Should I go with underdrive pulleys?

[Sask84gt]

Looking at doing underdrive pulleys on my 84 gt. Is it worth it? I've read just to change the crank and the water pump pulley and not to change alternator pulley because that can cause charging issues. Is that still true if I'm going with the 130 amp conversion? Anything else I should look out for or know before attempting this?
Thanks

[erratic50]

smaller crank pulley cures problems with excessive power steering assist. It causes some others.

On my 86GT my cooling became marginal -- even with an FB169 -- while doing anything but driving down the road in overdrive.

My answer -- underdrive kit plus a small water pump pulley to speed it back up. Its a knock off 93 Cobra pump pulley. Got it from Summit new for $50. It was slowed down slightly vs factory. Its around 1:1 crank vs pump now.

You want the smaller alternator pulley or to convert to 3G because it needs to keep spinning as fast as it ever has.

So basically the only things slowing down are the AC, PS, and smog pump. The fact that my car doesn't blow PS fluid everywhere at 6250 anymore made the switch more than worth it to me.

Granted I could have just put a piece of hose over the fill with a cap higher up...... that's what the old school of driving cars received.

[gmatt]

FWIW, this may or may not be applicable, but I had an '01 F-150, 5.4. I put a set of March under drive pulleys on it. I had no problem with charging(probably because of the 3g alt), but on hot days, AC running, in traffic, it would overheat and even go into 'limp' mode. Removed the pulleys back to stock and the problem disappeared.

I also have under drive pulleys on my Fairmont 5.0. Only the crank and wp, they're steel, I forget the brand(maybe ASP?). I also put a larger diameter power steering pulley on it. It has the 3g upgrade alt. No AC. No charging issues. The hottest I've seen the gauge is 206, stopped at a traffic light(radiator is new, 2 row copper/brass). Electric fan. Temp always drops when moving. This is with a 192 thermostat.

Not all under drive kits have the same diameter pulleys. Do your research.

[Sask84gt]

Thanks for the replies. Some more info in what I'm doing. I'm deleting smog pump and possibly a/c, not 100% on that though. I'm looking at this bbk set. https://www.summitracing.com/parts/bbk-1553/

[gmatt]

Thanks for the replies. Some more info in what I'm doing. I'm deleting smog pump and possibly a/c, not 100% on that though. I'm looking at this bbk set. https://www.summitracing.com/parts/bbk-1553/

Can't make a recommendation, but I checked those out on BBK's website, looking for dimensions(there were none). I also noticed they sell the same pulley set on their website as 'reconditioned' for $30 cheaper. Same part # with an 'r' added to the end. https://www.bbkperformance.com/musta...nditioned.html

[graphicdesigner80]

I don't recommend under drive pulleys to anyone with a street car. Been there, dwelt with the headaches of overheating and undercharging at idle. I took mine off a long time ago and they've sat in a box ever since.

If you're planning on mostly strip duty, go for it. For anything seeing regular street use, no bueno.

Just my 2 cents.

[quickshift]

I run underdrive pulleys with a high flow water pump and 4.10 gears. No problems at all.

[Sask84gt]

Hmmm lol from what I've been reading for every 10 people that dont have problems there are 4 that do lol. Not sure what to do. Car is not a daily driver and will only be used as a fun car to drive around a bit on nice days in the summer.

[quickshift]

Hmmm lol from what I've been reading for every 10 people that dont have problems there are 4 that do lol. Not sure what to do. Car is not a daily driver and will only be used as a fun car to drive around a bit on nice days in the summer.

Just leave it alone and enjoy driving it.

[Sask84gt]

Just leave it alone and enjoy driving it.

Lol I wish i could. Car is currently being restored by a rookie so it will be awhile before I can enjoy it.

[Sask84gt]

If I just want to get a new set of stock pulleys preferably in black what brand would you guys recommend. Nothing to expensive and something I can get from summit. Thanks

[mmb617]

I can't imagine what benefit there could be from underdrive pulleys that would offset the cost and labor involved with installing them. I could see them on a dedicated race car, but a street car? Do you really think you'd notice the tiny HP increase?

[Sask84gt]

I can't imagine what benefit there could be from underdrive pulleys that would offset the cost and labor involved with installing them. I could see them on a dedicated race car, but a street car? Do you really think you'd notice the tiny HP increase?

I dont know, that's why I posted the topic. My pulleys could use replacing so I was inquiring about going with underdrive pulleys. Obviously by everyone's reaction it's not worth it for a street car.

[wraithracing]

In my experience the seat of the pants difference between underdrive pulleys and stock was non existent. Sure, I might have noticed a slight improve at the track with everything being equal, but in just day to day driving, I didn't notice any benefits. All I did notice was the problems and issues mentioned above. Needless to say that was the one and only 5.0 Fox that I ever wasted time installing underdrive pulleys on.

If you just want/need to buy new pulleys then I would recommend March. They make quality parts and Summit Racing should carry most if not all of their parts. Here is a link to their different options that include underdrive pulleys. https://marchperformance.com/ford/fo...e-pulleys.html

[Two86fiveoh's]

I've been running underdrives for years, while the car was near DD status and now just a weekend toy during nice weather. With the stock alternator, the car wouldn't charge until around 1000rpm. Installed a 130amp alternator a couple years back and all charging issues disappeared. Output drops down to 13.5v at an idle with A/C running full tilt, electric fan running and headlights on.

Car has never overheated due to pulleys, even in 100+ temps. A good cooling system is a must.

[richpet]

I ran them and had zero issues what so ever. I am not sure how much power I 'really' gained, but it was cool to say they were there.

[Steve]

I've been running the crank under-drive pulley since the late 80's on my 85 GT. I think it was J. Biddle American that sold them. The engine was still all stock back then and it seemed to make a difference. The car was a little more responsive. At the time, I was looking for anything that would help the car be faster and squeeze out some more power. I would say the best thing to do is try it and see what happens. Maybe you could find some used parts on eBay or something so it doesn't cost too much. Belt length is also an issue. lmr.com is also a great source and they know what belts will fit. Good Luck

[Sask84gt]

Thanks for all the help everyone. I'm just going to stay with stock for now. Need to get the car running first before I start messing with stuff that's could give me more problems.