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Hey everyone, just wanting to know what everyone else is using for a driveshaft on a front engine build. With such high rpm, are you experiencing vibrations at all? Do I have to get a carbon fiber driveshaft that’s balanced to 10,000 rpm?

Also, if I use the hawk adapter, anyone know the flange bolt pattern?

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Drive shaft RPM doesn't have much to do with engine RPM, drive shaft RPM is determined by final drive ratio, tire circumference, and speed over the road. The driveshaft that is normal for your donor diff should be just fine (though you'll probably have to shorten it).

Your bike engine may spin at ten grand, but once it has gone through the reduction of the primary drive (crankshaft to clutch) revs will be low enough that the transmission can take care of the rest of it.

[Edit: changed "which" to "drive shaft RPM" 10/2/19 to avoid confusion re which which is which.]

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Locost builder and adventurer, and founder (but no longer owner) of Kinetic Vehicles

Except when you’re in 6th gear. Then you are likely in, or nearly in, an overdrive situation at the sprocket. In my case, the hayabusa output shaft will rotate over 10k rpm in 6th. My zx10r is even higher.

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If it’s not custom, I don’t want to hear about it!

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I see you're in Alberta... I had mine built by Driveshaft Specialties Inc in Calgary. Great guy to work with, very knowledgeable and deals with custom and performance applications a lot.

In the case of my arrangement, I had to use two short ones - one from the bike engine to a reverse box, then another back to the diff. In my case, I used 1310 u-joints and flanges appropriate to my application. I BELIEVE the flange coming off my engine's driveshaft adapter was a Spicer 2-2-899-1.

The tricky part was managing u-joint angles. Since the driveshaft output is so far offset on the engine, my front driveshaft had a pretty decent u-joint angle as it went diagonally from the engine to the reverse box. On my first crack at it, I had a working angle of about 7 degrees. The max driveshaft speed for that extreme of an angle is only 2500rpm, and sure enough I had a pretty decent vibration above about 70 kph. To fix this, I have had to bring it back to DSI for a rework including front and rear CV joints, plus custom made flange adapters since there were no off-the-shelf parts that would work.

There are calculators out there and I strongly suggest you keep your u-joints to as low an angle as possible to avoid making a costly mistake in your design.

Good points. At an ideal engine location, my driveshaft angle would be a little over 9* but I was told my u-joints would then be 4.5*?? On paper it doesn’t make sense to me though. Lol. Still looks like 9* on each side. Basically shafts would be offset 6” in a 42” stretch.

I was told go with a carbon shaft to minimize rotational mass, and probably one that was balanced to 10k rpm. Just want to get things right the first time before I mount the engine.

Do you have pics of the cv stuff you did the second time?

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If it’s not custom, I don’t want to hear about it!

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All power goes through the primary reduction which multiplies the torque and keeps the drive train speeds reasonable. At 11000 rpm, the transmission input is at about 7000 rpm. 6th is close to 1:1 so the fastest the trans output and drive shaft will turn is around 7000 rpm at top speed.

Don't go with a thinner wall tube to try to save weight since the wall is where failure occurs. Use as large an od tube as practical and have it balanced.

Use a dial caliper to measure the flange or ask the hawk adapter folks what is normally used for a busa. Use a steel adapter, not aluminum.

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Miata UBJ: ES-2074R('70s maz pickup)
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Actually mine is still in the shop for the CV upgrade, so no pics yet.

The 4.5* thing is correct. Basically the cv joint is also called a 'double cardan' joint. It gets a bit complicated, but basically it's just two standard u-joints with a very short connecting piece between them, and the flanges are also special because they have a pilot bearing in their centers to maintain alignment. However, even with this arrangement I would be concerned about a 4.5 degree angle if you truly do plan to see 10,000 RPM at the driveshaft. I'm not able to search at work right now, but there are tables out there that relate working angle to maximum recommended RPM. You may want to look at a combination of moving your engine forward, offsetting your driveshaft tunnel to the side, etc.

How far along are you? Do you have any pictures or drawings that we could look at to spur some creative ideas?

Just starting to mount the engine now. Decided to push it ahead and over a bit. Works out to just over 6* now. Not much else I can do really. Already going to be really tight for headers, and now my weight distribution will be off too.

Pics tonight when I get back on my computer

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If it’s not custom, I don’t want to hear about it!

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The driveshaft shop wasn’t talking about the cv style at the time though. He was discussing regular u-joints which is why I was confused.

All the BEC vehicles with a front engine rear drive setup would have this issue if they ever hit top speed though. For my build, I have a rear mounted Porsche transaxle that lets me choose my gear ratio and reverse so it’s likely that the drive shaft would see 10k+ rpm often. I could be cruising around with the transaxle in 4th and bike in 6th to get more acceleration from it.

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If it’s not custom, I don’t want to hear about it!

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Willy’s Hayabusa Build Log

I have a build thread located here.....
https://www.locostusa.com/forums/viewtopic.php?f=36&t=19848

Here is the most recent pics... Probably doesn't show a lot to help out.





Length of shaft is going to be roughly 47" and the engine is 5" off center. Hopefully it works out...



I didn't know there was a primary drive reduction. I assumed when it said 1:1 it was based on engine rpm. Missed it in JackMcCornack's post as well. (sorry)




All the balancing places are telling me they don't have the ability to balance it with my adapter. I'm being told that it won't work if they don't balance those too. Does that make sense?



I was considering this for the adapter...
http://www.kitcardirect.co.uk/bike-engine-car-sprocket-adaptor.html

It's the only steel one I can find, but I need to find out if the bolt pattern is common on this side of the pond

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If it’s not custom, I don’t want to hear about it!

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That should work if you pick the right year model busa. Hardened steel is what should be used for splined adapters.

The shaft shop will be balancing a standard design automotive driveshaft (ford sierra equivalent new parts) with flange couplers. The adapter is for the engine and not part of the driveshaft and does not need to be balanced with the shaft.

Rotate the pinion to point directly at the engine output shaft and tilt the engine so the shaft points directly at the pinion. Then you can fine tune the angles with a digital level.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

This^^, it lets you reduce the angles enough....

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
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Would the 6* angle be enough now or would you still move the engine and rear trans to line up?

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If it’s not custom, I don’t want to hear about it!

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Willy’s Hayabusa Build Log

The only issue with using steel is, from what I hear, you are far more likely to strip the splines on the output shaft. The aluminum ones are well documented to hold more than 350hp with no issues in all forms of vehicles.

_________________
If it’s not custom, I don’t want to hear about it!

Youtube Series

Willy’s Hayabusa Build Log

Shoot for zero degrees. Vibes from bad angles can damage the transmission. Cut a new tunnel if you have to.

I don't know what your plans are for reverse if any or a cush drive that would make it less critical.
It isn't about initial holding but long term. A tight aluminum or steel is fine if it stays tight but the fit when new, a used nut, engine braking, etc can all work against you and if the hub is allowed to rock on the splines, aluminum doesn't compare to hardened steel, but neither type can be ignored.
This pic is from a steel sprocket that was ignored for a long time.
You may never notice a problem with the aluminum but I'd go with steel if the price is about the same.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12