Underdrive pully and engine stress
Thread Starter
On The Tree
Joined: Jan 2002
Posts: 148
Likes: 0
From: Dallas area
Underdrive pully and engine stress I'm running a boosted car here so stress on the engine is a primary concern for me. My motor is completely stock, save the injectors, valvesprings, and the twins 
I have been told by several people that the real measure of concern is the cylinder pressure. IE if I make 500 horsepower with 6 lbs of boost, reduced timing and an otherwise stock motor; vs making 500 horse by running 4 lbs of boost on a heads/cam motor, the cylinder pressure is the same and therefore the potential risk is the same.
Now my question is this. Since an underdrive pulley increases RWHP and RWTQ by decreasing the parasitic loss created by engine accessories, is it therefore true that whatever power gains I got from installing one would NOT be a result of increased pressure in the cylinders? But rather, the gains would be created by freeing up power that's already being made, but is being directed somewhere other than the wheels?
If so, this is definitely a mod for me. I want to be safe with this setup as I'm not made of money TIA for any input.
I have been told by several people that the real measure of concern is the cylinder pressure. IE if I make 500 horsepower with 6 lbs of boost, reduced timing and an otherwise stock motor; vs making 500 horse by running 4 lbs of boost on a heads/cam motor, the cylinder pressure is the same and therefore the potential risk is the same.Now my question is this. Since an underdrive pulley increases RWHP and RWTQ by decreasing the parasitic loss created by engine accessories, is it therefore true that whatever power gains I got from installing one would NOT be a result of increased pressure in the cylinders? But rather, the gains would be created by freeing up power that's already being made, but is being directed somewhere other than the wheels?
If so, this is definitely a mod for me. I want to be safe with this setup as I'm not made of money
TIA for any input. 
Re: Underdrive pully and engine stress You are correct, the pulley increases HP through less rotateing weight and slowing down the water pump, alternator and the P/S pump. No additional cylinder pressure.
As for a good mod, I liked it but I am pretty much stock. You might not even notice it. With all your power, you might want to look into a "real" damper. Might even have to, depending on where you run.
As for a good mod, I liked it but I am pretty much stock. You might not even notice it. With all your power, you might want to look into a "real" damper. Might even have to, depending on where you run.
TECH Fanatic
Joined: Nov 2001
Posts: 1,695
Likes: 9
From: Raleigh, NC
Re: Underdrive pully and engine stress Yep, what he said. The only stress a pulley would put on an engine would be if it was not balanced correctly (And added stress on accessories). If the crank pulley is not balanced it can cause some serious stress on the crankshaft and bearings.
