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THE RELATIONSHIP BETWEEN PIPE AND CLUTCH
By Art Verlengiere, RLV Tuned Exhaust Products

This article is designed to help kart racers understand the relationship between the pipe and clutch. First, let’s make sure we understand how the clutch works and what it is meant to do.

A 2-cycle or 4-cycle clutch is a device that allows the engine to freewheel (a non-engage state) for starting and idling. This freewheeling is maintained up to some pre-planned slip point at which time the clutch achieves lock-up and drive occurs.

Clutch lock-up is achieved by the centrifugal force of rotation and torque overcoming the pre-load tension of the springs. When the RPMs reach a level of force that engages the mechanism, the clutch is said to “lock-up”. In the case of an engine clutch, this occurs at the engine. With an axle clutch, lock-up occurs through the gear ration between the engine and the axle clutch. After the clutch has locked up, the torque is transferred to the rear axle, then to the tires and down the track you go.

Torque is delivered through the crankshaft as a proportionate function of combustion and RPMs. After torque peak, as RPMs and combustion increase, torque will decrease.

There is one more thing to remember before we address the clutch and pipe: a properly operating clutch responds to the environment around it, rather than creating the environment. What I am saying is that a properly operating clutch may be a technological masterpiece, but it’s dumb. It will only respond to the amount of torque put into it, and nothing else! In other words, if the engine loses power during a race, the clutch engagement will drop. This occurs because the amount of energy being put into the clutch has dropped.

The quickest way to lose torque to the clutch is to lose power at the engine. If the engine is properly blueprinted and not worn out, the easiest way to lose torque is through excessive heat retention in the engine. The major sources of excessive heat would be: 1) too short of a pipe length, 2) improperly operating carburetor, 3) poor driving, 4) fuel, 5) missed set-up/rear ratio too high, 6) chassis bind, 7) incorrect tire selection – and on and on. These items and more will create excessive heat individually or as a group. Once excessive heat build-up occurs and torque drops, it’s nearly impossible to get the power back while on the track. So when you think you have a clutch problem, check these other items first. More often than not, a clutch that lays down during a race lays down due to a loss of torque.

What does the clutch have to do with the pipe? Our pipes are designed to deliver power over a given range. In the case of a piston valve with our G-2 pipe, the RPM range is 10,400 to 14,500+ with a flex length of 9.50”+/- ¼” to 10”+/-¼”. In this example, we have two peaks. The first is the torque peak and the second is the horsepower peak at 11,400 extending to 12,100.

TORQUE PEAK
The clutch is normally engaged at 200 to 300 RPMs before torque peak, rather that at torque peak. This allows for engagement and insures adequate power to drive through the torque peak and RPM range (the clutch stays engaged) without bogging the engine down. If we engage at torque peak, the clutch may lock and drop off, as there may no be enough power to sustain and carry the engagement forward. So it’s very important to engage the clutch at 200 to 300 RPMs before torque peak.

Make sure the clutch does not labor at torque peak after engagement occurs, as this will build heat and steal horsepower. The clutch should lock and go. If clutch engagement occurs at 10,400 RPMs and then drops to 9,800, the clutch is working too hard to get back up to speed and through the torque peak. Both of the situations create excessive heat retention in the engine. Each time you call on the clutch and it has to labor, an additional amount of un-dispersed heat is added to the engine and the horsepower drops. This makes the clutch response worse and worse in regards to its engagement, which becomes lower and lower. Too short a pipe or a bad carburetor as well as chassis or tire setup will create the same negative results.

Excessive heat is the enemy of your setup. If heat cannot be controlled at torque peak because of a need to run a very short flex pipe, say 9.25” to 9.75”, you may want to try engaging the clutch 300 to 400 RPMs before horsepower peak. More gear will have to be added and clutch slip raised. This arrangement works well when running as RPM setup.

HEAT
It takes at least one practice session to evaluate a setup. Run five or six laps, noting clutch and engine performance as it relates to heat. If the engine is going too slow and the clutch drop earlier and earlier, it should show itself in five or six laps. If it does, you may want to raise the clutch, lengthen the pipe, richen the carb or add gear to the setup. All these items will reduce the time spent at and around the clutch and reduce labor, thereby reducing heat.

