and it does fine on emissions, what's the problem with having MT do the same?

We don't know if the AT does fine on emissions. It might do really well or it may be borderline.

I guess the AT automatically kicks down a gear for acceleration which would reduce CO/HC and stuff, but last time I checked higher load in closed loop decreases CO/HC, so it's not clear to me that this is an emissions related thing.

If the vehicle has to enter enrichment, CO is the main thing to suffer--CO is very closely related to the AFR entering the converter. CO is the big concern on the US06 cycle. On other cycles it isn't such a big deal because the engine is under a lot less load. HC is typically a bigger deal on cycles that have a cold start component (LA4/FTP cycle) due to unburned fuel and catalyst light-off.

I did a few rough extrapolations and the AT gearing allows the car to be near the BSFC-optimal load point at 80mph, so I think fuel enrichment is only an issue if you're trying to floor the gas in 6th while at 2000rpm or if you're going like 100mph, which you shouldn't be doing on the highway.

Ah but the US06 goes to 80mph and with the standard shift schedule you are in 6th gear. And then it depends on the road load coefficients used on the dyno. When they run these tests, the dyno uses exponential road load based on a quadratic function. The coefficients of the function (A + (B)x+ (C)x^2) and the weight determine the road load. There's a whole process for determining these values. They are there to approximate wind resistance etc.

That's why I think something like a 15% decrease in 6th gear rpm would be nice, you maintain more passing power than the AT, it'll drop 75mph rpm to ~2600rpm and reduce noise

We don't know if it will reduce noise. It depends on the resonant frequencies of a bunch of things. It might though. Somebody in the NVH (noise, vibration, harshness) engineering department would know. But of course they're not talking.

, and will improve fuel economy by a little, which matters a lot to people who commute long distances.

Hopefully, but it's hard to say how much. I'd like to see how back-to-back tests on a US06 with two different 6th gear ratios.

I used the BSFC chart for a 1NZ-FXE and specific torque, so it's going to be a little bit different, but the fuel consumption difference was ~15% at 60mph, ~10% at 70, ~8% at 80.

The 1NZ-FXE is a 1.5L miller cycle engine for a hybrid (1st and 2nd gen Prius) with a power-split planetary gear set for a transmission. It's not a sports car with a 6 speed manual transmission or conventional 6 speed step automatic. FYI, You know Toyota just brought back the 1NZ-FXE in revised form for the new Prius C? They added a bunch of EGR to it and the BSFC map has changed.

If the FA20 is better at being efficient in low BMEP range then the difference is smaller, but the EPA test is coming back as 34 vs 30 which is a massive difference :/

Unless Toyota publishes a BSFC map, nobody will ever know the BSFC curve without spending $Texas to buy a production engine and do combustion analysis on it.

It's hard to say exactly what causes the big difference in mileage between the A/T and M/T, and I'm just curious as you are. The EPA numbers are calculated based on 5 test cycles and weighted according to an arcane formula. The throttle mapping, gearing, A/T shift schedule, lockup schedule, VTC mapping and all sorts of stuff could be causing the huge difference in numbers. A few people know, and they're not talking.

Part of the reason why I think this is a good idea is because the moment people start trying to rev this engine higher, people will start dropping higher final drives in to increase acceleration, and it would be particularly nice if that didn't mean cruising along the highway at S2000 like rpm.

If you're that far into the game, you would hope that you have an aftermarket cat, tuning to reduce enrichment under heavy loads (enduring higher exhaust temps), and a way to turn off check engine lights for catalyst efficiency. So the whole situation changes potentially. I was more referring to a situation of a mostly stock vehicle but bolting on a catback and different rear end like people do on Mustangs and Camaros.

[serialk11r]

Yea I guess you're right.

I didn't notice before, but the US06 cycle has some brief but quick acceleration in 6th gear, and I suppose that could possibly be an emissions concern.

[TheRipler]

I was told that the diff is an R200 (?I think by Hitachi?). If so, it's stout, and that also means there are plenty of OEM and aftermarket gears already out there. It's been used on a variety of cars out of Japan for decades.

[frusciantrix]

I hope there will be some aftermarket mod or shorter differential for a shorter final drive. The 6th gear is just too long.
Every hot hatch I've driven (Mini JCW, Renault Megane R.S.) could hit the rev limiter in 6th gear. If i want to look after fuel consumption I'd rather buy a Prius.

