final drive help

[toyotaracer9]

Hi everyone , I have a bit of a concern with what my final drive is going to beafter reading a post a while back that the final needs to be 6:1 . I cant find that post now so I dont remember who posted it . Ok here is my plan I have my kubota d722 turboed and ready for a frame I backed out on the govornor to 3800rpm but plan to use the extra just for acceleration , does anyone see a problem with this ? I am also planning on using the comet 94c which has a low of 3.49:1 and over drive of .78:1 . do you guys think this engine will be able to make it to 80mph ? which is what im hoping for to have the ability to move around on the interstate . so with that said I have an 11 tooth and 45 tooth which is 4:1 , does this sound doable or do I need to come up with different gearing ? I think the tire height on the bike I have my eye on is 24-25 inches . sorry for such a long post but much thanks in advance for all of the help . Thanks Shane

BTW I plan to make around 25-30hp

[albertaphil]

Hey toyotaracer,

I'm planning a project with a 16hp twin with a Comet 94C. I've been pondering the same question myself and keep coming back to the same conclusion...with a CVT you essentially have an infinite number of gears between your low ratio and high ratio. Thus, if you pick your gearing to give you a top speed (@3600rpm) that is acceptable to you, then all that really remains to be assessed is if "low gear" is slow enough. In your case, a 25" diameter wheel will have a circumference of about 6.5 feet. With a 4:1 final drive, you'll get your 80mph at 3600rpm, whether your engine will have the power to do it is another matter, although the other posts here tell me that you shouldn't have too big of a problem at 25-30hp. I think the 94C has a stock engagement of 2100rpm, which will give you a "first gear" minimum speed (without slipping the belt) of about 11mph, which is a lot slower than 1st gear on any standard motorcyle transmission I've ever driven. These are the numbers I've been working with. I guess the real question is how the Comet responds to speed/power in between low and high range, but I gather there is quite a bit of tweaking you can do to a Comet to get it to respond the way you want. What kind of frame do you want to put your engine in? Good luck.

Philip

[toyotaracer9]

Hey Phil thanks for the reply , the clutch that I am getting has an engagement of 1800rpm . I think 2100 would be a little high . but my main concern rightnow is that someone in another post said final should be 6:1 or else the engine will be lugged and could tear it up !?!? I had purchased the 11/45 to acheive 80 @ 3600 but now I am a bit worried . I am planning on putting the engine on a shadow vlx600 frame . hearing this engine run with the turbo has me anxious to find a bike ...

[albertaphil]

Well, I don't know how worried I would be about lugging your engine due to gearing. However, I would strongly suggest putting a boost gauge and exhaust temperature gauge on your machine so you know that you aren't overboosting or overtemping things. The fact of the matter is that if you go 6:1, you'll only be able to go 58mph, regardless of how much power you have, and that is about how fast the 10hp bike can go (though not up hills). With the CVT, if you find that you have to add too much throttle at, say 60mph to crest the hill or begin to accelerate before the transmission "shifts down" such that your engine lugs, you can get different parts (I think it is a spring change) on your secondary pulley to cause the engine to rev easier. I don't think you'll have a problem. A few guys on this forum are running CVTs...hopefully they'll chime in with some experience.

I was going to build on a Nighthawk 750 frame, but I'm thinking that I'll keep looking for a 450 or maybe even a 250 frame...16hp doesn't leave a lot of extra power to haul extra weight around with. I know what you mean about being eager to get you ride going...

Philip

[andrewaust]

If you can make 20+HP I would try the 4:1 Gearing! If the engine is new or has been rebuilt, Id take it a little easy for a while. From what I understand "as I have not ridden a comet cvt bike" rpm's build up a little anyway until you start running the second phase of the belting system in which rpm's climb. I'd check the torque figures for your engine and see if most of the ride is within these figures climbing as you read max speed. Most small high speed diesels make max torque around 2100 - 2200

I have to confess it's been about 30 years since I rode anything with a cvt, yes age of 8/11 riding a robin minibike ................... loll




A

[toyotaracer9]

Thanks for the info Andrew , the engine is actually brand new so ill keep that in mind . the torque #s are 33-35ft/lbs from 2000 to 2600rpm . before I installed the turbo so I would say around 40ft/lbs now . on the torque curve chart it shows from 2600 to 3200 its a slow fall from 35ft/lbs to 27ft/lbs and thats all the chart shows .

one more thing , I see you said take it easy on the engine . I am not familiar with the breakin of a diesel is their any suggestions ? thanks Shane

[dieselbikin]

This subject has been covered several times. Try
https://www.dieselbikeforum.com/view ... ATIO#p4672
https://www.dieselbikeforum.com/view ... INAL+RATIO
https://www.dieselbikeforum.com/view ... INAL+RATIO
https://www.dieselbikeforum.com/view ... INAL+RATIO
https://www.dieselbikeforum.com/view ... inal+ratio
https://www.dieselbikeforum.com/view ... inal+ratio
https://www.dieselbikeforum.com/view ... inal+ratio


I run a 4.60 final drive (13/60)/Comet 94C/10HP Yanclone with good results. I bought a 60t blank from Surpluscenter.com and cut and drilled it for my rear sprocket. I wish I would have bought the 65t. I do not recommend using a sprocket smaller than 13t due to friction and chain wear. I have used as small as a 10t. A 4.00 final drive should work well for your application. Buy . Be open minded about trying different clutch combos. The Comet did not always respond to changes the way I expected it too. Keep good records of each run, use a consistent testing method and route, and install a good bicycle computer to keep accurate results. My $10 computer gives me top speed and average speed of each run. Besides, motorcycle speedometers are generally not very accurate. It took me 2 years and untold combos to find the right one. It was worth it.
By the way I run a pink spring and 9 X 60 gram pucks.
Once your engine and bearings break-in the bike's performance will improve noticabley.
Do not let the engine idle too low or it will become oil starved.
The Comet will start to pull you before it engages, so creeping in traffic is no problem.
I think my puck/spring combo would be a good starting point for your bike.
Less weight and more aerodynamics are always a plus.
The weight will help acceleration and the aero will give you speed.

[dieselbikin]

60t sprocket. Friend cut sections out with plasma cutter.

[toyotaracer9]

Thanks for the links , that was very informative .

[TedV]

I was going to build on a Nighthawk 750 frame, but I'm thinking that I'll keep looking for a 450 or maybe even a 250 frame...16hp doesn't leave a lot of extra power to haul extra weight around with. I know what you mean about being eager to get you ride going...

Philip

I ride a 95 CB250 Nighthawk. yes it is light, but I'm not sure there is enough room to stuff a Vtwin and CVT down there.

[roodesign]

Hey there, I am building a little microcar (check out www.roopod.com) and using a kubota z482 engine and a comet 94c, as you can see on the website, I am just about ready to fire it up...my gearing is 4:1 with a 19.2" tire I will soon see how that works...I would love to hear more about your turbo...what unit, mounting details etc...

[toyotaracer9]

Hi Roo , I have a d722 with the rhb31 turbo . I will try to get a vid. clip today , the exhaust manifold is identical to yours except I have 3 ports . I made a 1/2 adapter plate and studded it . I have no way to put a load on the engine so I am not sure what kind of boost it will produce but hopefully ill find out soon . I really think with the CVT style transmission it should spool and keep boost all the way to hwy speed . I have turboed or supercharged everything I own except my 08 cbr 1000 and all vehicles have gained 3-5 mpg over stock so I am sure it will only help in this case too .