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Thread: 5-Speed max safe input RPMs?

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    5-Speed max safe input RPMs?

    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!

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    LS1 DMC Nicholas R's Avatar
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    Quote Originally Posted by Ashyukun View Post
    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.

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    Quote Originally Posted by Nicholas R View Post
    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.

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    LS Swapper Josh's Avatar
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    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.

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    LS1 DMC Nicholas R's Avatar
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    Quote Originally Posted by Josh View Post
    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.

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    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.

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    LS Swapper Josh's Avatar
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    Quote Originally Posted by Ashyukun View Post
    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.

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    Quote Originally Posted by Ashyukun View Post
    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.

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    Quote Originally Posted by Josh View Post
    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.

  10. #10
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    Quote Originally Posted by Helirich View Post
    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.

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