Hub Dyno and clutches

Hey Guys I have a bit of a problem with my clutch on the Dyno. I’m not a tuner (as yet) and a bit of a newbee. The issue is that my clutch seems to be slipping at around 420hp.

At this point we are only running around 20psi of boost, the engine has been built to easily handle lots of boost (around 30psi) but see little point pouring in more boost when the clutch is slipping already.

My question is, the clutch only seems to slip on the Dyno and not when racing. The issue is we cannot tune for higher boost because of this issue. Other than the obvious (fit a better clutch) is there a way around this issue?

Funny thing is I have another friend with a LS and he has the same issue where on the Dyno the clutch is slipping but never on the track.

your thoughts?

Improve the clutch clamping force. It's easy to say "we've never had a problem on the track", but I bet if you really analyzed the data, you would find the issue was actually happening (or you were avoiding it by spinning the tires).

Clutch capability is related to torque not horsepower. So what is the torque rating of the clutch, and what was the measured torque on the dyno?

Some ECUs (particularly OEM) have torque limit controls built in to avoid issues with clutches and transmissions. If you don't want to upgrade your clutch to support the torque you are generating, then you need to reduce the torque the engine produces (most likely with the timing and/or boost levels).

Unless you have pretty decent resolution on the output shaft speed it might be hard to catch it in logs on track, unless you are talking massive flairs. It is possible however that the additional elasticity of the tyres is allowing the peak impulse to pass where the hubs provide more resistance. The averaged torque handling capacity of a clutch doesn't mean the point of slip initiation won't be significantly different depending on cyclinder/chamber count, flywheel inertia and driveline elasticity.

I usually create a math channel with RPM / rear wheelspeed, or create an XY Plot with RPM vs Rear wheelspeed. Comparing these plots to others where you know there is no slip makes clutch slip jump right out using eyeball scanning.