Technical data for insomniacs!
When the flag drops and you stomp the right pedal, the acceleration from a hard hitting clutch feels awesome. Your head snaps backward, the wheels spin and you saw the steering wheel back and forth to keep the kart in the groove. Wow, that’s fast! Or was it?
Let me give you an engineer’s perspective.
Your tachometer indicates only the average rotational speed of the engine. But if you had a sensor that could measure instantaneous rotational speed, you would see that the crankshaft is turning fastest during the expansion stroke, slows down a bit for the exhaust stroke, slows down more for the intake stroke and then really slows down for the compression stroke. Pushing out burned gases, drawing air into the cylinder and compressing the air requires work. That is why the engine slows down during three strokes. Only the expansion stroke after the spark plug fires produces energy and increases rpm. The average rotational speed for the whole cycle may be 4000 rpm but the instantaneous rotational speeds for the individual strokes might be 4095, 4020, 3990 and 3895 rpm.While the piston, connecting rod, crankshaft, flywheel and clutch are moving, they possess energy or the potential to do work. The amount of energy varies with their speed.An engine that is not running has zero energy. It is necessary to get energy from an outside source (muscles or batteries) to get the cycle started. At idle speed the engine can just barely run by itself because the expansion stroke adds energy at the same rate as the other three strokes consume energy.
At higher speeds, the expansion stroke adds energy faster than the other three strokes consume energy hence there is a surplus of energy that can be used to move the kart and driver down the road.
The throttle determines how much energy the engine produces, but it is the clutch that determines how much energy gets to the axle and when it happens. Like the exhaust, intake and compression strokes, the clutch subtracts energy from the system. But unlike those strokes, the clutch does not extract energy with every turn of the crank. There are times when the engine produces a surplus of energy and times when it does not. The purpose of the clutch is to react to the engine’s energy level and siphon energy at the appropriate time and rate.
Clutch action is a function of rpm. It engages the engine at high rpm and disengages at low rpm. When the engine is turning slowly as in starting and idle, no extra energy is available.
The clutch senses this low speed, disconnects from the engine and takes zero energy from the reservoir in order to prevent the engine from stalling. When the engine is turning at high rpm, there is an excess of energy and the clutch senses the high speed and consequently connects itself to the engine which takes energy from the reservoir to move the kart.
Pulling Hard versus Hitting Hard
The “hard hit” clutch accelerates abruptly at first. It throws your head back but then acceleration tapers off quickly. The clutch is very popular because it has been around a long time and is fun to drive. And if every driver has one it is neither an advantage nor disadvantage.
The “hard hit” clutch takes energy from the reservoir as quickly as possible. But the aggressive nature of such a clutch also makes it slow to realize that it is stealing energy necessary to power the exhaust, intake and compression strokes. After the initial impact, the engine slows down a few hundred rpm because it just lost much of the energy needed to keep running. The engine needs time to recover but the clutch does not get the message immediately. It continues to drain energy and in extreme cases causes the engine to quit.
The “hard hit” clutch has another problem – it spins tires. Spinning tires look impressive and feel good but accelerate the axle not the kart. Instead of moving the kart forward, the energy from the engine is propelling stones and dirt backward and heating the tires. Now if your opponent’s tires slip less or not at all, then your loss is his gain. His engine moves the kart forward, your engine throws stones backward.
In contrast, the “hard pull” clutch accelerates at a constant rate. It feels much smoother and
perhaps a little less fun to drive. This clutch has not been around very long. A technical problem had to be solved to make such a clutch possible and for a long time we did not even know that a problem existed. Computer data acquisition systems provided evidence – hysteresis. Part of the solution was a faster reacting mechanism.
The “hard pull” clutch takes energy from the reservoir at a steady rate. It extracts surplus energy from the energy reservoir and nothing more. There is always adequate energy to drive the exhaust, intake and compression strokes. The engine does not bog down because the clutch is a very cooperative partner. The acceleration may be a bit less but it lasts a lot longer.
The “hard hit” and “hard pull” clutches are just like the hare and tortoise story. One jumps out quickly then takes a nap while the other starts off slowly but advances persistently and eventually wins.
SMC highly recommends cleaning clutch discs mechanically NOT chemically. We have found that brake cleaner and other chemicals are inadequate for removing dirt and other fine particles packed into the tiny voids. A stainless steel utility brush aka plater’s brush with a wire diameter of .006 is ideal for removing the hard-to-get-at dirt. Try this yourself and see the difference with a magnifying glass. Better yet, put a piece of white paper under the disc while brushing it. Check out the dirt!
The friction material is very porous and consequently works very well as a dirt collector. Once the voids are filled and packed, the dirt starts to act as a lubricant (think tiny ball bearings) and causes the clutch to slip for a greater distance.
Clutches like tires get dirty quickly. It is important to clean clutch discs every race weekend if not every heat if you want maximum acceleration.
Pictured above is a NEW clutch disc. The left side has not been brushed and the right side brushed with a stainless steel utility brush. Even a new friction disc benefits from a light brushing.
