Originally Posted By: Mean buzzen half dozen A.K.A. Hank
Just think of making the port window bigger. If you can make the window bigger it should flow more.
I would not make the sides of the port bigger, I would grind down the bosses, if you are going to keep the bosses & not go w/lump ports. .................... A great flowing head can be an absolute dog of an engine for driven daily driver. This great flowing head on a flow bench can look great on an engine dyno, but it could be a pig when actually installed into a car/truck or?
MBHD
Yeah, a street engine or daily driver works in the sub-4500 rpm, and big ports are don't work well in that range. Big ports at low rpm have low velocity, while at high rpm the work very well. It's like breathing in through you nose, small port and air moves fast, while breathing the same amount of air through your mouth is a big port which slows the air speed down. A street engine wants velocity to make up for the low rpm of the engine and shorter lift of a street cam, so you don't want to remove anything unless it is tripping up flow in the throat. Keep the port as narrow as possible, this is why the SBC Vortec cylinder head works so well. I made this little chart based on the flow tests I've seen:
Now the Autowerks (from tlowe) numbers are directly comparable to each other, but the test from the Santucci book and the T6Racing are done on different flow benches, so their numbers are not directly comparable with the Autowerks. But as Santucci recommends in his book, the stock valves with a good valve job and a little port and bowl cleanup showed a lot of flow improvement over stock. While taking the bosses out actually made the flow worse over just the minor improvements. I'm not sure what improvement adding bigger valves would make with the bosses in place. But adding the lumps with bigger valves obviously improved flow even more, and with the material from the lump added back to the port it likely improves velocity over just the valve job (tlowe noted that there was no improvement from a lump with stock valves). The flow numbers suggest that lumps are optimal for a street engine, but if you're on a strict budget a valve job and basic cleanup is still a significant improvement over stock.
