Underdrive pulleys worth it??

frankoman87 · Sep 2, 2005

My 87 has the basic mods at the moment (see signature) but one thing I have neglected to change were the underdrive pulleys. One of the main reasons I haven't done this is because I've heard it puts a bigger strain on your alternator and currently when I drive at night with my headlights on, the battery gauge goes down when I am idling.

If I put these underdrive pulleys on my car, will it strain my battery even more in a similar situation?? Do you get a noticeable power increase with underdrive pulleys?

tjm73 · Sep 2, 2005

frankoman87 said:
My 87 has the basic mods at the moment (see signature) but one thing I have neglected to change were the underdrive pulleys. One of the main reasons I haven't done this is because I've heard it puts a bigger strain on your alternator and currently when I drive at night with my headlights on, the battery gauge goes down when I am idling.

If I put these underdrive pulleys on my car, will it strain my battery even more in a similar situation?? Do you get a noticeable power increase with underdrive pulleys?

2 Things

1.) Underdrive pulleys suck if you get the "race" pulleys. Get the "street" pulleys is you do change them. I have the street pulleys and still plan to take them off due to idle charing issues.

2.) If you have stock pulley's and you're electrical system dims at idle you may have a bad alt or some other compontent that's not running at it's OEM spec.

frankoman87 · Sep 2, 2005

Thanks for the reply tjm73. Is it a pretty severe idle charing issue with these pulleys that you are considering removing them?? Does your car just die sometimes??

Should I get a higher output alternator and if so will this help the problem?? Do the pulleys really make a difference in power?

5.02GO · Sep 2, 2005

Underdrive pulleys work.

I have had an underdrive set on my car for about 9 years now. No problems.

I could feel a difference in performance with underdrives on.

Rerun · Sep 2, 2005

I had under-drive pullies on my LX when I first bought it. I ended up taking them off for charging and cooling issues and putting my stock ones back on. With that being said, you could definately feel a difference in the lower RPMs with them off. If you have cooling or charging issues, the underdrive pullies will amplify them. You should be fine.

tjm73 · Sep 2, 2005

frankoman87 said:
Thanks for the reply tjm73. Is it a pretty severe idle charing issue with these pulleys that you are considering removing them?? Does your car just die sometimes??

Should I get a higher output alternator and if so will this help the problem?? Do the pulleys really make a difference in power?

Not severe at all. Car never dies. Battery has never gone dead. I just don't want them anymore. I've actually been thinking about back fitting most of the stock parts and making the car "restored" and all original again. Crazy as that sounds.

But they DO work. And work well. A higher output alternator would help. But isn't nessacary.

Mustang5L5 · Sep 2, 2005

Yes they work.

WHat i did to counter the effects of the Underdrive pulleys was install an ASP 1 7/8" Overdrive pulley to speed the alt pulley back up to stock speed.

That, along with a 130AMP alt is enough to run all my accessories and lights at idle along with my e-fan and not have any significant draw.

I do not have any cooling probs either. My cooling system is well maintained so i wouldn't expect any. I can see some probs if you cooling system isn't up to snuff.

frankoman87 · Sep 2, 2005

I think I might give them a try. Is there a certain brand that is better? Do some brands have lighter pulleys than others and does that make a difference at all?? How difficult is it to install myself?

jmd2914 · Sep 2, 2005

i could feel a differance when i put mine on, and what i did is i only put the waterpump and crank pullies on, until i get an aftermarket alt. then ill put the alt under drive pully on.....hope this helps

Mustang5L5 · Sep 2, 2005

I like the aluminum pulleys better.

They are lighter than steel so they give a little extra HP

Project89 · Sep 2, 2005

Installed aluminum underdrives on mine, the motor appeared to rev much quicker. Have not had any cooling issues but my amps drop when at idle (red lights etc) and when running w/headlights on. The battery has never died on me or been slugish...but this also may be due to still having the factory radio installed and also no elect. fan as others may have.

red92gt · Sep 2, 2005

frankoman87 said:
My 87 has the basic mods at the moment (see signature) but one thing I have neglected to change were the underdrive pulleys. One of the main reasons I haven't done this is because I've heard it puts a bigger strain on your alternator and currently when I drive at night with my headlights on, the battery gauge goes down when I am idling.

If I put these underdrive pulleys on my car, will it strain my battery even more in a similar situation?? Do you get a noticeable power increase with underdrive pulleys?

yes and no if u are worried about the altenator dont use the pulley, underdrives do give more horsepower so use the crank pulley

93tealstang · Sep 2, 2005

I agree, just run the underdrive crank pulley and no problems will be amplified.

mob · Sep 2, 2005

so just the crank pulley does the job?

Whats the difference between the "race" and "street" pullies? tjm are you gonna sell your pullies?

04sleeper · Sep 2, 2005

mob said:
so just the crank pulley does the job?

Whats the difference between the "race" and "street" pullies? tjm are you gonna sell your pullies?

Yes, the crank spins all the acessories. Decrease the crank pulley size, slow down the belt speed. (Underdrive) Increase the crank pulley size, speed up the belt speed. (Overdrive)

It is just the opposite for all the other pulleys. Increase the size of them to slow them down more, decrease the size of them to speed them up.

The "Race" pulley is usually termed a "3 inch" pulley and reduced the belt speed by approx. 52%.

The "Street" pulley is usually termed a "4 inch" pulley and reduces the belt speed by approx. 25%.

The best setup for the street that I have used is the "4 inch street" pulley and the "1 7/8 inch alternator" pulley along with the stock pulleys for everything else.

Then for the track I would switch out the "4 inch" for the "3 inch".

Worked fine for me.

93tealstang · Sep 3, 2005

89 Sleeper:

What belt size is needed when you run a 4 inch crank and 1 7/8 inch alternator pulley with all other pulley's stock along with smog?

04sleeper · Sep 3, 2005

93tealstang said:
89 Sleeper:

What belt size is needed when you run a 4 inch crank and 1 7/8 inch alternator pulley with all other pulley's stock along with smog?

I'm not too sure on that one. I always ran no smog and the belt length was 81.5 inches.
The best way to measure it is with a peice of string or wire routed around the pulleys in the same groove. Take that measurement with you to the auto parts store and tell them you need that size belt.

Example: 81.5 inch belt would be part # K6815 or 815K6. (K=number of ribs on the belt)

Good Luck.

LT1Killa · Sep 3, 2005

I have the 3 inch crank pully "race" setup and I have no cooling or charging issues. I have an aluminum radiator and I believe an upgraded alternator, but I don't know for sure.

The small pullies have never given me any trouble.

Daniel50 · Sep 3, 2005

simply a must. great gain for around 100 bucks and an hour of simple install

aaros · Sep 3, 2005

i bought a set of alum. underdrives on ebay and have had no problems with them other than a charging ish. that i plan to fix with a 130 amp.

Underdrive pulleys worth it??

frankoman87

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tjm73

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