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  1. #1
    Paul2005GPR's Avatar
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    Cut heads and reliability

    Has any one had any problems with reliability after going to a higher compression head...back and forth between getting my 1300 head cut for 150 psi...


  2. #2
    mike1706's Avatar
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    yeah i want to know too very good question about that oh by the way paul what was your gain on putting the 1200 waterbox

  3. #3
    Paul2005GPR's Avatar
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    didnt drop any rpms with the free flow..

  4. #4
    "just sayin".. jetdave56's Avatar
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    Paul be more specific about reliabilty..what do mean... you'll have to run 93 oct. to go with the higher engine temps...

  5. #5
    "Hustler" Inkaddict's Avatar
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    Quote Originally Posted by Paul2005GPR View Post
    Has any one had any problems with reliability after going to a higher compression head...back and forth between getting my 1300 head cut for 150 psi...
    Quote Originally Posted by mike1706 View Post
    yeah i want to know too very good question about that oh by the way paul what was your gain on putting the 1200 waterbox
    As long as the head is cut properly it will be as reliable as stock however you will need to decide how much compression you want it cut for and you'll have to run a fuel controller..

  6. #6
    mike1706's Avatar
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    but my question is if the motor is going to last 300 stock with the head cut to 150 psi is going to last 200 hr or is going to be the same as stock

  7. #7
    Quote Originally Posted by Inkaddict View Post
    As long as the head is cut properly it will be as reliable as stock however you will need to decide how much compression you want it cut for and you'll have to run a fuel controller..
    agreed!
    I`m still running a milled OEM head. the lip was cut off to make it 145/145/142. Comp numbers vary a bit from test to test bc of the gauge, temps, and method used.
    I`m also using a controller with the milled head and Kawi FA. I have the stock SS back in...
    so,,, the controller has the transitions smooth and the mid still hits hard...

    having to use 91-92, could possibly get away with 89, but for "a few dollars more" (great movie) why chance anything...

    if you just want to gas and go, stick with the stock comp numbers... if you want a little more umpfff, little better accel and possibly the ability to run a steeper pitch prop then do the head...
    I know hopatcongDan, has run fast numbers with stock compression.

    reliability: I had done the head at 50 and now at 120+ hours and haven`t touched it since...

    how many hours are on your ski?

  8. #8
    Paul2005GPR's Avatar
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    I currently have 85 hrs on my gpr. I dont want to cut the head and then run the risk of throwing a rod or burning a crank bearing, it runs great right now and i dont want to mess that up...I am about as particular as Pale Rider about my ski, I see that he has had no problems, I feel a little more reasured...

  9. #9

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    The 150 psig has gotten a bad rap through the years. IMHO It is not the compression that is the issue, but how you treat the potential problems once the compression has been pumped up.

    The quick answer is that the stock yamaha cooling system is more than adequate to handle the extra heat, so where is the problem?

    Are you jetted properly?
    Is the jetting tuned properly?
    Was the head work done to stave off detonation i.e reshaped the domes or staggared compression?
    Will you always run with fresh 93 octane gas, or will it sit in your garage for weeks/months at a time?
    Is the bottom end (crank and bearings) strong enough to handle the extra compression, or is your bottom end worn out?
    Is your impeller to steep for your engine?

    Once you increase your compression, any one of these things (and a few others) may come up and give you grief. In other words, you are a lot closer to the edge than corporate Yamaha was willing to take you in the quest for high speed and accelleration. Their strategy has always been more cubic inches rather than RPM's to increase HP.

    So if you plan to "pump it up" do yourself a favor and follow the instructions of the builder/tuner who had the head cut for you. Different tuners have different strategies with different timing, fuel requirements, plug requirements, etc. They are the ones who show you how to get the most out of increased compression without risking your engines "life expectancy".

  10. #10
    Almost's Avatar
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    Is It better to buy after market heads like Riva's? Or is it possible to have the stock head shaved down well enough that reliability is negligible between the two?

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