650 open superjet

racerhx · 06-17-2009, 02:55 PM

Harry,

One of the promoters here in Texas has just started offering a 660 open ski class to try and get interest and participation from those of us that still have square noses and 650sx's laying around.

My question for you is would there be a benefit to running 62T cases on a GroupK ported 6m6 cylinder over either the 6m6 or 61x cases?

I've read all the Tech bulletins on the GroupK site several times, but figured this would be a question better served by this post.

Racing is a Supercourse format, 30 minute races on a mostly open course. I'm thinking that even ported, the 6m6 at 650 cc's doesn't need the extra flow of the 62t cases and dual carbs over a good set of 61x cases and a single 44 or 46.

I've got either a Pro-tec F body or a Factory Pipe type 4 dry pipe to bolt on it, and a girdled Bad Bones head that I planed to set up with pump gas compression (175 or less). I also have an old West Coast non girdled head (pump gas comp). Would I be better off with a modded stock head?

Do you need just the top case half and the cylinder?

What about the impeller and nozzle combination? Stock pump it's a 90 model hull, I know it's not the preferred pump set up but its what I have...

Thanks for your time and all that you do for those of us that will never know as much as you have probably forgotten over the years.

Group K · 06-18-2009, 04:36 PM

It sounds like a neat class. In short , I would strongly recommend a single 44 carb on either the 6M6 or 61X cases. A 78.5mm (657cc) 650 would struggle to make enough signal to make the 62T cases an advantage. The smaller inlet tract volumes of the 6M6 & 61x cases would be the ticket. I'd strongly recommend a repitched Solas "I" with a larger 93 or later nozzle, and modifying a stock head.

I would hesitate to use any dry pipe because they usually have such a poor low range characteric....a "B" pipe would be the ticket...and make sure you have the FPP manifold that matches the 6M6 exhaust port windows.

While the SJ hull is favored by many riders, We have built 77.5mm K650SXs that ran 52mph with a single 44 and a FPP pipe. The longer stroke of the Kaw motor would be an asset in a 660cc class....A well prepped 650SX could be a tough boat for a 660cc SJ to catch.

Respectfully, Harry Klemm

Quote:

Originally Posted by racerhx

Harry,

One of the promoters here in Texas has just started offering a 660 open ski class to try and get interest and participation from those of us that still have square noses and 650sx's laying around.

My question for you is would there be a benefit to running 62T cases on a GroupK ported 6m6 cylinder over either the 6m6 or 61x cases?

I've read all the Tech bulletins on the GroupK site several times, but figured this would be a question better served by this post.

Racing is a Supercourse format, 30 minute races on a mostly open course. I'm thinking that even ported, the 6m6 at 650 cc's doesn't need the extra flow of the 62t cases and dual carbs over a good set of 61x cases and a single 44 or 46.

I've got either a Pro-tec F body or a Factory Pipe type 4 dry pipe to bolt on it, and a girdled Bad Bones head that I planed to set up with pump gas compression (175 or less). I also have an old West Coast non girdled head (pump gas comp). Would I be better off with a modded stock head?

Do you need just the top case half and the cylinder?

What about the impeller and nozzle combination? Stock pump it's a 90 model hull, I know it's not the preferred pump set up but its what I have...

Thanks for your time and all that you do for those of us that will never know as much as you have probably forgotten over the years.