MichaelTT

I called one of these pulley kit companies once, asked about the harmonic balancer pulley, and got "well that is not a real harmonic balancer." I also one was talking to a dude who has a 10.4 second WRX who said he had the world's fastest WRX, and I politely reminded him that an automatic transmission WRX had turned a 9.6 and he said, "That car is not a street car!". "I think you have missed the point", was my reply in both cases.

One can argue the pulley question from two sides. First there is a stright forward technical issue of elimination of the harmonic balancer portion of the crank pulley. There is one series Honda engine for which they have stopped selling pulley kits because the crank main bearing are particularly sensitive. Harmonic balancers are a needed component to protect, usually the front bearing of the crank from periodic vibrations that can occur at certain rpm in any engine. Over time vibrations can cause or aggravate wear. Do not bother to argue with someone who denies this fact or tries to tell you some story about how racing engines do not use them or what ever. Rubbish. You want to keep your harmonic balancer in place. Period.

On the other side, these pulley kit makes act like they have invented some great new power saving device. The pulley kits are much more "effective" was what I was once told. OK, effective at what? Pulley kits have been around for longer than may readers have benn. What is a pulley set used for and how did they come into being?

A long time ago, British sports cars would be modified for racing. They would be given camshafts that would raise the power band up into the 6000-7000 rpm range on an engine that redlined at 5200 or 5600 rpm. Now a funny thing happened, some would over heat and others would kill generator or water pump bearings or both. These parts were being turned beyond there designed RPM. Now it is easy to make stuff out of aluminum anyway and it came into being that these aluminum "under-drive" pulleys were standard practice on racing production cars in the 1950's and 1960's. It was not a scientifically considered search for power, but a necessary solution to a problem. To my knowledge they were never sold to the general public and I have worked on a lot of British sports cars.

Now, it takes say 7hp to drive a A/C compressor. Not more, not less, and the alternator is a demand device also and it takes 1-2hp. So any power saving is out the window. If you rotate the slower you have to run them longer on duty cycle. And the power saving per minute is really, really small. Power saving yes, but effective? You be the judge.

Lower mass, eh? Well there is lower mass and there is low mass. These pulley kits are not low mass. They are lower mass, this is true, but again is it a meaningful gain to spend money on? At such small diameters relative to the flywheel mass and at such low mass relative to the rods and pistons the percentage gains of a pulley kit are ridiculously small. This is one of the great abuses of language so prevalent in the automotive aftermarket today. Claiming lower inertia and improved acceleration is just so much snake oil salesmanship. What we are looking for are significant improvements in say, acceleration, handling or braking and let us not forget, ergonomic improvements related to driver control. So, my argument is not that these people are lying, but that there is very little to gain from spending your money in real terms.

OK, fair enough, but I want to lower the rotational mass of my engine. The pulley kit makers idea is correct, even if the actual improvement is so small.

In this particular area you need to change the FLYWHEEL to a 14+ pound item. There are 12 pound units out there, but I want to run a 14 pound unit. I will explain way. We do not endorse ultra light flywheels for the same reason we do not endorse elimination of the harmonic vibration damper. We once lost WRX motor on the dyno due to low rotating mass, and in 1995 Prodrive broke both crankshafts in a WRC event because of too light a flywheel and a solid crank pulley. In that case it was actually the addition of titanium rods that put them over the edge, but there are also timing belt pulley and tensioner parts that need to be modified to safely run a light weight Subaru racing motor. That is not a place we want to go with a street car, even if it is 'dual-purpose'.

If you get the flywheel, pulleys and what ever too light it is possible to have the timing belt jump a tooth on the right side intake cam OR the timing belt can walk off the crank pulley or break prematurely. This is why I recommend a 14lb flywheel. To go lighter than 12 pounds you must use an Kevlar timing belt, a modified tensioner design and a billet aluminum pulley guide. I like the 2 pounds of insurance!

The light flywheel, especially because most of the weight reduction is towards the outer circumference, is a real change to the car. It makes the engine vibrate more at idle and is more tricky to start away from a stop light smoothly. In return the throttle response is sharper and combined with forged road wheels can make a slightly noticeable improvement in acceleration in the lower gears. Now, a really experienced driver will still wax you good at the track without these modifications, but low mass flywheel makes for better shifting as their is less wear and tear on the drive train as the power goes up.

Tee x2

NOT THAT I AM SAYING their arguements are wrong!!
maybe they don't sell those parts?? or business too good??? (just kidding...)

hoTTub

Good stuff in there, thanks Michael.

audaciousTT

Great info! Thanks!