5-Speed max safe input RPMs?

[Ashyukun]

As part of the extensive work I'm planning to do on 16655 while I have to fix several really bad rust problems on the frame I'm planning on swapping in a different engine, and one of the top contenders at the moment is a Mazda 13B Renesis from an RX-8, both because I rather like rotaries and because the car was originally planned to use one. However, most of the capability of the rotaries comes from their ability to rev to the moon and back- the higher-output 6-port version reaches max HP output at over 8,000 RPM- far higher than the PRV's max-HP RPM of 5500. I've looked and have been unable to find any info on how high the 369-08 5-speed can safely be spun, does anyone know? Thanks!

[Nicholas R]

As part of the extensive work I'm planning to do on 16655 while I have to fix several really bad rust problems on the frame I'm planning on swapping in a different engine, and one of the top contenders at the moment is a Mazda 13B Renesis from an RX-8, both because I rather like rotaries and because the car was originally planned to use one. However, most of the capability of the rotaries comes from their ability to rev to the moon and back- the higher-output 6-port version reaches max HP output at over 8,000 RPM- far higher than the PRV's max-HP RPM of 5500. I've looked and have been unable to find any info on how high the 369-08 5-speed can safely be spun, does anyone know? Thanks!

The Lotus Esprit V8 used what is essentially the most refined version of the Renault Un1/369 gearbox; the UN1-27. As I understand it, the Esprit V8 Redlines around 7200RPM (7400 with some ECU changes). With that being said, that transmission has better bearings for the input shaft (tapered roller bearings instead of angled ball bearings), a lower differential ratio (3.89 instead of 3.44), a higher 5th gear ratio (.76 instead of .82), 4 spider gears in the differential instead of 2, and cross shifts using shafts instead of a cable. I've also read that the castings of the later UN1 line are stronger/improved compared to our 369 gearboxes but I don't know anything specific. As someone that has cracked a 369 aluminum case in my DeLorean, I can confirm that this is indeed a risk at high output/high RPM.

All this is to say, I wouldn't push it. You can probably squeeze 6500RPM out of the 369 but if the horsepower output is continuing to increase in the upper power band, you're really pushing it.

[Ashyukun]

The Lotus Esprit V8 used what is essentially the most refined version of the Renault Un1/369 gearbox; the UN1-27. As I understand it, the Esprit V8 Redlines around 7200RPM (7400 with some ECU changes). With that being said, that transmission has better bearings for the input shaft (tapered roller bearings instead of angled ball bearings), a lower differential ratio (3.89 instead of 3.44), a higher 5th gear ratio (.76 instead of .82), 4 spider gears in the differential instead of 2, and cross shifts using shafts instead of a cable. I've also read that the castings of the later UN1 line are stronger/improved compared to our 369 gearboxes but I don't know anything specific. As someone that has cracked a 369 aluminum case in my DeLorean, I can confirm that this is indeed a risk at high output/high RPM.

All this is to say, I wouldn't push it. You can probably squeeze 6500RPM out of the 369 but if the horsepower output is continuing to increase in the upper power band, you're really pushing it.

Thanks! I guess I probably need to either reconsider the engine choice, or find another more suitable transaxle for the project.

[Josh]

I am working with an owner in the UK to adapt a Honda K-series to the stock transaxle.

Other adapters I have designed or helped with designing:

GM Ecotec to stock transaxle
Honda J series to Porsche G96 transaxle
GM LS to stock transaxle
GM LS to Porsche G96 transaxle

My background is mostly with LS stuff, just sent out the 15th LS swap kit last month.

For the stock transaxle I use a hybrid clutch setup with some Nissan 350Z components to hold more power. the stock clutch cannot hold much more than 225ftlbs at the crank without slipping.

[Nicholas R]

I am working with an owner in the UK to adapt a Honda K-series to the stock transaxle.

Other adapters I have designed or helped with designing:

GM Ecotec to stock transaxle
Honda J series to Porsche G96 transaxle
GM LS to stock transaxle
GM LS to Porsche G96 transaxle

My background is mostly with LS stuff, just sent out the 15th LS swap kit last month.

For the stock transaxle I use a hybrid clutch setup with some Nissan 350Z components to hold more power. the stock clutch cannot hold much more than 225ftlbs at the crank without slipping.

