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  1. #1
    King Dumbass McCloudsZJ's Avatar
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    Under Drive Pulleys

    So… Now that FaceBook has discovered these shiny March Performance under drive pulleys that all the cool kids have, this article from KOR gets posted at least once or twice a week (or every single time someone posts pictures of their pulleys).
    http://www.kevinsoffroad.com/techart...j-pulleys.html
    By: Scott Mueller

    There are currently two pulley kits on the market for the 5.2L/5.9L
    Magnum engines, one by March and one by Jet. They both include a
    smaller crank pulley as well as larger water pump and alternator
    pulleys. Unfortunately for mid-'98 and newer Magnum engines the water
    pump pulley is no longer bolted onto the shaft and removable, instead
    it is a direct part of the pump shaft. This means that the water pump
    pulley cannot be changed to the larger one in the kit. Actually this
    turns out to be a blessing in disguise, since unless you are racing
    only, you do NOT want to use all three pulleys.

    I computed the precise ratios of under drive compared to stock and
    found that by using all three pulleys, March and Jet were
    under driving the water pump by 34% and 37% (respectively), and the
    alternator by 46% and 48% (respectively). Unfortunately these ratios
    are WAY too steep for a street driven vehicle IMHO.

    Even if you could, using all three of the pulleys from the Jet (or
    March) kits would result in about a 35% reduction in water pump speed
    and a nearly 50% (unacceptable to me) reduction in alternator speed.
    That much speed reduction on the alternator would mean that the
    battery would begin discharging at idle with any accessories on, and
    lowering the water pump speed that much could cause overheating,
    especially in stop and go traffic with the A/C on, or possibly under
    towing conditions as well. In fact both companies specifically
    recommend against towing if you use their full kits.

    On the other hand, by using ONLY the crank pulley from either of
    their kits, you would end up with a total under drive for ALL
    accessories of only 23% or 25% for the March and Jet pulleys
    respectively, figures which are acceptable and which don't lead to
    charging or cooling problems.

    The March pulleys are machined billet T6 aluminum and clear
    powder coated. The Jet pulleys are machined billet steel and anodized
    black. I prefer black for the totally stock look, that way the dealer
    (or anybody else) would never know it was changed. I was also
    concerned about the durability and longevity of the aluminum. The
    drive belt is highly abrasive, and over time the belt will wear the
    pulleys down. Also aluminum particles will transfer to the abrasive
    belt causing it to slip. There is no OEM manufacturer I am aware of
    using aluminum pulleys on a production car for the simple reason that
    they aren't durable.

    Bottom line: I decided that the only way to do an under drive setup
    correctly would be to change only the crank pulley, and use only a
    steel (not aluminum) one. This meant I wanted only the crank pulley
    out of the Jet kit.

    Rather than having to purchase the entire pulley kit, and realizing
    that Jet does not make their own pulleys, I ended up researching who
    made the pulleys for Jet and found I could purchase the same crank
    pulley alone from a distributor:

    Evergreen Performance
    14840 N. 74th St.
    Scottsdale, AZ 85260

    (800-498-6951) orders
    (602-443-3333)
    (602-443-3636) fax

    <http://www.airaid.com>
    <http://www.4evergreen.com>
    <mailto:sales@4evergreen.com>

    Ask for John Levits (ext. 210), tell him I sent you, he's a friend of
    mine.

    The crank pulley is the same one Jet sells in their kit, and is
    machined from steel and treated to a black oxide coating. Besides
    being the most durable, it also has nearly 2.3% greater under drive
    than the March crank pulley, and it has the advantage of looking 100%
    stock under the hood. The pulley is attached to the harmonic balancer
    by six 1/2" bolts which are very easy to get to from underneath.

    Since the new pulley is smaller in diameter than stock, a shorter
    belt is required. The Grand Cherokee V8s (both 5.2 or 5.9L) use a
    7-rib 25mm x 2265mm belt stock, which needs to be changed to a
    shorter 25mm x 2190mm belt (two sizes smaller than stock). This belt
    is just a slight bit shorter than it should be to be perfect, meaning
    the belt tensioner ends up near the end of its travel range with this
    belt installed. Unfortunately the next size belt up or down is way
    off.

    To make this belt work perfectly I removed the belt tensioner and
    slightly relieved the alignment tab with a file causing the tensioner
    position to change slightly when installed. This allows the tensioner
    to be in the proper travel range (indicated by an arrow on the
    tensioner) for this belt. For replacement belts, I recommend Gates,
    they make OEM quality belts and their part number K070855 is the 25mm
    x 2190mm belt I used. Note that many of the aftermarket belts found
    at discount parts stores are of vastly inferior quality to stock, as
    such I only recommend Gates or Goodyear for replacement belts.

    Note that by installing a new OEM tensioner, plus the stock belt and
    pulley, the vehicle can be returned to stock in about 15 minutes
    time.

