the only reason i could see for you to get underdrive pulleys is if you're running a hot cam/ported heads combo and turning real high rpm, then the underdrive pulleys would help out, mainly by slowing down the water pump speed (to prevent cavitation) and slowing down the alternator (not sure about the alternators on the Mustangs, but on the older Chevy engines i've built before, if you didn't put a reduction pulley on the crank or alternator when turning high rpm, the alternator would crap out on you).

if you're going to spend the time and money, it would be better spent on the exhaust. instead of getting u/d pulleys, wait until your water pump needs replacing and replace it with an electric one (a Meziere unit costs about $325-$350). that would probably free up more power than u/d pulleys.

 

Man, I kinda disagree with everyone. When I swapped h-pipes for a high flowing one I noticed 0 gains. I could tell the difference with the Steeda pulleys.

 

I would do Steeda UDP's again on a non-FI Mustang. With that said however, if you haven't done exhaust yet I would do a midpipe and catbackfirst.

I gained almost 3 mpg with Steeda UDP's on my 2000. The UDP's made it rev faster but it also had less engine braking on downshifts. I don't think it added a lot of power but it does increase the efficiency of the motor which is good for performance and longevity on any motor.

Let's face it, any mod other than FI for our modular motors is strictly cosmetic (sound, appearance, feel) anyway.

 

My buddy has a 2000 GT and we have raced ours before and after he did the UDP, the only gain that we noticed is the mid-RPM range, zero gain on lowend and zero gain at high RPM, prob not worth the money in my opinion.

 

youll feel a tad bit of difference with either mod, most of its mental though. only diff is with the catless midpipe you hear it always. im going with the steeda udp's in my 97 cobra. i still have to install the jlt cai also.

heres where i noticed the difference, when i had my 88 gt 5.0, it was an aod, at 20 mph & 45 mph when i stomped it, it just picked up, and when i installed the udp's on it, at 20 & 45 i started chirping the gears. so it is a difference but 9/10 you wont notice it.

 

get the mid pipe....bigger bang for the buck

 

Hey man I agree with the guys who say get the udp but I would only get the Steeda pulleys, after I installed them I noticed that the crank damper absorbed more vibration than that crappy stock one. Plus your alternater and water pump last longer. it was a smart investment for me. But only the Steeda Pulleys and go aluminum.