Cal, go back and read the article you linked. Does it say other mods need to be made for porting to increase power? No, it does not.
What it clearly says, is that to
achieve superior performance gains, porting in conjunction with camshaft modifications and valve sizes and exhaust tuning is required. This is the only point I've made repeatedly. I have not said that porting isn't important, nor that it's the basis of improvement, I have only said that as a single, standalone modification, it can not itself produce significant gains.
Speaking of numbers, that article stated that for every 1 CFM in increased flow, that cylinder would have an increase of .255 HP. Looking at the graph from the old Branch article shows an increase of about 9 CFM at a lift of .300", with the stock carb, which would add up to 9.18 HP.
I didn't write the article, so I have no idea of the 0.255HP is a constant across all internal combustion engines, but in speaking with numerous engine builders over the past years, and as recently as yesterday specifically about this topic, porting modifications
can only yield these gains
if the rest of the system (exhaust for instance) can scavenge the added air flow. The volume of the cylinder is the volume, regardless of how quickly you fill it. Combust it, then you must expel it and scavenge it. Therefore, absent of an exhaust modification (which this article does address in terms of balance) you can not get the power out of the engine.
I'm unfamiliar with the "Branch graph" but I do know that the stock 500 cam (which is the motor the OP is running) has a lift of around .270. So I think we are measuring apples and oranges in terms of potential HP gains out of a single, given motor.
As I said when I linked that article, I found it very educational and it
along with other research and dialogue with engine builders had formed my position that porting alone (especially on our primitive engines) is insufficient to produce
significant HP gains. I did not cite that article is a verbatim of
my opinion.
I feel like we've kicked this dead horse enough. I am in disagreement with someone's posted claims about the significant performance gains he derived on his
350 from simply porting. If you want to PM me and educate me, I am happy to benefit from your knowledge. But I have created too acrimonious a distraction in this thread for my participation or opinion to beneficial. Don't you think?
