Don Terrill’s Speed-Talk

Well, I guess we can drag up the golf ball-type surface topic again now that a well-known engine builder is offering it as an upgrade to their regular CNC programs: http://www.besracing.com/cylinder-head- ... t-dimpling

Just add $400 to the cnc price.

Carnut1 wrote:Just add $400 to the cnc price.

And what do you get for your $$$?

Is this now considered a given way to improve the induction system performance, or does the discussion still go on... just not in this thread?

No debate in my mind from along time ago, like how fast super stockers where even before they threw in the Towel and allowed porting!

Does this work better with a carburetor or EFI? Dry air or "wet" air? Or does it not matter?

jim mcfarland was doing the dimpling deal back in the day when he was with edelbrock
intake ports and combustion chambers,its nothing new i personally like the burr finish that chad does on his cylinder heads

Another marketing gimmick.

Most of the gains are at the seat.






But they look really pretty so must therefore work?

Highly efficient seats are not the key to real good BSFC numbers!

joe 90 wrote:Another marketing gimmick.

Most of the gains are at the seat.

But they look really pretty so must therefore work?

Any w/wo dimpling tests on dyno or track? (Same engine, has to be max-effort deal, heads identical , same CNC shape/volume runners- dimpling ONLY difference)

Someone stated "all pro top teams want them", which do mean it Works?

Normal CNC porting leaves a somewhat rough texture, why would that be better?

Velocity changes within a port make for pressure changes.
Pressure changes make for fuel drop out.
Drops of fuel love to cling to a smooth surface and not break back up into finer easy to burn state no less vaporize!
This makes for more fuel being needed to make a given level of power and can lead to fuel wash on the cylinders walls and fast waring rings and Bores.

To prove this happens just place a drop of water on a stone kitchen counter top and then blow on it.
All the water does is stay in a ball, but move around the counter top.
Next place a drop OD water on some 80 to 120 grit sand paper and blow on it, now you will see the ball of water break up into a mist , or at least far finer drops!

smooth or rough, that fuel is on the walls of the manifold/ports, period.

The finer the fuel droplets are (better atomized) in the combustion chamber the faster and more completely they burn. This creates more power out of the same amount of fuel and less emissions because there is less raw and unburnt gas running out of the exhaust.

The fuel puddling is seen very easily in EFI systems with datalogging. In fact, the best systems use OEM-style "wall-wetting" transient algorithms to account for the dynamic conditions that affect addition to and subtraction from the "puddle."

Ever take a high mileage Ls head apart? You can see the pattern on the port walls where the fuel is spraying and "pressure" washing the port walls, the rest of port usually has a suprising amount of carbon and gook built up on them.

If there was anywhere this would be beneficial a high speed ssr comes to mind. If surface texture would help the air stay attached at higher speed before separation that would make a ssr that is shape challenged perform better.