RX7Ratty

Hey All



Just wondering if anyone knows the advantages / disadvantages of this, as i've seen a few RX7's running with RX8 box's and just wonder if it would be worth it



Thanks

89 Rag

Im exploring this option as well, I'm hearing the ratios are closer across the board but there isn't any overdrive gear, aside from having to mod it to fit the car.

Signal 2

1. The RX8 transmission was not made for the extra torque of the FD. Hence, it's not likely to be as strong.



2. The final drive of the RX8 (FE) and FD transmissions is IIRC, the same. All they did was stick an extra gear in somewhere. I think it was between 3 and 4. Why? They wanted to improve acceleration with the lack of torque on the NA Renesis (see #1)



3. Because of #2, there are no real performance or top speed gains from the RX8 (FE) transmission.



4. The FD transmission is robust and properly geared for the FD's differential. It works.



5. I don't believe the RX8 (FE) transmission will just bolt up. Modifications will be required to mate it with the engine and, I think, with the length of the drive-shaft. Alot of trouble and money for no gains.

GreyGT-C

5th gear in the FD sucks. Dunno if the final drive is the same, if they are..like mentioned by Signal, it's a waste of money. Use the FD tranny and put the truck 5th gear in it... much mo betta.





Signal... you need to buy my SC C5 Vette...

Signal 2

A JDM FD transmission is another option for better/lower top gear.

But for my purposes (primarily streeted car w/occasional autoX) the OD 5th gear is fine IMO.



Daughter's college tuition is killing the family budget...and my disposable 'fun car' budget right now. But hopefully in a couple of years. I kinda want to do one myself though.

thatpoorguy

what's this about a "truck" 5th gear? never heard of that one but i did get a 97 jdm trans. my fuel mileage on the interstate dropped from 23-26 to 18 mpg

Signal 2

That's the shorter 5th gear in the JDM transmission. I can't recall what the ratio is suppose to be, but it's not overdriven like our North American cars. I understand how an OD gear would be worthless for a track car. But as I said earlier....for my car I like the OD, especially here in the wide-open spaces of the midwest.

Gladius

@Signal 2 - Hate to prove you wrong, you know being a n00b and all but:



1) The RX-8 Transmission isn't built by Mazda. It's built by Aisin-Toyota and it's called the AZ6. It's the same gearbox used by the Mx-5, the Honda S2000, the Toyota Altezza / IS200 and the Nissan S15 Silvia.

Nissan Silvia owners say the gearbox is good for no more than 400hp. Not sure how that translates to SR20dett torque figures, i suppose around 450/500Nm.



2) RX-8 final drive: 4.44:1 Rx-7 final drive 4.1:1

1st gear: 3.76:1 -- 3.483:1

2nd gear: 2.27:1 -- 2.015:1

3rd gear: 1.65:1 -- 1.391:1

4th gear: 1.19:1 -- 1.000:1

5th gear: 1.00:1 -- 0.719:1

6th gear: 0.84:1 -- ----------



All of the Rx-8's gears are slightly shorter compared to the 7's, so it would seem that swapping gearboxes would be fruitless. It isn't if you consider the difference in final drive ratios, or better yet if the final drive is made longer



3) On the surface i would agree, i would like to run the numbers on a rpm vs speed graph to check if this is true though as the FD's longer stock final drive may be an advantage.



4) True, but if everyone thought this way nobody would modify their cars



5) I didn't think the 13b-msp bellhousing differed so much from the 13b-REW's if that's the case then some sort of adapter would have to be created, but i don't think that's too much work.

Signal 2

I don't mind being proven wrong...you know, being old and all. But then if the question is whether the swap makes any sense, it's not clear that you have. Since I have no interest in changing transmissions I've never really looked into it beyond what I relayed above. If your ratios are correct, then I do stand corrected, FD 4th and FE's 5 are the same. But feel free go ahead and swap them.

Signal 2

The other things to consider other than the bell-housing/engine interface...

*input shaft differences? Length, pilot bearing interface?

*Clutch linkage/slave cylinders?

*starter?

*How will the FE tailhousing mate up with the FD PPF?

*electrical/tranmission-ECU harness?

*speedometer?

*Which driveshaft to use, and are they different lengths. My guess is, they are.



Some of the above may not be any big deal, others may be a PITA. I don't know. I do know that the FD transmission, gear ratios and differential work with the FD power band. And it would probably be alot easier and cheaper to rebuild a FD transmission than to deal with the issues of a swap. Anything can be done with enough effort, and it's entirely possible that someone out there has. But just because it can be done, doesn't mean it should be done....or that it makes any sense.