Clutch Upgrade: Which one?
01-04-2012, 09:54 AM
#46
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Thread Starter
I'd really like to see dyno results to resolve this. All of the math is hard to dispute because, well, it's math. But my experience in my Saab with the lightened flywheel tells me there's a power benefit to it; definitely noticed a seat-of-the-pants difference, plus my basically stock clutch didn't slip as much (IIRC, I changed out the pressure plate and disc for a Saab 9000 clutch kit; this was many moons ago). Maybe I was getting a lot more loss from clutch slippage than I realized? Sadly I didn't do a before and after dyno with the change (because I was on a shoestring budget during that project!).
Would it make sense that a clutch could better grip a lighter flywheel, and thus generate the sense of more power while not actually being anymore powerful?
Would it make sense that a clutch could better grip a lighter flywheel, and thus generate the sense of more power while not actually being anymore powerful?
01-04-2012, 11:47 AM
#47
Developer
I think if you focus on a light flywheel as a power-adder, you will be disappointed. Saving 3 pounds on a 200 pound rotating assembly (crank, rods, pistons, harmonic balancer, flywheel, clutch, pressure plate, driveshaft, input shaft, primary gear shaft, a pair of half shafts, a pair of wheels and a pair of tires and a pair of rear brake rotors - all of which must be rotated before the tires can move) - it is an reduction of 1.5% of the entire rotating mass when the clutch is OUT. Measured at the tire (chassis dyno) the improvement will be there, but it is slight.
However, if you focus on the improvement in throttle response for shifting, the clutch is IN, and the rotating assembly is now just crank, rods, pistons, harmonic balancer, flywheel, pressure plate. 3 pounds out of maybe 50 pounds. Much better.
I would buy an aluminum flywheel because I want faster throttle response, especially useful if you are an old-school down-shiftter like me. True heel-and-toe stuff. I don't know that I'd buy one as a power-adder. Its there mathematically, but too slight to feel in the seat of your pants.
However, if you focus on the improvement in throttle response for shifting, the clutch is IN, and the rotating assembly is now just crank, rods, pistons, harmonic balancer, flywheel, pressure plate. 3 pounds out of maybe 50 pounds. Much better.
I would buy an aluminum flywheel because I want faster throttle response, especially useful if you are an old-school down-shiftter like me. True heel-and-toe stuff. I don't know that I'd buy one as a power-adder. Its there mathematically, but too slight to feel in the seat of your pants.
Last edited by Carl Fausett; 01-04-2012 at 12:03 PM.
01-04-2012, 11:55 AM
#48
Developer
Kibort,
I agree that link I posted makes poor use of the word "power" and thats the most confusing element always in these conversations.
"Power" can be used as a verb, a noun, and an adjective.
As an engineer, you know that Torque is not power. Torque is work. Power is work over TIME. (I know you know this, just talking to the larger audience.) Hence, torque has no timeline, while power (common HP) does have a time element.
In that link, the author is speaking to laymen, not engineers, and the word "power" and "powerful" are being used like laymen do - to describe both torque and HP. I am not a degreed engineer myself, and I still find it very difficult to write to a broad audience of both academics and lay persons and get it right.
If I write for a laymens understanding, the engineers will have a field day with it. If I write in engineer-speak, the laymen can't understand it and I have failed to communicate an idea.
Its hard to please both readers at the same time, and the topic of HP vs Torque is one of the most common examples I see.
I agree that link I posted makes poor use of the word "power" and thats the most confusing element always in these conversations.
"Power" can be used as a verb, a noun, and an adjective.
As an engineer, you know that Torque is not power. Torque is work. Power is work over TIME. (I know you know this, just talking to the larger audience.) Hence, torque has no timeline, while power (common HP) does have a time element.
In that link, the author is speaking to laymen, not engineers, and the word "power" and "powerful" are being used like laymen do - to describe both torque and HP. I am not a degreed engineer myself, and I still find it very difficult to write to a broad audience of both academics and lay persons and get it right.
If I write for a laymens understanding, the engineers will have a field day with it. If I write in engineer-speak, the laymen can't understand it and I have failed to communicate an idea.
Its hard to please both readers at the same time, and the topic of HP vs Torque is one of the most common examples I see.
01-04-2012, 12:02 PM
#49
Developer
Greg,
Thank you for your post. I think I answered your questions in post #47 above.
I hope my explanation answers your question how torque can remain unchanged while BHP goes up.
They are linked, true, but not equally. HP is linked to torque, but torque is not necessarily linked to HP.
