wider rave valve for the 951?

[chris w]

Bill-

I assume you would be the guy to ask this question. Is there one available? at what cost? what is the width?

The cord width at the sleve is 61.4 mm as I measure on my cylinder. Then it chokes down a little near the rave valve. If the port is widened to match the sleve the effectivness of the rave would be reduced as I see it. A wider valve woud remedy that.

[Bill O'Neal]

Yes, aftermarket wide billet rave valves are available for both the 951 and the 785 motors.

They are 4mm wider than stock valves and require that you remove the clyinder and ship or bring it to us to modify the slot for the wider valve.

4mm oversized billet valves, $85.00 each
Machine clyinder slots for valves, $ 125.00
Set up valves, $60.00

Total for all of the above, $355.00

Or you can just buy the billet valves from us and machine the slots and set them up yourself, $170.00 per pair of valves.

[chris w]

Hmm-

So now is it worth it for a stock piped ski?

The stock valve is 60mm but the stock cord width of the port is 61.4 with room for improvement, a little.

also, the bottom of the exhaust port is 2mm higher than BDC. This is the first I have seen on a motor. If the same radius was kept and brought down to TDC, this will give more time in blowdown, and with the wider valves allow for a slightly wider port. This should make for improvement in acceleration even with a massaged stock pipe.

Am I on track or way off base?

OK- Help me justify the change. When should stock valves be replaced? Mine have a little of the plating chiped / blistered away. How critical is changing them.

[ December 11, 2002, 01:26 AM: Message edited by: chris w ]

[Bill O'Neal]

Chris,
This is a modification that is usually reserved for full out racing superstock motors with extensive porting. I have no idea what it would do with a stock pipe, and oem porting or even mild porting. Lowering the exhaust port will do you no good. You can make gains by widening them though, even with OEM rave valves.
As far as your valves being a little chafed or scored up, well, just about all the valves I see have some scoring or chafing. I inspect each oem valve, then decide if I think it needs replacing. Usually, I look at the shaft for excessive wear, and if too much is present, I replace the valves with oem style valves from SBT (much cheaper, but made to oem specs or better).

[chris w]

so the port can be widened with the stock valves? The only reason I was thinking of lowering the bottom of the port was to keep the same radius of the bottom of the port for ring life, while giving more port area in blowdown before the xfers open. But that would be alot of hand work for questionable gains. Maybe I will go to a larger radius of the bottom to gain the area at the wide part of the port with far less grinding.

[Markrxgti]

Chris, you are playing with fire!

[Technical Support]

Leave the porting for the experts. It's not something you want to just experiment with unless you have an abundance of parts to ruin.

[chris w]

you know Mark, cant leave well enough alone. [img]smile.gif[/img]

It looks like I am not going to screw with any port timeing but there can be small improvements in matching, there is also small differences in the xfer ports that need to be corrected/ matched left to right. Particularly removing the choke point of the exhaust port the cast width of the exhaust port is almost 2mm narrower than the cord width of the port.

Have some insight for me?

[ December 11, 2002, 04:53 PM: Message edited by: chris w ]

[Markrxgti]

As you know Chris I have experimented with cyl porting among other things.I have an extra set of cyl that are proof of what can happen.Match porting is fine,make sure to have a chamfer.As little as .015 on transfers will affect the performance of this engine.Not nec good.The widening of the exhaust might get you something,but it will definately stress the rings as far as longevity.Sea-Doo has really gone to great lengths to match all the pieces of this motor specs to get the output they do.
This motor with current port specs will spin 7500 rpm w/ coffmans etc.Messing with the porting and turning 7100 rpm is trouble brewing.
The minute one parameter is changed it seems that other changes need to be made to get the motor to run right.
As it is when you are just rebuilding the motor if you do not set it up right you will certainly notice the lack of power.

[chris w]

SBT Tech-

granted indiscriminant grinding would be foolish (the practice of many socalled "experts") I have given up being an expert.

[Bill O'Neal]

Chris,
$450.00 will buy you an excellent recreational porting job that will give you some very mild, but good gains that are noticable in performance, and will not adversly effect the longivity of the motor.

Do not attempt this at home unless you are qualified and have experence with the 951 engine.