Torque converter or performance dry clutch for Drag minibike w/ gx390.

[HHTurboVert]

I'm trying to decide how to set up my gx390 on my minibike. I need to decide on whether to use a torque converter like the comet 40 series or a quality dry clutch like the Red Hawk. I plan on using the bike for street drag runs on the weekends and will be using a jackshaft to keep the engine centered regardless.

I like the idea of the variable ratio from the torque converter, but I hear that they tend to slip at higher rpm's. Is there anyway to limit/prevent this? I plan on having the bike up around 70-80mph, but I would still like to have good acceleration at low speed. I do plan on moding the engine, but I don't think I will be reving it much above 6k, since I would like this engine to last as long as possible.

Well let me know what you guys think. Thanks in advance for you input.

 

[minidragbike]

The smaller cheaper TC won't handle that speed. They are only intended for low RPM applications. Yes, they have sme that can handle a lot of power, but not high RPM.

If you really want to use a TC you will have to look into the jr dragster TC's. And they are very expensive, starting at about $600, and you have to buy the jackshaft setup for a extra $200.

The Red hawk can handle 40hp, but the only bad part is that it's a outboard clutch. Meaning the clutch gear is on the edge of the crank.

 

[delray]

so what you are trying to tell him, is if he is running 1/4 or 1/8 plus drags he need to go with high performance disc clutch set up?:smile:.................thats if he is running ton of hp like some of the engines that you have built minidragbike.

 

[minidragbike]

so what you are trying to tell him, is if he is running 1/4 or 1/8 plus drags he need to go with high performance disc clutch set up?:smile:.................thats if he is running ton of hp like some of the engines that you have built minidragbike.

No, it depends on his budget. RPM is the killer of the TAV's. But a jr dragster TC is made to handle more RPM. It's made more like a motorcycle TC.

The big HD 1" shaft TAV that's made to hanle 18hp is made for V-twin lawn mower engines. Low RPM, but high TQ.

TAV's are not good for constant 6500+ RPM. All of the bikes in my videos all run from 6,500-10,000 RPM.

 

[delray]

i see, not really knowing what he has into his engine. its hard to say. if he is turning over 6500rpm's he could have problems with the belt slipping............ with disc clutch setup it locks up at higher rpm's. more like a direct drive:thumbsup:

 

[minidragbike]

Yeah, once the race clutch lock it never unlocks until the motor goes back to under the clutch stall.

Most of the TAV's are only good for 5500, but they are only rated for 4500.

The racing Torque Converters are super wide belts that don't stretch as much, there also adjustable. But even they stretch in time, but only because the motors they are used on make from 30-50hp and run from 8,000-10,000 RPM.

Here is a picture of a jr dragster version, cost about $800

 

[5hpminitech]

the 40 series doesnt do to bad on a mild 390 ask stang my brother he ran it

 

[minidragbike]

the 40 series doesnt do to bad on a mild 390 ask stang my brother he ran it

I know, but how high was the motor turning with it on it?

 

[Stang]

It turned 7500+ on the tach. The torque converter did feel nice on the take off. The clutch of course feels better when it is locked up, once the power band hits it's time to just hold one LOL. But we are still playing around with stall speed and might possibly change cams. Seems like the powerband is a bit too high and losing quite a bit on the bottom end. Either that or crank the stall up to about 5k ;P

 

[minidragbike]

It turned 7500+ on the tach. The torque converter did feel nice on the take off. The clutch of course feels better when it is locked up, once the power band hits it's time to just hold one LOL. But we are still playing around with stall speed and might possibly change cams. Seems like the powerband is a bit too high and losing quite a bit on the bottom end. Either that or crank the stall up to about 5k ;P

Yeah that's way to much stall for a big motor.
But it also depends on how much lift you have at the valve.

 

[Stang]

it's ~.450 at the valve. It's the NE .320 lift 260 duration grind on a 390 cam with the 1.3 rockers. Math says it should have been less lift but we measured it at the valve and that's what we got.

Was just talkin with JD about it. His current setup seems to get out of the hole a bit faster then my bike but when the power band of my cam hit it is pretty radical.

 

[minidragbike]

it's ~.450 at the valve. It's the NE .320 lift 260 duration grind on a 390 cam with the 1.3 rockers. Math says it should have been less lift but we measured it at the valve and that's what we got.

Was just talkin with JD about it. His current setup seems to get out of the hole a bit faster then my bike but when the power band of my cam hit it is pretty radical.

Yeah on the video JD's bike still has a stock cam in it. Should be way faster next time with the head, cam, and alky.

My gx200 motor has .432" at the valve. It has a .360 cam with 260 degrees of duration and 1.2 roller rockers. The clutch stall is set at 5400 for best performance. I'm guess you should be much lower, from 4000-4500 stall.

 

[Stang]

Currently its only about 3400 stall I was just saying it seems like I need to turn it up closer to 5k since the power band seems to start there

 

[minidragbike]

Currently its only about 3400 stall I was just saying it seems like I need to turn it up closer to 5k since the power band seems to start there

Oh yeah trun it up, start at 4,000, but you shouldn't need more than 4,500 at the most.

 

[5hpminitech]

yeah it needs more its kinda a dog out the hole but the cam comes on explosive like a 2 stroke

 

[minidragbike]

yeah it needs more its kinda a dog out the hole but the cam comes on explosive like a 2 stroke

Yeah, it's all in fine tuning.

What you do is run it all out and make sure you have a tach on it. Seem just how far it will rev to. Let's say it will turn at most 8,000 RPM. That way you can figure out your gearing, and power band. The power band is normally about 2,500 RPM. So it may be 4,500-7,000, then the acceleration slows slows down, but your still gaining speed.