Can this be done? Can I mate a 3G tranny onto the 12a? Reason is I dont like sitting on the highway doing 3.5k all the time nice powerband but would like to see it lower.

 

3G ?????? is that an Rx-8?

 

3G 3rd Generation, The FD,

 

I did not know they had a 6 speed.

 

Lets Find Out!

 

Yep It Has A 6 Speed!

 

I Think Of It This Way If It Has A 13b And The Trans In A 13b And 12a Are Interchangeable Then It Should Work Bolt Wise. The Size Of The Trans Are What Might Not Fit In The Smaller Body Or Even The Shifter Location (not An Expert So Don't Quote Me On That)

 

What speed are you traveling at when you are at 3800 RPM?

Forgot to add. The Fd is a 5spd, the RX-8 is a 6 spd.

 

Six Speed Dont Always Mean A Longer Power Band My Evo Mr Has Six Speeds And I Hit 60 At 25k 65 At 28k And So On It Blows Burns Alot Of Gas And Its Premium Too.

 

For Turbo, TII tranny is much more desireable than the FD.
For N/A, I prefer miata internals (but cut the input shaft as the miata has a longer input shaft) on a 5speed FB housing. Ask me. I got one.

 

fd dont come with 6spd

 

RIght. There's no such thing as a 6-speed FD tranny. The RX-8 has a 6-speed, but they are not all that strong. Besides, in an RX-8 tranny 5th is 1.000, same as 4th in any RX-7 tranny, but 1st-5th are close-ratio. Meaning, 6th gear is not going to bring your RPMs down much (if at all) at highway speeds; you're just going to be shifting more often at lower speeds.

 

x2

rx8 6th gear is 0.84 and fb 5th gear is 0.758 and 0.807 for SE. You will be shifting more often and won't get better gas mileage or lower rpm on the highway.

Frank

 

So swap in a taller rear end.
The close ratio 1st-5th become more normally spaced, and you get the extra tall 6th

 

At 3800 rpm im at just over 80mph or just below 140km/hr. So how would I go about getting just a taller fith gear in my stock gearbox easy to do? where can I get them? any suggestions would be great.

 

Changing the final drive ratio won't change the spacing of the gears. It'll just make all the gears taller.

 

A T2 tranny will do what you want, it's really strong and is much taller in the upper gears. It is also the easiest to mate to your FB. There are several threads explaining how. You mate your 12a tranny shifter housing with slight modification, to keep the shifter in the stock location. You will need to modify the
T2 drive shaft to fit the rearend. A local shop should do it and balance it for about $100. I beleive you need the clutch and flywheel from the T2. Other's who have done this can confirm.

Good luck

 

lol i got a 6 speed including reverse =)

 

The TII tranny is solid,they used it in F-150 full-size trucks! Its quite over-built for a small 2 seat sportscar. Many FD guys swap to a TII box for this reason.

The RX-8 may have a 6-speed (big rip).....but the Renesis also has sh*t for torque,so its likely that the ribcase box the 8 uses,isnt on-par with the earlier Type R boxes.
If you like shifting and are short on torque,then get the 6-speed.
If you have enough power to justify a TII tranny......you dont need 6 gears!

 

If your profile is right about your year than you have the lowest 5th gear of all the RX-7 models which is .825.

The 86-92 N/A transmissions have the tallest 5th gear there is at .697.
That is what I have in my 85 SE and at 80MPH with the stock gears of 4.076 I am only around 3100 rpm at that speed. I believe at 95 Mph I am around the 3800 rpm range.
The 86-88 N/A trans would be the easiest to install if you want the tall 5th gear.
You only have to swap out the shifter housings between the the 2 and installl. There are no other mods.
The only thing depending on how your engine is. Meaning stock or modded. 5th
gear at 55 Mph would be somewhat boggy and not have alot of available power. You would be keeping it in 4th uphills or have to downshift to 4th on the freeway at speeds of 65 mph or below to gain some momentum.
To really use the 5th gear on the freeway I would presume that your average cruising speed would be 70-75 mph.

 

1st...2nd...3rd...4th...5th...Don't make me go into R on you!!

I just wanted to mention that you shouldn't assume that because a tranny bolts to a 13b that it will bolt to *any* 13b. The bolt holes may match up, but the clutch assembly and fork aren't always the same. The Rx8 I believe uses a "pull-type" clutch.

Jon

 

as long as you get the trannys flywheel, clutch n pressure plate i belive it should be ok.

 

What year trucks? Would this not be a better way to get them cheeper then the $250 a TII goes for from a 7.

 

The RX-8 went back to a push clutch if I remember correctly.

 

They did. The pull clutch was probably the only way to get a strong clutch back then with a semi-normal feeling pedal effort. Of course clutch technology has come a long way since then. I'm glad Mazda went back to the push type.