Pictured above is a USED clutch disc. The left side has not been brushed and right side lightly brushed with a stainless steel utility brush.
3rd Place (1st among USA schools)
Shell Eco-marathon Americas 2016
April 22-24, 2016“A big focus for the team this year was a highly efficient and reliable drivetrain. SMC’s Vortex Red clutch gave us the tuning capability to match our engine’s highly specific operating conditions, while providing consistent engagement characteristics and 100% reliability.”On to the next one…Best Regards,
Dorian CappsApril 28, 2016
Jr. Sprint Class Winner
May 9, 2015
San Diego, California
“My son Kaden and I wanted to thank you for making a great product and all your feed back.”
Note: Kaden was using a SMC Vortex RED 3 Disc Engine Clutch.
Ken McKownMay 9, 2015
Lonestar Kart Nationals
Payton Pierce qualified 8th. He finished 2nd in his first heat and won the feature by over a half lap! He raced the Outlaw Cage Modified class running a PSE modified Briggs Animal. Payton used a 3 disc Bully with SMC Roller Levers prepped by David Martin at Martinbuilt Clutches.
“My son Devin Dowell is 17. He has been racing dirt ovals with 2-Disc Vortexes for 2 years now in Stock Flathead & Stock Animal & Stock Clone Engine classes. Racing in the North Carolina King of the Clay series & several local tracks: Wood Leaf Speedway & Coleridge Speedway in North Carolina. We Find the 2-Disc Vortex to be a good consistent & reliable clutch in the classes we run. With the new Roller Levers from SMC, the Vortex Clutch also seems to work really smooth. We like the silver springs in the third hole on our 2-Disc Vortex in Stock Flathead & Stock Clone, and when we Race Stock Animal we like the black springs on the Vortex in the third hole seems to work really well. Just keep the clutch clean after each weekend of racing by blowing the dust off and wiping the basket clean. The only problem I see in Dirt Racing is about once a month the tabs on the weight levers rust a little bit and need to be sand blasted with the hub. But overall the clutch works real well from what I have seen in oval racing.”
“Good luck to everyone racing SMC clutches & products.”
Michael & Devin DowellWelcome, NC, August 2011
Indiana State Champion Open Class
“We recently purchased two of your new three disc clutches for our brand new wedge body twin F200 outlaw go kart,we just got these in time for the Indiana State Championship race held Sept 2nd-4th, 2011 in Crawdfordsville, at Ben Hur Speedway. We feel the new roller clutches were instrumental in us winning the State Championship Outlaw class for 2011. We may very well switch our other outlaw kart over to the same clutch soon for the Indoor Series at Duquoin Il for 2011/2012.”
Cecil GrubbWashington, IN, September 2011
2011 WKA Mid-Atlantic Series Junior Sportsman 1 Heavy Champion
“I have used your clutches on my son’s kart since he started racing four stroke racing. This year we upgraded to the new roller levers and won the WKA Mid-Atlantic Series Junior Sportsman 1 Heavy championship. Apart from the speed, I like how easy the clutch is to adjust and maintain.
Spencer, Bandit , GT Machines (Dave Koehler) and an SMC Roller Lever clutch were an unbeatable combination in 2011.”
Guy PattersonHarrisburg, PA, 2011
“Here are a pictures of my daughter Charlotte who won the pre-final and final at our last club race in Ottawa, Ontario Canada last weekend (Sept. 2011). We have been running the dragonskin clutch for 7 years and so does all the club members.
I bought a Vortex clutch (non roller style levers) a couple of years ago but could not fit it on either my kids kart due to it’s size and the way we had the seat positioned, would clear the engine or seat, so it sat in the trailer for 3 years. This year we became CRG dealers and Charlotte wanted to try one out. Bolted a new LO 206 Briggs and off to the track we went.
Engine break in fine. Start pouring it on and clutch fails. Stick another Draggonskin on, snap the key way……..out of clutches……Let’s try this thing that’s been bouncing around the trailer for a couple of year. To our amazement, we were faster just by bolting the Vortex on. After a half dozen races we realized this thing (the Vortex) is amazing, very little to maintain, easy to set up and change engagement, release and engagement are precise and consistent.
It’s been our little speed secret until last weekend when other racers noticed it at tech when Charlotte lined up for a tear-down. Awesome product, reliable, cheap to maintain and fast out of the box.