Dont forget GM LS to Subaru Transaxle! or maybe you are trying to forget that one... ;)

I use the same 350z clutch that Josh mentioned. It's a necessity and is the biggest and most aggressive clutch that can fit inside the stock bellhousing. It's tight but it fits.

[Ashyukun]

My original plan was to use a GM/Pontiac L67 supercharged 3.8L V6, and it may end up that I move back to that approach but I've not totally nailed down what I'm going to use yet. The Renesis was about the right power level that I'm looking for (I want something with more power than the original engine, but don't see a real need for any more than 300HP for simple road use of the car) but obviously I don't want it blowing up the transaxle from spinning it too fast.

Can the G96 take the higher RPMs? I believe that it was the transaxle used for the DMC somebody put a 20B into, but was a sequential twin-turbo and was putting out more of its power at lower RPMs I believe.

[Josh]

My original plan was to use a GM/Pontiac L67 supercharged 3.8L V6, and it may end up that I move back to that approach but I've not totally nailed down what I'm going to use yet. The Renesis was about the right power level that I'm looking for (I want something with more power than the original engine, but don't see a real need for any more than 300HP for simple road use of the car) but obviously I don't want it blowing up the transaxle from spinning it too fast.

Can the G96 take the higher RPMs? I believe that it was the transaxle used for the DMC somebody put a 20B into, but was a sequential twin-turbo and was putting out more of its power at lower RPMs I believe.

I doubt the 20B car had a G96, I think it had an older porsche transmission. 915 perhaps. I would not assume that it was a good fit for the motor.

[Helirich]

but obviously I don't want it blowing up the transaxle from spinning it too fast.

Can the G96 take the higher RPMs? I believe that it was the transaxle used for the DMC somebody put a 20B into, but was a sequential twin-turbo and was putting out more of its power at lower RPMs I believe.

This discussion seems backwards to me.

One of the basic engineering rules of thumb is that you can transmit more hp through a shaft or gears if it is turning faster. I've seen helicopters that are transmitting 800 hp through a hollow shaft that has walls less than 50 thou thick. Of course the shaft is coupled to a turbine Turning 25,000 rpm. The flip side of that example is when people swap in Diesel engines in to gas vehicles. They have to upgrade the trans and diffs because they turn slow with lots of torque.

That being said, there's lots of concerns like will the bearings be lubrcated at that speed. And even centrifugal force on the larger rotating components. (Clutch) Obviously, you would be gearing it down at some point in the transaxle, so your concerns would only apply to the parts that see the high rpms.

I suspect that you would be fine running the stock or modified transaxle at the speeds your contemplating. I can vurturly garentee the cars mentioned have red lines that have nothing to do with the transaxle.

Before someone jumps me on this, I'm not saying the slight increase in speed is going to make the stock tranny more reliable or be able to take hp your going to. I'm just saying it is likely it will handle the same power with the same reliability or better.

[Ashyukun]

I doubt the 20B car had a G96, I think it had an older porsche transmission. 915 perhaps. I would not assume that it was a good fit for the motor.

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.

[Nicholas R]

This discussion seems backwards to me.

One of the basic engineering rules of thumb is that you can transmit more hp through a shaft or gears if it is turning faster. I've seen helicopters that are transmitting 800 hp through a hollow shaft that has walls less than 50 thou thick. Of course the shaft is coupled to a turbine Turning 25,000 rpm. The flip side of that example is when people swap in Diesel engines in to gas vehicles. They have to upgrade the trans and diffs because they turn slow with lots of torque.

That being said, there's lots of concerns like will the bearings be lubrcated at that speed. And even centrifugal force on the larger rotating components. (Clutch) Obviously, you would be gearing it down at some point in the transaxle, so your concerns would only apply to the parts that see the high rpms.

I suspect that you would be fine running the stock or modified transaxle at the speeds your contemplating. I can vurturly garentee the cars mentioned have red lines that have nothing to do with the transaxle.

Before someone jumps me on this, I'm not saying the slight increase in speed is going to make the stock tranny more reliable or be able to take hp your going to. I'm just saying it is likely it will handle the same power with the same reliability or better.

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.

[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.:burnout:

[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:
66013660126601166014

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