    I tested the vehicle and with the headlights and rear defog on the
    system retained full voltage at idle, meaning the alternator was
    working well enough to maintain battery charge. This is important for
    winter driving under stop and go conditions. I did not measure the HP
    increase, but estimate a few HP are gained, and the engine may rev a
    bit quicker as well. Scott.
    Tired of repeating myself, I’m writing this for a quick copypaste reference.
    Under drive pulleys make your shit turn slower. Who’da thunk? To get into the mystery math Scott “precisely computed” (which is really just one equation that I guarantee you learned in 9th grade):

    With the March pulleys installed, the belt will physically move 16.6% slower.

    With the March pulleys installed, your water pump will spin 33.1% slower. Not a huge problem, especially for us e-fan elitists.

    Aaaand with all three March pulleys installed, the alternator will turn 44.7% slower. Which might legitimately be of some concern for us efan and 10 speaker, electricity hungry elitists.

    However! March also makes a billet OVERDRIVE alternator pulley (Google: March Power Series) that I can’t find for sale anywhere. It would put the alternator output back up within 10% of the original operating curve (line, really, but whatever).
    And for those of you with no idea what’s going on:








    Will be updated (eventually) to include WP and HB part numbers, belt lengths, and reviews from someone that actually installs the damn things.
    Last edited by McCloudsZJ; 03-11-2015 at 10:58 AM.

  2. #2
    Member ZJ-John's Avatar
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    PM GregZ over at RM. He works at March and may be able to tell you what the PN is for the overdrive alt pulley.

  3. #3
    King Dumbass McCloudsZJ's Avatar
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    Quote Originally Posted by ZJ-John View Post
    PM GregZ over at RM. He works at March and may be able to tell you what the PN is for the overdrive alt pulley.
    PN is March 645 (I think?) I just don't see it for sale anywhere.

  4. #4
    Member ZJ-John's Avatar
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    645 is for the PS pulley...

    http://www.summitracing.com/parts/mch-645

  5. #5
    King Dumbass McCloudsZJ's Avatar
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    Quote Originally Posted by ZJ-John View Post
    645 is for the PS pulley...

    http://www.summitracing.com/parts/mch-645
    That's what it was. That's something else I need to get soon.

  6. #6
    Member ZJ-John's Avatar
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    That will be cool if it works!

    A worthy upgrade for all you plastic pulley guys

  7. #7
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    thanks

    Subscribed, thanks for posting this.

  8. #8
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    I'm guess this was reference to my post on FB earlier today. I've known about UD pulleys for a long time (had them on a Camaro I had built). Just basically trying to figure out belt length and the problems with the alternator on the 5.9 considering I do have the efan and 10 speakers.

  9. #9
    Eddie MonaDeRio's Avatar
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    In mostly cases people have changed the crank pulley only.
    Bigger alternator pulley-charging problem
    Bigger water pump pulley - overheating problem.
    Last edited by MonaDeRio; 03-11-2015 at 06:40 PM.
    SCT X3. Custom cam. Crane gold race roller rockers. Fully ported 2.02 R/T heads.. Mike Leach Headers. Full 3" cat back exhaust. Custom full return fuel system. Aeromotive 340 in-tank fuel pump. Aeromotive dual port adjustable fuel regulator. Holley 2 x 52mm TB. High stall torque converter 2800 . 24# Bosch Ford Racing injectors. MSD ignition box and coil.

    --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

  10. #10
    im super special x10radsponge's Avatar
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    Give me the cliff notes. Do they work without cooling or charging issues?

  11. #11
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    So far Kevin I am havin no cooling or charging issues what so ever. That being said I am only using WP and crank.
    '98 Grand 5.9 "Black Pearl" totaled
    '98 Grand 5.9 "Eleanoir"
    "No Officer, all four tire tracks are mine, it WAS all wheel drive......yes ma'am Im aware this structure is normally used to 'park' cars"

  12. #12
    im super special x10radsponge's Avatar
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    Cool.. I have just a crank one.

  13. #13
    Eddie MonaDeRio's Avatar
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    From Wikipedia, the free encyclopedia

