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Aftermarket Underdrive Pulleys

This is a discussion on Aftermarket Underdrive Pulleys within the External Engine forums, part of the LSx Technical Help Section category; Hello once again friends, I don't know squat about aftermarket pulleys, but see them in pics on LS1's from time ...

  1. #1
    Member Castle's Avatar
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    Midnight Blue
    1998 Camaro Z28 A4

    Aftermarket Underdrive Pulleys

    Hello once again friends,
    I don't know squat about aftermarket pulleys, but see them in pics on LS1's
    from time to time and am considering ordering one.

    The only one I have been able to really find is SLP's:
    http://www.slponline.com/view_product.asp?P=100221

    I don't see a ton of people with these secondary pulleys added to their cars,
    so my real question is, are there any pros/cons to adding an aftermarket
    underdrive pulley?

    Thank you for your help!

  2. #2
    Car Nut ICRAZY6's Avatar
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    Pro: Less rotating mass, faster revs and little hp. Con: If you’re running a stereo system the alternator won’t be able to provide the voltage needed. To fix this just purchase an overdrive alternator pulley, but that in it’s self will shorten the life of the alternator. There are plenty of aftermarket pulleys manufactured out there. I personally use the SLP (Powerbond) pulley because of the walls around the belt is taller, keeping you from throwing a belt. Good luck with you decision.

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    Moderator Firebirdjones's Avatar
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    Something else not mentioned that I noticed with my underdrive pulley is the fact that the water pump is turning at such a slow speed when idling around that the engine heats up much faster and the fans continuously run and never really cool the engine down enough for them to shut off,,,,,due to slow water circulation. If I click the engine up in neutral and hold it around 1,200 to 1,500 rpms the fans will click off within 10 seconds or so,,,,but idling they never shut off. This is when the ambient temp outside is around 85 degrees or higher.

    I don't really care for this plus the fact that the volt gauge is almost always below 13 volts when idling,,,especially when air is on, or other electrical accessories. Like mentioned above you can purchase an aftermarket overdrive pulley for the alternator but then you are defeating the purpose of the underdrive crank pulley.

    If I had it to do over I wouldn't use one. The very tiny HP gain isn't worth it in my opinion. As a matter of fact, I noticed no ET or MPH gain at the track when I installed mine,,,,worth absolutely nothing at the track in my case. When I do my header install in the near future the underdrive pulley from ASP will most likely come back off in favor of the stocker being reinstalled. Just my experience with it.
    And just to add, I agree with above,,,the SLP pulley is a nicer piece than the ASP since it is the only underdrive crank pulley out there that offers the deep groove that I am aware of. Larry.

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    Quote Originally Posted by ICRAZY6 View Post
    Pro: Less rotating mass, faster revs and little hp. Con: If you’re running a stereo system the alternator won’t be able to provide the voltage needed. To fix this just purchase an overdrive alternator pulley, but that in it’s self will shorten the life of the alternator. There are plenty of aftermarket pulleys manufactured out there. I personally use the SLP (Powerbond) pulley because of the walls around the belt is taller, keeping you from throwing a belt. Good luck with you decision.
    So if I like to have my ipod and loud music on the whole time I'm driving, it'd be a bad idea to get one of these? I've seen in so many places that they give about 20 HP but I was thinking more along the lines of 5-10 which still sparked my interest but if it's only 1-2 and may hurt the music it's not worth it.

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    Moderator Firebirdjones's Avatar
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    Well I have nothing extra on my car at all,,,all stock with no add on music stuff or anything else that would strain the electrical system,,,,and I still don't like how the volt gauge acts. The gauge now moves up and down with just a simple turn signal on while idling. Thats a little much if you ask me. Once I have the air on,,,or the fans kick on (which seems to be constantly now with this underdrive pulley) or I have lights on etc....the volt gauge gets very very low and the lights actually dim quite a bit. With the stock pulley none of this was ever an issue. It's your call.
    Keep in mind, I have had no driveability problems at all,,,I just don't like the way it acts at all. As far as a 20 HP claim,,,,ya right. That should have easily given me 1/10th and 1 mph in the quarter,,,but I gained nothing at all. Like I said the HP gain is so minimal that it was not noticed on the drag strip at all. Car ran exactly the same after 3 trips to the strip, I could not better my times. Others may have had different experiences, and I heard both pro's and con's,,,but I decided to try it myself and these are the results I found with my own car. In my honest opinion, there are better bolt ons to buy for the $2-300 these things cost. Luckily I found mine used and didn't pay full price, knowing this was simply an experiment in my case.

