Clutch Engament Speed - RED Slide

What is a good engagement speed for a Hillard Fire clutch and red slide? Would 4 white springs be too low? Peak torque is pretty low I believe.


I’m not sure, but I’m here to see the responses :slight_smile:

4 black springs with the shoes non-leading and weighted up should be your lightest engagement speed, but depending on your application that might be too low.

@spribyl any ideas from your own experience or maybe conversations with others?

I have this from briggs just for your question.

Most of the slides are best engagement 2900-3000, but the red slide is lower, almost 2500, you can probably 2700 and be about right. Its also likely you won’t reach 6100 on most tracks and will need to gear for maximum speed with a bit of guessing, we actually geared the green slide for 5800 on Concept Haulers which has a long back stretch. The key to the slide is don’t slow down and keep the revs up.

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Thanks. I put in 4 whites to see how that works. I agree with you Steve, the key is to carry the speed through the corners. My boy is 6 and still figuring things out. He has tons of seat time with the senior slide. It was a lot more forgiving. Now that he has started racing and is limited on power we need to work on running a good line on every turn. I doubt the clutch will make a noticeable change until we have everything else in place.

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This is good timing because I have to move my kid from black slide to red as well.

The engagement speed generally doesn’t matter for much other than standing starts.

Unless some folks are slipping them on track? I have seen some (Masters) do this, not sure if it helped them however.

James, you would be surprised. Many will say once it’s locked up it doesn’t matter but there are times when it’s not and how much slip and time slipping plays a big role in lap times. We’ve tested a few different things and I can say that the old rule of just put the springs on and race isn’t ideal at the top levels when you’re looking for any tenths you can find.

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ok…can you please explain how else you would tune the clutch if not for just peak torque?

When is clutch slip a good thing? To me anytime a clutch is slipping it isn’t sending torque to the rear.

Consider this; engines don’t produce horsepower (HP) they produce torque, at various RPMs in various amounts, then HP is calculated. “torque x RPM / 5252.1 = HP”. Look up James Watt for an explanation of that formula. When the axle RPM, multiplied by the gear ratio, is less than the engine, the clutch is slipping. At what ever RPM the clutch is slipping, the torque being produced by the engine, at that RPM, is transferred through the chain to the axle. There are some losses to heat and friction, but we’re not going to worry about that now. You can use that formula to calculate the horsepower at both the engine, and the axle. If the torque, at the engine, and at the axle, are the same (and they should be) but the RPMs are different, you have less horsepower calculated at the axle then you do at the engine. If the clutch is holding the engine at peak torque, that means you have peak torque at the axle. With peak torque at the axle, you have maximum HP at the axle. Sounds good to me. The only conclusion I can come to is; set the clutch to hold the engine at peak torque, always!
To find peak torque, at the axle, use the old bathroom scale against a strong wall trick. Put a bathroom scale between the front your kart and a strong wall. Sitting in the kart, warm the engine up, floor it, observe the RPM and the number of pounds on the scale, quickly, you don’t have a lot of time, write them down. Now, adjust the clutch to slip more or less and repeat. Do this until you find the RPM where you get the highest reading on the scale. It works every time.

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Ok so I hear people say 4 whites, 2 whites and 2 blacks, or all blacks. Are they referring to the clutch springs and what’s the different between black and white? In a clutch, what’s the difference between springs and slides? Also, how do you determine which slide to use for the best clutch engagement?

Also, how does clutch engagement speed affect your race?

[quote=“da_sniffa32, post:10, topic:4231, full:true”]
Ok so I hear people say 4 whites, 2 whites and 2 blacks, or all blacks. Are they referring to the clutch springs and what’s the different between black and white? In a clutch, what’s the difference between springs and slides? Also, how do you determine which slide to use for the best clutch engagement?

Also, how does clutch engagement speed affect your race?

You understand the engine makes torque, right? That torque is transferred the axle, through the chain. The formula for horse power (HP) is torque X RPM / 5252.1 = HP

Coming off the corner, if the axle RPM, times the gear ratio, is less than the engine RPM, the clutch is slipping. The torque the engine is making, at that RPM, is transferred to the axle through the chain. Using the formula, you can calculate the HP at the axle. HP is a rate of work. The higher the rate of work, the more acceleration there is. If the clutch is holding the engine at peak torque, that means peak torque at the axle, meaning peak HP at the axle, means maximum acceleration.

The key is to find the RPM where your engine produces peak torque. Set the clutch to hold the engine at that RPM coming off the corner.

This is no theory, this is a fact, “fact displaces theory” plain and simple. The proof of this fact is very easily discovered, at the track. Try it, you’ll like it.

This makes much more sense! How do I find my peak torque? And if I understand correctly, you use the springs and slides in the clutch so that the engine RPM does not drop below the peak torque?

To answer question one; if you know anybody with a dyno, test your engine and see where the peak torque is. Barring, an danalog bathroom scale, placed between your kart and a strong wall, will tell you where the point is. At least it will tell you where it is now. The highest reading on the scale means “peak” torque. Some testing and adjusting may be required. It only takes 2 or 3 seconds of full throttle operation to get a read.

I only just now saw this topic, but to answer your question which I’m sure a lot of people have, the engagement speed actually plays a huge role on the 206 relative to other engines.

The clutches on a 206 are closer to the high-stall clutches on a Yamaha, where coming out of corners, having the right clutch engagement will play a huge part on how well you pull out of the corner. 3,000 rpm doesn’t sound like a lot, but when you only have 6,100 rpm to use, you’ll find yourself on the clutch more than you think.

As far as finding the best speed for your clutch to engage at, I would dyno the engine or just go off the charts that Briggs provides, as I would assume they’re fairly accurate to find peak torque rpm. To know what the engagement actually is, just watch the engine RPM as you pull from a stop on the grid. If you look at engine rpm data afterwards, you’ll find where the rpm flattens out while you’re pulling away and that’s where the clutch is engaging.

This is one of favorite ideas I’ve read of yours. I’ve requoted this one a few times.

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So if the peak torque is 3000 RPM, then you would set up your clutch to engage at that RPM? Would you achieve this by using different springs or slides or a combination of both? I get very confused with the difference between the two.

Also, the scale idea, I have a bathroom scale, but how exactly would I use it? Would I set up the scale so I drive forwards and the weight that the kart pushes on the scale will give me the peak torque? What numbers should I expect?

Yes, or just slightly before peak torque but I used to shoot for right at the peak when I ran Yamaha. For the 206 clutch, you’ll have to play with different spring types/combinations to find what works, but for junior and senior 206 2 white and 2 black is where I would start. Not sure about the scales thing as I’ve never done it but that sounds right to me.

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Ok thats what I heard as well. What are the difference between clutch springs and clutch slides? Are they interchangeable, as in you can choose either to use slides or springs for clutch engagement?


Nevermind, just answered my own question :joy:

Make sure the same color springs are installed opposite each other. Both Briggx anc Hillard have plenty of info available online to figure out where peak torque is and springs are needed to match that. No need to burn up your equipment with the bathroom scale. I think we rsn 2 black 2 white on red slide but i would havd to wait until sprinb to check me notebook in the trailer.