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  1. #1
    TopCop931's Avatar
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    Impeller Question

    I am running the extended pump in my 96 SLT780. The impeller that was in there is 5131371 swirl. I got a pump assembly from a 96 SL780. The impeller in there is 5131035. The impeller is in great condition. When put my extension on it is within specs. I am assuming that the swirl on the blades has something to do with the performance when using the extension as I have noticed that the swirl seems to be typical in all listings of the extended pump. I read that using anything other than the recommended impeller could result in engine damage. The guy I bought this pump from said it came out of an SL780 which still would not have a swirl in it either. The stators are identical even though the chart indicates that they should have two different part numbers. I came across a 5 year old discussion on here about the Polaris Manuals being incorrect. I realize one is a 4 blade and the other is a three blade 15/20. What I don't understand is the difference and why if I were to use the 4 blade it may affect my carb settings as per that discussion I was reading. I also recall someone saying on here last week that the pumps were interchangeable. If someone knows please let me know because I can still get my money back. I will just start over from scratch.

    My question is can I use that impeller and if so will it affect performance?

    Here are some pics:

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  2. #2
    TopCop931's Avatar
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    Damn....Another one of my threads that has a five star rating with nobody answering my question.

    I think I have found my answer anyway. I have read that the 4 blade can actually improve my performance but the swirl improves the bottom end. I am learning this from other people that have posted here over the years. Not everyone is always correct, so if anyone knows different and I should not run this 4 blade in my ski please let me know.

    As I stated above, both stators are part number 5630475 so I can't see how it makes a difference other than performance. Aftermarket swirl impellers are made for skis that came stock with 4 blades.

    Bowsniper, I am ready for that stator you have if it is the same part number. I have decided to rebuild my old pump with the swirl in it so I will have both. PM me. If I am going to go broke on this I am going to do it right.

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    Arrow Matching impeller pitch (impeller part number) to engine power

    I will try to answer your questions, without necessarily answering your question ...

    The impeller provides a load for the engine, which the engine power works against. Different impellers have different pitches and blade shapes, and thereby require more or less engine power to spin them at target max engine RPM.

    The objective is to match the impeller to the engine so the engine just reaches optimal engine RPM at full throttle, which the impeller then converts into maximum possible thrust at that RPM with that amount of engine power.

    In general, the steeper the impeller pitch or the more blades the more power it will require to get the RPM up at WOT. The corollary is that the steeper impeller will provide more thrust at the target RPM, provided the engine can get the RPM up there.

    This is why the Fuji 780 engine uses a different and more steeply pitched impeller than the 750 engine. The 780 has the additional torque and HP to turn the 'bigger' impeller, while that same impeller on the 750 engine would present so much torque load that the engine could never achieve the correct operating RPM.

    If you put a '750' impeller on the 780 engine, the 780 engine would probably hit red-line and trigger the RPM limiter, since the impeller pitch is insufficient to properly 'load' the engine.

    As long as the impeller allows the engine to rev up to the proper peak RPM, there is no big concern with engine damage. The risk of damage comes from asking the engine to turn an impeller that is too 'steep' for the available engine HP, resulting in the engine max RPM being dragged down at WOT.

    This is akin to asking a car engine to pull a heavy load up a steep hill in a too high gear. The engine cannot rev properly, and 'lugging' the engine at the lower RPM can cause detonation damage to the pistons.

    For a given engine, the target or optimal maximum sustained RPM is specified by the manufacturer or tuner. The impeller is then selected to provide just enough load to the engine to prevent the engine from over-revving, so that wide open RPM is on target.

    The Swirl impeller design came about as manufacturers looked for ways to improve jet pump efficiency. Also, the swirl blade design is better than the straight cut leading edge for shedding weeds.

    As long as the installed impeller allows the engine RPM at WOT to be where it should be, the impeller will work fine.

    If the impeller was originally specified for an engine with the same HP and operating RPM, then it will work properly with your engine.

    Note regarding jet pump stators;
    The job of the stator is to 'untwist' the water flow coming out of the impeller.

    The impeller not only pushes the water through the pump, it also imparts a spin on the water flow. The stator vanes redirect that spin into rearward water flow, which improves thrust.

    The six vane stators are simply more effective than the five vane stators. The effect on engine RPM is fairly small between the different stators.

  4. #4
    TopCop931's Avatar
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    Quote Originally Posted by K447 View Post
    If the impeller was originally specified for an engine with the same HP and operating RPM, then it will work properly with your engine.

    Note regarding jet pump stators;
    The job of the stator is to 'untwist' the water flow coming out of the impeller.

    The impeller not only pushes the water through the pump, it also imparts a spin on the water flow. The stator vanes redirect that spin into rearward water flow, which improves thrust.

    The six vane stators are simply more effective than the five vane stators. The effect on engine RPM is fairly small between the different stators.
    Thanks Keith. I understand what you are saying and actually looked it up on the Polaris Impeller Charts that are posted and became even more confused. The 96 SL780 came stock with a 4 blade according to the chart but it was 5131079 and not 5131035 which is what I have. I assume the pitch is slightly different between the two. The guy that sold me the pump said it came out of a 96 SL780 and it would work that is why I took it. I know my pictures suck but the impeller is in great condition and is just a little over .010 inside my ring.