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    Member Castle's Avatar
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    This was some really good advice from you all, I appreciate the input.
    Your explanations more than cover why I don't see these more often on F-Body's.
    If my car was a track car only, I could see the pulley being worthwhile...

    Thank you everyone.

  7. #7
    Member Empatho's Avatar
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    Im using a march performance UD pulley on my DD and I dont have any problems with it, I dont know about the temp since my 02 gauge is a dummy but after the install I notice that the car revs quicker and that when I floor it from a stop I dont just chirp the tires anymore it will burn them before the tires would just chirp a little thats with new Yokohama's
    2002 Z28 Auto (3.23 gears)
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  8. #8
    Member Castle's Avatar
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    Quote Originally Posted by Empatho View Post
    Im using a march performance UD pulley on my DD and I dont have any problems with it, I dont know about the temp since my 02 gauge is a dummy but after the install I notice that the car revs quicker and that when I floor it from a stop I dont just chirp the tires anymore it will burn them before the tires would just chirp a little thats with new Yokohama's
    Are your fans always on?
    Do you run a stereo system in your car and have any problems with it?

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    I wouldn't waste my time with them. That money can be spent better elsewhere.

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by RedRocketZ28 View Post
    I wouldn't waste my time with them. That money can be spent better elsewhere.
    My experience exactly. Better off putting $300 towards headers, torque converter, rear gears or a good dyno tune.

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    I Like It Stroked 99Ls1fever's Avatar
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    the best pulley kit is through asp and is on improformance.com for $219.00 and comes with altornator pulley and crack pulley both smaller and states to improve 13rwhp and improve gas mpg by3-4 in hot rod in sept 2007 issue and does require diffrent belts. these pulleys are racing pulleys.

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    Quote Originally Posted by 99Ls1fever View Post
    the best pulley kit is through asp and is on improformance.com for $219.00 and comes with altornator pulley and crack pulley both smaller and states to improve 13rwhp and improve gas mpg by3-4 in hot rod in sept 2007 issue and does require diffrent belts. these pulleys are racing pulleys.
    I think that my have been the same issue I got my info from about them. Was it in a article of "proven bolt ons"?

  13. #13
    Member Castle's Avatar
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    Midnight Blue
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    Great feedback so far guys!

    I have most basic bolt-on's & am looking for that little bit extra on a daily driven engine,
    so spending $2-300 on an underdrive pulley kit does not bother me.

    What would bother me is if I am going to have issues such as my stereo not functioning properly or the car running hot, fan always on, etc.

  14. #14
    I Like It Stroked 99Ls1fever's Avatar
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    Thumbs up

    Quote Originally Posted by Castle View Post
    Great feedback so far guys!

    I have most basic bolt-on's & am looking for that little bit extra on a daily driven engine,
    so spending $2-300 on an underdrive pulley kit does not bother me.

    What would bother me is if I am going to have issues such as my stereo not functioning properly or the car running hot, fan always on, etc.
    the underdrive crank pulley wont effect anything, the under drive alt pulley is reccommended for race only but i just bought an optimia battery and i daily drive mine, i dont have a big system in my car though... but the web site also has a better after market alt. pulley they state will free up some hp and not effect your daily driving.

  15. #15
    Member Empatho's Avatar
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    Quote Originally Posted by Castle View Post
    Are your fans always on?
    Do you run a stereo system in your car and have any problems with it?
    I have the stock stereo and later adding a tv but I dont plan on getting subs, and Im not really sure if the fans are on all the time but if you are worried about that all you have to do is raise the idle a little with a tune and that will help spin the water pump during trafic

  16. #16
    Senior Member JonB's Avatar
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    First are you an m6 or and A4. A4 tend to have lower voltage and less circulation of water because they idle lower in gear, I want to say 750 or so while and m6 is like 900-950. I have been running the asp pulley on my car for 2 years with no real problems. The only draw back to me is the a/c is not as cold at idle which in the fl heat and an all black car is rough sometimes, but its fine when driving just as cold. The only time I notice a drop in voltage is at idle with everything on, lights, a/c etc but its just a hair under 13 which is no biggy goes right back to normal when driving. I also have no problems with my fans on all the time. If my a/c is off they hardly ever come on even in the 95+ degree wheater in FL. I can't say I felt a set of the pants difference but my car makes very good power 360rwhp 370rwft lbs with lid, mac midlengths, catback, ported tb and underdrive and I still pull 22mpg around town. I'd like to think the underdrive has something to do with the numbers.
    Last edited by JonB; 08-31-2007 at 02:52 PM.
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    Sold 01 z28

