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Using alternator as idler pulley for Roots blower belt?

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  • Using alternator as idler pulley for Roots blower belt?

    Can one use an alternator as an idler pulley on a Roots blower belt?

    The alt would be mounted on the 'inside' of the belt, and by using a cogged pulley on the alternator it would get driven without slip because of the small contact area on the belt.

    I've searched for setups like this but couldn't find any.
    Am I overlooking anything why this could not be done?
    Last edited by BigBlockMopar; February 7, 2013, 03:51 PM.

  • #2
    I only thought of the vibration of the teeth disrupting the alternator.

    it is trying to create its own frequency..would not want to bother that.
    Previously boxer3main
    the death rate and fairy tales cannot kill the nature left behind.


    • #3
      That might be a valid reason not to use this setup.
      Although, after searching some more now, I'm thinking I should look into other ways of driving the alternator, as finding a 1/2" pitched, 3" wide, small enough pulley is an issue all by itself perhaps.


      • #4
        I wouldnt use it for multiple reasons... first would be trying to find
        or making a 3" wide pulley... second would be the bearings in the alt
        couldnt take that load hanging of the front(the distance out)
        Put a standard V pulley on the crank like all the street rods use
        when running a blower
        Last edited by MR P-BODY; February 7, 2013, 04:27 PM.


        • #5
          I agree a V or multigroove-pulley would be easier, was it not for the fact that the position of the v-pulley will put the alternator closer to the engine-block, leaving only 5.5" of 'depth' for an alternator before it hits the block.

          I'm also looking into using an alternator from a little Jap/European car which might be small/short enough to mount.

          Below is a pic of the blowerpulley-spacer still in the lathe, as I'm now needing to decide between a V-belt or a multigroove setup, and how to mount the alternator and possibly a power steeringpump aswell on the driverside of the engine.
          Attached Files


          • #6
            I'd look at cutting the V groove in the spacer(2 if you want PS) and set the alt down
            low on the pass side... this is on my small block... you can
            sorta see the alt on the pass side down low
            Does that spacer set your blower pulley to the right distance out
            to match the top pulley
            Attached Files
            Last edited by MR P-BODY; February 7, 2013, 06:08 PM.


            • #7
              Originally posted by BigBlockMopar View Post
              I've searched for setups like this but couldn't find any. Am I overlooking anything why this could not be done?
              It probably could be done, but probably should not be done. The bearings in the idler on a blower drive are pretty big, and they're mounted in the center of the idler pulley.
              Last edited by squirrel; February 7, 2013, 08:26 PM.
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              • #8
                have you ever thought about mounting the alternator to your rear end housing and have the driveshaft power it ?
                Charles W - BS Photographer at large


                • #9
                  I see that the word 'Roots' might lead one to think so, but this setup will not end up on a racecar. It needs a fulltime charge mainly during idling for the ignition and possibly an injection system later on.

                  The alt was already planned to be mounted slightly lower than stock, but if put too low, like at your motor it will get cozy with the chassisrail and swaybar bracket. But definitly a good option.
                  The spacer positions the blowerbelt to just clear the waterpumphousing. The blower pulley needs to be spaced out a bit aswell.
                  In the pic below you see a CSI electric waterpump, but I also want to keep room for a stock waterpumphousing if by any chance the electric one can't keep the engine cool enough. The block is 1/3rd filled.
                  Attached Files
                  Last edited by BigBlockMopar; February 8, 2013, 01:37 AM.


                  • #10
                    Two more questions... is that a high volume water pump... (not sure if CSI makes one)
                    but Mesere (sp) makes 3 versions 30, 35 and a 50... the 50 being flow will
                    want a nice oil cooler for your filled block to keep the oil cooled down.. next... will you
                    be using a engine plate on the front to mount the engine... if so you can mount the alt
                    on the chassis rail... it can work fine that way... I had to mount my alt on the chassis tube
                    on my Rampage... on mine I have front and mid plate but even with just the front plate
                    the alt will work on the chassis... the front of the engine and chassis rail become one piece
                    so it doesnt toss the belt.... in the pic I showed I made a bracket at uses the old fuel pump
                    bolt holes.... the bracket also is the block off plate for the pump hole


                    • #11
                      Not sure about the waterpump being HV. Checked the CSI/CSR website and they indeed only seem to supply one pump.
                      I got it as rental-payment once and decided this would be the engine to use it on. Otherwise I would still have used a stockstyle (HV) pump probably.

                      Engine oil cooler is planned for. I've got a dual filter remote oil-cooler for this.
                      An engine-plate was not planned for, but somekind of movement-limiter on the block would be mandatory to keep the stock engine mounts alive and happy.

                      Good idea on using the fuelpump boltholes for possible alt-bracket mounting.