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  1. #1
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    How to build 2006 GP1300r for top speed?

    I live in Florida and as you know we like our top speed racing....

    I have a 2006 GP1300r with 90 hours and perfect compression. Current mods are:
    D-plate
    14/20 impeller
    Riva intake grate
    R&D steering nozzle
    Riva free flow exhaust
    Factory sponsons in up position
    It may or may not have a performance air filter from the previous owner, I forgot.

    Depending on the weather I'm doing right around 70mph on the GPS. I can beat stock RXP's and keep up with Stage 1.

    What is the next step in mods to gain more top speed without making it a trailer queen? I do enjoy riding on the weekends and I know it's not the fastest ski in the water, but I would like to get it closer to 75mph.

    Tell me if I'm wrong, but I was thinking:
    Island Racing modified Riva or R&D ride plate
    Fuel tuner
    R&D heads to raise compression
    Riva trim tabs


  2. #2
    Prism's Avatar
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    That seems that pretty quick for the mods you have. What rpm are you turning that 14/20? I would forget the Riva tabs as they are not going to increase your speed. Find stock metal ones from a 1200 and shim them .060 to start after you get an Island or FF plate. 800 intake grate for top speed. Get rid of the free flow and go back to the stock sound suppression. Add a 1200 water box, fuel controller, timing key and mill the stock head to get 145-150 psi. Repitch the prop to 14/23 and recheck rpm. You should then be near the speed you're after or more if you know how to tweak stuff.


  3. #3

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    If you mill the head and add the keyway, wouldnt the free flow exhaust work out for you?

  4. #4
    Prism's Avatar
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    The free flow will always be slower than the stock sound suppression. 2 strokes rely on a sonic wave reflection to keep the fuel and air charge from leaving the exhaust port on the compression stroke. The 1200 box and stock sound suppression enhance that sonic wave and the outcome is increased rpm. The only downfall when maximizing that sonic refection is exhaust back pressure increases. With high compression, radical porting and timing this can cause detonation because of lack of flow. That is when the free flow is needed. I run raised jugs, 147psi compression and a 3 degree key all with a 1200 box and stock sound suppression without issue. I also have a friend who's ski I built that is Lowell ported, 3 degree key, 150psi comp with a 1200 box. We tried using the stock SS but would detonate cyl 3 at times. We tried many things to keep the suppression installed (dumping cyl 3 water, richening the fuel, decreasing timing to #3 etc) because we knew it would be fastest with the suppression. Finally we just installed the free flow and eliminated the issue. Its a fine line. You may like the piece of mind running the free flow, but in my experience your leaving speed on the table unless you really need it. IMHO its needed with comp over 150 and radical porting.

  5. #5

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    I see. I wasnt sure at what point you would want to run a free flow.. I like the sound and all, but I know the 2 stroke needs back pressure.. I used to run nitro rc, there is a very fine line at 48,000 rpm lol

  6. #6
    Prism's Avatar
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    Yes indeed. I own several as well. The sickest is the 1/8 scale on road that turns about 48000 with the short pipe installed and 30% nitro.

  7. #7

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    i miss mine, i had about as much into it as i have im my GPR LOL.. was a 4x4 traxxas revo with loads of parts on it. i hit a parked car at 30 and all it did was break a control arm and pop out a ball joint.
    Back to the op, i really dont see that much benefit buying $350 heads over just sending your head off to jim and have him mill it for you.

  8. #8
    Prism's Avatar
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    I have an older Revo 2.5 I put an OS 18tm engine into. All kinds of mods on it too. Lots of fun. Now about the heads...I guess guys run individual heads with changeable domes to alter compression as needed. The ones without changeable domes don't offer an advantage over milling IMHO. They were offered by the manufacturers as a way to increase compression which is easily obtained by milling the stock head for a lot less money. It is a product to increase sales for them but don't perform any better than a milled stock head.

  9. #9
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    Okay did some testing yesterday.... 90*F, 82* water temp, high humidity. 87 octane gas. 3/4 tank.

    On the GPS I got 66mph and 6800rpms. I'm 6'2 195lb.

    What steps should I take to get this thing moving in the mid 70s? Like a roadmap? My buddy's neighbor owns a machine shop getting the head milled is not an issue, how much to remove?

    Is this what I want to buy to remove the Riva intake that is slowing me down?
    http://www.ebay.com/itm/2005-Yamaha-GP-800R-Intake-Grate-/400733161597?pt=Personal_Watercraft_Parts&hash=ite m5d4d8ec87d&vxp=mtr

  10. #10
    Prism's Avatar
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    No that's not the intake grate you need. That's a stock intake grate that came off of a GP800R. When we (forum guys) talk about an "800 grate" we are speaking of the aftermarket version from R&D. Its a scoop grate. The difference between the aftermarket 800 or 1200 is the angle of the scoop. The 800 is more for top speed due to its shallower ramp. The RPM you are turning is low. You need more power or less prop. RPM needs to be at least 7050. Milling will help but you'll need a fuel controller as well. Most milled heads are milled between .015 to .020. any more than that and the squish band in the chamber needs to be cut. What ride plate are you now using? There are lots of small things you can do to increase power (RPM) and I would look at the sticky about everyone posting one speed trick. Are there any airflow mods done? Where is the pump shoe in the hull? Is it recessed slightly? (especially the front) Do a search on some of the things I've mentioned. You should be able to get that 14/20 to the needed RPM fairly easily which will bring your speed closer to 68 or so. 70+ if the hull, plate, grate, and small mods are done properly. To make a really fast ski its all the little things that add up. The biggest gains come from plate angle, power and hull stability at speed.

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