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by Empatho View Post
    I have the stock stereo and later adding a tv but I dont plan on getting subs, and Im not really sure if the fans are on all the time but if you are worried about that all you have to do is raise the idle a little with a tune and that will help spin the water pump during trafic
    I have my idle bumped 150 rpms to compensate but it didn't do any good,,,,still not fast enough to spin the water pump enough,,,and the fans still run continuously while idling around,,,only when I hold the throttle at about 1,500 rpms will the coolant temp come down enough for the fans to turn off,,,,and,,,,well,,,,,you can't have it idle that high,,,lol. Besides, you have to be carefull how high you set up the idle,,,the IAC step counts get out of wack and you cause other problems.

    The 2-3 mpg increase is a joke. I get the same 22 mpg I always get with the car,,,no changes there.
    The volt gauge is below 13 most of the time,,,only when the engine reaches about 1200 rpms or more does the volt gauge return to normal,,,,this is with the stock alternator pulley,,,,only the ASP crank pulley is used.
    Alternator voltage isn't as big of a deal to me, it hasn't caused any drivability problems, but I still don't care for it. The temp problem is what concerns me the most, anything over 85 degrees and the fans continuously run while idling.
    Quarter mile times and mph's did not improve either on my car,,,I have raced this thing with every single bolt on,,,one piece at a time,,,and this ASP pulley gave me nothing.

    I don't mean to knock it,,,it hasn't given me problems. But for the money they cost? It did nothing for the car at all. I would rather have my cooling capability back and feel more comfortable with a steady volt gauge too.

    If you still feel you have to have one,,,,mine will be coming off soon when I do a header install within the next few weeks and up forsale it will go along with the belts required. My advice though would be to spend your money on more usefull bolts ons that actually give you some speed.

  18. #18
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    Like any mod does a pulley help more if you have other mods? Wouldnt i make more power on a modded motor compared to a stock motor?

  19. #19
    Moderator Firebirdjones's Avatar
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    I would say probably not. If it were worth anything at all I should have seen it on my car. Now there is truth to your theory when it comes to other bolt on's such as the induction system and exhaust.

    Have you ever put headers on a stockish motor and only see maybe 1/10th improvement in the quarter mile? Then put headers on a car that has a large cam and some head work,,,the difference is tremendous. I have done this with another car a couple years back. Alot of the air intake and exhaust mods work together to help other things,,,such as guys installing the fast 90/90 intake setup on a stock motor,,,,hardly worth the $1,000 in coin to gain maybe 10 hp if your lucky,,,,but on a motor that is stroked,,,say a 408 LS1 for example with a large cam and heads,,,,this difference can be 30-40 HP.

    But the pulley I don't think would fall into that catagory so much. It claims to free up power by reducing the parasitic drag of the accessories. But I think the change is so small,,,it would barely be visable on a dyno and it surely doesn't show up on the drag strip. I have tried several different exhaust systems, headers, and other simple things to find what works and what doesn't. Some may be surprised at some of these exhaust systems,,,people seem so biased towards a certain brand or name, but in reality I have seen similar results with just about every name out there. I am keeping a log of drag strip times, Density Altitude, etc...with all my changes and so far the underdrive pulley is one bolt on that doesn't pull it's weight. I would rather have better cooling ability while sitting in traffic,,,and have my volt gauge reading in the healthy section so mine will come off,,,it didn't make my car faster so it's wasted money. But as I said,,,I bought this used, knowing it was only an experiment for my car,,,,and I was a little skeptical of it's abilities anyway so I didn't want to pay new prices.

    Alot of people use them though and some swear by them.

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    I run an underdrive, and a Mezeire electric water pump. Also a 160 thermostat and reprogrammed fan activation. This setup runs cool even in the heat wave we are having in Central CA.
    How much HP is that worth? My best guess is 10-15, my RWHP is 337.

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