My search game seems to be off because I'm sure I already read the answer to this at one point but I can't seem to find it.

I need to bolt a gearbox (but not a RX8 6 speed as the shifter is in the wrong place apparently) to a Renesis that's going into a first gen and am wondering my options.

Will the 12a gearbox do this, and what flywheel / counterweight combination do I need?
Or are there other better options?

 

Your profile says you have a 1982 UK spec rx-7. The RX-8 trans will fit.

 

you need the Rx8 counter weight for the automatic, and then you use a light flywheel for the 12A/non turbo

clutch stays stock.

 

I was under the impression that the shifter would be in the wrong location (too far forward) with the RX8.
Is that not the case? For sure an RX8 transmission is incredibly easy to come across over here so that would make things easier. Our scrapyards are full of RX8s.

@j9fd3s Cheers. So stock 12a clutch, lightened flywheel & rx8 auto counterweight. Hopefully the clutch is up to it. But I guess I have the option of going with a 13b NA gearbox as I have 2 of those in the garage? Clutch wise are they any improvement?

 

its the same? Mazda has the 79-82 size, 215mm, the 83-91 size, 225mm and then the T2, FD and Rx8 use 235-240mm

 

If you use a high quality 225mm clutch/pressure plate on the 225mm flywheel you select, you will be fine. I always used Center Force clutches on my race car when a stock style clutch was required. I would not recommend using a clutch disc with a solid hub on the street.

To me the issue with this swap will be the transmission. Be gentle with it and it will last a while but the NA transmissions are not very strong. Since you are in the UK, reach out to Quaife https://www.quaife.co.uk/ and look into their close ratio gear sets for the FB transmission. These gear sets have been used over here in Miatas and RX7s pretty successfully. The gears are beefier and the ratio stack is allot better than the stock transmission. I looked into using a gear set from them in my race car but shipping times and access to replacement parts makes this more difficult on this side of the pond.

 

My understanding is that the RX8 tranny is the same length as the SA (or series 1) transmission. So it will probably be too short for the FB (series 2 & 3) unless tail shaft munging and fix it. I would love for this to be confirmed as I would think about swapping this into my SA. Theres also the issue for the crossmember, not sure how compatible the RX8 will be with the series 2 crossmember.

 

the Rx8 transmission is the same length as the T2, however compared to the T2 the shifter is further forward, which makes it complatible with the SA, probably.

the Rx8 has no crossmember, however it does have 2 giant studs for the PPF, you would need to fabricate something, but it could be really basic/simple

 

The real stopper for using a Rx8 transmission is the fact that AFAIK there is no speed signal to be had from it, the Rx8 uses wheel speed sensors.
So that's no good, in the UK a GPS speedo isn't legal & I wouldn't want one anyway to be fair.

Which leaves my existing 12a transmission, MX5 (with the bell housing swap & mod as described on the Mazdatrix site) or going FD or TII.
Both of those gearboxes are hard to come by here, especially the TII.

I'll stick with the 12a until it gives up & then look into changing.

 

Good point, didn't realize the speedo cable wouldn't work.

 

One could also build a speedometer that uses a hall effect sensor, Arduino, and stepper motor. That's what I had considered doing.

 

You can use a device called "cable x" from Abbot industries. It will work if you dont want the GPS speedo. I actually LOVE my speedhut GPS speedo, strange that it would be illegal?? Big brother watching a little close there!! lol

 

@yeti As a none ABS car I don't have anything to use for measuring the speed in that way. And its a lot of work to go to when I can probably safely use my existing box which is still in good condition.

@73rx313b That won't work either. The RX8 gearbox has no speed output at all, not electronic, nor mechanical. The RX8 calculates it from the wheel speed sensors that it uses for the ABS. I guess the whole GPS speedo thing is because they don't work in all areas.

 

https://www.dakotadigital.com/index....rod/prd886.htm

you would need a speed sensor somewhere on the car, usually an ABS sensor is pretty simple, the SA/FB is an interesting challenge though!

 

@theDevilX The solution I was proposing would not need ABS. It would watch the transmission output shaft, calculate the rotation via hall effect sensor, and control the stepper/servo motor.

https://www.reddit.com/r/arduino/com...text=8&depth=9

Just do a search for "speedometer hall effect stepper arduino" on your favourite search engine. There are other solutions and I did find an out-of-the-box one but I have misplaced the link. Probably the hardest part outside of the code would be adapting the mechanical cable to the motor. I didn't do a lot of research just enough to see that it's doable. I was considering getting an rx-8 tranny as SA trannies are going to be hard to come by and it appeared the shifter location was close.

 

I think if I was going to the trouble of getting the speed from either the hubs or the transmission shaft then I'd convert the speedo to an electric signal. I saw a write up on the FC on how to do it with a speedo from a honda so I guess it can't be too hard to do it on the FB as well.

I guess the shifter is still a big issue though, I want a stock interior if possible, though maybe its possible to move the gear shifter location.