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    Compression RXP-X

    What would be the best compression for a RXP-X?. The ski is fully modded for CC racing. Ive been told the higher you can go the better. But was also told today, lower compression is better?


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    R88ory RXP's Avatar
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    Quote Originally Posted by dave76 View Post
    What would be the best compression for a RXP-X?. The ski is fully modded for CC racing. Ive been told the higher you can go the better. But was also told today, lower compression is better?


    Lower is safer for big boost when you say fully modded, what spec/class are you running in?? What mods have you done??

    Compression depends on cam timing alot, on a good engine you should get from 135-150psi depending where you have the crank setup, advanced will give you better bottom and mid which is good for CC and retarded will see better top end power.

    I tend to run mine in the neutral position as its best of both then.

    R88

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    It got WIFI and touchscreen ! PWCGUY's Avatar
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    Quote Originally Posted by R88ory RXP View Post
    Lower is safer for big boost when you say fully modded, what spec/class are you running in?? What mods have you done??

    Compression depends on cam timing alot, on a good engine you should get from 135-150psi depending where you have the crank setup, advanced will give you better bottom and mid which is good for CC and retarded will see better top end power.

    I tend to run mine in the neutral position as its best of both then.

    R88
    I have an 08 P-X and can say that after experimenting with cam timing that the best position is 135 - 140 psig cranking compression. 150 psig is way to advanced for the stock 08 cam and the boat will run slower all around in that position. The earlier model stock cam's ( pre 2006 ) run best with higher cranking compresion.

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    R88ory RXP's Avatar
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    Quote Originally Posted by PWCGUY View Post
    I have an 08 P-X and can say that after experimenting with cam timing that the best position is 135 - 140 psig cranking compression. 150 psig is way to advanced for the stock 08 cam and the boat will run slower all around in that position. The earlier model stock cam's ( pre 2006 ) run best with higher cranking compresion.
    Good info, I have only ever run the earlyer cams apart from in stock class boats where it has to stay the same but then I dont bother playing with the cam for that.

    R88

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    Quote Originally Posted by R88ory RXP View Post
    Lower is safer for big boost when you say fully modded, what spec/class are you running in?? What mods have you done??

    Compression depends on cam timing alot, on a good engine you should get from 135-150psi depending where you have the crank setup, advanced will give you better bottom and mid which is good for CC and retarded will see better top end power.

    I tend to run mine in the neutral position as its best of both then.

    R88


    Maybe this will help. The ski is open class. It has a C-kit, Motec ECU, 05 model cam, lightened valves, valve retainers, bigger intercooler, race manifold, bored throttle body, 60 PSI injectors, rrfpr, timing has been retarded, 4 inch front air intake, ported heads and the other stuff is not worth mentioning as it has nothing to do with making power. All of the equipment is from Les Cooke. The ski was built by Gold Coast Seadoo in Australia.

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    R88ory RXP's Avatar
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    Quote Originally Posted by dave76 View Post
    Maybe this will help. The ski is open class. It has a C-kit, Motec ECU, 05 model cam, lightened valves, valve retainers, bigger intercooler, race manifold, bored throttle body, 60 PSI injectors, rrfpr, timing has been retarded, 4 inch front air intake, ported heads and the other stuff is not worth mentioning as it has nothing to do with making power. All of the equipment is from Les Cooke. The ski was built by Gold Coast Seadoo in Australia.
    Sounds like a beast, Gold coast know what they are doing so I would be inclined to leave it alone. Who supplyed and mapped the MoTec???

    What I have done in the past is Just played with the cam timing untill I get the most RPM, then when you adjust it and you get no more RPM just take it back a touch so that its sitting where you made the most power. To be honest so long as you got 135psi warm engine cranking compression you have a healthy engine, you will be able to get far more power by playing with the map so that it is perfect for your motor.

    Dont forget to clean and loctite the cam bolts if you remove them or undo them to adjust the cam.

    R88

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    Quote Originally Posted by R88ory RXP View Post
    Sounds like a beast, Gold coast know what they are doing so I would be inclined to leave it alone. Who supplyed and mapped the MoTec???

    What I have done in the past is Just played with the cam timing untill I get the most RPM, then when you adjust it and you get no more RPM just take it back a touch so that its sitting where you made the most power. To be honest so long as you got 135psi warm engine cranking compression you have a healthy engine, you will be able to get far more power by playing with the map so that it is perfect for your motor.

    Dont forget to clean and loctite the cam bolts if you remove them or undo them to adjust the cam.

    R88
    Gary watson supplied the Motec, Gary and Motec Pete are doing the mapping for VP109. The ski does go "ok" to say the least, but very interested in lightened crank and connecting rods. Just don't know weather to go higher or lower with the compression?

  8. #8
    R88ory RXP's Avatar
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    Quote Originally Posted by dave76 View Post
    Gary watson supplied the Motec, Gary and Motec Pete are doing the mapping for VP109. The ski does go "ok" to say the least, but very interested in lightened crank and connecting rods. Just don't know weather to go higher or lower with the compression?
    Well with a C kit and if you will only be running VP109 you could go up with comp, it will make more power and with the right mapping it will be reliable.

    The Riva pistons are getting some very good reviews on build quality, design and performance. They would be my choice!

    The Carrillo rods are prob your best option unless Les uses something different, Lightwieght crank will only make it rev "faster" and you will get that by going with higher comp, I have seen a lightwieght crank break clean in half on a Bkit boat.

    Obviosly everything hase to be balenced up when going with the light conrods.

    I would say that going lower comp really only suits the turbos, it allows them to run mental boost but you need anti-lag to make it go good from a stand still, If your staying SC then sure up the comp, she will fly.

    The 1 problem you may face is prop spin, the high comp engines rev so fast with so much torque they spin the prop out of the hole.

    R88

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    R88ory RXP's Avatar
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    ! other thing to watch is pump overstuff.

    Your ski must be in the 80s flat out which puts it in the danger zone for overstuffing the pump which can be very violent and throw you off at very high speed.

    I dont know all your setup tho as you may have done something to fix the issue or have something that helps reduce the risk.

    R88

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    I'm not in the 80's. Only going 77 MPH, running a bent 14/18 3 blade skat. I have a 1 inch pressure relief set up and still the RS grate. I don't have prop spin at the moment, but maybe i will with higher compression?. If I start getting prop spin maybe I could look at the pump, as that's still stock also??. Just looking for ideas at the moment. I don't think Les runs carrillo rods, I think he lightens the stock ones, but not 100% sure on that.

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