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  1. #1

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    Ultra 150 Compression/heads

    ON 98 octane, whats the most comp you can run on std carbs?
    How far can you cut the stock heads before you run out of quench?


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    gtxscrider's Avatar
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    Quote Originally Posted by Spanners View Post
    ON 98 octane, whats the most comp you can run on std carbs?
    How far can you cut the stock heads before you run out of quench?
    I had my stockers cut to 145psi. It was a notable diffrence over stock. Dont knoe how much farther it could go.

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    Quote Originally Posted by gtxscrider View Post
    I had my stockers cut to 145psi. It was a notable diffrence over stock. Dont knoe how much farther it could go.

    What cc were they do you know?

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    gtxscrider's Avatar
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    dam there you got me . I have no idea my mechanic did all the work.

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    Quote Originally Posted by gtxscrider View Post
    dam there you got me . I have no idea my mechanic did all the work.

    No probs.
    Someone will churp in with some numbers soon

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    jonny5's Avatar
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    You can cut the stock heads to get about 155-160 with a 16 degree angle but a R&D red head at 150 psi will provide better performance, burn better and run cooler. Stock heads are just ok. Squish on stock was .060 ish R&D is .055.

    You can also get skiworx heads or ADA...with 98 octane about 165psi should be ok I dont know about the stock carbs because most people know how I feel about them. One of the best mods is any other carb than those.

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    Quote Originally Posted by jonny5 View Post
    You can cut the stock heads to get about 155-160 with a 16 degree angle but a R&D red head at 150 psi will provide better performance, burn better and run cooler. Stock heads are just ok. Squish on stock was .060 ish R&D is .055.

    You can also get skiworx heads or ADA...
    What head cc would you expect for 160psi?
    I'm always built all my 4st heads via cc in the head, not crank compression... nothign wrong by doing it that waym but its easier for me to cut a chamber to xxx size rather than hope it gives me 160.

    98 octane... whats max that I can go? 160??

    You and Morris are great with all this info... not excluding all those others out there who help

    This thing is going to be a hotrod from hell when I'm finished
    Whats the Ultra 150 speed record at the moment?

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    jonny5's Avatar
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    I think 40cc is going to be right at 160ish for stock heads. You can go a little more but not sure since havent done it.

    Single pipe ultra with light porting...maybe 74 if your lucky triples will get you to 80mph...give or take alittle depending on hull/tunner builder "money"

    You can go higher on compression if you like some have got R&D heads and milled those for flat top to 200psi but would need like 108 octane or 110 leaded.

    Once you hit 175psi you need about 108 36cc gets you 180psi

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    Quote Originally Posted by jonny5 View Post
    I think 40cc is going to be right at 160ish for stock heads. You can go a little more but not sure since havent done it.

    Single pipe ultra with light porting...maybe 74 if your lucky triples will get you to 80mph...give or take alittle depending on hull/tunner builder "money"

    You can go higher on compression if you like some have got R&D heads and milled those for flat top to 200psi but would need like 108 octane or 110 leaded.

    Once you hit 175psi you need about 108 36cc gets you 180psi
    Sweet.. so 38/39cc (170psi) on 98 should be good to go? thats about where I had worked - we get 98 at the pump here
    I know you can build a catalog machine, but I prefer to do it myself - part of the "Number 8 wire" culture we have here

    What I'm intending on doing is tiding up the ports and maybe some more work if I can find info, possibly coat the piston crowns, 38ish cc heads, gut the waterbox, mod the intake grate, change prop and build a nozzle ring setup.
    Hoping that will put it over 70 on CV carbs
    Depending on which class I race will look at carbs and triples... like the hp, but the test is going to be whether it ncan run with the modded RXPs on the track.
    Really need to just keep it on 98 as I don't want to be having to haul racegas around the place.. let alone the $$.. its super expensive here.

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    Well depending on where and what type of racing you will be doing with the ultra 150 ethier way you will have your hands full. They have never been a great race ski or even good for that matter as the hull suffers from handling. Now a good rider can make up some differance but the hull just doesnt hookup really well unless it's light chop and not really ruff.

    I myself also build my ski differant then just buying whats in the book. Now the stinger mod was just there so I bagged it. And I got a smoking deal on the heads and after trying a set of milled stock and the R&D it's no question I will stay with them. I need some 36cc heads to.

    Now I would do steps on the water box. If you gut it to much you could hurt it. If you gut it all the way the bottom could come to life but mid and top could suffer from no back pressure.

    You could try a gp1200 yamaha water box as those have been modified in some old kawi race ski's and are some of the best water boxes. Never messed with mine as it is fine for me as I do racing more part time ....and trying not to spend thousands like I used to..."trying" is the key word.

    Make sure you rejet the stock carbs ...

    Ya know in all honesty.....if you up the compression,clean up the cylinders, stinger mod, coat pistons and what ever else ...I bet the results be very close just adding 44-46mm aftermarket carbs and 150psi.

    I actually bet the aftermarket carbs and just 150 psi will run better then using the stock carbs....spending time on the cylinders..and not knowing if it will help you or not...Because I assume you dont have a flow chart program and also coating the pistons and what not.

    The carbs are a big problem if ya wanna race. For rec sure us them but for racing your ski .....you need bottom and mid and you will get so much more from just changing those out.

    It's my opinion but I have already done some of that stuff and I went back to stock compression just for referance....and put some 44 mikuni's on and wish I had done it first. Im now with 46's because I could not find some at the time. And I also had the 44's from a friend.

    Anyway just some food for thought I guess...but take notes on what ya do and do some testing and get back to us. It's the people who go on there own who find the other speed secrets and good set ups.

    Ok well good luck and let us know if ya have more questions.

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