Tame my 4-speed Stroker....
I'm lost on how a steel flywheel is a better heat sink than aluminum.
The pressure ring in most pressure plates is aluminum as well. Less weight and less rotating mass.
Part of it is about how quickly the heat transfer must take place. If you were relying on convection to transfer heat into the air, aluminum works pretty well. But there isn't enough time for convection to happen with a clutch, not to mention the clutch is in a confined space. Add to that with an aluminum flywheel you are trying to transfer heat from the insert to the aluminum. There are small gaps and spaces between the two materials which act as insulators to inhibit heat transfer. Remember the heat conductive gel used when mounting some electrical components? It's used to fill those gaps and spaces to improve heat transfer between two surfaces, but that gel is not really practical for a flywheel/insert application.
Then there's the insert being attached to the aluminum, with the aluminum providing most of the structure to keep the insert flat at room temperature. When slipping, the insert absorbs heat faster than it can transfer it to the aluminum. Because the insert has little mass it's temp rises very quickly, causing it to grow at a faster rate than the aluminum. When this happens, the areas of the insert that are bolted to the aluminum are restrained somewhat compared to the areas that are not. This is causes the insert to warp, and with that warping comes loss of intimate contact between the two materials which is needed for direct heat transfer. Pretty much the point of no return as not only does the insert temps skyrocket at this point, but so do the disc temps.
I agree with running a sintered iron disc with the clutch tamer. The disc Jpar posted earlier is NOT sintered iron. The common name back in the 80's was vel-ve-touch or something similar. It won't take slipping for very long. And the tune up window between slipping and living and slipping and peeling the friction off the disc is very narrow. I could never find it. And I tried it with both Ram 6 and 3 puck discs. If you slipped it enough to make the car move and not kill parts, 6 runs was about max.
The friction materials used in a clutch are basically the same as those used in a brake system. As with a brake system, they will all last a long time as long as temps are kept in check. It's the reason an oval or road course car with heavier rotors can post quicker lap times when that course requires a significant amount of braking. There's a reason you don't see steel inserts on aluminum rotors.
As for FW weight, I'll say it again. The less rotating inertia you can get, the higher you can be on the chip and still make the car leave. That means the average guy can get a catalog out and find the standard 15 pound FW. Mine weighed in at 11 pounds FWIW, which is what it was said to be.
You and I both know that most cars out there have chassis that are questionable...at best. Some are just junk. Most guys think a 3 way adjustable shock up front and a 9 way in the back is the cats ***. We also both know that the RPM limit at launch is RPM/IC/rotational inertia/available traction. That's about it for the simple math of it. And shock tuning ability.
If you have a 30 pound FW and you can set the chip at 5000 at the most, you can go to a 15 pound FW and move the chip up. How much requires some testing. But you can move it up because you reduced your rotational inertia by 50% (at least the FW part of the equation...the disc and PP also add to that) and the tire can now take the higher RPM. Now it takes less clutch manipulation to control clutch application etc. And, you have less RPM to pull back in first gear.
If someone is using FW weight to move the car, they either don't have the correct SLR or their gearing is just wrong. And probably too big of a tire. Seen that a bunch. 14x32 tires on a 3200 pound car running 10's is more than plenty.
A flywheel is an energy storage device. The entire rotating assy is the actual effective flywheel, the part we call a flywheel is only one part of that. When you spin that flywheel up, you are charging it with energy. That energy contained is a function of the flywheel's rpm. The more energy you charge it with, the faster it will spin. And when a flywheel loses rpm, it's because energy exited that flywheel.
You can quantify the energy contained in a flywheel. Lets say a given flywheel spinning at 5000rpm contained enough energy to supply a 500ftlb boost of torque for 0.25 seconds. The clutch is what determines the rate that you draw that stored energy out of the flywheel. The clutch could draw out 500ftlbs for 0.25sec, or the clutch could draw out 250ftlbs for 0.5sec. Both are the same amount of energy that gets dumped into the chassis, 500x0.25=125ftlb/sec or 250x0.5=125ftlb/sec. The difference is that an additional 250ftlbs over 0.5sec is a hell of a lot easier for the chassis to process than 500ftlbs over 0.25sec. The CT allows you to dial in the rate that the clutch pulls energy out of the effective flywheel. Rpm isn't a factor in determining the flywheel's discharge rate like it is with your adjustable clutch, which allows CT users to launch off the high side and dead hook as long as they have enough clutch.
The starting line advantage isn't flywheel weight as any added inertia boost during launch due to added weight has to be paid back as slower acceleration before you reach the finish line. The added weight thing cancels itself out in the end. The advantage comes when you can process a higher staging rpm while dead hooking without damaging the clutch. The flywheel is going to be fully charged when you cross the finish line, so any additional power you have to spend spinning up the flywheel is power being diverted from accelerating the car. Power in basically equals power out, so why start the race with the flywheel half charged when you no longer have to with the CT?
Grant
