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Thread: Seeking information about Miura

  1. #11
    Senior Member IKAROS's Avatar
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    Maybe relocate the pedals & change the angle of the seats if its possible?










    And many more...
    https://www.google.gr/search?client=....0.ORR81zv5wtE

    3d model...video.
    Last edited by IKAROS; 02-01-2018 at 10:45 AM.

  2. #12
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    C5GTO, I know you said that you were in the investigative stages, but have you thought about the transaxle? Bloozberry has a good point. The Miura was transverse mount and any gearbox like that is going to be difficult to source. Because of the transverse mounting, the seat is very close to the rear axle. Using the diagrams that you and Ikaros have provided and scaling from known dimensions, I am getting about 20". With a conventional longitudinal mount, any of the transaxles of choice are going to be about 9"-10" from the front of the bell housing to the axle centerline. Then add a 3/4" adapter plate and a Chevy small block (the shortest motor block) of 21-7/8". Then use the short option water pump and add 7" for belts and accessory drives. That is a minimum of 38+ inches going into that 20" space. You asked for thoughts on this, I say figure out a drivetrain and work outward.

  3. #13
    Senior Member C5GTO's Avatar
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    Quote Originally Posted by 76mx View Post
    C5GTO, I know you said that you were in the investigative stages, but have you thought about the transaxle? Bloozberry has a good point. The Miura was transverse mount and any gearbox like that is going to be difficult to source. Because of the transverse mounting, the seat is very close to the rear axle. Using the diagrams that you and Ikaros have provided and scaling from known dimensions, I am getting about 20". With a conventional longitudinal mount, any of the transaxles of choice are going to be about 9"-10" from the front of the bell housing to the axle centerline. Then add a 3/4" adapter plate and a Chevy small block (the shortest motor block) of 21-7/8". Then use the short option water pump and add 7" for belts and accessory drives. That is a minimum of 38+ inches going into that 20" space. You asked for thoughts on this, I say figure out a drivetrain and work outward.
    Yes, I've been thinking about the engine/transaxle part a lot. Do I have it figured out yet? No way.

    My design methodology is just as you suggested. I seek out and find answers for the "fixed size components" like engine, trans, suspension, etc. and design/size the other parts of the chassis/body around them. I used this approach when designing the C5 GTO chassis/body it worked out well for me.

    I'm convinced that a transverse engine/trans is the only layout that will work in a properly proportioned mid-engine Miura. When I look at the Liberty Walk Miura built on a GT40 chassis (longitudinal engine layout) the proportions just aren't right (in addition to the quirky fender flares). There's too much space between the door back edge and rear tires. There's also the green Miura (also built in Japan) with a front engine but I don't really want to go down that path. It's body proportions look right but "super cars" are all mid-engine not front engine.

    The only OEM transaxle that I've found so far that might work is from a Ferrari 308. There's one on eBay right now for $5,500 transaxle and $3,000 for bellhousing/transfer gears. Beyond feeling pricey, I really don't want to go down the path of using rare parts where the price will just keep accelerating skyward over time.

    I have a friend that's built a mid-engine transverse V8 and transaxle, it just so happens to be in a 1937 Ford roadster. He's got 75K miles on the car/setup now so it's proven the test of time/miles. If you follow street rods, you might have seen this car in a magazine about 10 years ago as it's been featured in articles a few times. Pete Aardema is his name. Pete and I have been collaborating on a design for this Miura project but as I said above, the details are still fuzzy.

    There's an engineering challenge at the core of this that wasn't apparent to me until Pete pointed it out. If the engine is located too close to the rear axle centerline, then most of the engine weight will fall on the rear wheels resulting in light front end handling problems. In other words, you need to locate the engine far enough forward of rear axle centerline in order to achieve the leverage needed to keep the front wheels on the ground. Pete's rule of thumb from his experience is that the crankshaft centerline needs to be about 12 to 16 inches in front of rear axle centerline. This rules out use of transaxles like the GM F40 (used in FWD Pontiac G6) that has been used on Fiero V8 conversions.

    So there's a fairly obvious conflict here. To get additional cockpit space, you want to locate the engine further rearward. To give the car proper steering control, you want to locate the engine further forward. Oh yeah, throw in that I'm still hoping to use a V12 for power. This actually helps a little bit as the 60 degree V12 engines tend to be narrower than 90 degree V8s. V12s are longer though so it means the transmission will need to sit side by side with the engine similar to the original Miura layout.

