Porting is defintely a skill. I've been porting cylinder heads for almost 10yrs now, and there is always something new coming around it seems. I've done most of the domestic V8's out there. AFR's, Brodix, Topline, TrickFlow, FordMotorsports, etc. I mastered the skill part a long time ago, but the subtle shaping of a manifold or Intake & Exhaust port is paramount. Shape is everything. Combustion Chambers have a huge effect on port flow also. I've seen the most beautiful port work gleam and glitter and just dazzle you to no end, slap em' on the ole' SF600 and you got a giant terd. But, i've also seen some that were partial port jobs that just rocked on the flow bench. A common mistake most people make is to focus on peak flow, which is not the way to do it. The flow from .100 to .400lift is the critical zone. Average portflow is the key to making anything run. Especially a pump gas motor. How many engines do you know of that have a .700 lift cam in them? Not too many.
If you have one of these giant cams, the engine will see peak flow once. It will see the lower lift (.100-.400) ranges twice. It is in these low lift ranges where most of the power will be made. You want the Head & Intake Manifold filling the cylinder(s) as soon as possible. With as much velocity as possible also. Small ports that move a ton of air is the secret. Make a port too big, and you can kill anything. Sorry for the long post, just thought i'd try to help shed some light on the subject. "Hint" Short side radius & Valve Job ??? There is alot to be gained there.

 

well you certainly got my attention... So have you played with the DS with your port work? I would love to hear more !

 

Well, unfortunately i have not obtained another DS motor. I'm interested in starting a 720cc build up. Yes, it would defintely start with the cylinder head. I really like the Falicon roller-bearing conversion for these bikes. But it's all money, right? I had done a complete Big-Bore engine on my last bike, which was an 86' 350X. With astounding results. It had oversized valves, fully ported head, custom cams, 12.5 Piston, Custom rod, Titantium Retainers, Springs & Locks, the whole deal basically, racing header, flatslide carb, Ignition upgrade, and gearing to match the new powerband. From a dead stop, it would consistantly put about 8-10 bikes on my buddies Bone-Stock Banshee. Which, i thought was pretty good for that bike, considering it wasn't even close before i did all the motor work. I mean, it only weighed 316lbs ! It was fast, for a stock swingarm 350X.
But, like i said, i'm looking for another DS motor. I've talked to Eric about maybe just getting a cylinder head, but man, they are really proud of those suckers. I intend to baseline the stock DS head before any porting. Before, during, and After all the port work, it will benched repeatedly. It will actually be on the flowbench several times during this process so the optimum short-turn radius can be achieved to the new bowl arrangement & valve job. So there will be some good math for me to go off of, as far as determining HP per cylinder figures, with a stock and ported head. I will do everything i can to get the most low-lift flow out of the stock head and valves and compare those numbers to the baseline. Then, i will install the oversize seats and valves, and continue to maximize that set up until i've reached the limit of airflow potential. I really need the detailed information of the head, like port volumes, bowl diameters, flow figures, etc. The process i use, is, first thing is to determine the Bowl Dia. to Valve size % i want to use, (which is found through a small formula that is based on displacement) then rough in the bowl, rough in the valve job, Straighten the straight wall & raise the roof, then do a small blend on the short -turn radius, and flow test it. Then keep workin the short-turn in small amounts and repeat flowtesting after each adjustment, until the low-lift numbers peak. Finally, touch up the the valve job with stones, Correct any errors with valve tip heights, and BAMMO !!!! I'm ready to shoot myself !!!
Well, i hope that helps some. There is a ton of information on the subject, which, i couldn't stand to type that long. [img]i/expressions/face-icon-small-happy.gif[/img]