Thank you for your post. I think I answered your questions in post #47 above.
I hope my explanation answers your question how torque can remain unchanged while BHP goes up.
They are linked, true, but not equally. HP is linked to torque, but torque is not necessarily linked to HP.
Last edited by Carl Fausett; 01-04-2012 at 12:32 PM.
01-04-2012, 12:21 PM
#50
Rennlist Member
Thread Starter
Thanks for your clarifications, Carl. I'd still like to know, though, if a clutch can better grip a lighter flywheel so as to alleviate power loss from a slipping clutch/weak pressure plate.
01-04-2012, 12:27 PM
#51
Developer
No. If the problem is a weak pressure plate, changing the flywheel will not help much ACCEPT:
Both the flywheel surface (on one side of the frictions disks) and the pressure plate surface (on the other side of the friction disks) wear with time. Replacing the flywheel will put back some metal where it was lost, so the stack will be a little tighter and therefor have more clamping pressure.
The same effect as having your flywheel re-surfaced, if the grinder cuts down the entire flywheel face, not just the friction disk contact area. The metal must be also removed from under the pressure plate mounts to move the pressure plate down.
Both the flywheel surface (on one side of the frictions disks) and the pressure plate surface (on the other side of the friction disks) wear with time. Replacing the flywheel will put back some metal where it was lost, so the stack will be a little tighter and therefor have more clamping pressure.
The same effect as having your flywheel re-surfaced, if the grinder cuts down the entire flywheel face, not just the friction disk contact area. The metal must be also removed from under the pressure plate mounts to move the pressure plate down.
01-04-2012, 12:37 PM
#52
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anyone want to make a lighter intermediate place and a lighter stronger pressure plate?
I know Greg is getting a whole kit put together.....
I think that alot of improvements are cumlative. I think that an aluminium flywheel makes sense when other things have been done to reduce weight in the rotating assembly. if you have an aluminium flyweel, Ti connecting rods, lighter crank, pistons, wrist pins, & cams then you might see some measurable differences. Adding lighter rotors and wheels, and then it all adds up to potentially significant gains....
I know Greg is getting a whole kit put together.....
I think that alot of improvements are cumlative. I think that an aluminium flywheel makes sense when other things have been done to reduce weight in the rotating assembly. if you have an aluminium flyweel, Ti connecting rods, lighter crank, pistons, wrist pins, & cams then you might see some measurable differences. Adding lighter rotors and wheels, and then it all adds up to potentially significant gains....
01-04-2012, 12:44 PM
#53
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Thread Starter
Interesting. Thanks! Makes sense that installing something "fresh," like a full-thickness flywheel, would provide a perceptable change. Like installing new brake rotors to be slowed by old pads. You get some improvement out of that, but obviously not the maximum benefit of replacing every component.
01-04-2012, 02:32 PM
#54
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I think if you focus on a light flywheel as a power-adder, you will be disappointed. Saving 3 pounds on a 200 pound rotating assembly (crank, rods, pistons, harmonic balancer, flywheel, clutch, pressure plate, driveshaft, input shaft, primary gear shaft, a pair of half shafts, a pair of wheels and a pair of tires and a pair of rear brake rotors - all of which must be rotated before the tires can move) - it is an reduction of 1.5% of the entire rotating mass when the clutch is OUT. Measured at the tire (chassis dyno) the improvement will be there, but it is slight.
However, if you focus on the improvement in throttle response for shifting, the clutch is IN, and the rotating assembly is now just crank, rods, pistons, harmonic balancer, flywheel, pressure plate. 3 pounds out of maybe 50 pounds. Much better. I've found that 928 cranks weigh about 60 pounds and adding in the other pieces add in the other reciprocating pieces and you get way over 100 pounds, quickly. That's the less that 3% reduction I'm talking about, when I was wondering what an aluminum flywheel could do. As I said, no one that I had listen to two different engines rev with the clutch in, could tell if there was a much lighter dual disc clutch or a heavier single disc clutch....and that change is much greater than 3%.
I would buy an aluminum flywheel because I want faster throttle response, especially useful if you are an old-school down-shiftter like me. True heel-and-toe stuff. I don't know that I'd buy one as a power-adder. Its there mathematically, but too slight to feel in the seat of your pants.
However, if you focus on the improvement in throttle response for shifting, the clutch is IN, and the rotating assembly is now just crank, rods, pistons, harmonic balancer, flywheel, pressure plate. 3 pounds out of maybe 50 pounds. Much better. I've found that 928 cranks weigh about 60 pounds and adding in the other pieces add in the other reciprocating pieces and you get way over 100 pounds, quickly. That's the less that 3% reduction I'm talking about, when I was wondering what an aluminum flywheel could do. As I said, no one that I had listen to two different engines rev with the clutch in, could tell if there was a much lighter dual disc clutch or a heavier single disc clutch....and that change is much greater than 3%.
