AU N EGL

which would provide better performance?

1) a larger intake runner diameter for more volume of air going into the heads

or

Large diameter intake decreasing to a smaller intake to increase the air volocity
2) small intake runner diameter for faster velocity of air going into the heads

I am looking at using either AFR205s or GMPP SWGT LS6 Heads. The SWGT heads have a slightly larger volume at each lift increment then the AFR205s.

LS6 block

I have not decided on a cam yet, car is for road racing, not drag and no street use. ( not that I would want to get caught at )


TIA
Tom

teke184

iTrader: (5)

your post is a bit confusing...and i think you're confused.

there are 2 different things you're talking about

intake runner size...measured in CC. that's the "205" in the AFR 205, and the "215" in the TrickFlow 215 heads.

smaller runners build speed, and help boost power in the lower rpm range, at the expense of flow in the upper range.

then there is head flow data...measured in cfm. and that is also measured at specific lift increments.

flow is not everything...it's a compromise between air velocity from the runner size, and flow rate from the runner design.

AU N EGL

Ok thanks for the clarification

1989GTA

Couple of thoughts.

1. Best to have a taper. Maybe 2 1/2%.
2. The smallest cross sectional area of the runner needs to be larger than the pinch point in the head.

AU N EGL

Found this:

inlet restrictors have led turbo builders to develop carefully radiused and polished designs, whose shape is calculated using a factor called a Lemscape curve......
(source: Racecar-Engineering, August 2007, page 71)