Re: Port Dimpling??
 

What was the outcome? Did dimpling reduce the drag? Can you make the car draw or fade depending on the swing? Perhaps, even induce power fade?!

Re: Port Dimpling??
 

While I was joking, I was somewhat not....everyone gets excited about pretty porting but top porters will often tell you what looks nice and what flows can be two different things...

Larry Meaux

In 2010 I talked my best engine building customers into letting me try something I’ve wanted to test for the last 30 years or so. I took one of my old chipped up and slightly bent Alumina Burrs and rough ground just the entire intake ports on a big block Chevy Dart head all the way to the bottom valve job angle cut. Back on the dyno the engine gained almost 15 HP on a 950 HP engine. You could theorize that the intake ports are slightly now larger and it should have made more horsepower.

We kept testing this on the next 5 or 6 various types and engine CID sizes, grinding over the previous 60-Grit finish with the rougher alumina burr finish and gaining anywhere from 10 to 15 HP and lower BSFCs and sometimes shifting Peak HP RPM point 100 or 200 RPMs higher.

Textured manifold runner
Textured manifold runner
After those test results I talked another Engine Builder into trying out the rough carbide finish. That engine/car was previously tested on his chassis dyno as a baseline. I originally ported and polished the ports and chambers with 60-Grit finish in the baseline test. Next I rough carbide finished the intake and exhaust ports and chambers. Back on the chassis dyno it gained 17 rear wheel horsepower which is about 20-25 engine flywheel horsepower.

Re: Port Dimpling??
 

If I am interpreting the data correctly, the dimples on the golf ball are not actually for its drive distance per se. It is because the "dimples" create little pockets of low pressure "air" and air to air contact has less friction and allows the ball to fly straight and not wobble in the air. I can see where this possibly too simplistic explanation could also apply to the roughing up of a surface thus creating miniscule pockets of low pressure air that move less slow but allows faster moving air to slide off of it as opposed to all the air in the chamber moving at the same slower speed against a smoother surface. Does that sound right or am I full of it? Keep it PG gentleman.

Re: Port Dimpling??
 

Yes you are right in the ball park excuse the pun. This is also possibly why CNC heads are more favorable over hand ported. They may have the similar amount of material removed but the even lines in cnc porting probably has similar effect to the dimples like I said I need to grab a junk yard head and do some playing on the flow bench.

Dave Hetrick