underdrive pulley feedback

[SSDan]

Originally Posted by strych9

I chose not to install a UDP when I did my cam, for three reasons:

1. Increased coolant temps (water pump output lower @ idle)
2. Decreased charging output @ idle
3. Past claims of UDPs causing harmonics issues, resulting in timing chain breakage

Bottom line: the juice wasn't worth the squeeze, although I would like the HP they provide.

Hmmm! Not sure I agree fully with your three points.

For me on the first two points - my accessories are spinning at the same or higher rpm than stock at idle. My idle speed now is 900 with the cam - so 900 X .75 (25% UDP) = 675. When stock my idle was about 600 - 650 rpm. I don't know of anyone idling a cammed car at the stock idle speeds. Which is another reason to do a UDP with a cam swap and not as a stand alone mod for an otherwise stock car. My coolant temps and charging are well within the norms on my gauges. What idle speed are your running?

On your third point I've seen that quoted before but never read any hard evidence to support it - just people saying that. Maybe a cheapo UPD might be out of balance and cause harm but I'm running a proven Power Bond 25% pulley with about 12 K miles of trouble free use so far.

[Bell040]

Originally Posted by SSDan

Hmmm! Not sure I agree fully with your three points.

For me on the first two points - my accessories are spinning at the same or higher rpm than stock at idle. My idle speed now is 900 with the cam - so 900 X .75 (25% UDP) = 675. When stock my idle was about 600 - 650 rpm. I don't know of anyone idling a cammed car at the stock idle speeds. Which is another reason to do a UDP with a cam swap and not as a stand alone mod for an otherwise stock car. My coolant temps and charging are well within the norms on my gauges. What idle speed are your running?

On your third point I've seen that quoted before but never read any hard evidence to support it - just people saying that. Maybe a cheapo UPD might be out of balance and cause harm but I'm running a proven Power Bond 25% pulley with about 12 K miles of trouble free use so far.

good point about the idle. Mine is set at 850 rpm, but should probably be closer to 1000. 850 just sounds so good that it is worth the headaches associated.

Originally Posted by Rohdeo16

My UDP has been working just fine for me. I'm not sure how much HP it was worth because it was done at the same time as my cam, but I honestly can't tell a difference in it being installed now vs before...probably just because of the cam though.

I have no issues driving around a parking lot, starting my car, lights dimming, etc...

What is your idle set at (set by the tune)? What is your MAP (manifold pressure at idle, set by the cams overlap)?

both of these determine how well your car will deal with parking lots (and pushing less power the the accessories)... since every time you push in the clutch the engine is trying to find idle. Finding idle is usually what stalls my car... when the AC is at max, performing a hard turn, and I go in to the clutch from 2-3K rpm.

see "drivability scale" 1 and 2 below...



http://www.gmhightechperformance.com...n/viewall.html

[BowlingSS]

Originally Posted by Jason 98 TA

We typically see 8 rwhp from a pulley install.

Hang tight, we are finishing up a run of TSP's new underdrive pullies & I promise the price will be nice!

Are TSP pulleys 25% ones?

Bill

[strych9]

Interesting. My LSA is 113, but my cam is a little more aggressive. I have no idle hunting or stalling issues. Not even close. Idle is set @ 775.

Originally Posted by Bell040

good point about the idle. Mine is set at 850 rpm, but should probably be closer to 1000. 850 just sounds so good that it is worth the headaches associated.



What is your idle set at (set by the tune)? What is your MAP (manifold pressure at idle, set by the cams overlap)?

both of these determine how well your car will deal with parking lots (and pushing less power the the accessories)... since every time you push in the clutch the engine is trying to find idle. Finding idle is usually what stalls my car... when the AC is at max, performing a hard turn, and I go in to the clutch from 2-3K rpm.

see "drivability scale" 1 and 2 below...



http://www.gmhightechperformance.com...n/viewall.html

[429]

Originally Posted by Bell040

This is with the stock pulley. It's the reason that I don't want a UDP.




Maybe so. But either way, adding a UDP would make it worse.

You are 110% incorrect, the pulley would lower/lessen the stalling, as it would put less of a load on the engine at low rpms. UDPs generally increase idle quality, since there is significantly less accessory load at idle.

[Bell040]

Originally Posted by strych9

Interesting. My LSA is 113, but my cam is a little more aggressive. I have no idle hunting or stalling issues. Not even close. Idle is set @ 775.

duration?