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  1. #1
    EZ Dock of Long Island Shibby1485's Avatar
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    A Closer Analysis of Dyno Charts

    Kinchyele brought my attention back to the Riva Dyno Charts:

    http://rivaforums.com/groupee/forums...4/m/3871080771

    1. I have no followed closely Jerry's findings with his new A/F guage setup from DynotuneNitrous.com, but I found it for starters interesting that Riva can maintain a NEAR identical A/F for every mod they install... That's with the stock ECU. I wish that we could throw one fo our skis on there equipped with a RR ECU to see what it would say.

    2. The boost reading continually increased with EVERY part added, EVEN the Riva Intercooler... They showed boost readings stock, with power filter, with Vortech, and then with power cooler... i would have thought boost would have stayed the same or dropped minimally when they added the Riva intercooler

    3. for years now we've be trained to think 8100, 8100, 8100..... why according to that Dyno cahrt, 8000 is the magic number. it yields the highest torque reading and highest HP readings in every single column pretty much, except for one, but the difference 0.4 hp... yet the other 3 columns shows max HP at 8000 rpms.

    4. the HP drops starting at 8100 rpms, and DRASTICALLY drops somewhere between 8100-8150 ... . which also means that it reaches it's maximum somewhere either dead on at 8000 rpms, or slightly thereafter at about 8050 rpms...

    just bored, looking over comments on all the threads as a whole, and that thread about stock rev limiter really drew my attention more closely at the Riva dyno charts, and I thought it was worthwhile bringing up and having more people take a loko and take a stand on where we should be. Does anyone else see that maybe we aren't running optimally at 8100? I'm more inclinded to run my ski at 8000 rpms... 8050 at the absolute most and stay away from 8100 since that IS the point where it begins to fall back down in power.

    god do i wish Riva would let us put a ski with the RR ECU on their dyno so we can see where the power maxes and fades with the RR ECU with our own eyes on a format like they did with the stock ECU


  2. #2

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    Its my thoughts that at 8100 rpm the stock ecu starts to retard timing and take away some fuel to regulate the max rpm at 8200 and that the racing ecu starts this same event at 8400 rpms. With the set up (the mods done to your ski) and with either ecu--would not you ge going faster at 8150 rpms than at 8000 rpms and with the rr ecu be going faster at 8450 rpms than at 8300 rpms From my many years at drag racing you do not necessarly stop twisting your motor just because you have reached its max hp and/or torgue range. There is a happy meduim (sweet spot if you will). If a radar gun or gps shows a higher speed at 8200 and 8400 rpms-why not just go there As long as the fuel that has been cut back (volumme--not ratio) I would think you would be ok. You do bring up an interesting debate Shibby.

  3. #3
    Site Admin Green Hulk's Avatar
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    Shib, if i set your prop up to run at 8100 and you obtained a GPS reading and then i repitched your prop to run at 8000 im betting you would lose 1 mph.

    I have found that RPM's = MPH.

  4. #4
    Quote Originally Posted by Green Hulk
    Shib, if i set your prop up to run at 8100 and you obtained a GPS reading and then i repitched your prop to run at 8000 im betting you would lose 1 mph.

    I have found that RPM's = MPH.
    Same here Hulk,When I put the Rotax stock class ECU with my Riva stage 1 there was no change but then repitch prop to get 8,400 and I gained 2-3 mph without any other changes.

  5. #5
    Site Admin Green Hulk's Avatar
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    Thats why im looking forward to the EMS setup and setting my rev limit at 8700

  6. #6
    ROTAX RACING performance
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    in a race car you can go for peak HP / RPM , because you have gears, but on a ski you have only 1gear, so RPM's will allways be = mpH.


    even in a race car you dont shift on peak HP rpm's , because you want the next gear kick in at a high RPM level

  7. #7
    way2fast's Avatar
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    Higher RPM's will only equal more speed if you are using the exact same prop and getting more RPM out of it. If the prop pitch is changed, more RPM may or may not = more speed. You could down pitch a prop so the engine is turning way over 8,000 rpms and you will loose top end speed for sure.

    The engine has to be able to turn the most pitch yet keep the RPM in the range where the maximum torque/HP is. This should equal your top speed.

    Another important factor is, jet pump performance. The RPM has to be kept in the range where the pump performance is highest. This is why Yamaha uses a reduction gear to bring their 10,000 rpm 4-stroke down to a pump compatable 8,000 range. Personally, I think todays pumps perform best at 7,800-8100 RPM. Go over that and you are not using any added horse power efficiently.

    Richard

  8. #8
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    Quote Originally Posted by way2fast
    Higher RPM's will only equal more speed if you are using the exact same prop and getting more RPM out of it.

    I think todays pumps perform best at 7,800-8100 RPM. Go over that and you are not using any added horse power efficiently.

    Richard
    +1

  9. #9
    Site Admin Green Hulk's Avatar
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    In theory that sounds great, but it doesn't explain why Bosio & Lemoine running 9000 RPM's are achieving 85+ MPH. Drop their RPM's down to 7900 where would they be?

  10. #10
    Quote Originally Posted by way2fast
    Another important factor is, jet pump performance. The RPM has to be kept in the range where the pump performance is highest. This is why Yamaha uses a reduction gear to bring their 10,000 rpm 4-stroke down to a pump compatable 8,000 range. Personally, I think todays pumps perform best at 7,800-8100 RPM. Go over that and you are not using any added horse power efficiently.

    Richard
    i used to think that until the 4 tec came out. the higher you spin these things the faster they go. the factory RXP's rev 9100+, go 82~83 mph in closed course trim, and go 0 to 70 mph in a tick under 3 seconds

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