Accepted power/torque limit for S5 TII-tranny?

[Luthor]

Hi!

I've searched and looked around, no one has really put any number to this, what's the accepted limit for the S5 TII-tranny?

English is my second language, so my question might come off wrong, but basically, where is when you put your hands up and say that "Nope, the S5 turbo transmission just won't cut it here"?

Application is street and track, no drag.
Closest thing I've got to an answer online was "frequently used in cars with over 500bhp".

[RICE RACING]

Originally Posted by Luthor

Hi!

I've searched and looked around, no one has really put any number to this, what's the accepted limit for the S5 TII-tranny?

English is my second language, so my question might come off wrong, but basically, where is when you put your hands up and say that "Nope, the S5 turbo transmission just won't cut it here"?

Application is street and track, no drag.
Closest thing I've got to an answer online was "frequently used in cars with over 500bhp".

This is power and torque at the rear hubs on my old FB RX7 with T2 S5 tranny Link here for more detail > http://www.riceracing.com.au/resources/Zoom-27.pdf & http://www.riceracing.com.au/water-injection.htm

T2 S5 trans in FB (divide by 3.9 *diff ratio* and multiply by 1.15 TCF *< drive line loss correction factor, commonly used by JAPS who run dynapacks on FD's to estimate engine power* to get engine torque)

I never broke a trans but I went through two of these units, one simply twisted the input shaft (Tilton twin plate clutch) could not remove the trans from the engine!) and the other wore the case hardening off 3rd gear, after about 30,000km of running at this power level and the trans became quite noisy.

I have run these to over 600rwhp (see Mazda Capella on my site) but that same car when loaded up with people on 27psi simply exploded the gear box case and 3rd gear!

How much power you can run through something is relative to the weight, it plays a huge factor. If you keep the mass around 1300kg total you can run a 700bhp engine behind these transmissions (though long term they will wear out). IF the weight of your car (say loaded with sluts on a Friday night) is much higher and you really give it full power then I say you will break it easy.

Twisting of the input shaft happens when you run sticky tires and you are on full power in 2nd and 3rd gear and you hit bumps and the wheels get air born, this creates a shock loading and this pretty much always twists the shaft, thsi happens much worse on GHETTO twin plates and above that have separate drive hubs rather than one fully splined floating hub (like on all top shelf clutches today).

Hope this helps.

[RICE RACING]

So this works out to 520Nm (remember that is a car running a long time) in a 1070kg FB chassis (old RICE factory car from 1997).

Since Power (watts) = N (rpm) x T (Nm) / 9.55
^ 381kw (511bhp) @ 7000rpm on my old yellow car, peak power happens another 500rpm later.
*This set up did ~550bhp engine power* at this low boost setting (sub 19 psi see dyno Autronic data log that was off above dyno run)..... on the street I ran it regular @ 23psi and well over 600bhp!*

You can see the answer to the "how much power" is proportional to the engine speed for peak Tq.
I have seen some FD's put down 700rwhp (exaggerator 3000 dyno's) and run for fucking ages on the stock gearbox, but this is on extend ported motors with big turbos revving to 9000rpm.

It gets tricky in this respect, on the street with a metric cock load of jizz power you accelerate SO QUICK in 1st, 2nd, and 3rd! that the box is not under that much load, in 4th gear you are going direct through the gearbox (not using ANY gears) and so the power is basically unlimited as to what you can feed into it! This is where the WEIGHT plays an effect in the 2nd and 3rd gear especially you load up the car for longer at the high boost (say 30psi) and it really stresses the gearbox, when you do it often enough you will see the case hardening wear off the main shaft and counter shaft 3rd gears especially.....

Hope this all makes sense to you?

Moral is you can get away with a huge fuck off amount of power on one of these boxes, and most people do. Others don't the answers can be numerous and varied as to why, but most people have zero issue running a honest 600bhp through a S4 S5 or FD gearbox

[RICE RACING]

My current demo car RICESP uses a stock port motor for much much more mid range power (read torque for homo's) and it runs 35psi boost! on a bigger turbo than I ran in the FB! The power is around 650bhp or more! and the tq is over 65kg/m My clutch is rated to 67kg/m lol and sometimes it will slip if not warmed up correctly.

So it takes and has been taking about 650Nm through the box and I do hundreds! of 90-140kmh tests!!!! I mean hundreds!!!! with full traction, car will do this in near 2 seconds flat with a vehicle weight of 1320kg as tested on sticky GG rated Toyo R888's of 275 width

These boxes can take allot. So in third with a street ported motor, higher tq at higher rpm you could easily see 700bhp in 3rd gear without breaking the tranny, then in 4th gear you can wind the boost to as much as you like as its direct drive + the fact the shaft is turning faster so it can take even more power!!!

In 4th gear you could easily feed 1000+bhp into the gearbox and not break it, and this has been done many times on dyno cars btw

[Luthor]

Sorry for a late reply, I was waiting for mail subscription to inform me, but that never happened.

Yes, thanks a bunch for the input!
I originally just asked this question out of curiosity, but now I've actually done something bad to my tranny :s

In case you forgot or didn't make the connection, I have the Norwegian silver RX-7 SA that Frode built (but now with half-bridge and 72mm PT Turbo).
After two turns of the axle it's damn near stuck and you REALLY have to put some muscle on it to turn it a quarter round, then two more turns and same thing happens.
So, time for a new tranny and a full rebuild/overhaul of the current one.
Also running the Tilton twin disc ofc.

What I was doing before it happened: I was showing off with a mate in the car, so I let her rip from a stand still, completely missed the shift to 2nd, but then got it in 2nd and burned some rubber before I put it into 3rd and kept it going for a bit before I shifted into 4th and 5th. Everything was doing fine still, but about 5km later when we got back into town, I did a normal downshift from 3rd to 2nd around a turn and then suddenly I got some banging noises from the transmission and that's where I am today.
Well, tranny is out of the car with said symptoms. Thrust/release bearing seems like it's brand new, I thought that was the issue first, since I had some noise with clutch engaged.
Now it's time to learn how to rebuild/overhaul a tranny, which is why I stumbled upon this post again =)

[Oyvindjs]

Ah, its you who has that car now, that thing is an absolute beast!

[Luthor]

Originally Posted by Oyvindjs

Ah, its you who has that car now, that thing is an absolute beast!

Yep =) Almost too much really :s