Dimpled Ports, Power or Myth?

So glad someone finally shed some light on this myth.

Excellent holes for carbon deposits on direct injection

It IS cool to know that you can "reduce" the port size using this though.

Glad the golf ball was immediately brought up for cross reference. 👌🏽

On carbureted engine, intake ports needs to be rough to promote fuel and air to mix better. The exhaust port is usually polished to a rough sheen to lessen carbon deposit. Fuel injection already do perfect fuel delivery, no use for rough surface on the intake. You won't see plastic intake with rough surface inside bc you don't need it.

We used to leave intake ports rough on carb motors because the turbulence would help mix the air/ fuel on the way in.. but with port or direct FI more flow velocity equals more power

The boundary layer basically makes your port act smaller at higher flow numbers

There is one thing that he points out that is often overlooked as to why it can benefit when applied properly. On engines with short radius that is to aggressive, it causes separation. Dimpling the short radius help with the low pressure recovery as the air rounds that corner giving better flow at the valve. It is still somewhat as he says since it is reducing the port through that area, but it can correct areas that are inherent issues on the heads that you can't change otherwise.

So, save the dimples for the rear bumper cover :) .

Never really knew the mechanics of this, great info

I always thought the dimples were placed in specific areas of the intake tract to help with the flow of air. For example, you would place the dimples on the tract as it approaches a bend. At the bend you would put the dimples on the inner part of the curve but not at the outer part of the curve. This area would slow the air flowing over the dimples but allow the velocity to remain faster along the outer part of the curve. So that the air isn't crashing into a wall so to speak and being pulled around the curve of the intake tract toward the intake valves. It's like how F1 tried having 2 brakes one set for each side of the car. They would apply more brake pressure along the inside part of the turn slowing the inner wheels but allowing the outer wheels to have a higher speed.

I may be uneducated but I always thought it was to cause turbulence and mix the air fuel more in the intake port

Really interesting take on the old shot blast theory

You could use it on one side to make the air tumble.

If you have ports that are so big that it moves the optimal flow outside of your rpm range then yeah sure it's gonna work but like another commenter here said it basically makes your ports act smaller.

i didn’t know chad from cold ones was so well versed in engine mechanics 😂

I always thought that the purpose was to promote that turbulence at the surface to help prevent fuel pooling in the port. I've never actually heard anyone claim that it aids airflow.

I have seen people leave the bottom of the port rough to atomize any droplets so they don't run into the valve and dribble in , but ive never seen dimpling

Flow tests have literally shown that dimples on 90 degree bends in a intake runner do help but dimples all throughout the runner will cause to much turbulence plus this was big for carb guys because it also would atomize the fuel better creating a cleaner more powerful burn.

The closest thing to the behind the ball in a port imo is the short turn radius, particularly in a sub optimal design that you mught be stuck with due to class rules or budget, I wonder if a strategic bit of dimpling can help the air come around a nasty radius? I cant imagine it would hold trye across the rpm/velocity range, probably still result in a choking point higher up, but if you are running some big inch V8 on the street with vintage heads there may be a tradeoff worth making there. Unfortunately, those of us working with pennies tend not to have the ability to sacrifice several sets of even the cheapest old heads to such an experiment.