In closing, remember that excessive heat retention the engine usually shows up first in the clutch, then on the stopwatch.

Article courtesy of RLV Tuned Exhaust Products

ETHANOL OFFERS BENEFITS AS RACING FUEL

A comparative study of racing fuels, conducted by Ron Anderson Performance of Lexington, Illinois, could lead to more drivers filling their tanks with corn-based ethanol fuel. The technical analysis of ethanol and ethanol-based fuels, methanol, and VP-15 racing gasoline gave ethanol the checkered flag for overall performance.

From the performance perspective, ethanol is very comparable to methanol, which is currently the racers fuel of choice but ethanol offers several other advantages, according to Ron Anderson who managed the race fuel test.

The general public is using ethanol-blended fuel widely as an automobile fuel, yet ethanol used on the racetrack has not yet reached similar proportions.

Compared to methanol, ethanol fuel offers: similar performance, no corrosion or excessive engine wear, lower fuel consumption (20% on the average), lower fuel costs due to consumption rate, and the ability for racers to end races with a higher rear percent weight.

Compared to racing fuel, ethanol offers: better performance, longer shelf life, no change in fuel stability and lower fuel costs because of cost per gallon. Ethanol, which is 35% oxygen, contains 76,000 BTUs while methanol has 50% oxygen and 56,800 BTUs per gallon.

What are some of the other advantages noted by Anderson Performance? Methanol and racing gasoline are EPA spill hazards and have health concerns. Ethanol has neither spill nor health concerns. Ethanol is renewable and better for the environment compared to other racing fuels.

Ethanol offers the following savings in fuel costs Vs. Methanol – 47%; Vs. Racing Gasoline – 22%. Ethanol offers these savings Vs. Methanol 42%; Vs. Racing Gasoline 14%.

The fuel study was sponsored in part by the Illinois Corn Marketing Board.

ADVANTAGE: CRYOGENICS
By Bill Barnes, BKM Racing

I contacted Pete Paulin of 300 Below after reading an article he had written on cryogenics (freezing parts at 300 degrees below zero). Together, we decided to find out if cryogenics had any advantage in kart racing engines.

The engine we used was the cool bore uncle of the Raptor. I disassembled and sent the complete engine (less flywheel and carb) to Pete from processing.

After the engine returned, I took it and an unprocessed engine to Mike O’Toole for machining. I told Mike what had been done, and asked that he analyze if the tempering had any effect on the machinability of the engine. His comment to me was that the processed engine machined much cleaner and acted more like a piece of aircraft aluminum, not a typical Briggs engine. Additionally, the block was harder, and it took 4 to 5 times longer to hone the processed engine as it did to hone the unprocessed engine.

The engine was assembled the same as any other engine we run, with one exception: we decided to put in more timing and make it intentionally run hotter. The reasoning was that if the cryogenic process was going to stop block and head distortion, then let’s find out in a hurry.

The engine was run as the primary engine for an entire season (approximately 2,000 laps with head temperatures of 420-450 degrees), with only periodic check under the head. At the end of the season, I tore the engine down to see how it fared.

First, there was no visual or measurable distortion in the areas of the exhaust valve, cylinder or head. The wear in the cylinder consisted of only 4 10-thousanths of taper, barely even measurable. We also experienced no wear on the rod or crank journals. Rebuild on this engine consisted of a quick hone to clean up the cylinder and a valve job!

When the cylinder head was honed, it took less than 1-thousandth to remove the taper and bring the cylinder back to perfectly round condition. Deep cryogenic processing of the valve springs showed about a 10-15% increase in spring pressure, and all indications are that the springs last much longer without losing tension.

A lot has been said about Briggs cryo-tempering their cranks and the process not working. This test motor showed virtually no problem with crank wear. It appears that surface-hardened cranks benefit from cryo-tempering due to the removal of stress and its stabilization of the material.

END

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