Underdrive Pulley Seems To Make a Difference!

[FRM3]

Added an Underdrive Pulley from Modern Performance several days ago. They estimate a 8 to 10 hp gain. While I can't confirm the hp increase the throttle response seems much more spirited and tires break away with downshift from 3rd to second (auto). No evidence at all in alternator or A/C preformance. For $100 bucks seems like a real value.

[Punch]

part numbers?

[FRM3]

Punch

Here's the link. Take a look at the site. Lots of other products as well. Take a look at great looking valve covers too (I've seen them in person).

http://www.modernperformance.com/dcx/mpx2000p.shtml

[Punch]

hmm special belt required, that would be a pain if you ever break one?

[FRM3]

Belts come with the under pulley. Replacements available at any auto parts store. Can't remember the last time I broke a belt.

[3BarBoost]

There isn't 8-10 hp to be found just spinning your alternator, AC and powersteering pump a little slower.

However, the fact that the crank inertia is substantially lower should make it feel like there is.

[Mike Radowski]

So, 3Bar, we all know that a UDP does not make horse power, it frees up what was taken away, So on a Turbo Cruiser, how much will we get back if we add a much lighter, 25% under drive pully? 5 may be 6? More or less? I know that on my 98 Neon R/T when I installed one, it sure felt like a lot, reved quicker and had a much better throttle response and picked up a few tenths in the quarter, as a side note.

Mike

[FRM3]

For what it's worth, here's a link to dyno results of neon with underdrive pulley.

http://www.modernperformance.com/dcx/neundyno.shtml

[3BarBoost]

Honestly, I don't know how much load is on the accessories (AC, alternator and power steering pump) on a PT Turbo. My swag (engineering term: Silly Wild Ass Guess) is normally you see about 8 hp total loss driving the accessories at peak power. So a 25% underdrive pulley might free up 2 or so.

A chassis dyno is going to show more than that, maybe a lot more. Depends on how much power is being sucked up accelerating the production pulley - and the lower the gear, the more power delta. Remember, spinning mass shows up as a square of the delta (assuming the radius of inertia is the same). An underdrive pulley is lighter, and lower radius of inertia. If it weights only 25% as much as stock (1.5 lbs versus 6 lbs) there might be that extra 6 hp at the top end. I could do some math, but not really interested in doing that right now...

[FRM3]

As usual, thanks for your informed input 3Bar. Your number is consistent witht he Dyno run linked above. If, in fact, one gains 6 HP at top end and added responsiveness for $100.