brillo

I wanted to start a post about the durability of our transmissions as I searched and didn’t see a thread on this. With FI in the not to distant future (I hope anyways) my biggest concern would be how much power we can run through the stock tranny. A couple of discussion points:

1. I’m curious to know how much strength a better clutch and lighter flywheel would add. Does this then allow you to launch the car harder with less worry over clutch/tranny/drive train damage?

2. At what point would the stock gears/syncros/differential not be able to handle the power? Over 150WHP? Less?

3. Other similar cars to ours with high revving power such as the S2000, Miata and RSX seem to be able to handle an extra 50-100WHP from various forms of FI with no worry, since our tranny is similar to the Miata/S2000 (I think, made by same people?)

4. How did the FD RX7 do as far as power increases through the stock tranny? Is the FD tranny much different than ours?

I not thinking so much as problems for the few people that are planning 500+ HP monsters, more like the majority of people who are looking to get back into FD land in terms of power, something like another 50-100WHP

epitrochoid

ill take a shot...its not outright tq that kills gears in our case, but driveline shock..ala wheel hop or dumped clutches. so...

1. a stronger clutch wont hurt, but not a cheap one. you'll need a smooth engaging clutch/flywheel combo with upgraded power ratings. mazdaspeed anyone?

2. i think 50-100 is very reasonable given you have intelligence. i guess it depends on where in the powerband the power is added. low end tq would mean more hurt on the gears. more high end power may slip the clutch. sports car or not, just dont do 8k clutch dumps.

3. the miata 5 speed is the same as the fd, very strong. the miata 6 speed is the same as ours, and even they have problems with power adders. the edm rx-8 5spd tranny *may* be very similar to an FD tranny. something to look into.

4. see #3

i stand to be corrected on most of that, as it's just what I've picked up over the months on this forum.

brillo

Ok, if we can confirm that the 6spd in the Miata is the same as ous, thats good info, we can use the Miata folks experiences to know how much power you can safely run through it. Amazing how much of our car comes from other cars, not that I'm complaining, if its a good part, why re-invent the wheel.

robertdot

How high does theirs rev?

sferrett

I think the miata's rev cut somewhere around 7500-8k

I test drove the MS (turbo'd) Miata at the rev-it-up in San Diego and found the rev limiter on the first take off (brrrrrr-brap-brap-brap - d'oh suppose I should change gears now...)

shelleys_man_06

Referring to 1), I am curious about getting my hands on Exedy's Twin plate clutch. From what I've heard in EVO Land, this clutch is excellent for FI, and it feels almost like the stock clutch. I know the RX-8 and the EVO VIII are unrelated; I hope I can get a stock-type feel from a twin plate clutch. It's not out of the realm of possibility.

I always thought transmissions should be rated on torque capacity. Is this true? I suppose the only way to truly test how much torque or power the transmission can handle is to subject it to serious loads, i.e. FI, nitrous, etc. Unfortunately, empowering the 13B-MSP has been a slow process.

brillo

This is why I wanted to flesh out what other tranny's are similar, that way, we can use the Miata 6spd? as a base line for what to expect. I'm hunting around the Miata boards as we speak.

this was an interesting thread.

http://forum.miata.net/ubb/ultimateb...=012299#000000

epitrochoid

i think the strongest option would be an FD tranny. i've heard great things about that exedy clutch from the evo land as well. when it's time, i'll go that route for sure.

brillo

bump

shelleys_man_06

After talking with Jason on Tuesday, he suggested swapping out the 6-speed for a Turbo II 5-speed. It sounds like a good idea, especially if I can get an adapter from Advance or something. I don't think it would make a difference if I lost a gear; my power goal (380 rwhp) will overshadow that.

I was also considering waiting until Mazda came out with a stronger 6-speed gearbox, but it might prove to be too expensive versus the TII tranny.

Charles R. Hill

iTrader: (7)

The most likely weak point in the trans would be the case, itself. As torque makes a path through the gear racks they try to seperate from one another and the case flexes. This causes the case to first leak at the seam and then, eventually, pull apart. One way to contain the torque is to hold the case together in strategic spots with the appropriate methods.

Charles

Nemesis8

iTrader: (3)

Do the under braces connect or support the tranny case? or are they just bolted to the frame? I'll bet it is just to the frame. Like these: https://www.rx8club.com/showthread.p...ghlight=braces

Charles R. Hill

iTrader: (7)

The only thing that touches the transmission case is the PPF, itself. The horizontal underbraces don't.

Charles

Gord96BRG

The Miata 6 speed is very close to the RX-8 6 speed, but they're not identical. The RX-8 version has stronger synchronizers on 1st, 2nd, and 3rd gear, IIRC. I don't know if the ratios are identical either. The IS-300 Lexus also uses a version of this gearbox.

Regards,
Gordon

brillo

as long as our tranny can handle stock FD power with no issues, I'm fine....and from what I hearing here, that sounds like the case.

I was a little concerned about the folks that destroyed their trannys at the strip (not just eh clutch) while trying to match Mazda's 14.32 1/4mi times. But this kinda stress may destroy any transmission, not just ours.

Charles R. Hill

iTrader: (7)

When I used my nitrous shot (55 h.p.) I had no disconcerting sounds from the trans. I launched at 4K. The other night I did a nitrous-free run and launched hard at 6k and, again, no problems. The difference, for me, is that I don't dump or sidestep the clutch pedal. I release it quickly but I don't hammer the trans too hard. Soon, I will replace the stock lube with Red Line in both the trans and diff.

Charles

PoorCollegeKid

The gear ratios in the RX8's 6MT and the Miata's 6MT are identical except for fourth gear (1.258:1 vs 1.187:1) and reverse (3.564:1 vs 2.222:1). The Miata has a slightly higher torque rating, so I would think that the Miata's version should be the one that's reinforced, although owners of RX8s are more likely to care about smoothness and shift quality than Miata drivers are which may have been incentive enough for Mazda to further strengthen the synchros in the '8's tranny. They make no mention of synchros in information on either the RX8 or the Miata, however, so I can't go more in depth on either without more research.

The IS300 has a 5MT gearbox, so while it may be made by the same supplier (I can find nothing that either supports or disproves this assertion) it should not be used to judge the strength of the RX8's transmission.

shelleys_man_06

We know the 6-speed transmission is weak, but why?

wakeech

it's not so weak that if you don't beat the hell out of it that it'll fall apart on you. obviously not every unit is goign to be perfect, but some people want video game durability.

it's less than some hope for 'cause everyone wants to dragrace, and the transmission internals aren't built so stoutly to make its performance around a track or a bunch of cones more versatile and easier to manage.

shelleys_man_06

I've been babying my 8 so that something like that would happen. Suppose I want to beef-up the tranny to support more power. What kind of material would be used to strengthen the internals, while not going overboard in price?

Hymee

iTrader: (1)

Nice thread guys!

Looking forward to test the waters, explore the possibilities myself

Cheers,
Hymee.

shelleys_man_06

Did Judge Ito ever explain what actually failed in his RX-8 transmissions? I'm curious about the fatigue lives of the gear shafts, and other moving parts.

Ireguku

Say I wanted to go well over board and ditch the orginal engine for a custom built 20b turbo with idealisticly 1200 hp, would getting the original 6MT rebuilt to accommodate this power be the safest path or should I be looking at going down the sequential gear box path? Thought? Or can someone suggest a better route?