    An underdrive pulley refers to a crankshaft or accessory pulley (a/c, alternator, power steering, water pump, etc.) designed to turn at a slower speed than stock. To Underdrive means to slow the rate of rotation in a system. Underdrive is achieved by either making the crank/main (drive) pulley smaller or the accessory (driven) pulley larger than the original diameter pulleys.
    Underdrive pulleys increase engine output by reducing the draw of the engines accessories by slowing them down and reducing the HP they use. Horsepower gains from underdrive pulleys can vary by vehicle, engine, number of accessories and the amount of underdrive (Improvements of up to 5-15 HP at the wheels have been seen). Additional and significant performance improvements can be seen by reducing the weight of the pulley versus the original pulley. Gains can range from 3-6HP per pound of weight reduced.
    Poorly engineered underdrive pulleys can cause unwanted side effects, this is due to not spinning the alternator, power steering, and/or air conditioning fast enough. This leads to low alternator voltage, weak/no power steering assist, and weak/no air conditioning effectiveness, especially at idle/low rpm. The most commonly seen result is lighting may dim, or the stereo may cut out. Too much underdrive for a race car is not much of a concern due to the high rpm's they run at, but for daily driven vehicles it can lead to a dead battery if too much time is spend at idle or low/rpm.
    In addition changing the original crankshaft pulley can have negative effects if the replacement pulley is not manufactured properly. A crankshaft or accessory pulley not machined or balanced properly can cause severe damage leading to thousands of dollars in repairs.
    SCT X3. Custom cam. Crane gold race roller rockers. Fully ported 2.02 R/T heads.. Mike Leach Headers. Full 3" cat back exhaust. Custom full return fuel system. Aeromotive 340 in-tank fuel pump. Aeromotive dual port adjustable fuel regulator. Holley 2 x 52mm TB. High stall torque converter 2800 . 24# Bosch Ford Racing injectors. MSD ignition box and coil.

    --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

  14. #14
    sfn's lonely vajay jay
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    Is that power steering pulley stock replacement? Meaning, no underdrive /overdrive or different belt required type install?

    - - - Updated - - -

    P.S March 645 won't fit...

    - - - Updated - - -

    http://thespeedfreaks.net/showthread...-PS-9008-AL-AR
    - Sandy

  15. #15
    sfn's lonely vajay jay
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    Got mine today. The alternator pulley looks larger than stock. They should just give you the overdrive as part of the kit to compensate.
    Last edited by BoostinChick; 12-09-2015 at 07:37 PM.
    - Sandy

  16. #16
    RallyJeep GO
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    Think of it this way: Larger alt pulley is underdrive (less rotations for a given distance of belt pulled across it). Smaller crank pulley is underdrive (less belt moved per rotation).
    1998 ZJ 5.9 Limited - Deep Slate
    Mods: Big trans cooler, 231 swap, Indy 2.02 heads prepped by IMM, Comp 20-744-9 cam, 1.7 HS roller rockers, 52mm TB, Airgap manifold, DT headers and full 3" exhaust, SCT tune homebrewed by me, Martin Saine valve body, B&M tranny pan, magic suspension made from unicorn tears, power steering cooler, lots of lighting mods

  17. #17
    King Dumbass McCloudsZJ's Avatar
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    Look at the math. Crank diameter determines belt velocity at RPM. Belt velocity (w.crank x crankpulleyradius) is constant all the way around. You know this. And even if you don't, it's right up there ^^^

  18. #18
    Forum CONDUCTOR Man Z88Z's Avatar
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    I ended up going with a bit of an underdrive crank pulley, although it was more out of necessity than choice.

    In this pic the stock pulley is almost a foot closer to the camera than the new one, so the relative sizes are really skewed.
    I didn't think to take a good comparison shot at the time - this pic was more of a "hey look what I got!" pic I was sending to a bud. If you take the bolt hole pattern into account you can get a better idea of the size of the new pulley.





    My motor isn't pushing much besides the Jeep so I wasn't worried about the drag, just had to find stuff to fit my weirdness.


    You'll notice my stuff is six rib. Partly to do with the weirdness of my setup and partially cuz it's much easier to find off sizes in six rib than in seven. FYI - The P/N for that alt pulley was under stuff for the Magnum motors. Out of caution I spoke to March on the phone to make sure that pulley fit the shafts of the newer denso style alts that we use and they assured me it did. Having said that, it really wasn't a super precise fit on the shaft. Not enough room to really go anywhere or wobble - but not as tight as the OE pulley by a thou or so.


    On a cool note - if you're ever doing bizarre custom-ness on a serp belt setup that's a lot longer or shorter than normal - I found a great solution. (NOTE: In cases where you're getting way, way off stock, you might find you need to build for what belts are available rather than setting something in stone and hoping to find something that fits what you built, lol)

    Get a very rough idea of what kind of length you're working with or trying for. Then hop on Summit.com and enter serpentine belts or accessory belts into the SEARCH box.

    Under NARROW YOUR RESULTS on the left side, skip all the brand/make/model/engine size/ belt fitment stuff - and just go right to the correct number of ribs and select that . (7 for normal people, lol)

    Then skip down to the BELT LENGTH section and you'll see a HUGE long list. (Note: on some belts I think there's an angle for the edging you might have to take into account. Can't remember exactly how I figured that part out, lol)

    Find the sizes closest to what you want and choose that one or ones and a few should come up. Then type that belt brand and p/n into google and you should be able to find out what vehicle it's for - then just go order it at your local parts store
    Summit may have the vehicles it fits listed under application for some belts, but they don't always have enough info...

