5-Speed max safe input RPMs?

[Josh]

The most detail they give is that it was a 6-speed out of a '95 Carrera 2, according to Wiki that would be a G50/31 transaxle.

That sounds about right. THat is the G96/00 /01's predecessor. Much more expensive to obtain as well but near the same capabilities. Still no confirmation of max rpm, perhaps the porsche forums will have covered this. If not already appearent, I really like the G96/00 /01s as an uprated option to the UN1. Both still have their place.

ALSO NEVER A SUBARU TRANSAXLE! I went through this pain already.

[Helirich]

There is a lot to consider here. Horsepower and torque increase with RPM. As those increase, the load driving meshing gears apart increases. This is load that the bearings and the case have to react. In addition, because these are helical gears, the axial loads (in the direction of the shafts) increase, additional load that the bearings and case must react. I mentioned in post #2 of this thread that I have cracked a case; the axial load is what caused this. The input shaft bearing pushed longitudinally through the back of the case.

Every bearing also has radial and axial/thrust load ratings, as well as along with speed ratings. I have no data sheets on these bearings to consider, but I think a reasonable assumption can be made that the hardware used was considered based on the vehicles the gearbox was designed for. Its not a coincidence that when the gearbox went into the Lotus Esprit V8, improvements to the bearing arrangement were made to accommodate.

I agree with this. But what you are saying is kind of coded. You are saying, If you increase rpms on an engine, most likelihood the hp and torque will go up. This is true. That increase in hp or torque may distroy the gearbox, not the rpms. In fact, the increase in rpms would make it less likely to fail.

To put this in practice, let's say our current stock gearbox is bulletproof at 130 hp. (Not likely) If you increase the rpms by 30%, its bulletproof ratting may go up to 145 hp. Obviously, that's not enough to take what he's planning, but it is the extra hp (or torque) that is the problem, not the speed. (These numbers are made up, but the rules apply)

I assure you the modifications on the Esprit were to accommodate extra power, not rpms. Also, I would bet everything I own that the rpm limit is engine based, not transmission based. It is very unlikely to exceed bearing speed ratings. Most likely the only thing in the transmission to fail from speed is the clutch come apart. But I doubt the numbers he's talking about would do that.

[Josh]

I agree with this. But what you are saying is kind of coded. You are saying, If you increase rpms on an engine, most likelihood the hp and torque will go up. This is true. That increase in hp or torque may distroy the gearbox, not the rpms. In fact, the increase in rpms would make it less likely to fail.

To put this in practice, let's say our current stock gearbox is bulletproof at 130 hp. (Not likely) If you increase the rpms by 30%, its bulletproof ratting may go up to 145 hp. Obviously, that's not enough to take what he's planning, but it is the extra hp (or torque) that is the problem, not the speed. (These numbers are made up, but the rules apply)

I assure you the modifications on the Esprit were to accommodate extra power, not rpms. Also, I would bet everything I own that the rpm limit is engine based, not transmission based. It is very unlikely to exceed bearing speed ratings. Most likely the only thing in the transmission to fail from speed is the clutch come apart. But I doubt the numbers he's talking about would do that.

Everytime you post it takes a week off my life.

[Ashyukun]

Something else i'm going to have to consider that I'd not thought of earlier that was pointed out when I asked a related question elsewhere: if the Renesis makes most of its power at 3K RPM higher than the PRV, I'm probably going to have to try and change the final drive ratio to better match up with where the RPMs will be for each gear/speed.

[Helirich]

Everytime you post it takes a week off my life.

Sorry about that. Maybe you should take up yoga.

[Josh]

Something else i'm going to have to consider that I'd not thought of earlier that was pointed out when I asked a related question elsewhere: if the Renesis makes most of its power at 3K RPM higher than the PRV, I'm probably going to have to try and change the final drive ratio to better match up with where the RPMs will be for each gear/speed.

with any of the limited rear engined transaxle options we have there are none or minimal options for different final drives. It is always a compromise. Unless you want to start paying 10-15 K for a custom transaxle.

For my LS swaps I would love to have a taller final drive (and taller 1st gears in both the UN1 and G96) but the option is just not there. The G96 has a slightly taller ring and pinion setup (3.00 vs 3.44) but it is built in limited runs and about $3000. That is almost twice the cost of the whole transmission itself. Furthermore it is a very laborious process as the pinion is the secondary shaft, you need to press all the gears off of it. It is just as involved as a full rebuild.

[Ron]

Everytime you post it takes a week off my life.

[Nicholas R]

Just know that there are limits. Be smart and don't be abusive.

I spent several years working on a 1 piece shaft, and got so comfortable that I pushed it until it cracked the case. Bottom line, there's always the next failure point. And there's no question in my mind that the G96 is a superior gearbox.

I dont think I've ever actually posted these photos here before but this is what getting comfortable and cocky can get you:
Gear Shrapnel.jpgCase Blowout.jpgBearing Journal Blowouts.jpgShafts Removed.jpg

Also, this is an area where the UN1-27 exceeds the 369 because instead of a double row ball bearing on the input shaft with a retaining ring, it has two tapered roller bearings inside of an outer race/carrier, similar to what the output shaft already has. That retaining ring groove is where my cracks propagated from.

[Helirich]

Just know that there are limits. Be smart and don't be abusive.

I spent several years working on a 1 piece shaft, and got so comfortable that I pushed it until it cracked the case. Bottom line, there's always the next failure point.

Wise words. That's quite a spectacular failure. I assume your engine is/was producing over 300 hp at the time. Had you done a number of full power launches prior to the failure? Was there anything particularly abusive when that happened? (Like wheels spinning and suddenly getting traction?)

[Helirich]

ALSO NEVER A SUBARU TRANSAXLE! I went through this pain already.

I want to say right up front, I don't sh*t about transaxle, but this guy does everything top notch. I read the whole build thread on this car. I think it's 500 horses going through a Subaru.


https://m.youtube.com/watch?v=jzB1Vc1h-Tc&feature=share