Yeah, I have literally built all of the above mentioned in my head and there aren't really any better ways that I can think of. The drive shaft directly from motor to diff is out because of ratios. I have ran that gearing program several times. Max speed at the top of 6th is 77. No thank you.
I may end up cutting the diff up and running a sprocket on the ring gear but I want to try this first.
Miata rear end extracted and will begin test fitting Wednesday in the starlet.
Wow....but think of the 0-60!
The next best would be the sprocket in place of the ring gear route.Tons of info on different ways to build the housing to hold the lube.Some nifty maching to include eccentric chain tensioning.
The chain needs to be as long as possible and the counter sprocket as large as possible for chain life/cooling.
This tread has had me thinking about the sand rail frame I just picked up. what about those motorcycles that are shaft drive ?
With those, you end up with a completely different bag of issues. Probably the biggest difference is Cost/HP. A lot of the shaft bikes are touring bikes (Like the goldwing) that make smaller amounts of power compared to sport/hoon bikes. There are exceptions but just something to consider. They also tend to be more expensive because the bikes were pricier to begin with. The next issue is shaft rotation. There are many bikes with the shaft on the left and if memory serves (correct me if I am wrong) those rotate backwards compared to chain bikes on the left. Then you are looking at a rear mounted engine or having to only consider the ones that are right side shaft. Basically, you can adapt a chain bike to use a shaft fairly easy and as long as the oiling issues are addressed then you should be good to run it sideways.
sell the miata diff, go to the junkyard for some sort of IRS diff and mount the driven sprocket to one of the axle flanges... After locking the diff so it does not turn independently...
HAve you calculated how big a rear tire you would need to be able to get decent ratio not to an intermediate gear and still use the miata diff?
Ford 8.8 IRS came in the Explorer for a number of years in the early 00's. You can get a wide range or ratios and a cheap lsd as well.
Adrian_Thompson wrote: HAve you calculated how big a rear tire you would need to be able to get decent ratio not to an intermediate gear and still use the miata diff?
Yeah, something like 29" or the like. It has been a long time since I ran that calculation. It was prohibitively tall for the car size.
I already have the miata gear so lets keep that for the moment. If it doesn't want to work the way I have described, I will consider a ford diff or tear the Miata diff apart to make a direct drive with a sprocket. I am trying what I described first, your opinions are noted.
what about running the bike's trans output to another IRS diff through one of the outputs, welding the spiders, and coupling the input to the Miata diff input?
Bonus points for attaching another engine to the other side.
I researched this awhile back and found this page.
I would suggest that you start reading at "Endurance racing a bike-powered car gives Alex Vendler a uniquely experienced perspective on this peculiar form of hybrid, though, and it only took three or four destroyed gearboxes for him figure out that while their engines are surprisingly robust, sportbike gears simply aren't beefy enough for car-sized loads. Then, in the midst of one of his many mid-race transmission rebuilds, the answer hit him."
After that paragraph they talk about how to work with the motorcycle output shaft for decent gear ratios.
Another option might be to mount a transaxle in the rear suspension. Cut a plate of aluminum to bolt where the engine was with a pillow bearing on each side with a center hole big enough for a tube to pass through with the center of a clutch disk welded to one end and either a sprocket or ujoint yoke welded to the other.
Bonus for giving you reverse and being able to toss the transaxle in a lower gear for tight autocross courses so you can use more of the sequential gears.
Minus is weight, which might not be too bad.
Is the problem noted with the rotation of motorcycle engines being reverse to what is needed for a conventional differential a common issue?
Bike engines spin the right way,I think there's a couple of touring bikes that don't but why use those anyways right.
Yeah, I have seen the Miatabusa. I may end up going that way but there are lots of Locost guys that are running bike transmissions without too much trouble.
This is not a race car. I don't have much ability to go to the track and the best I can hope for is coming in under a challenge budget.
A heavy bike engined Locost is about 1100 lbs. You're not going to get a Miata down there. Thus the transmission life.
Having driven a bike engined Locost - they're not great for pootling. They want to be run hard and shifted fast. Light throttle use has them lashing around.
If its not for the track I wouldn't go bike engine for power....I say that as HUGE fan of bike engine cars.
What Keith and Kevlarcorolla said. Bike engines like to rev and shift hard. Loafing one around town will get tiring real fast.
If you want a Miata with more normally aspirated power a better bet would be a motor swap from another car. Something bigger, something more modern, or go the well trod route and turbo charge the Miata motor. All those options will give you a better product for street use than a motorcycle engined Miata.
I may end up back at the original plan, SHO powered.
oldopelguy wrote: Step 1: remove Miata diff from car. Step 2: remove and modify rear cover/ mount from diff by cutting off mounts and rear cover Step 3: remove and discard pinion shaft, gear, and bearings and ring gear. Seal pinion input hole in diff with frost plug. Step 4: mount motorcycle rear sprocket to differential center section and reinstall in housing. Step 5: cut flat plate in size and shape to replace rear cover/ mount and locate and support diff installed upside down with the pinion pointing to the rear. Step 6 mount engine so chain lines up with diff and can enter and exit diff housing through rear opening. Step 7: fabricate cover for chain that seals to the new front of the diff, enclosing the entire chain and a tensioner so that the differential oil lubes the chain but it mostly all drains back to the diff. Step 8: profit?
Thats too hard.
Step 1: remove Miata diff from car.
Step 2: remove LSD from housing and remove ring gear
step 3: seal windows in lsd, pack with grease before final closing, add seals for axles
step 4: bolt sprocket in place of ring gear
step 5: find sealed bearings which fit in place of miata diff bearings and fabricate mount for bearings to chassis
step 6: installation is reverse of removal, kind of.
step 7: fabricate chain guard so it doesnt berkeley E36 M3 up if you throw the chain.
This would be significantly easier if you only wanted a spool because then the LSD wouldnt need to be sealed.
With boost? Please?
Dusterbd13 wrote: With boost? Please?
Do you mean with the SHO motor? Talk about overkill.
If you mean bike engine, then eventually yes. But you guys have mostly talked me out of that for a street car.
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