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Underdrive pulley question??

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  • Underdrive pulley question??

    A while back I seem to recollect that a few 7ers had some problems with underdrive pulleys. Could any victims please PM me with any do's or don't's on these. Do they really make much diff when the cars are not loaded with power accessories? TIA!!

  • #2
    i use lightened pullies on my subarus. the crank pulley is almost as noticable as a flywheel. by using an underdriven pulley, u may be limiting accessory hose suppliers in addition to compromising ur alternator's abilities,
    2002 SV zetec/sierra; yellow over green


    • #3
      I have a smaller pulley and that works just fine. Even in the best case I guess it will make only a difference of a hp or two and also reduce the inertia a bit compared to the massive stock pulley. But after all, every gram counts and there is no need to keep the water pump and alternator buzzing when they don't need to.

      Minor disadvantage is the lower alternator output at idle speed which may not be sufficient to e.g. support lights or fan but who leaves the engine in idle for a long time?

      I heard concerns that the alloy underdrive pulleys don't have a rubber damper built in but I did NOT hear of confirmed trouble with crank resonance or even failures.

      I believe Chris had problems with the pulley quality but don't know details.



      • #4
        Will put this cheap pos aftermarket underdrive (4" instead of 5") pulley made by Focus Central of Tehachapi on my engine that had an alloy timing ring attached to the back w/ 4 tiny little alloy set screws. After some time 3 of them sheared completely off and the thing just rattled around on the pulley. Cost me a track day it did. Pbbbbbt.

        Here's a (somewhat - different engine) related article that offers some wisdom:

        Underdrive pulleys ain't worth a shit in terms of power gain, offering only a little. If they're not well engineered they can be (way) more trouble than they're worth.

        Underdriving alternators and water pumps shouldn't present as much potential for problems but again, the gains to be had are negligible.
        Last edited by moosetestbestanden; April 18, 2007, 11:20 PM.
        A day you don't go a hundred is a day wasted


        • #5
          I am sure the article Chris posted a link to is correct. I have read opnions from other experts to the effect that the harmonic balancer is really tuned to the entire drive train, so as soon as you put the engine in something else it isn't really doing the job it was designed for.

          The bottom line is that lots of them are installed and I have not heard of crankshaft failures. At least for Zetecs.



          • #6
            Thank you very much for all of the replies. The link was especially interesting.