Has anyone noticed a correlation between continuous high lateral G and trans failure? I'm suspecting a failure due to lack of lubrication. Failures are occurring at constant throttle in 5th gear during high speed sweeper, not on shift or on launch.

We're running at UTCC next month in a turbo Exocet. I'm considering overfilling the trans by jacking up one side and installing a catch can on the trans breather. 1500lbs and ~300 whp on sticker A7s. A similarly set up Exocet is showing 1.8G continuous, 2.4G peak lateral G on its Traqmate recorder. I'll get a Racepak or Race Capture in this car before the event so we can get awesome data.

Incidentally, wish us luck at UTCC. We'll be going up against stuff like a Lamborghini Super Trofeo, and Viper and 911 GT3 cars. LOL

 

<p>Good luck!</p>

 

In for data. Are you going to get tranny oil temp?

I always thought these were splash lubricated (no pump), so as long as the oil is contained and doesn't start leaking out the breather . . . .

Just guessing though. I might need to build myself one of those Exocet thingies.

 

If you suspect that heat may be the problem (I know you said lubrication, but stay with me), overfilling the trans will make it worse, not better.

I can tell you that on some Superchargers, they recommend underfilling them a bit when used in race applications, due to the average "higher RPMs", running them at normal oil level's overheats them. Running them at slightly reduced level drops the HP going into the geartrain by A LOT, I read 15 HP, which is a ton for a SC that's probably only using 60-70 total.

Basically, if you're gonna experiment, I'd look to running less oil, and definitely have a transmission oil temp sensor for before/after comparison.

 

I don't think it's heat. We're not making any more power than other people, and we're 750 lbs less weight. We're also talking about 25 minute sessions. I have a hard time believing that we have out of control temps in a 25 minute session (even with the power), when a Miata 5-speed is known to be reliable in endurance racing.

Whipping up the oil will cause more windage losses. But a broken trans has infinite loss. Broken trans is game over, go home a loser.

 

What tranny, how much power, and how many failures have you seen?

 

<p>Why not 6-speed?</p><p>&nbsp;</p>

 

Well if you are driving faster (due to less weight, grippier tires, anything) then you are sending higher average power through the trans than someone with a heavier/slower vehicle, even with the same engine. If average power through the trans is up, so is load and heat. Something to consider.

Whipping the oil is going to increase the temperature of everything in the transmission, as you are adding friction. And of course the whole point of having oil is to reduce friction.

 

This is so fundamentally incorrect, and belies such a grave miscomprehension of basic physics, that I'm having difficulty even knowing where to begin correcting it.

Power through the transmission is a function of engine power output.

Period.

Full throttle = Full throttle, regardless of whether it's a stock-bodied Miata going up a 20° incline or a 1,500 lb Miata cruising across a frictionless surface on level ground. Either way, the engine is outputting X amount of power, and that's the amount of power being transmitted to the wheels.

 

I agree with what you wrote.

What I'm saying is, if his car can corner like he says', he's ON the throttle more since the car is faster, so his average power is higher. That's what I wrote, and that is correct.

Take a stock miata and put the best wheels/tires/brakes you can, and put it on a track, and it will now be capable of using more engine power as it can now corner faster, and sooner. Thus average power goes up.

Well aware of basic physics, I thought what I wrote explained this but perhaps not.

 

Any of the fastest miatas here will tell you that as you get faster, loads go up on everything. Brakes, engine, suspension, cooling. And it is physics, you're right.

 

Quick example. Give a stock miata to a fast and capable miata driver, let them race it. Datalog TPS% vs time.

Then take the same miata, and put better tires/brakes/suspension on it. Give it back to the same driver and let them race it again.

They will be on the gas longer, brake in a shorter distance, corner faster, and on the throttle sooner.

Thus average HP goes up. Now I think what I wrote should be perfectly clear, and withing the confines of the laws of physics.

 

 

Out of curiosity, what is the clutch and flywheel you are using?

 

Average life of used 5-speed transmission in 1480 lbs 300+ hp locost with slicks before : ~50 minutes, gone through 6 before. Broke 2nd, 3rd and 5th gears under load, Also going straight (5th on backstraight of Road Atlanta)

Noted that the frame allows the motor rotate under severe torque. I can see VVT solenoid moving through louvers. The transmission is supported at the tail end with stock PPF bolts, but only from bottom. After testing to rotate motor with levering it long jackhandle simulating 300 lbs/ft torque, I thought there can be torsional stress resisted by transmission case, because the planar frame is not stiff enough to keep it solid. Flexible motormounts will cause the same under high loads. If the torsion on transmission case causes deflection, the tolerances for gears go off and can contribute to early failure.

After adding three jackscrews between frame and head to limit motor movement in this direction transmission is at 40 minute time at the moment, sounds ok, and not whiny like the other 6 before this.

May or may not help.
I would vote against extra oil in case, oil could get foamy and have less lubrication in addition of higher temps.

 

I don't get using a 5-speed on a 300RWHP car. ??

 

NA 5 speed, 250 dynojet, 3 or 4 (this is not my car)

Will be running XP4 at UTCC with NB 5 speed @ >300 dynojet

 

FM Happy Meal

 

<p>Y u no 6-speed?</p>

 

There isn't enough data to statistically correlate "high-G cornering" and "5-speed failure".

There is a lot of data to correlate "250whp" and "5-speed failure".

Put a 6-speed in it already.