Trueno102

iTrader: (1)

Has anyone swapped the stock 4.1 transmission to the 4.3 GTUs
if you have what do you think about the 4.3 and hows the 5th gear
i want to know if its wort swaping b/c I've been thinking on doing this to my 91 n/a

RETed

Uh, you're very confused.


-Ted

Sideways7

iTrader: (7)

Wow, no kidding.

To elaborate, 4.3 is the final drive ratio, which is in the differential, not the tranny. You will have to swap the diff, or at least the ring gear from the GTUs diff, to get the 4.3 final drive.
As for the trannies, there are very small differences in ratios between all trannies, but they are quite close and not worth swapping. The exact ratios are in the FAQ.

Trueno102

iTrader: (1)

O.k. thanks and sorry for the misunderstanding
its that i need a tranny and someones selling a GTUs tranny and i thought if it was better than the stock tranny or any difference

Sideways7

iTrader: (7)

Nope, same basic tranny. Its definitely not worth the swap unless your tranny has synchros that are going bad and the new one doesn't.

jpd3253

Exactly. If you're referring to the mythical different gearing in the GTUs transmission, check the sales brochures in FAQ section, which lists the GTUs transmission gearing being the same as the standard NA.

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/frequently-asked-questions-2nd-generation-rx-7-faq-fc-494667/

Black91n/a

Actually the GTUs has a shorter 5th, at ~0.75:1. They're quite desirable to ITS racers.

Shainiac

iTrader: (7)

^ What he said.
Although most people daily driving wouldnt notice a difference, the standard 5th gear would be more practical as 5th gear is what impacts most fuel economy.

If you need a new tranny and the GTUs unit is both close and within your budget, it will work fine, but dont go overpaying for an "upgrade" that really has no benefit for you.

BurlesonRX7

ok to kinda hijack the thread for a moment what benifits would going from a 4.1 to a 3.9 rear gears have on MPG?

anyone know if its even worth the trouble?

Icemark

Probably gain you about 1 or 2 mpg at highway speeds, and loose power slightly in city traffic.

Shainiac

iTrader: (7)

Im running a 3.9 in my 5speed NA right now.
There is a slightly noticible difference in acceleration, but I get another 20 or so miles to the tank.
It's not something I would really recommend, but I destroyed my original diff and happened to have access to a free 3.9 that was already pulled.

jpd3253

Is this factual? Mazda indicates the GTUs 5th gear to be 0.697.

Specifications Sticky

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/specifications-what-did-2nd-generation-rx-7-come-w-options-standard-features-642372/

Futher, link suggests 5th at:
1986: 0.711
1987: 0.711
1987.5: 0.697
1988 Coupe: 0697 Convertible 0.711
1989: 0.697
1989 GTUs: 0.697

I have not found any concrete of definitve information that the GTUs trans has different gearing than the standard NA. But, that is just me. However, I have heard that a Miata 5th gear can be used in place of the standard RX-7 gear. I have not verified this.

Black91n/a

I'm sure, the Mazda Motorsports catalogue lists it as 0.756:1.

RX7Tuner.

So is the miatas, which would be illegal in ITS...

Twins80s

iTrader: (3)

How could it be illegal in ITS if the GTUs came with it stock? There is a simple way around things like that. If you make your car to be exactly like a GTUs(the no sunroof might be hard) it would be the same as owning a GTUs. Atleast that is how we localy do it.

batmanfc

what is ITS

Black91n/a

ITS = Improved Touring S, it's an SCCA road racing class for things like the FC, 13B FB's, NB Miatas, BMW 325is' and stuff like that.

All FC's are on one spec line, and AFAIK you can "update/backdate" within the spec line, so you don't even have to make the whole car GTUs, besides, the wheels are illegal, you're required to use wheels no bigger than 15x7's, and about the rest of what makes it unique can be changed under the rules anyway.

RX7Tuner.

The miata transmission (especially 5th gear) is ideal for many of the race tracks used the the SCCA. I was not saying the GTUs tranny is illegal in the ITS class, but the miata tranny.

Brian

jpd3253

Thanks. Forced me to do more research. Mazdatrix also lists the same ratio. If I did a correct look up, the parts manual shows different part numbers.

Other input frm an old thread.


https://www.rx7club.com/2nd-generation-specific-1986-1992-17/gtus-diff-s5-na-tranny-551524/

DamianSoul

iTrader: (4)

I have a swapped GTUs differential and GTUs transmission. With my tire width and aspect ratio 70 MPH is ~3500 RPM. I saw a drop in highway fuel economy of about 2 MPG. At first I didn't think this gearing would be useful for daily driving, but today I passed a car without having to downshift to fourth. I guess it has its uses in certain situations if you don't mind using the extra fuel.

Black91n/a

I've got a ~0.8:1 5th and I frequently drive on mountain roads, and having that extra grunt to get up hills in 5th is nice. Before I'd always be having to shift into 4th where I was maybe even getting worse milage overall due to the time spent in 4th at higher rpm's.