    Any thoughts/ideas on how to solve this challenge are welcome. I haven't given up yet and will give updates on design progress.
    Joel Heinke
    (Classic Roadsters Cobra, Ferrari 250GTO under construction)

  4. #14
    I dont know your choice for engine and trans manual or automatic. However. How about LS4 and matching trans from the Impalas though I think they only came with automatics.
    Last edited by chimaera; 02-02-2018 at 02:39 PM.

  5. #15
    Senior Member C5GTO's Avatar
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    Quote Originally Posted by chimaera View Post
    I dont know your choice for engine and trans manual or automatic. However. How about LS4 and matching trans from the Impalas though I think they only came with automatics.
    My transmission preference is manual, 5 or 6 speed. I'm not opposed to an automatic but I plan to fully vet the manual trans options and ruling them out prior to going there. One of the problems with using a Mercedes V12 is that they only came with automatic trans, except in the Pagani Zonda. I've seen one instance where someone retrofitted a flywheel and clutch to one but it was definitely custom. I'm leaning towards a BMW V12 right now just because they did come with a manual trans and thus an OEM flywheel clutch assembly.
    Joel Heinke
    (Classic Roadsters Cobra, Ferrari 250GTO under construction)

  6. #16
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    The bmw v12 came with a manual ? I never saw that I thought they were all automatics in the 750/850 and only the v8 has a manual option in the 8 series . So yeah you can find a manual that will fit but I don't think they came together in the original v12 car

    Likewise The ls4 didn't come with a manual but it does have a six speed manual that will work with it , I think it's called the g60 transmission
    If I recall correctly it came with the Pontiac Grand Prix

  7. #17
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    Quote Originally Posted by C5GTO View Post
    My transmission preference is manual, 5 or 6 speed. I'm not opposed to an automatic but I plan to fully vet the manual trans options and ruling them out prior to going there. I'm leaning towards a BMW V12 right now just because they did come with a manual trans and thus an OEM flywheel clutch assembly.
    Apart from GM's F40, and the 1991-1998 Acura NSX manual transaxles, I can't think of any others that would handle the torque of the BMW engine and that aren't full blown exotics. The F40 is conservatively rated at 300 lbft, and while I'm not sure what the NSX transmission was rated at, the max engine torque was 225 lbft. You've already stated you're not keen on the F40, but the NSX tranny is probably not as capable as the F40, is semi-exotic from a price and availability perspective, and is quite a bit wider than the F40.

    So, to put a few numbers on the minimum width you'd be dealing with:

    29.25" = BMW V12 E32 (1987-1994) engine total length from end of crank pulley to rear block face;
    13.2" = F40 width bell housing flange to outer case;
    0.75" = Transmission to engine adapter thickness

    43.2" = Powertrain width

    Furthermore, limiting yourself only to engines that came originally with a manual transmission to avoid a custom flywheel will restrict your selection of an already very small pool of transaxles to ones that have a bell housing large or deep enough to accommodate that flywheel/clutch assembly. I'm not sure that the BMW flywheel/clutch would fit either the F40 or the NSX trannies. The absolute max diameter of the F40 bell housing is 12.3"... the BMW flywheel would have to be smaller than that. Then there are depth issues to consider too.

    Finally, there is a lot of tech data and support for the F40 including scale drawings, aftermarket custom flywheels and clutches that fit the bell housing, custom shifter cables, hydraulic line adapters, axle conversion information, and a host of helpful people on several forums with tons of experience installing and running these transmissions hooked up to a variety of engines. None of this is available for the NSX transmission, and likely not for any other transaxle either.

  8. #18
    Senior Member C5GTO's Avatar
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    Quote Originally Posted by Bloozberry View Post
    Apart from GM's F40, and the 1991-1998 Acura NSX manual transaxles, I can't think of any others that would handle the torque of the BMW engine and that aren't full blown exotics. The F40 is conservatively rated at 300 lbft, and while I'm not sure what the NSX transmission was rated at, the max engine torque was 225 lbft. You've already stated you're not keen on the F40, but the NSX tranny is probably not as capable as the F40, is semi-exotic from a price and availability perspective, and is quite a bit wider than the F40.

