Underdrive Pulley Questions

[jb92563]

Would you notice much increased effort on the steering wheel required at lower speeds due to the fewer RPMs on the PS pump, say while parking?

I'm considering it as well.

I spend most of my drive time above 2500 rpm and frequently peak it up in the 6k-7k region with spirited driving.

1st gear is a pain but Im starting to get the hang of it and not redlining anymore.

[Topless]

I have seen no difference in coolant temp, A/C, or steering efficiency with the UD pulley. My car now has 102K miles, 70+ track days, and the original 14 yr old PS pump. I inspect it every oil change and no sign of failure yet.

[Homeboy981]

Great information guys! I will put the UD pulley on my "to-do" list!

I too was worried about "street-ability" of the mod. That is the only reason I have not pursued it.

Glad the question was posed to our resident experts. I wanted to ask, @thstone thanks for posing the ???. Happy to glean information where I can about our street-legal racecars!

Is the HP increase throughout the RPM range?

So that 5HP increase will drop our F-150 passing time by about a 1/10 of a sec or so. Yippie!

[shadrach74]

Originally Posted by Homeboy981

Great information guys! I will put the UD pulley on my "to-do" list!

I too was worried about "street-ability" of the mod. That is the only reason I have not pursued it.

Glad the question was posed to our resident experts. I wanted to ask, @thstone thanks for posing the ???. Happy to glean information where I can about our street-legal racecars!

Is the HP increase throughout the RPM range?

So that 5HP increase will drop our F-150 passing time by about a 1/10 of a sec or so. Yippie!

Disclaimer: I don't have an UD pulley...yet

But let's think about this critically. We are not talking about gains in engine horsepower, we are simply removing parasitic drag from the drive line so that more of the existing horsepower is transmitted to the rear wheels. So the gain at the wheels is equal to the drag removed from the engine minus whatever the drive train losses are. The drag being removed in this case is dynamic in nature as opposed to static. This means that the effort (read hp) to turn the pump increases as you turn it faster. So this leads me to believe that the HP gain at the rear wheels follows the same curve as the HP required to turn the pump does, across the rev range.
If this is in-fact the case, then no you would not see 5hp gain across the range. You would see little to no gain at idle with a progressive increase in gain as RPMs increase peaking at Jake's 5HP number at the top of the rev range.

Still, 5HP is 2% in my 02 S and in 2.5% in a base. While not huge, it is likely just enough to make the car feel like it has been awoken a bit. Kind of like when you go for a drive on a crisp 40df fall morning compared to a warm summer morning...the car just feels like it's doing everything a little bit better in the cool air...not a huge difference, just healthier.