Race ski to freestyle ski

number5isalive

number5isalive

XXX
Hi everyone, I have a r/n superjet that is a Bill Chapin R&D prepped superstock, it has a mag pump, total loss, R&D dry pipe, M16 reeds, fully ported 787cc engine with Girdled ADA head (140psi) etc ect. I have pulled it down to put foot holds in and want to put a B-pipe on it and a single 48mm carb.
I have been told a B-pipe wont work because of the port timing being so high.
Does anyone have any knowledge on these engine setups and do you think it can be done.

Number 5.
 
BROSS

BROSS

The future right here
Location
Lake Norman, NC
A b-pipe will work well, it won't work as well as the dry pipe but for throwing the ski around the b-pipe is the best IMO. Has the ski always had low compression? The rings could be getting worn or maybe thats just the compression, either way you need to bump the compression to get it to hit on the bottom. Well good luck.
 
Cross

Cross

X
Location
WA
number5isalive said:
Apparently you run low comp to make up for the port timing?
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You wouldn't lower compression to make up for taller ports. You would actually want to increase the compression and/or the timing to help gain the loss of bottom from taller ports.
I would guess that Chapin would use his own R&D head not a ADA head. Does the dome list what size cc it it is? There could be multiple reasons why you have low compression. Time to start doing some investigating.
 
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number5isalive

number5isalive

XXX
Thanks for the replies guys, it had an R&D head on it but has been changed not long ago to the ADA but the R&D still ran low comp. The motor has been rebuilt with new flat top Kawi pistons which is what it had in it so nothing really has changed from when Chapin had it, I was just hoping someone had a similar engine setup so I could find out if it does have tall ports?
 
tricky1

tricky1

XXX
Location
Alabama
Yes I have several of them. What CC Domes are you running and what is the squish? If you don't know pull the head and check it out. Also are you trying to run pump gas one this setup?
 
number5isalive

number5isalive

XXX
Cannot tell what domes it has Tricky but do want to run pumpgas, should be able to work out what domes they are from the compression?
 
Matt_E

Matt_E

steals hub caps from cars
Site Supporter
Location
at peace
number5isalive said:
Hi everyone, I have a r/n superjet that is a Bill Chapin R&D prepped superstock, it has a mag pump, total loss, R&D dry pipe, M16 reeds, fully ported 787cc engine with Girdled ADA head (140psi) etc ect. I have pulled it down to put foot holds in and want to put a B-pipe on it and a single 48mm carb.
I have been told a B-pipe wont work because of the port timing being so high.
Does anyone have any knowledge on these engine setups and do you think it can be done.

Number 5.
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Why do you want to go to a single carb?
Why mess with the carb setup that's on it now? IMHO, you've got a complete and tuned engine package in there now.
Anything that you propose to do to it will take power and reliability away (most likely).
Again, IMHO....it might be better to sell the complete motor package and start over, if that's what you are after.

Oh, and I think you might find your current motor to be plenty suitable for freestyle, perhaps surpassing most "freestyle" motors in punch.
 
Big Kahuna

Big Kahuna

Administrator
Location
Tuscaloosa, AL
actually the motor sounds more like a true race motor, especially if Bill Chapin built it. may not have any bottom end. One of Jacobs motors was like that years back, it was all top end, the the point of being really hard to ride, when the mid range came in it pulled like a monster all the way through. The next year 2001 I think, they toned it back some to make it more manageble, It was a heck of alot slower on top end than Rius, Mac and others..... but he still won the WF on it...... you may could pitch the prop down but it may help, may not....... best bet is to just ride it and see how you like the power.
 
number5isalive

number5isalive

XXX
Yes I rode it a few times before we pulled it apart and it had more bottom end power than anything I have ridden before.
My buddy just bought it and he wants to put a single carb etc on it but I may talk him into keeping it as it is and just put the B-pipe on it and see how it goes.
 
thegoldenboy

thegoldenboy

RN Surgery... soon
Location
Toronto
number5isalive said:
Yes I rode it a few times before we pulled it apart and it had more bottom end power than anything I have ridden before.
My buddy just bought it and he wants to put a single carb etc on it but I may talk him into keeping it as it is and just put the B-pipe on it and see how it goes.
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I wouldn't worry about bottom end in the surf anyways... B pipe and single carb is easiest to dial in, and reliable.

Personally I'd focus on making the ski sealed up, draining water well, and being reliable.

It really doesn't matter what power you have in the surf. I'd rather have a mild setup than a wild one. You'll ride more days at the end of the year with a mild one. Less down time, less $.
 
Matt_E

Matt_E

steals hub caps from cars
Site Supporter
Location
at peace
thegoldenboy said:
I wouldn't worry about bottom end in the surf anyways... B pipe and single carb is easiest to dial in, and reliable.
Click to expand...

The motor is 100% dialed in right now.

Personally I'd focus on making the ski sealed up, draining water well, and being reliable.
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I would think that the current configuration is going to be more reliable than anything the average rider will whip out in order to create a "reliable freestyle engine".
 
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