Underdrive pulley - what are pros / cons?

**Glenn_03Cobra** · 06-08-09, 10:34 PM

I've heard good and bad things for an underdrive for a NA motor. Anyone here have any experience with one of these? What are pros and cons??

**SVTRonDogg** · 06-09-09, 12:17 PM

They make more power by slowing down the Accessories, usually the Waterpump and Alternator. Not the things I want being less productive.

I ran a set on the 98GT for awhile, then ran into issues with the factory tensioner. I took them off once I went to the Procharger. I wouldn't do it again, not much HP is gained and other issues may arise.

**Glenn_03Cobra** · 06-09-09, 12:27 PM

Since the 5th Gen motors have a more aggresive pulley delivery, I hear that it's not much of an issue. However, I have read just what you mentioned as well. Also, I find it interesting that Ford Racing offeres UDPs. Makes me wonder if they approve of using one or just sell it 'cause people want them?? A couple of guys on the Net said that replacing the water pump with an electric pump was a better option. An interesting note mentioned was that the e-pump could be left on between runs at the track... what'cha think about that Julie? :mrgreen:

**SVTRonDogg** · 06-09-09, 12:40 PM

Electric Pumps have a larger chance of failure than the mechanical ones. Not always the best choice for a street car.

I'm not sayin, I'm just sayin

**blind** · 06-09-09, 01:34 PM

I'd run an electric water pump long before I would ever run UDP's on a mod motor, the balancer is integrated into the crank pulley stock, why mess with that?

**Glenn_03Cobra** · 06-09-09, 02:08 PM

I've read that some UDPs have a better balancer than stock yet, I've also read that some UDPs are not constructed well and can cause serious problems.

What bugs me is that the industry creates mods like UDPs but, there never seems to be absolute clarity regarding the pros and cons. Some mods are clear - ie. Installing a blower on a stock motor can increase HP but, will be risky to the motor's survivability. But, with UDPs, it seems that experienced opinions are the driving force behind purchase decisions. I would like to find a difinitive read that states tested facts... anyone have a link or two?

**blind** · 06-10-09, 06:21 PM

If you search on corral.net forums, there's plenty of posts of mod motor owners that have destroyed their engines because of UDP's, the balancers are critical, and the crankshaft can break if not dampened correctly, it mostly seems to happen to n/a motors with ported heads/short runner intakes that are revving them high and drag racing. Not worth the risk IMO.

**Glenn_03Cobra** · 06-10-09, 07:21 PM

There are a lot of people that abuse their engines with cheap parts. I'll do a search on corral.

**Glenn_03Cobra** · 07-12-09, 12:36 AM

I was talking to Alan at Barber Driving Experience, who said they install Under Drive pulleys on all of their BDX cars. But, he cautioned that some do not have the balance needed to protect the engine. The research continues.

**Glenn_03Cobra** · 07-24-09, 12:50 AM

UPDATE:

So... we went with Summit Racing's 25% underdrive pulley kit. The install was done by Granatelli Motor Sports under the direction of Ray McClelland (ShelbyXX). Before/after dyno with the stock tune increased 9 RWHP. We're monitoring the temp and alternator to verify that no issues come up but, since the S197 alternator has a higher output than earlier models, there shouldn't be a problem.

These guys did an exceptional job. They were focused on doing the right thing and discussed the details along the way.

Nice work guys!