gawdodirt

Have a unique project underway. Well, for THIS site anyhow. It's a LUCAS Mini Open short course truck. It's getting a 13B Peripheral port, to be bodied as a B2500. Mostly tube framed with big travel and lighter weight. Rod Millen actually had great success racing one of these engines off road.

So, the question is that I have a 1991 T2 manual trans behind it now. Was bulletproof when we road raced it and the ratios were good. So what kind of abuse will this thing really take?

kevinbtz

iTrader: (4)

I have had pretty good luck with them, currently have a jdm short ratio 5th T2 transmission in my repu that I daily drive/abuse and its holding up great at over 500rwhp. I think the main thing to the t2 and 3rd gen transmission holding power is the condition of the transmission to begin with. In my 3rd gen I would strip 3rd gear off every 3 to 4k miles @2,527 lbs and over 600whp, but again I was very abusive and brake boosted/roll raced it a lot. All on used usdm transmissions also, so probably had high miles.

peejay

The ratios were good? Good for what?

abeomid

The ratio's were good for a PPort? Really? If you have a 5.12 gear in the rearend maybe, but otherwise you are jumping out of the PPort power-band pretty darn quick!

23Racer

I have almost always found that the stock NA and TII ratios were just out of the proper ranges for racing. Main issue is that 5th is too high to use unless you have a 5:12 diff and the jumps from 3rd to 4th are always too high.

I ran an older FB SE box with a stock 4:10 diff, on a shorter track that had top speeds of around 100 mph and I found that the 2nd and 3rd gears ratios were better and I only used 4th for a short bit so the huge jump wasn't that noticeable. Will use that again this year until I can get the time to put together a Miata box.

Eric

gawdodirt

Good for the rear end, tire size, power band and track length we were running.

Was that a rhetorical question?

GD

gawdodirt

No, at the time it had a street port in it. It is a 4.30 now, and we do have shorter tires.

The truck has a 6.00:1 to start with, and a 6.50:1 on the shelf in case we go to 35" tires.

GD

gawdodirt

We used to race a Class 2 desert car and had a 5.88 R&P with a 1.08 fourth. With a full bridge, it was on the top of the band most of the time. It was more of a tire choice issue. 33's" were great if they were a lighter carcass and less aggressive tread and it was allowed to spin the tires. If we used a BFG BAJA T/A33x10.50 x 15, it was 30 lbs heavier, very aggressive and knocked the top end off.
So is the Miata box stronger, or just has different ratios?

Thanks to all who offer their experiences!

GD

peejay

Not really. The T2 ratio spreads are worse than almost any N/A trans spread and even those are still too wide to be useful on a loose surface. IMO.

Shift at 10k with the tires spinning, engine drops to 3-5k when the tires grab unless you shift fast enough to keep the tires spinning, which is a trick even with the N/A trans, the T2 trans shifts worse.

'Tis why I have a (relatively) close ratio T5 being prepped to go in. And it won't have synchronizers on the important gears.

gawdodirt

Honestly, thanks for the info. My experience on dirt is pretty broad. As long as I can spin the tires, and control the velocity, it can work. When it gets hooked is when the ratios matter. I know, kinda odd, but that is what it is. As long as they're spinning, they're moving dirt and providing forward bite.
It's kinda like a sprint car in the ideal that it's the sharp square edges that bite.
The saving grace is the broad powerband and flat torque curve that allow good control.

I'm interested in the trans ability to absorb shock, and the loading and unloading is the failure point.

Thanks for the great information and personal experience.

Carl

peejay

That's very true, but then you either have to take your head out of the racing and into watching the tach to keep the engine happy, or upshift and then put the engine into a hole where it's not spinning the tires and throwing dirt backwards as reaction mass. In my little corner of motorsports, anyway.

100% absolutely. That's why I have the bridge port, and every time i think of a piston swap I think of how narrow piston engines' powerbands are. And then they ventilate the block and you can't drive home on a holed block and half a bottom end the way you can drive a rotary home on one rotor.

T2 trans is most likely a bunch stronger than the smoothcase. I eat smoothcases with frightening regularity, fidelity101 put a T2 trans in his car and he's still on the same one years later.

gawdodirt

Thanks! That's what I was looking for. I have looked at other trans for this with custom gearing, and the G-force or Jerico are just too costly. I do have a friend with the Mazda racing 5 spd from Mazda Motorsports. But not sure what the ratios are.

Thanks

peejay

Mazda racing 5 speed's ratios are frighteningly close to being the same as 2-6 in the RX-8 box.

j9fd3s has posted the ratios of the comp box on the forum before, the numbers are within a few percent of RX-8 and then the RX-8 also gives you a 3.7x granny first gear.

C. Ludwig

iTrader: (27)

You're just not going to find anyone on this board that has experience with what you're doing. As you said, what's going to prove most abusive is the loading and unloading of the trans. So any of us with roadracing experience just aren't being as hard on the equipment as you will be. You'll need to try it and break it to see what it will take.

Albins, PPG, maybe Phitzer have straight cut gear sets for the R trans case. That may be a lower cost option over a new Jerico or the like. Honestly, used 4-speed race transmissions are not that expensive. A good straight cut dog box is going to be stronger and will be a whole lot happier shifting at high revs than a stock synchro box. Quicktime has SFI bellhousing options to mount just about anything.

zak rabbit

I got to see the old Mickey Thompson stadium trucks back in the day, it's very cool to see something like that come back.
Quaiffe makes/made a gear set for the "m" box that was reportedly good for 300+ lbs/ft. They're available in a "close" and "wide" ratio spreads in both dog and synchro versions. Can't wait to see you on the track!

gawdodirt

So, thanks a lot for the ideas and advice. What about the strength of an RX8 box? They still bolt to earlier irons, right? Not much has changed there, correct? I have an opportunity to pick one up cheap.

Thanks!

GD

Fleemer

In drifting they don't seem to last. But the one guy I have experience with was running an unsprung puck clutch (anything unsprung puck in a non road race scenario is a nono) he was eating 2nd and 3rd gears all day. Went through 4-5 transmissions until he bought a sequential.