Drag Clutch Death Illustrated
04-25-2008, 07:20 PM
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Drag Clutch Death Illustrated Drag racing a manual transmission car can quickly destroy almost any clutch. I have data that shows how drag racing clutches often fail. The attached graphs show an increase of clutch slippage as clutch failure approaches.
To be most effective, a drag racing clutch needs to slip during launch. I always launch above 4000 rpm on ET Streets. Under these conditions a tremendous amount of heat is generated when the clutch slips. Slip causes wear. Eventually wear causes increased slipping. This point begins a downward spiral that leads to clutch failure.
My data was collected using HPTuners Scanner. The graphs show engine speed (rpm) and clutch output speed which is calculated from rear wheel speed. Clutch slip (the difference between clutch output and input speeds) is displayed in red.
The graphs show clutch slip during the launch period of three very similar runs. The first graph was recorded during the 25th pass with this clutch. The second graph is from the 47th pass. The third graph is from the 53rd pass – the last complete pass for this clutch. I have very similar data for a different clutch that survived approximately 60 passes.
To be most effective, a drag racing clutch needs to slip during launch. I always launch above 4000 rpm on ET Streets. Under these conditions a tremendous amount of heat is generated when the clutch slips. Slip causes wear. Eventually wear causes increased slipping. This point begins a downward spiral that leads to clutch failure.
My data was collected using HPTuners Scanner. The graphs show engine speed (rpm) and clutch output speed which is calculated from rear wheel speed. Clutch slip (the difference between clutch output and input speeds) is displayed in red.
The graphs show clutch slip during the launch period of three very similar runs. The first graph was recorded during the 25th pass with this clutch. The second graph is from the 47th pass. The third graph is from the 53rd pass – the last complete pass for this clutch. I have very similar data for a different clutch that survived approximately 60 passes.
Last edited by Gary Z; 04-25-2008 at 09:44 PM.
04-25-2008, 09:35 PM
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One was a Spec 4, the other was a Ram Powergrip HD. Both with the manufacturer's billet steel flywheel. I believe both are excellent clutches and the fact that they had nearly equal (albeit short) lifespans says more about the extreme conditions during launch than it does about how they compare to other clutches.
Last edited by Gary Z; 04-25-2008 at 10:59 PM.
04-25-2008, 09:51 PM
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I am a granny shifter. I shift normally, with full clutch and throttle pedal travel, as quickly as I’m able. I am not nearly as quick as some others. At launch, I lift my left foot and mash with my right. I have attached a graph of a complete run. My total shift time is approximately 0.9 seconds. The green trace is throttle position. I think quicker shifting (sidestepping, powershifting) may extend clutch life at the transmission’s expense.
Last edited by Gary Z; 04-26-2008 at 10:38 AM.