I would buy an aluminum flywheel because I want faster throttle response, especially useful if you are an old-school down-shiftter like me. True heel-and-toe stuff. I don't know that I'd buy one as a power-adder. Its there mathematically, but too slight to feel in the seat of your pants.
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greg brown
714 879 9072
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Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
01-04-2012, 02:36 PM
#55
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Interesting. Thanks! Makes sense that installing something "fresh," like a full-thickness flywheel, would provide a perceptable change. Like installing new brake rotors to be slowed by old pads. You get some improvement out of that, but obviously not the maximum benefit of replacing every component.
01-04-2012, 02:50 PM
#56
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anyone want to make a lighter intermediate place and a lighter stronger pressure plate?
I know Greg is getting a whole kit put together.....
My primary goal wasn't reducing weight, it was to build a clutch/flywheel assembly that would hold 750 horsepower without chattering the gears out of the transmission or shaking off my fingernail polish, like people experience with the "Spec" clutches. A clutch that chatters is fine on the racetrack, but really sucks, on the street. My secondary goal was to reduce the mass of the actual clutch discs...to make the life of the syncros inside the gearbox easier. Porsche found that this help greatly, when they switched the Cup Cars from "Spec" style clutch discs to lightweight Tilton discs.
If the whole thing ends up lighter than the stock stuff, that will be fine with me, since I'm making efforts to reduce the reciprocating weight of high performance 928 engines, in order to move the power range up 800-1000 rpms.
I think that alot of improvements are cumlative. I think that an aluminium flywheel makes sense when other things have been done to reduce weight in the rotating assembly. if you have an aluminium flyweel, Ti connecting rods, lighter crank, pistons, wrist pins, & cams then you might see some measurable differences. I completely agree, especially when the stock stuff weighs in like pieces from a Big Block Chevy engine. Adding lighter rotors and wheels, and then it all adds up to potentially significant gains....
I know Greg is getting a whole kit put together.....
My primary goal wasn't reducing weight, it was to build a clutch/flywheel assembly that would hold 750 horsepower without chattering the gears out of the transmission or shaking off my fingernail polish, like people experience with the "Spec" clutches. A clutch that chatters is fine on the racetrack, but really sucks, on the street. My secondary goal was to reduce the mass of the actual clutch discs...to make the life of the syncros inside the gearbox easier. Porsche found that this help greatly, when they switched the Cup Cars from "Spec" style clutch discs to lightweight Tilton discs.
If the whole thing ends up lighter than the stock stuff, that will be fine with me, since I'm making efforts to reduce the reciprocating weight of high performance 928 engines, in order to move the power range up 800-1000 rpms.
I think that alot of improvements are cumlative. I think that an aluminium flywheel makes sense when other things have been done to reduce weight in the rotating assembly. if you have an aluminium flyweel, Ti connecting rods, lighter crank, pistons, wrist pins, & cams then you might see some measurable differences. I completely agree, especially when the stock stuff weighs in like pieces from a Big Block Chevy engine. Adding lighter rotors and wheels, and then it all adds up to potentially significant gains....
01-04-2012, 02:52 PM
#57
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01-04-2012, 03:02 PM
#58
Developer
I do think that your prices for an aluminum flywheel are excellent!
01-04-2012, 04:04 PM
#59
Rennlist Member
Thread Starter
The thickness of the flywheel has nothing to do with this....the clutch has no idea how thick the flywheel is....doen't even enter into the equation. If there is a giant groove worn into the flywheel (from the disc wearing on that surface), relative to where the surface where the pressure plate bolts onto, then resurfacing might increase the holding ability, a few percentages.
Sorry to be a noob. Thought I understood how clutches, flywheels, and pressure plates work, but it's certainly possible I'm missing something.
01-04-2012, 05:23 PM
#60
Race Car
When I swapped out the single-disc clutch in my '91 for a dual-disc one, I could tell the difference in the speed at which the RPM dropped in neutral. With the DD sometimes the engine would die when pressing the clutch in certain situations, whereas it did not do this with the SD clutch. Nothing I couldn't tune out with the ST2. The difference could easily be logged. I'm not sure I would be able to tell a difference by just changing out the flywheel for a lighter one...
Dan
'91 928GT S/C
475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft