Re: Launch problems
[Re: 68LAR]
#2113152
07/19/16 11:44 AM
07/19/16 11:44 AM
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Joined: Apr 2006
Posts: 729 Lebanon,IN
mr2performance
super stock
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super stock
Joined: Apr 2006
Posts: 729
Lebanon,IN
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"Launched hard, but due to the aluminum flywheel issues, the clutch would slip in high gear. Hell, I'm using the same clutch assembly from last year with the steel wheel and it grabs hard."
You just answered your question. I guarantee you if the clutch was slipping down track, it was also slipping on the starting line enough to let it leave without destroying the tires. I'd buy an adjustable cover (Ram/Mcleod) and throw the centerforce away. Mike
MR2PERFORMANCE RACE CARS
765 483 9371
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Re: Launch problems
[Re: dvw]
#2113866
07/20/16 10:33 AM
07/20/16 10:33 AM
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Joined: Jan 2003
Posts: 10,011 Frostbitefalls MN (Rocky&Bullw...
gregsdart
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 10,011
Frostbitefalls MN (Rocky&Bullw...
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Remember, I said that I started with the shocks on the highest setting (9). Went lighter thinking that it would hit the tires harder. Usually I run the shocks on the highest setting (9). From what I've read so far, it seems that a new set of slicks maybe the ticket. I'm going to hate pitching these slicks, even though they look good to me. What about,...I also run tubes in the slicks. Maybe dropping the tire pressure way down (for me), to about 9 or 10 psi? Do you all think maybe this might work? Sounds like it's time to step up to a shock with stiffer rebound valving. You were full tight and now you're hitting the tire even harder. A good slow motion close-up at launch will lead you to what is needed. Doug Same thoughts here. New tires, better shocks. Once you make it work, I would think the 60 ft will be better than ever with the heavier flywheel.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: Launch problems
[Re: gregsdart]
#2114051
07/20/16 02:15 PM
07/20/16 02:15 PM
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Joined: Oct 2014
Posts: 104 Washington
weedburner
member
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member
Joined: Oct 2014
Posts: 104
Washington
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Once you make it work, I would think the 60 ft will be better than ever with the heavier flywheel. If the clutch slips in a way that there is no gain or loss of rpm during launch, flywheel weight won't affect the launch at all. Where flywheel weight will make a difference is when you are balancing stored inertia against the clutch's torque capacity. Here's a simplified explanation- generally the clutch's torque capacity is higher than the torque that the engine makes. Let's assume the engine makes 500ft/lbs and the clutch's capacity is 700ft/lbs. When you launch the car, the clutch is going to draw 700ft/lbs…the 500ft/lbs that the engine is making plus another 200ft/lbs of stored inertia energy that will cause the rotating assy to lose rpm. This is where the balancing act comes in- after engine rpm is drawn down to the point that engine rpm sync's up with vehicle speed, rpm ceases to drop and that transfer of an additional 200ft/lbs of inertia energy stops. If you raise rpm or add a heavier flywheel, more energy is stored in the rotating assy which extends the amount of time that the clutch will be forced to slip. When you extend the time that the clutch slips, you are delaying the clutch's lockup to a point farther down the track where the car is traveling faster, which means less "bog" at the point when speed and rpm sync up. In the end, installing a heavier flywheel or raising staging rpm are just ways of forcing the clutch to slip longer, minimizing the bog. The downside is that after you have lost the rpm and used that inertia energy to force the clutch to slip longer, that spent energy then has to be paid back in full before the engine can recover the rpm that it lost. That inertia energy transfer which made the car launch harder initially now slows the car, as it reverses and some of the engine's power must be used to recharge spent inertia energy back into the rotating assy. This is why temporarily holding back some clutch clamp pressure at the throwout bearing to prevent rpm loss, is a better way to launch. The initial hit of the clutch is softer as you are not borrowing inertia energy from the rotating assy, but then again you won't have to pay that borrowed energy back either. The softer launch is easier on parts, easier to make the tires stick, and actually quicker as you can now easily extend the clutch lockup point far enough down the track that you won't lose any launch rpm at all. Remember- the car actually gains speed at a faster rate during that period of time before the clutch locks up. After the clutch locks up and the rotating assy is gaining rpm, some engine power is siphoned off and stored in the rotating assy, which means the overall acceleration rate will be slower after the clutch locks up because the rotating assy is being accelerated as well. If you want proof and collect rpm data, all you have to do is lay a straight edge along your rpm graph from the point that the clutch locks up in 1st gear until the shift point. The angle of that straight edge represents the average rate that the car gained speed after the clutch is locked up in 1st gear. Then lay a straight edge from the "0" beginning point to that same point where the clutch locked up...the angle (rate of acceleration) before the clutch locked up will be steeper. To a point the longer you delay clutch lockup, the longer you can ride that steeper rate of acceleration. My ClutchTamer is just a simple way to temporarily hold back some clutch clamp pressure at the throwout bearing, but you can do it with your foot if you put in enough practice.
Last edited by weedburner; 07/20/16 06:47 PM.
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Re: Launch problems
[Re: gregsdart]
#2114782
07/21/16 01:45 PM
07/21/16 01:45 PM
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Joined: Oct 2003
Posts: 4,013 South Park, Pa.
68LAR
OP
master
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OP
master
Joined: Oct 2003
Posts: 4,013
South Park, Pa.
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Moving on.... I've got my new slicks mounted and balanced. Went with the 29 10.5 x 15 stiff wall MT's.
Last edited by 68LAR; 07/21/16 03:40 PM.
4 speed street legal. Best time 10.99 @ 124 mph on 93 octane pump gas @ 3926# total weight
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Re: Launch problems
[Re: FastmOp]
#2114890
07/21/16 03:52 PM
07/21/16 03:52 PM
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Joined: Oct 2003
Posts: 2,403 WASHINGTON, PA
11secaarcuda
top fuel
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top fuel
Joined: Oct 2003
Posts: 2,403
WASHINGTON, PA
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Larry, will you be at the Mopar Nats?
67 Dart GT 340 4 speed 70 AAR Cuda 408 6 barrel 96 Indy Ram original owner 2011 Hemi Durango
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Re: Launch problems
[Re: 11secaarcuda]
#2114996
07/21/16 06:16 PM
07/21/16 06:16 PM
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Joined: Oct 2003
Posts: 4,013 South Park, Pa.
68LAR
OP
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OP
master
Joined: Oct 2003
Posts: 4,013
South Park, Pa.
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Larry, will you be at the Mopar Nats? Probably on Saturday only, but not racing...
4 speed street legal. Best time 10.99 @ 124 mph on 93 octane pump gas @ 3926# total weight
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Re: Launch problems
[Re: FastmOp]
#2114997
07/21/16 06:17 PM
07/21/16 06:17 PM
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Joined: Oct 2003
Posts: 4,013 South Park, Pa.
68LAR
OP
master
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OP
master
Joined: Oct 2003
Posts: 4,013
South Park, Pa.
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Pulling them up 1-3" is normal, even with some tire spin. Here's hoping that we're back to those type of launches...
4 speed street legal. Best time 10.99 @ 124 mph on 93 octane pump gas @ 3926# total weight
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Re: Launch problems
[Re: 68LAR]
#2116373
07/23/16 10:47 PM
07/23/16 10:47 PM
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Joined: Oct 2003
Posts: 2,403 WASHINGTON, PA
11secaarcuda
top fuel
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top fuel
Joined: Oct 2003
Posts: 2,403
WASHINGTON, PA
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Larry, will you be at the Mopar Nats? Probably on Saturday only, but not racing... Hopefully I will see you. I'll be there Saturday and Sunday with my Cuda.
67 Dart GT 340 4 speed 70 AAR Cuda 408 6 barrel 96 Indy Ram original owner 2011 Hemi Durango
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