Does anybody have any flow data on the GS head?  I'm going to do some porting and would like to know where to focus my efforts.

The standard rules/techiques for porting side-draft heads applies.

There is only a limited amount of work you can do to a GS head without making things worse. If you get the radius of the turn down toward the valve face wrong it will screw up flow.
The best results I've had have been with conservative, cleanup of the walls and a slight cutting down and fairing the valve guides. Also going to a 34mm opening with a gradual taper to the valve pocket looks very good (ask Dgyver if he has any pics of that head).


hope that is what you were looking for?

I have some pics if you want. Be warned, they are big-un's. Not sure how much can be seen from them. The ports are tough to take pics of. Nothing like actually seeing the head in person.

I cropped them down...

http://img.photobucket.com/albums/v64/dgyver/GS500/GSportedintake01.jpg

http://img.photobucket.com/albums/v64/dgyver/GS500/GSportedintake02.jpg

http://img.photobucket.com/albums/v64/dgyver/GS500/GSportedexhaust01.jpg

http://img.photobucket.com/albums/v64/dgyver/GS500/GSportedexhaust02.jpg

Ok, I see....  Watch the short side radius, mild cleanup, enlarge the opening to 34mm and taper to the valve.  

Are the intake/exhaust matched well already?  On the car heads I've done, you always have to increase the exhaust flow vs. intake.  Then the only other bike head I've looked at (CB350) they recommend to leave the exhaust as-is and focus on the intake.

Sounds like with the GS it's just a cleanup and call it good?

Yeah, the intake matches pretty well, but the exhaust side kinda sucks. the stock head has a lip on the bottom of the exhuast port at the face that must play hell with flow. Compare a stock port with GSportedexhaust01.jpg and you will see what I mean.  You still want to leave a mm or two lip all the way around to constrict back pressure waves but the the stock one is excessive.

oh I forgot to mention that if you do a 34mm venturi opening then you will have to use 34mm boots and carbs.  though I put my 34mm CR carbs on a stock headed motor and it ran fine.  
might want to consider leaving the diameter of the intake at 32mm if you don't want to invest in bigger carbs.

Hate to interrupt, but LOOK WHO IS BACK!! WB James!

Thanks!
Wish it were physically true. But its just that the hell hole I am at has gotten more consistant internet/phone service. So I can surf a bit in between going out to get blown up.  


Been posting more because I'm jones'n to build another GS when I get home.
:mrgreen:  :mrgreen:

I wasn't going to mention it but since somebody else did - good to hear you're ok!  Keep your brain on straight.

It's a good thing you mentioned leaving some of the lip - I would have ground it right off....  That's strange that they put it in the head AND the header.  If you look in the stock exhaust opening (header) it has a lip in there too.  I always grind that out and it seems to help flow a bit (seat of the pants is a little subjective though...).