    FYI - If you look at six rib you'll notice there's a literal shitte-ton more choices in widely varying lengths than you'll find under seven rib belts, especially in the shorter lengths.

    Theoretically you could look through some kind of belt catalogue at the parts store but unfortunately with the type of kids most parts stores end up with these day they'd be lucky to find the catalogue


    If you're getting into something that's as bizarre as mine and you're not using the Magnum accessory bracket - March also carries some super slick turnbuckle type adjustable arms in several lengths for spacing out and providing proper belt tension for alternators and various components.
    They're WAY expensive and they're made for Chevy (cuz, of course, why not?) so I'm not sure about the bolt sizes they're made for but I'm guessing they're pretty close. March should be able to confirm that. Maybe!

    I'm just setting mine up for now to get it running but I'm thinking of revisiting the alternator setup later on and trying one of these arms so I can eliminate the idler arm or tensioner completely.


    BTW, the belt I ended up with was made as a power steering belt for like a 90s Camry or something!
    Last edited by Z88Z; 12-22-2015 at 11:47 AM.

  19. #19
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    What fun! I jumped through the same hoops when I calculated the size to make the extra idler pulley for my supercharger... like you, I had to work backward from the available 7-rib belts. It's not as easy as one might think. I designed it to fit the stock tensioner pulley with a 106.5" belt, so once it's all together if it's a little too loose, a little too tight, or just right, I'll make a custom tensioner pulley a little bigger or a little smaller that will match the other pulleys.
    Oddly, that 106.5 belt doesn't show up in most of the belt cross-reference charts, but it does on Summit, and that's how I found it too! Most of the 7-rib charts jump from 104.5" to 113" with nothing in between - I thought my plan was screwed until I checked Summit.

  20. #20
    im super special x10radsponge's Avatar
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    In my chatting with Sandra, I stumbled across this. http://www.ebay.com/itm/191609970246...%3AMEBIDX%3AIT might help someone. Only issue is making sure the Alt shaft is 17mm.

  21. #21
    RallyJeep GO
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    AFAIK, that'll fit our alternators. From what I can find (haven't measured to confirm), our stock alt pulley is most likely a 58mm one. So that 48mm one would be a ~21% overdrive (would spin the alt just a little slower than stock with most UD pulleys). I definitely wouldn't use it without a UD crank pulley though, I'm not sure what the rpm limit on the alt is before things start to come apart.
    1998 ZJ 5.9 Limited - Deep Slate
    Mods: Big trans cooler, 231 swap, Indy 2.02 heads prepped by IMM, Comp 20-744-9 cam, 1.7 HS roller rockers, 52mm TB, Airgap manifold, DT headers and full 3" exhaust, SCT tune homebrewed by me, Martin Saine valve body, B&M tranny pan, magic suspension made from unicorn tears, power steering cooler, lots of lighting mods

  22. #22
    sfn's lonely vajay jay
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    Quote Originally Posted by comptiger5000 View Post
    AFAIK, that'll fit our alternators. From what I can find (haven't measured to confirm), our stock alt pulley is most likely a 58mm one. So that 48mm one would be a ~21% overdrive (would spin the alt just a little slower than stock with most UD pulleys). I definitely wouldn't use it without a UD crank pulley though, I'm not sure what the rpm limit on the alt is before things start to come apart.
    x10radsponge spoke with March today. Their 6-rib version of their "OD" alternator pulley is 58mm/2.3-inch diameter. Looks to be the stock size if your measurements are correct, comptiger500.

    So, it seems like the one he linked may work? Just not sure the about the size of the alternator shaft...and my problem is it's not billet lol.
    - Sandy

  23. #23
    RallyJeep GO
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    From everything I can find, our alternator shafts are 17mm. They're the standard large case Denso alternators, nothing too uncommon.
    1998 ZJ 5.9 Limited - Deep Slate
    Mods: Big trans cooler, 231 swap, Indy 2.02 heads prepped by IMM, Comp 20-744-9 cam, 1.7 HS roller rockers, 52mm TB, Airgap manifold, DT headers and full 3" exhaust, SCT tune homebrewed by me, Martin Saine valve body, B&M tranny pan, magic suspension made from unicorn tears, power steering cooler, lots of lighting mods

  24. #24
    sfn's lonely vajay jay
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    Quote Originally Posted by x10radsponge View Post
    In my chatting with Sandra, I stumbled across this. http://www.ebay.com/itm/191609970246...%3AMEBIDX%3AIT might help someone. Only issue is making sure the Alt shaft is 17mm.
    Big thanks to x10radsponge and Logan (I forget his SFN name) for finding this and confirming fitment of the OD alternator pulley! Just waiting for Logan to button up his Jeep and test overall function.
    - Sandy

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