Been looking for a stronger trans to put into my ae86 autocross car and would love a 6 speed since the car still sees a lot of street time. I found a company that makes an adapter plate for a 4age to rx8 trans.
What years should I look for and how strong are they?
Just a guess but I think the rx-8 makes a bit more power than your 4age and the rx-8 is also probably a good bit heavier than your ae86. Both the rx-8 and the 4age should be low torque high rpm motors. Seems like a good match.
So i'd say the trans is plenty strong. Go for it!
In reply to Robbie :
I’m planning on 250-300whp. Think it’ll hold okay? My 86 is roughly 2000lbs in race trim.
Anecdotally, the RX8 transmission isn't able to handle much additional torque from what the RX8 makes stock. Personally, I have no experience with it. Internally, it is the same transmission used in a number of other cars (S2000, MX5, IS200/Altezza, Frisbee twins).
Fitzauto said:In reply to Robbie :
I’m planning on 250-300whp. Think it’ll hold okay? My 86 is roughly 2000lbs in race trim.
If you have a 300hp 4age (must be turbo then, yes?) and an rx-8 trans, I think the trans will live longer than the motor. 300hp is pretty turned up for a 4age! If you think of it this way, you are nearly tripling - 300% - the stock output of the 4age but only asking the trans to work 15-20% harder than it's stock application. Also your car is so much lighter you really might not even be asking the trans to work any harder than stock. And add to that the transmission was produced in the 2000's and the engine was produced in the 80's, so the trans also has a 20 year engineering head start on the motor.
The RX8 6speed will most likely be strong enough to handle your projected HP goals.
People seem to start having issues with this transmission with anything over 300lb ft/tq - other's report problems earlier, while some claim they've had no issues with even more power. I personally think it's fine to about 280lb ft/tq - any more than that and you're probably on borrowed time.
The Series 2 transmission is supposed to be slightly stronger, however, I don't think it will be necessary and it is also a bit more expensive than a Series 1 transmission.
In reply to PHAN :
I think even a boosted 4a will struggle to make that much torque. It’s still only a 1.6 after all.
I wish you were closer, I've got an RX-8 six speed, driveshaft and LSD differential just taking up space. I think it would be fine for your goals.
In reply to Brett_Murphy :
Where are you located? Might be road trip time.
In reply to Robbie :
I dislike that transmission. It has the same spread as most 5 speeds and just requires a bunch of shifting.
I bet the car is actually faster with a trans and rear end ratio that is well matched to the torque curve of the engine.
In reply to wvumtnbkr :
It can only be better than the stock t50. That not a good trans for much.
In reply to Fitzauto :
Raleigh, NC. A bit far for a transmission.
In reply to Brett_Murphy :
Yea that’s a little far from OKC.
wvumtnbkr said:In reply to Robbie :
I dislike that transmission. It has the same spread as most 5 speeds and just requires a bunch of shifting.
I bet the car is actually faster with a trans and rear end ratio that is well matched to the torque curve of the engine.
I don't know what 5 speeds you've been driving (American?) but most 5 speeds don't have that issue. The S2000 6 speed is actually very closely spaced for shifting and maintaining the power badn.
Plenty of boosted miatas going plenty fast on what is essentially an Rx8 transmission.
Some people say the trans is junk because the RX-8 has problems with it.
On the other hand, the same trans is used in a whole lot of other vehicles (Miatas, Frisbees, Altezzas, S15 Nissans, more?) and they don't have the same problems.
Theory: Transmissions don't like high input RPM, and the RX-8 revs higher than MXR or 3SGE or SR20DET or FA20 engines. If you are not taking the trans to 9500 on a regular basis, you should be fine.
Note that the RX-8 trans is not a massively overdriven trans! It is best thought of as a close ratio 5 speed (1st gear like 2.2:1, 4th gear 1:1, 5th gear .8?:1) and a granny low (3.7ish:1). This is not a Viper T56. It's a race trans with an extra gear so you don't have to slip the clutch a lot in city traffic. We did a comparison of ratios, and the RX-8's ratios are almost identical to the Mazda Competition transmission from the RX-7 GTU days, comparing the RX-8's 2-6 vs the Comp's 1-5.
In reply to Knurled. :
Sounds like a good fit. The car will eventually see some road course action at our local track and it seems to favor close ratios.
Knurled. said:Some people say the trans is junk because the RX-8 has problems with it.
On the other hand, the same trans is used in a whole lot of other vehicles (Miatas, Frisbees, Altezzas, S15 Nissans, more?) and they don't have the same problems.
Theory: Transmissions don't like high input RPM, and the RX-8 revs higher than MXR or 3SGE or SR20DET or FA20 engines. If you are not taking the trans to 9500 on a regular basis, you should be fine.
Note that the RX-8 trans is not a massively overdriven trans! It is best thought of as a close ratio 5 speed (1st gear like 2.2:1, 4th gear 1:1, 5th gear .8?:1) and a granny low (3.7ish:1). This is not a Viper T56. It's a race trans with an extra gear so you don't have to slip the clutch a lot in city traffic. We did a comparison of ratios, and the RX-8's ratios are almost identical to the Mazda Competition transmission from the RX-7 GTU days, comparing the RX-8's 2-6 vs the Comp's 1-5.
Thanks. That was basically my point. This trans with the rx8 gearing doesnt seem to provide any benefit over a regular 5 speed. Unless you like shifting all of the time....
I didn't quite get why they picked the ratios for the RX8 trans until I took it to the track. It's basically a close ratio 5 speed with pretty optimally spaced gears with a significantly taller 6th gear on top for highway use. Going up through the gears the rpm drops less and less for better acceleration overall and you'll probably never find a track with a long and fast enough straight to get into 6th gear. The series 2 transmissions are supposedly better and there are a number of parts changes through the production run, so the later, the better.
The rx8 6th gear is BARELY taller than the 5th gear. It is NOT a super tall gear.
Hell, I was always thinking the damn thing was in 4th when I was on the highway and wanted to shift to a higher gear.
1st gear is unusable and then gears 2 through 6 are the same as you would find in a normal sporty 5 speed gearbox.
The correct way to find out if this trans will work for you is to creative a motive force versus speed in gear chart and see if the ratios are where you want them. If you are going to go to all of the work of swapping in this trans, at least see what it is gonna do at the end of the day.
You just need to know your tire size, rearend ratio, a dyno chart, max engine rpm, and trans ratios. Once you make the chart, you can play around with how tire size, rearend ratio, etc affect the actual force you are putting down at the wheels.
If you are road racing and like to shift alot because you have a crazy peaky powerband, this is the transmission for you. If you cant check the box for each of those 3 items (road racing; liek to shift alot; and peaky powerband), this is NOT the trans for you....
carguy123 said:wvumtnbkr said:In reply to Robbie :
I dislike that transmission. It has the same spread as most 5 speeds and just requires a bunch of shifting.
I bet the car is actually faster with a trans and rear end ratio that is well matched to the torque curve of the engine.
I don't know what 5 speeds you've been driving (American?) but most 5 speeds don't have that issue. The S2000 6 speed is actually very closely spaced for shifting and maintaining the power badn.
rx7 NA trans, rx7 Turbo trans, Chevy T5, Mazda 6, etc.....
I dont understand your response, TBH. What issue do you think I am having with a 5 speed trans? Im actually suggesting a 5 speed would probably be better in most cases (unless fuel mileasge is a major concern).
In reply to wvumtnbkr :
The biggest annoyance I have with the 5 speeds is that the drops are so large. You're always in the wrong gear.
I like the idea of the 6 speed because then I'd be in less of a wrong gear all the time.
Doing a gear sped calc (not the best way to judge obviously) it looks like the spread is about right
I think a lot of it depends on how much torque you're able to make at the rpms you will drop to after shifting. I made a post about 3.63 gears in a 6spd turbo'd miata here and while driving that car I found myself wishing it was a 5spd because i found the 6spd tedious and unnecessary for the street even after being 'spread out' a bit by the 3.63s. Unfortunately i think the 5spd has issues somewhere around that power level. But, race cars can have different priorities. I just found that, aside from/after adding power, the thing that most improved the Miata for street use in my opinion was taller gearing. In an rx8 I doubt i would feel the same way because the rpm of the engine would mean only 2 or 3 gears would be usable WOT on the street. So, if you're planning to rev to ~9k that could be a factor too.
In reply to Vigo :
The car in question hits the limiter at 8600rpm. It’s main use is autocross and fun around town. For autocross it looks like 2nd is plenty tall and the rest of the gearing should be fine for a low torque, high rpm 1.6 turbo.
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