Underdrive Pulley Question

[TOOQIKK]

i have one on my sentra and have them on several vehicles and only time i had to replace alternators was due to fautly rebuilds from autozone...after the 5th or 6th one got one that was rebuilt right...lol....I beleive they help gas mileage on the top end(ie highway driving)....Motor definitely revs faster/easier...


i say get it and enjoy it! couple one with removing the a/c belt and you will see the difference in your mpg!

and post pics of your underdrive pulley! who makes it? I have an Unorthdox Racing Under Drive Pulley....also have under drive pulleys from G-SPEC performance(greg is the man!) for my turbo 2.0 GTI-R Motor(not eco driving friendly...LOL)

[California98Civic]

Originally Posted by HannahWCU

Yes, I realize from my research that there should be almost no savings from the Alternator, but I have got to think that there will be some savings from the Power Steering. At highway speeds (which is 95%+ of my daily commute) the power steering isn't doing much work at all. But there are still parasitic losses that will be reduced from under driving. To what extent no one seems to know.

I haven't seen any ABA tests for underdrive pulleys, nor have I seen anyone on this forum who has tried one. So it looks like savings estimates are just an educated guess. If there ends up being no savings, then I am out about $120.

Well have fun finding out. If you turn out correct at the rate you are guessing I suppose the part will pay for itself in a few years, no? Just guessing. Is the UDP lighter than the stock? Weigh it before it's installed, and ask for the removed stock part so you can weigh it and compare. Good luck.

[d0sitmatr]

I think a lot of it would depend on the stock weight/size of the UDP. if you go with a much lighter, but same diameter UPD, then I can see a definite gain. I think it also depends a lot on the engine itself.
a lightweight UPD in my Ranger would have shown about a 1% gain in FE as established by several people on the ranger forums Im a member of, and it was a planned MOD if I hadnt traded it off. but then again, my Ranger had the 3.0L engine, which is known in the ranger world as the 3.0slow engine. it had crappy torque, nil HP, but was arguably one of the better engine's Ford made in reliability.
so if your car seems to be slightly underpowered, then I think you would see some immediate benefits from this mod.
I also plan on an aftermarket UPD for my MP5 down the road.

[California98Civic]

Originally Posted by d0sitmatr

I also plan on an aftermarket UPD for my MP5 down the road.

Even though 1% is a marginal gain, it is intriguing and thanks for adding your thoughts. Question: how would I research UDPs for my 98 Civic? The racing sites would all be giving me the opposite of what I need. There must be measurement specs for my stock pulley. Could I use them to search for just any like-sized, mountable and lighter pulley? I imagine I could. Do you know good sites or suppliers where I might start? I'm still looking... EDIT: here's an installation of larger pulleys: http://www.civicforums.com/forums/11...t-install.html EDIT 2: since I only have the alternator still connected, here is a $60 option: http://www.civicsiperformance.com/pr...d=p1541-c64415

[d0sitmatr]

for a civic, Im sure there are tons of aftermarket parts, and places that supply them. if it was me, Id contact one of the more reputable shops and ask them if they could make a UPD that does exactly what your looking for. they will have far more detailed data on which does what.

the UDP for my ranger was the same size/diameter, just made so much lighter it worked perfectly for both increasing FE and torque.

[California98Civic]

What if the UDP was larger and lighter than stock? It is just for the alternator. I am reducing electric load on the alternator too (deleted AC and adding LEDs).

[Daox]

Then it would be an overdrive pulley. The benefit would come from reduce rotational mass, but it wouldn't really be anything you'd see when you fill up. As far as alternator output, it would have more output at lower engine RPMs since it woudl be spinning faster. However, since it is spinning faster, the brushes and bearings would wear faster... Depending on how large you go, it may not be designed to handle the RPMs you spin it to if you rev up the engine.

[California98Civic]

Originally Posted by Daox

Then it would be an overdrive pulley. The benefit would come from reduce rotational mass, but it wouldn't really be anything you'd see when you fill up. As far as alternator output, it would have more output at lower engine RPMs since it woudl be spinning faster. However, since it is spinning faster, the brushes and bearings would wear faster... Depending on how large you go, it may not be designed to handle the RPMs you spin it to if you rev up the engine.

I think actually the alterator will spin more slowly when it has a larger pulley. The crank pulley remains the same size, so a larger alternator pulley will spin less than stock and a smaller pulley than stock would spin more in order to "keep-up" with crank pulley's RPMs. So if it were larger and lighter, I should be reducing rotational mass and reducing ware on the alternator as well as its load on the engine and its output. Right?

[EdKiefer]

Originally Posted by California98Civic

I think actually the alterator will spin more slowly when it has a larger pulley. The crank pulley remains the same size, so a larger alternator pulley will spin less than stock and a smaller pulley than stock would spin more in order to "keep-up" with crank pulley's RPMs. So if it were larger and lighter, I should be reducing rotational mass and reducing ware on the alternator as well as its load on the engine and its output. Right?

yes, UD pulley set generally has a light weight smaller dia aluminum crank pulley and slightly larger alternator pulley . both slow down accessories .

[Daox]

Haha, yeah I got em reversed. You're right.