Clutch slip debates.

WillDuhhBeast · Mar 29, 2007

Okay so me and my brother are having a huge debate over how a clutch slipping affects max HP on a dyno.

My brother's side:

He believes that if the clutch doesn't slip all the way through the gear, the PEAK HP numbers will be the exact same as a car without a slipping clutch. He says that while the clutch is slipping it will show a dip in the power band but as soon as it bites back, it will be right back on the power band, and show the same peak numbers on the dyno.

My side:

I believe it doesn't matter if the clutch slips all the way through, or a little bit, the dyno will show less peak HP. I believe even if the clutch only slips for a grand or two, you will see LESS peak HP compared with the same car without a clutch slipping.

School us.. what's the deal on a dyno?

I don't want to hear about quarter miles, or actually moving the car, or momentum or any of that, just dyno purposes.

Dragstr05 · Mar 29, 2007

I'm gonna have to say your brother.

I have no knowlege to back it up, but look at it this way. If a car makes 400hp at 6,000rpm, and the same car in the same conditions slips the clutch all the way through the power band up to say 5,500 and magically bites, the car will be right back at peak power output with all power going to the rollers. Sure the dyno graph will look like **** but it will be provided the clutch grabs at peak, it should still put down peak.

In the right conditions with everything in working order, if a car dynos 400hp at 6k, its going to put down 400hp at 6k everytime - theoretically with everything in working order.

Tim2002GT · Mar 29, 2007

Dragstr05 said:
I'm gonna have to say your brother.

I have no knowlege to back it up, but look at it this way. If a car makes 400hp at 6,000rpm, and the same car in the same conditions slips the clutch all the way through the power band up to say 5,500 and magically bites, the car will be right back at peak power output with all power going to the rollers. Sure the dyno graph will look like **** but it will be provided the clutch grabs at peak, it should still put down peak.

In the right conditions with everything in working order, if a car dynos 400hp at 6k, its going to put down 400hp at 6k everytime - theoretically with everything in working order.

+1

supergoat · Mar 29, 2007

Yup, your brother is right.

Redfire03GT · Mar 29, 2007

You are both right to some degree. Either of your assumptions could be correct given proper circumstances. If the clutch continues to slip and never fully grabs, then you are right, if it does grab at some point, then your brother is right.

Stan Weiss · Mar 29, 2007

Over in Talk --- My whipple dyno..

Check out what someone had happen

2K1GtfromSC said:
OK first my clutch is stock with 52k miles on it. I'm not sure if the tires spun or the clutch was slipping, listen to the vid.
Number are 565/505 17psi not what I was looking for but I know I need to get the clutch installed. sorry the vid is far way, that's where you have to stand. I'm getting the clutch installed next week & will redyno after the breakin. looking for 600rwhp 550rwtq.

2K1GtfromSC said:
Update:
With a new clutch it put down 609rwhp & 546rwtq

WillDuhhBeast · Mar 29, 2007

I discussed that thread with my brother, and thats where this whole debate came from.

In theory, if my brother is right, and the tires don'tm spin.. say max power is made at 6 grand, couldn't you just be at like 5500, slam it to 6000 and left off for a peak HP reading?

I just don't know about this. Its confusing.

Could it be a fact that the clutch can slip very bad at first, and then SEEM to bite back finally, but really.. it could be slipping the whole time?

Stan Weiss · Mar 29, 2007

First is the clutch slipping because it is bad or because it is made to slip and lock up at some point. A Pro Stock car will slip the clutch as it leaves the starting line and will slowly add pressure until it is fully locked up.

geoffsgt · Mar 30, 2007

Taken literally, your brother is right. If at any point the clutch is locked up tight, the number shown will be the engines full power at that time, minus drive train loss. Its simple physics.

However, unless you have some way to measure the clutch speed and the engine speed, and determine when they are equal and when they are not, there's no way to know if the clutch is still slipping. It could slip real bad at first, get better, but still be spinning the drivetrain a little slower than the engine is spinning, at which point the numbers would be lower than they should be.

Stan Weiss said:
First is the clutch slipping because it is bad or because it is made to slip and lock up at some point.

According to the other thread, the clutch was slipping because it was bad. Was just a Cobra with a Wipple blower and stock (I think?) clutch, no crazy set up.

twogts4us · Mar 30, 2007

You guys are assuming that the slipping clutch will finally bite fully, without any friction loss...I think that's a big assumption.

Dragstr05 · Mar 30, 2007

twogts4us said:
You guys are assuming that the slipping clutch will finally bite fully, without any friction loss...I think that's a big assumption.

It is a big assumption, but this is a theoretical discussion.

Clutch slip debates.

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