Hi all, first time Ive posted here, although been a regular to the site for quite some time. I own a 91' Mustang GT mainly stock except for a few mods:
2.5 Catless flowmaster exhaust
BBK Fender Cold air
BBK Underdrive pullies.

Since ive installed these pullies, my car has ran a heck of a lot hotter, my battery is drained (im going to install a hi output alternator soon), and my car has actually ran slower in the 1/8 mile (no 1/4 mile track here), from a 10.0 to a 10.4. I did manage to throw in some Eibach sportline springs, but overall, my car is so much slower since ive installed the pullies. Any suggestions, besides selling them? Ive heard changing the thermostat might help. Thanks

 

Underdrive pulleys are the biggest joke in the world, you gain what 3-5 hp out of them only to put up with dimming headlights and a hotter motor! CHUCK them NOW! Not worth the headaches in my opinion!

 

The Mach 1 comes stock with underdrive pullys and I have never had a problem. The car might have somthing else causing this problem.

 

I really doubt that is the case, considering the very day i changed the stock pullies with the aluminum ones, the car heated up the first time i drove it since the change. Im just going to fix the problem by swapping back to the original pullies and sell the BBK ones. It made my car slower, and its taking a toll on my alternator. Any one want them for $90?

 

I dunno, pulleys and a gear are the two best bang for the buck mods out there. When I installed my SVO pulleys I could feel a difference in the car.

The classic simple mods for a bone stock 5.0

A. Remove the silencer
B. Install gears
C. Install pullies
D. off-road pipe and mufflers
E. Bump the timing

D does the least for the car and is more of a ego thing rather than a performance thing.

I'm out on the thermostat thing, a 180 degree thermostat might help a bit by keeping the colder longer, believe it or not an engine makes the best power at around 220 degrees of water temp.

Is your cooling system up to snuff??? If the cooling and charging system are worn out then pulleys will become a liability fer sure.

 

No...my cooling system was absolutely fine before i installed the pulleys...and i even changed the fluid a few months after. Im going to solve the problem by just selling the darn things, any buyers?!! I dont think the timing has been bumped...how can i bump it a few degrees?

 

Underdrive pullies are not a "joke" they do work BUT...here is the problem. Most companies out there offer the pullies as a driveway bolt-on because many people lack the knowledge or ability to measure for a new smaller belt so they adjust the water pump and alternator sizes larger so that you can use the stock length belt. The fix for this is to keep the crank pulley, get a '93 Cobra water pump pulley and a smaller diameter alternator pulley....I have used this combo for YEARS with great results and no problems charging or cooling. But doing this will require you to measure and get a smaller belt for the car. You can take an old belt and cut it and raise the tensioner and clamp the belt together with vice grips so you can take it to the parts store and measure it.

I highly recommend upgrading to a 3G alternator and make sure your radiator is not clogged with corrosion anyway.

 

Keep underdrives.With underdrives must keep rpm up for alternator. Use smaller alternator pulley as stated above. Check to ensure no bubble locked under thermostat. I would drill 1/8th in hole in thermostat or buy on with the hole predrilled.This will ensure no air blocks in cooling system.These two easy changes should fix the situation on hand.

Rus

 

Thanks RUS....im going to look into it, maybe its a quick fix after all!

 

Russ is pretty nollegable at that stuff. I would of never thought of that. Good Job!

 

Dont robert shaw t-stats come with the hole already drilled in the t-stat?

It makes no difference I suppose, but I could have sworn that they did

 

I am going to try what SVO paul said, but I have had the same problems with my Underdrive pullies. AND... I left the original alternator pulley on and installed a 3G alternator (to help charging) an electric fan (to help cooling) and a shorter belt and STILL had problems! I took mine off altogether.

 

My lights dim at night at idle with the underdrive pullys but the car runs as cool as ever. Of course, it does have a fairly new rad in it.

 

Yeah, i hear all of those nightmare stories...get a new radiator, hi-perf alternator, this and that...and for what, 10-15 horses? It would be nice to get those things, but hey, im in college and have better things to spend money on. I'm gonna tinker with it a bit, but if it comes down to sinking more money into making these things work properly, then forget it, im going back stock.