The Transmission / Differential FAQ

[Whizbang]

updated!

[afgmoto1978]

Don't forget to add the JDM FD3S tranny with the .806 fifth gear. I will be adding an RX-8 4.44 lsd gears to my FD diff. Do you want pictures of the install or any usable info?

[Whizbang]

Originally Posted by afgmoto1978

Don't forget to add the JDM FD3S tranny with the .806 fifth gear. I will be adding an RX-8 4.44 lsd gears to my FD diff. Do you want pictures of the install or any usable info?

sure! make a thread and ill link it into the FAQ to keep clutter down. Can you verify this .806 gear?

[afgmoto1978]

Originally Posted by Gravity Fed

sure! make a thread and ill link it into the FAQ to keep clutter down. Can you verify this .806 gear?

http://www.ooparts-international.co....ion/index.html

FC3S RX-7 [1 - 3rd gear] R5M-D - 2.714 1.742 1.267 - -

FD3S RX-7 [1 - 3rd gear] R15M-D 2.714 1.742 1.267 - -

FC3S RX-7 [1 - 3rd & 5th gear] with Input Shaft R5M-D 2.578 1.772 1.289 1.000 0.821

FD3S RX-7 [1 - 3rd & 5th gear] with Input Shaft R15M-D 2.578 1.772 1.289 1.000 0.821

Stock JDM Gear Ratio Data - - 3.483 2.015 1.391 1.000 0.806

This is the Kouki Gear ratio, Zenki are different still due to the change is rim diameter.

I'm thinking of getting the OS Giken 3 Gear kit as well.

[TitaniumTT]

I was also under the impression that the OD ratios were .84 for the RX8 box as well as the JDM S5/6 turbo trans. I could be wrong though

To answer Vex's question, no, I doubt you could swap internals. The mainshafts and countershafts are different diameters.

Normally I would say dive into the parts fiches and start comparing part numbers but this won't work either.

Just out of curiosity, why would you want to swap internals when there is very little that has to be done to swap the TII trans into the NA driveline. There's really not a big difference in ratios though so I would assume that you would do it for strength concerns as the gears are on the order of 30% larger. BUT, you get a lot of strength from the case as well and that's one of the reasons trannies blowup under huge torque, the case flexs and clearances are widened until the contact is such that teeth strip etc etc.

Now a 6spd

[TitaniumTT]

Originally Posted by afgmoto1978

I'm thinking of getting the OS Giken 3 Gear kit as well.

That's some really good info right there. As opposed to the OS Giken set, have you considered cryo-treating the internals?

[afgmoto1978]

Not concerned with strength as much as gear ratios and the ability to do no lift shifting in at least the first three gears.

Currently have the jdm tranny and a RX-8 4.44 final drive gear. Should be interesting.

JDM Gear Ratios
Ratio Max MPH
1st Gear 3.483:1 40.45MPH
2nd Gear 2.015:1 69.93MPH
3rd Gear 1.391:1 101.3MPH
4th Gear 1:1 140.9MPH
5th Gear 0.806:1 174.82MPH
Final Drive 4.44:1

OSGiken Transmission Three Gear Kit
Ratio Max MPH
1st Gear 2.714:1 51.92MPH
2nd Gear 1.742:1 80.89MPH
3rd Gear 1.267:1 111.21MPH
4th Gear 1:1 140.9MPH
5th Gear 0.806:1 174.82MPH
Final Drive 4.44:1

[TitaniumTT]

Damn......
What's your redline?
Hp/Tq
wheel size

Those are crazy mph's for each gear.

[afgmoto1978]

8500 rpm's with a soft cutout at 8750.

My butt dyno tells me I was in the healthy 450~460 whp and high 300's ftlbs range. Had a voltage surge, which dropped fuel pressure and boost spiked on my way to the dyno interestingly enough. Motor is rebuilt, but with not all the cool aftermarket engine parts, so it will be less power for sure, especially the torque.

275/285 30 18's

I would like to get a 30 mph split between each gear if possible.

Originally Posted by TitaniumTT

Damn......
What's your redline?
Hp/Tq
wheel size

Those are crazy mph's for each gear.

[TitaniumTT]

Very nice. I like the no lift shift definately, but the type of racing I do, mostly auto-x and track days, that OS 1st would KILL me. Some of the tighter courses I was dropping into 1st which is one of the big reasons for the 6spd, tighten everything up.

It just seems to me that with a 4.44 rear, those seem high, but I haven't done the math. You're also at a much higher rev limit than I am, I was basing my calcs @ 7800, not 8500, but it's 10% either way.... hmmm... I may play arouns with my excel spreadsheet later on today.

[Whizbang]

if we could, move this to another thread since this is meant to be the FAQ. This thread will been cleaned up later.

[infernosg]

I usually won't post in stickies but I though this might be useful. I turned all the gear ratio information provided by Gravity Fed (and Mazdatrix) into a spreadsheet used to calculate engine speed based on tire diameter, vehicle speed and transmission gear and final drive ratios. The transmission types and ratios are fixed (but can be edited in the second worksheet) but I left the final drive ratio up to the user. I even put in a "custom" transmission type for those feeling ambitious.

[Whizbang]

get this man a women!!! stat!!!

but seriously, damn good work.

[sen2two]

Found this for the people wanting to do a T5 swap... good general info.

http://www.flatheadv8.org/ernie/ernie-t5.htm



Also, the Rx8 diff internals do fit into TII casings with no modification, correct?

[infernosg]

Originally Posted by infernosg

I usually won't post in stickies but I though this might be useful. I turned all the gear ratio information provided by Gravity Fed (and Mazdatrix) into a spreadsheet used to calculate engine speed based on tire diameter, vehicle speed and transmission gear and final drive ratios. The transmission types and ratios are fixed (but can be edited in the second worksheet) but I left the final drive ratio up to the user. I even put in a "custom" transmission type for those feeling ambitious.

So has anyone checked my spreadsheet? I was looking at this again at lower speeds and something seems off - either my spreadsheet or my car's tachometer. I could swear that going 30 mi/hr in 3rd gear, the tachometer is telling me the engine is spinning around 2600-2800 RPM (need to verify), not the ~2300 RPM being calculated by my spreadsheet. FWIW, the indicated engine speeds at 60, 70 and 75 mi/hr seem about right. Am I missing something in my calculations or is my tachometer off at lower speeds?

For refernce my car is a '89 RX-7 GXL 5-speed so it has a 4.1:1 rear end and a 1.366:1 3rd gear according to what I have seen and the tire diameter is 24.7 inches according to Toyo's website (Toyo T1-R in 225/50R16), which IIRC, is very close to stock.