Why Do yoU get belt slippage¿?¿?
- Thread starter R6 MiG
- Start date
The blower requires a certain amount of torque to turn. By going to a smaller pulley (hence running the blower faster) it requires more torque than stock.
A belt operates on friction. The shear of the belt pulley interface is proportional to the surface area of the belt (hence why Ford did away with V-belts and went to serpentine belts with many V's in them)
So the belt slips because
1)A smaller pulley has less surface area.
2)A smaller pulley spins the blower faster hence requiring more torque to turn at any given engine RPM.
3)A smaller pulley gives the belt less leverage on the pulley due to the decrease in radius.
So the shear of the belt/pulley interface doesn't go up linearly with dropping the upper pulley size, it is in fact exponential (because 1-3 stack up for the worse)
This is why a small pulley diameter change can make a big difference in whether it slips or doesn't....because the shear goes up exponentially with pulley diameter.
A belt operates on friction. The shear of the belt pulley interface is proportional to the surface area of the belt (hence why Ford did away with V-belts and went to serpentine belts with many V's in them)
So the belt slips because
1)A smaller pulley has less surface area.
2)A smaller pulley spins the blower faster hence requiring more torque to turn at any given engine RPM.
3)A smaller pulley gives the belt less leverage on the pulley due to the decrease in radius.
So the shear of the belt/pulley interface doesn't go up linearly with dropping the upper pulley size, it is in fact exponential (because 1-3 stack up for the worse)
This is why a small pulley diameter change can make a big difference in whether it slips or doesn't....because the shear goes up exponentially with pulley diameter.
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Yes, theres a limit to how much tension you can put on the belt before it causes excessive wear to other components.
Thats why lower pulley exchange is better since lower pulley gets bigger with more boost.
Personally, I have yet to see any belt slip, even with the stock belt and the 2.93 pulley. Just my 2 cents.
And you know that how?
JT
Because it will chew up the belt if there is any slip, and so far, with about 1800 miles of driving since the pulley change, the belt still looks brand new, and there are no rubber specs on the guard or engine compartment
I am sure mine slips, none of the signs you mentioned are there on mine either. Belt looks fine.
What does your boost gauge say, and does it stay constant?
JT
What does your boost gauge say, and does it stay constant?
JT
I don't have an aftermarket boost guage yet, but I don't think the boost drop is from belt slippage, in any case. Check this thread for my theory:
http://www.superstallions.com/forum/viewtopic.php?t=1162
Terry from South Florida Pulley HQ convinced me to invest in a smaller 74.0" belt, cuz I bought a 74.5" belt and am experiencing some slippage with my 2.80" pulley.
So, I'll know by this weekend if the new shorter belt makes a difference. If so, how long will it last before it starts to slip? ... hopefully a very, very long time.
I've recently put in a *real* boost gauge with more than two #s that clearly indicated my slippage ... 15 boost then drops to 10
So, I'll know by this weekend if the new shorter belt makes a difference. If so, how long will it last before it starts to slip? ... hopefully a very, very long time.
I've recently put in a *real* boost gauge with more than two #s that clearly indicated my slippage ... 15 boost then drops to 10
coleman: I put the 740 belt on my 2.93 pulley and it didn't change a thing! boost still drops.(12.5-10) I may still have belt slippage but i think the boost dropping can somewhat be alleviated by freeing up the intake track, ie bigger t/b & spacer, and bigger air filter. I do not know this for a fact, but jim v's car has a 310 pulley and the intake stuff and his boost doesn't drop so???. good luck and if you figure it out for sure please share
Leon
Leon
I would think that getting a larger lower pulley and putting on underdrives on the accessories would be a good solution.
Shall I show you mine?? I currently have a belt on order, wrong one has come in 3X's. You're right about it getting chewed up though. The leading edge of my belt is rough and I has a run. Nothing wrong with my pullys though but when the belt slips it's pretty stinky. The belt isn't going to break in half anytime soon but still it need to be replaced .
I originally had the same theory as you. I played around with the intake to the blower on a dyno. I tryed some less restrictive stuff on there, boost drop stayed the same.
I found a power consumption curve for the Eaton. It only had 5 and 10 psi levels, and it only went to 12000 RPM. Anyway I did my best to add 1 14 psi line and extrapolate it to the 16000 rpm the blower goes to at redine with a 2.93 pulley. Looks like the power consumption is between 150 and 175 HP. Using that to calculate the torque, the blower is requiring 590 inch lbs at 16000 rpm and 150 hp. the 2.93 has a moment arm of 1.485 inches. That means the belt has to supply 397 lbs force at the edge of the pulley to make it turn.
Now I looked on line to find a resource to see how much power can be transmitted with that 8 rib belt with no luck. My gut feel is that the belt will slip on the pulley before you get to 397 lbs at the edge.
I thought about testing it by putting a torque wrench on the blower pulley nut with the car off and in gear with the brake on (so the engine), and hence the belt can't turn. Then appling force to see at what ft lbs the pulley turns without the belt. But I decided that bolt looks a little small for 590 inch lbs (49.16 ft lbs) and I'd hate to break the head of that bolt off.
JT
That won't quite be an accurate test. You also have to consider that its not static and the belt is moving with the fact that as the belt goes around that tight turn at whatever speed it will be thrown outwards away from the pulley.
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