THE BATTLE OF THE FLYWEIGHTS
Lighten flywheels, good or bad?
I see a lot of people putting lightened flywheels on everything. Is this a good idea? Not always. In this article I will go over what a lighten flywheel does for you and what a stock weight flywheel can do. Then you can make the best choice for your car.
What does a lightened flywheel do? It is less mass to get moving, so the engine will rev up faster. That sounds good, right? Well, the bad thing is, once in motion a lighten flywheel doesn’t want to stay in motion. Another way to put it is; it takes less gas to get it moving, but will take more gas to keep it moving.
A stock weight flywheel takes more energy (gas) to get moving, but once in motion, it will take less gas to stay in motion.
That all makes sense, but how does this affect me? Let me first say this is my own opinion. If you have a bus, a lightened flywheel is a bad idea. Been there done that, have the t shirt. What happens is you go to move from a dead stop and you step on the gas, the engine revs up and you start to let out the clutch. There is not enough mass on the flywheel so the weight of the bus drags the engine down then you give it more gas, then the bus starts to move. With a stock weight flywheel, you will use less gas to get this brick moving. Also a bus usually sees a lot of freeway miles, so a stock flywheel helps here.
How about a street Bug or Ghia? Well here is what you should look at. If this car is just a town car, then a lighten flywheel can help as it takes less energy to get the motor revved up. So in town you would save some fuel. Now the opposite is true for a driver that is frequently on the freeway. A stock weight flywheel takes more energy (gas) to get moving, but once in motion takes less energy to keep in motion. So if you keep your RPMs in one place you will save gas on the freeway.
It gets a little tricky when you’ve got an off-road car. It all depends on how you drive. If this is a crawler, then stay with the heavy flywheel. If this is an “OMFG lets get it on” car, then a lightened flywheel is the way to go because you want to get RPMs up fast and we will be on and off the gas constantly. If this is a sand car, then yes a lightened flywheel is the way to go. There are usually no trees in the sand and hell yes we are on and off the gas.
A drag car is easy. Hell yeah we want the RPMs up fast! So a lightened flywheel is the way to go here as well. The biggest problem with drag cars is keeping the flywheel on. The RPMs go up so fast with all that power that when you let out the clutch it puts a big strain on the gland bolt and pins that attach the flywheel to the crank (Hence 8 dowel, wedge mating and flanged cranks).
Now we have an idea of what to use. So if we said that we are going with a stock weight flywheel because this is a freeway car what about adding a heavy pulley to the nose of the crank? Well it’s not a bad idea, but for what you’re going to spend verses what you’re going to gain, I’m not sure its worth it. Keep in mind, you have to get that mass going. The other thing I have seen is motors with a lot of compression you can rip the snout off the crank. So again, in my opinion, for what you gain on the freeway verses what it takes to get it moving I find it hard to spend the money.
What is considered too light? Around 12lbs seems to be the norm and works well. I have tried the old 6lb flywheels and man they are just too light. Letting out the clutch was a chore. I did a comparison on a circle tack car and found we really didn’t gain anything from the 6lb flywheel verses the 12lb flywheel. I can see why those aren’t made anymore. There is no gain and they weren’t cheap, even back in the day.
One last note, if you are going to use a lightened flywheel you can’t just buy one and bolt it on. You have to reset the endplay. That is a must. Also, torque your gland bolt on. The torque should be 217 to 250 ft lbs. Do NOT use an impact. If you don’t have a torque wrench that goes that high then buy one, borrow one, or rent one. If your flywheel comes loose, not only do you get to replace the flywheel, you will be getting a new crankshaft as well. Over torquing a bolt will either roll the threads or crack the bolt. Either way the flywheel can come loose.
So what have we learned? A lightened flywheel is not a bad thing; it can be a good thing on the right kind of car. It all depends on what you want to do with your car. The only thing I can say for certain is that if you have a bus, putting a lighten flywheel on that is a bad idea.