[Jeff Lange]

The differential is not an R200, it is a Toyota unit. In the past referred to as the G-series (8.0") it is now referred to as the F20SX/F20TX/FD20A/FD20AT (205mm) unit. The same basic differential was used in many Toyota cars and trucks, notably the 86-92 Supra, 01-05 IS300 (with the same Torsen T2 LSD that the Zx6 gets), and the 06-15 IS250. The older models usually have a different outer case (pumpkin), however the internals are still near identical. The newer models like the IS300/IS250 have the same case and internals as the Zx6 in the 86/FR-S/BRZ.

There are many ratios available for these cars, and quite a few part numbers out there from Toyota, even for the same ratios (ring & pinion sets typically include the pinion seals, stake nut, ring gear bolts and retainers -- if applicable). Using older Supra ring and pinion sets will require you to get a different pinion seal, as the housing is different.

Still, here is a partial list of some of the ratios available from Toyota, along with some of their part numbers that will work in the Zx6:

3.58:1 - 41201-80125
3.73:1 - 41201-80050
3.91:1 - 41201-80052
4.10:1 - 41201-19605
4.30:1 - 41201-29606 (Included pinion seal will not fit)
4.56:1 - 41201-19557 (Included pinion seal will not fit)
4.88:1 - 41201-80183 (Included pinion seal will likely not fit)
5.13:1 - 41201-80300 (Included pinion seal will likely not fit)

As for the TL70 (Aisin AZ6) Transmission, it is very similar to the Toyota-designated J160 transmission from the Altezza RS200, but the ratios are actually the same as the AZ6 used in the Silvia S15, Nissan-designation FS6R92A. The TL70 in the Zx6 is a newly developed version of the AZ6, though it shares most of its design with predecessors. While most of the gear and synchro setup between the TL70/J160/FS6R92A are all the same, the external cases vary quite a bit, and the TL70 has a different shift pattern, placing reverse beside 1st instead of beside 6th. That gear pattern difference obviously necessitated considerable revisions to the shift linkage internally. The TL70 in the Zx6 also has a larger case, allowing for a higher gear oil capacity (1.8L for the FS6R92A, 2.2L for the TL70).

The TL70 shares a similar style case to the J160, both utilizing remote-mount shifters, while the FS6R92A had the shifter mounted directly on the tailshaft housing.
The TL70 shares gear ratios with the FS6R92A, while the J160 has a taller 1st gear and a shorter 6th gear, the TL70 and FS6R92A have a shorter 1st gear and a taller 6th gear (selected presumably for better fuel mileage).

EDIT (04/30/2016): Updated some information, added a couple more available ring and pinion sets.

Jeff

[Apex Chase]

The big hang up for me deciding to buy one of these cars is the lack of power but knowing that a gear swap is an option (and maybe a reliable FI package) would help make the decision a lot easier. My background is with modern muscle cars (Camaro, Mustang, Challenger) and with the 6 speed transmissions these days you can get away with more aggressive rear end gearing without it effecting fuel economy much. The lower gearing improves "city" economy and the tall 6th gear helps minimize the impact at cruising speeds. We typically see no more than about a 2 MPG loss when swapping a Camaro SS from 3.45s to 4.10 but the equivalent torque gain is approximately 20%.

[BPAuto]

We don't know tuning specifics yet here in the States, but in Japan, we have a few companies we are working with some companies that have come up with final drive kits. As to the overall impact to fuel economy / power gained, we have to communicate with the companies directly with consumer concerns and desires. Here is one example we are currently offering from ARROWS Japan...



offered currently in 4.556 or 4.3.

Please PM us for other options or for more information. Best thing to do is give us a call with your overall goals so we can custom tailor product packages for you and your budget.

check it out in our thread of other Arrows products if you'd like (here)

[Apex Chase]

Originally Posted by BPAuto

We don't know tuning specifics yet here in the States, but in Japan, we have a few companies we are working with some companies that have come up with final drive kits. As to the overall impact to fuel economy / power gained, we have to communicate with the companies directly with consumer concerns and desires. Here is one example we are currently offering from ARROWS Japan...



offered currently in 4.556 or 4.3.

Please PM us for other options or for more information. Best thing to do is give us a call with your overall goals so we can custom tailor product packages for you and your budget.

check it out in our thread of other Arrows products if you'd like (here)

PM sent.

[Dimman]

@Jeff Lange

Jeff, are the Marlin Crawler 8" ring and pinion sets the same 8" guts?

If so that would give us heavy duty 4.11:1, 4.56:1, 4.88:1 and the 5 something options...