    The 5131035 is listed as actually only being installed in the 96 SL-SLT700. So this is where it gets confusing a little again. You stated that if a 750 impeller were to be installed on a 780 it would probably red-line yet this pump is said to have come off an SL780. I have read here over and over that a lot of the Polaris literature is incorrect so I don't know what to think. I have had two other people tell me today that the only difference would be my bottom-end performance between the two impellers.

    My old impeller pictured (the swirl) is still usable I just have to get the broken piece of the stub shaft out with a screw extractor. My extension ring has no damage at all so it seems that the outer bearing seized at a high rpm and snapped my stub shaft. Also my drive shaft had over .070 run-out. The thing is, the swirl seems to be very loose inside the wear ring. Of course that may be because it is not on a stub shaft and the clearance is checked on the most outer edge of the blade when the ring and stator are assembled and the impeller is tightened on the shaft.

    I was hoping that someone here had experimented with this before and would be able to tell me for sure because I would like to try the 4 blade. I am being told that I would get better performance with it. Of course that is coming from the person that sold me this one and someone else that sells them as well.

    I think I am still going to rebuild my old pump and try this one out also. If the impeller is insufficient as you describe it should trip the rev limiter and then I will just pull it out and find another impeller I guess. The other option is to just take my old impeller and put it on this pump after I take the piece of the stub shaft out.

  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Well, let's compare

    We will ignore differences in low end acceleration, and just focus on matching impeller to engine power, max RPM and load.

    Per the posted impeller chart

    5131035 4 blade 'Progressive'
    1994 SLT750 80 HP @ 6250 rpm
    1995 SLT750 80 HP @ 6000 rpm
    1996 SL700 80 HP @ 6250 RPM
    1996 SLT700 80 HP @ 6250 RPM
    Here the Fuji 750 has similar HP ratings to the domestic 700 engines in 1996, and 80HP will spin the 035 impeller to about 6250RPM.
    Not sure why the 1994 and 1995 SLT750 are spec'ed for the different RPM with the same rated power

    5131079 4 blade 'Progressive'
    1994 SL750 80 HP @ 6150 rpm
    1995 SLX780 90+ HP @ 6250 rpm
    1996 SL780 90+ HP @ 6250 RPM
    1997 SL780 93 HP @ 6250 RPM
    This suggests that 80HP will spin the 079 impeller to about 6150RPM, and 90HP will get it up to 6250RPM.

    5131371 3 blade 15-20 'Swirl'
    1995 SL750 80 HP @ 6000 rpm
    1996 SLX780 90+ HP @ 6250 RPM
    1996 SLT780 90+ HP @ 6250 RPM
    1997 SLT780 93 HP @ 6350 RPM

    The '035 impeller takes 80HP power to spin up to 6250RPM. Your 780 engine is rated at 90+, so I would expect another 100+RPM with the '035 installed, to maybe 6400RPM. Still well within the 6700 RPM limiter of the engine CDI.

    The '371 was the beginning of the change from four blade to the three blade impellers, but otherwise seems similar in engine power requirements to the '079.

    Note that the three seater SLT hulls have more weight and water drag than the smaller SL hulls. That translates into a little more engine load from the same impeller when running in the SLT hull.

    The larger SLT hull also accelerates more slowly, which puts more emphasis on the impeller's ability to 'hold on' to the water and resist cavitation when launching from idle.

    I expect the '371 impeller is a better match overall for the SLT hull than the '079, but the '079 impeller would work OK.

    The '035 impeller would also work, but allow the engine to rev higher to about 6400RPM.
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  6. #6
    TopCop931's Avatar
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    Quote Originally Posted by K447 View Post
    I expect the '371 impeller is a better match overall for the SLT hull than the '079, but the '079 impeller would work OK.

    The '035 impeller would also work, but allow the engine to rev higher to about 6400RPM.
    First of all, I would like to thank you for going to all this trouble to help me out.

    With the 371 on I was topping out at 6240 WOT according to my MFD. If my shaft was bad the entire time, as I suspect it was I guess that may have slowed me down a little. I ran good at 6240. The question is should I push the old girl a little more just for the sake of trying the 035 impeller? You never know if the extra rpm's will tire her out. I can't stay up on WOT too long because of my shoulders so I may try it out. If I don't like it I can just pull it right back out.

    Thanks again dude. The chart you pulled up wasn't even the one I found on here earlier today. I appreciate you taking the time.

  7. #7
    bowsniper's Avatar
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    ok let me know when ya want it.. keith has it all layed out for ya here looks like..the wrong prop could put too much load on the engine.. like lugging in 5th gear going up a hill. that could hurt the engine. i would use the reccomended one for you ski and engine combo. stay on the safe side.

  8. #8
    TopCop931's Avatar
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    Quote Originally Posted by bowsniper View Post
    ok let me know when ya want it.. keith has it all layed out for ya here looks like..the wrong prop could put too much load on the engine.. like lugging in 5th gear going up a hill. that could hurt the engine. i would use the reccomended one for you ski and engine combo. stay on the safe side.
    I am going to get the broken stub shaft tip out of the swirl later today. Then I will reinstall it and see what the clearance looks like. One blade has a minor burr on it that can be taken off with a file. It may have gotten there from when the shaft broke but there is no damage at all to my extension ring.

    I will send you a PM on the stator.

    Thanks.

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