Alcatraz23

Can anybody tell me what these are for and if they should be added to the car or are they stock? Found a package that came with them and a cold air intake and tuner.

SteedaGus

Underdrive pulleys are resized pulleys that reduce accessory load and when designed properly, rotating mass as well. These reductions increase both performance and gas mileage.

Norm Peterson

Underdrive pulleys are just another automotive compromise, so there might be a couple of downsides depending on where you live and how your car is equipped.

You should consider your location (ambient temperatures with respect to engine coolant cooling) and whether you have in-car equipment with much larger than OE electrical demand before purchasing. The improved vehicle performance (including fuel efficiency) comes at some cost in the ability to run the auxiliaries efficiently, particularly at low rpm's. Note that this also includes low rpm A/C performance, so your own personal comfort is potentially affected. Read any warnings carefully, especially if you live in a warmer region or have a huge sound system.

I'm not trying to discourage you. Just inform you that there's more to this than "everything gets better", because engineering compromises don't work that way (and that's what a UDP mod is really all about). Give up a little of something in order to get a little more of something else. AKA, no free lunch.


Norm

SteedaGus

Good points, although on newer cars things such as low rpm a/c performance and cooling system performance are really no issues. A/C may be an issue if you are in the Arizona or California desert in the middle of summer or an area with similar summer heat, but otherwise you will have nothing to worry about. Here in Florida we have never seen issues with the heat even in road course endurance testing.

Electrical will be fine as long as you have a stock electrical system with all O.E. components. Aftermarket stereo's with external amplifiers should consider not doing pullies though. Only older cars with cooling and electrical systems that are not working like they were new could possibly have issues. I have owned 4 Mustangs all with underdrive pulleys. The only one that gave me issues was my fox body due to the puny alternator. An upgraded alternator and wiring solved those issues.

Skizzors

Can anyone elaborate a bit more on what underdrive pulleys do as far as the pros? The cons have been covered but I need a little more of an explanation for the benefits. Typical HP gain/gas mileage gain? I've got an 08 GT with CAI/tune and exhaust. Everything else stock.

R-code17815

Advertised gains 11-15 hp depending on vehicle

Real gains 5-8 hp depending on vehicle

Electric water pumps actually deliver more hp.

Murphdog

I don't have one yet, but from what I know. The UDP's are designed to be bigger than stock. This will allow the engine to run slower which = less rpm's and therefore gives better gas mileage.

I've heard of gains anywhere from 5-12 horsepower.

Ken04

the engine doesn't spin slower, the engine runs the same speed.

underdrive means the pulleys spin LESS than the OEM pulleys. So your power steering pump, alternator, a/c, water pump and everything that's run from your engine run SLOWER. Running those accessories slower takes less horsepower, freeing it up for your use. You don't actually make more horsepower from the engine, you just get to keep a little more of it to drive the wheels. Remember that your alt won't spin as fast to recharge the battery, your a/c may not be as cold in traffic, the car may run hotter on 102 degree days because the water pump doesn't spin as fast, etc. But for most cases, they're fine.

v606er

from experience, udps do increase mpg(for me about 2-3 mpg) and performance(i dont know if it is psycological, but i definatly felt it).

at an idel, it does affect lights and heating/ ac. when you step on the gas you notice lights get brighter and the air flow of the heater/ac increases.

steeda udp are the way to go

Ken04

they will defintely free up horsepower, and you can feel it. They can also increase mpg since more horsepower is going to drive the wheels so the car is more efficient. There can be a small trade off at idle. But hey, nothing is free.