    So, to put a few numbers on the minimum width you'd be dealing with:

    29.25" = BMW V12 E32 (1987-1994) engine total length from end of crank pulley to rear block face;
    13.2" = F40 width bell housing flange to outer case;
    0.75" = Transmission to engine adapter thickness

    43.2" = Powertrain width

    Furthermore, limiting yourself only to engines that came originally with a manual transmission to avoid a custom flywheel will restrict your selection of an already very small pool of transaxles to ones that have a bell housing large or deep enough to accommodate that flywheel/clutch assembly. I'm not sure that the BMW flywheel/clutch would fit either the F40 or the NSX trannies. The absolute max diameter of the F40 bell housing is 12.3"... the BMW flywheel would have to be smaller than that. Then there are depth issues to consider too.

    Finally, there is a lot of tech data and support for the F40 including scale drawings, aftermarket custom flywheels and clutches that fit the bell housing, custom shifter cables, hydraulic line adapters, axle conversion information, and a host of helpful people on several forums with tons of experience installing and running these transmissions hooked up to a variety of engines. None of this is available for the NSX transmission, and likely not for any other transaxle either.
    The main issue with the F40 transaxle is the location of drive axles relative to engine crankshaft. They're too close together and thus there won't be enough weight transfer to front wheels.

    Here's a sketch Pete did for me to give a rough idea for what might work.



    The engine to transmission transfer case would be purpose built and differential case/gears also purpose built. The bell housing, clutch, transmission, differential carrier, and drive axles could all be sourced from various existing OEM applications. Like I said before, this is still at the idea stage and there's lots of details to work out before I could say it's a viable approach.

    One other idea I've come up with is to mount the engine not in the traditional orientation with each bank 30 degrees from vertical but in a rotated orientation. So mounting a 60 degree V12 such that the forward cylinder bank is vertical instead of angled at 30 degrees. This would move the crankshaft towards front of chassis and hopefully more weight to front end without intruding into the Miura cockpit space. I got this idea while looking at the Miura side view sketch and seeing the open space between engine bottom and lower cockpit area. The carburetors are tight to the back window but there's open space down low. This idea may have some flaws in it such that it's not feasible but I think it's worth chasing for a bit anyway.

    There's got to be a way we can improve on a 50 year old design, isn't there?
    Joel Heinke
    (Classic Roadsters Cobra, Ferrari 250GTO under construction)

  9. #19
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    Quote Originally Posted by C5GTO View Post
    The main issue with the F40 transaxle is the location of drive axles relative to engine crankshaft. They're too close together and thus there won't be enough weight transfer to front wheels... there's got to be a way we can improve on a 50 year old design, isn't there?
    Weight transfer is a dynamic property accomplished with suspension design. For example, Porsche hangs their engine off the back of their rear axle and still makes their cars handle with world-class success.

    If static weight bias is what you're worried about, you should calculate how far away you'd need to mount your transmission from your crank centerline to make a significant difference. Don't forget to take into account the effect of your own weight into your calculations. I think you'll be surprised at how little a few inches accomplishes, especially for the amount of work, money, extra weight, and complexity you'll be introducing to implement your friend's design. You could save yourself some time by asking your friend if he's worked out the empirical weight transfer benefits he claims, but I suspect he hasn't.

    If what you really want is a transverse transmission capable of transferring +350 lbft of torque, then your friend's design may be the only way to get there... though by the time you're done, I think cost-wise you'll be within striking range of an exotic transmission anyway.

  10. #20
    Senior Member C5GTO's Avatar
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    Quote Originally Posted by Bloozberry View Post
    Weight transfer is a dynamic property accomplished with suspension design. For example, Porsche hangs their engine off the back of their rear axle and still makes their cars handle with world-class success.

    If static weight bias is what you're worried about, you should calculate how far away you'd need to mount your transmission from your crank centerline to make a significant difference. Don't forget to take into account the effect of your own weight into your calculations. I think you'll be surprised at how little a few inches accomplishes, especially for the amount of work, money, extra weight, and complexity you'll be introducing to implement your friend's design. You could save yourself some time by asking your friend if he's worked out the empirical weight transfer benefits he claims, but I suspect he hasn't.

    If what you really want is a transverse transmission capable of transferring +350 lbft of torque, then your friend's design may be the only way to get there... though by the time you're done, I think cost-wise you'll be within striking range of an exotic transmission anyway.
    Thanks for your input.
    Joel Heinke
    (Classic Roadsters Cobra, Ferrari 250GTO under construction)

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