Daytona Road Racing Championships
Daytona Beach, FL
Junior Animal Sprint Heavy Champion
“Just a sincere “Thank You” to SMC for an incredible clutch. My son won Jr. Animal Sprint Heavy at Daytona yesterday with the new Roller Lever single disc Vortex. And the best part….we didn’t have to touch the clutch the whole week !!! Not one single adjustment was necessary !! This bulletproof clutch let us concentrate on his driving and the chassis. What an amazing piece !!! Thank You !!!“
Don DelaneyTuscaloosa, Alabama, December 28-30, 2011
Norwalk Karting Association, Norwalk, CT
2011 Sprint Senior Raptor Class Champion
2011 Nutemeg Kart Club – 2nd place points finish in Flat Kart Clones
“Aside from the fact that the Vortex clutch is extremely durable and almost indestructible, it is light and engages smoothly so it will not spin the rear tires. From a mechanic’s point of view it is the easiest clutch to rebuild and maintain. There is no need to measure spring heights for rpm engagement, the five adjusting holes make it a snap to set up. You can rebuild this clutch in virtually seconds. The rebuild kit comes with clutch discs, drive plates and screws to do the job. There is no need to send the clutch out. Even the beginner dad or mechanic can do it. This clutch powered my son to his 2011 Championship. I would not use anything else but Vortex!”
Spring Nationals of the
Midwest Chase’n Race’n ProKart Tour
P&R Photos Image Solutions
“I qualified 19th for the Pro Animal feature paying $1000 to win. In the 20 lap feature, I passed 18 karts with the help of only one caution to take the win. I was on a 2007 Phantom Icon racing everyone else on 2012 Tritons, Impulses, and other karts. I was using a two disc Vortex Roller Lever clutch. I ran Animal 340 and Animal 375 also that day. I won Animal 340 and placed 6th in Animal 375.”
“The clutch performs perfectly race after race. Running an eighteen tooth sprocket really works the clutch hard but the engagement was always smooth. Even after a bunch of caution laps it never overheated. It’s nice to know I don’t have to worry about the clutch chattering or slipping unlike others I have had in the past. After making the switch to a two disc Vortex Roller Lever clutch I won’t ever change again. It’s simple to work on and setting the engagement can easily be done at the track with common tools and no guess work. Thanks SMC for a great clutch to put my Faster Motors power down!”
Branden ZinserApril 2012
Purple Plate Novice Class
Mid Michigan High Bank Nationals
Owosso Kart Speedway
“We got everything you sent last week and got Nicholas’ kart back together and headed out Friday afternoon to give it to em. The new clutch gear helped a ton. Still having trouble with our tach, but I think I’m close based on how he’s running against the other karts.
We took second in both heats and won the feature! It was his fifth racing, in his life, never drove a kart before. 🙂 It’s an amazing feeling to watch your child grow and evolve on the track and hearing the crowd cheering for him (they’ve watch him go from getting lapped several times to a feature win in just over a month) was icing on the cake. I’m not sure who was more proud of that trophy, him or me.
Ever since the first time I spoke with Tom and bent his ear for a half hour asking questions and discussing children’s racing, everyone at SMC has been more than helpful and a pleasure to deal with. We have many years of racing ahead of us and I am sure that every kart we campaign in the future will be running a SMC clutch.”
Rikk KolaczAugust 31, 2012
2012 Carolina Maxxis Kart Series Winner
2012 Maxxis Nationals
Thunder Valley Motorplex, Neeses, SC October 12-14
JR1 Lite Champion
2012 King of the Rock points championships in both JR1 and JR2
18th annual Thanksgiving Thunder
Jr. Big Dog Championships
November 22nd-24th 2012
Georgia Karting Complex
Jr. Big Dog Purple Plate Winner
“We have been using the single disc Vortex clutches for 3 years now. In 2010 my son, Jeremy Steele started kart racing in the Chase’n Race’n kids class. We won 23 races that year at 4 different tracks and one points championship. The 2011 season we moved up to purple plate/JR1 and had another very good season winning 17 races, another points championship and picked up wins at tracks we had never been to.This year we have ventured out to bigger races picking up a Carolina Maxxis Series win, had VERY strong runs at the JR Maxx Daddy race and went on to win JR1 Lite at the 2012 Maxxis Nationals. Then we ended the season winning the 2012 King of the Rock points championships in both JR1 and JR2….that makes three leather jackets for the 2012 season!! Awesome, awesome clutch that is simple but VERY tough! I love the fact that I can rebuild it myself in just a few minutes and we are not without a clutch waiting for someone to rebuild it for us. Saves us time, money and the hassle of mailing clutches off. Looking at going to a 2-disk for next year as we try to repeat as National Champions!”
update: November 25th 2012
….add JR Big Dog Purple plate winner to the resume’! That is like the biggest karting event of the year with racers there from 26 different states! We brought home the trophy that stands near 5ft tall! SMC Clutches have once again put us in winners circle for a HUGE win!
2013 WKA Gold Cup National
103 Street Sports Complex
“We would like to thank everyone at SMC Clutches for their help in winning the Sportsman Pro Gas class at the first WKA Gold Cup National of the 2013 season in Jacksonville, Florida. Tom’s guidance and the new SMC Vortex Red Two Disc clutch helped propel my son, Matthew Miller, to victory in his Jim’s Racing Tires/R.A. Spooner Contracting/GT Machine powered Bandit Chassis. SMC Clutches has once again raised the bar and set the new standard with the new Vortex Red Kart Clutch.
Brian MillerPerry Hall, MD, March 8-10, 2013