we saw a ford sedan gain 11% gas mileage because of the aero advantage it provided. the basic principle being, i believe, the divets creating a slip stream by filling those divets with ar and therfore having the air against air instead of the surface of the car. so.. why, at the right scale and placement, couldnt it work for engines?

it seems odd, but from the wind tunnel tests they showed it cut turbulence down and directed the air in a smoothed out the air flow. it seems that if you created a cushion of air for the air to move on it wouldnt negatively effect the engine?

 

mythbusters? lol

 

Are you talking about putting dimples in the intake runner? Not sure if I follow.

 

 

u wouldnt randomly go at it wth a dremel, it would have to be carefully machined and measured. you would need just enough depth/diameter and spacing of each dimple to allow air to fill it creating a combined cushion.

before there was an advanced tech section it was talked about in internal BUT the consensus was that it would cause more turbulence but after seeing the wind tunnel figures on, yes, mythbusters, it just doesnt make sense that it would. if the science holds true it should cut down turbulence and increase velocity/flow. i think its safe to say no ones really experimented with it hence the discussion.

think of what the dimples do.. it helps the ball slip through the air by creating an envelope of air. why wouldnt it work at some level or specific rpm level?

 

i think this is the reason they dont port and polish anymore, just port.

 

Ya when you cut down on turbulance you get too much laminar flow which causes a pressure decrease there for less density and with the laminar flow being smoother the fuel would ride along the top instead of mix around. You actually want turbulance in a cumbustion chamber for many reasons.

 

It's been a while since I've seen either one of them in person but I don't remember dimples on a SR-71 or a Space Shuttle. I haven't seen one in person but I bet the X-15 didn't have any dimples on it either. If it's good enough for the fastest aircraft ever flown, it's good enough for me.

 

The dimples induce turbulent flow which causes separation from the surface. This does reduce drag. However, the reason you don't see race cars or airplanes using this is because they need drag (space shuttle operates mostly in space-no air, and super/hyper-sonic flow is a different situation). Drag is the same force that creates lift for airplanes (turbulent flow over the wing = stall) and downforce for race cars.
For an intake I've read it both ways, smoother is better and roughed up is better. Someone probably knows, I don't. However, I'm not sure if the same principles apply here. The idea behind the turbulent flow reducing drag is that the rough flow prevents pockets of low pressure to form (as efficiently) behind surfaces (relative to airflow). In an intake the low pressure is being applied by the engine and it's a closed system for the most part. Plus it appears that manufacturers strive for laminar flow, and if anybody has done the research on the subject I'd bet on them.

 

I once worked for a team that Dimpled all of the rocker panels as well as crush panels in their super speedway cars.. then painted the underneath with a paint that looked similar to a stucco wall.... Aside from looking like complete crap it showed some gains in the tunnel

 

Regarding rough vs. smooth intake runners. Rough runners were generally used to keep the fuel suspended in the intake charge on carbureted engines. However, I have read that this is not entirely true as the runner design and charge velocity play a bigger role.

Regarding the dimples, I think we all agree it works on a golfball, and the delay in boundary separation created by the dimpling thereby reducing drag. However, the question arises, how would you put the dimples in the runner? NANO-ALUMINUM-EATERS?

 

well, both a smooth and dimpled surface would have a laminar boundary layer. the dimpled surface would have a smoother transition as shown n the picture.



in terms of mixing fuel and air, wouldnt it be a much smaller issue on todays EFI and to an even greater extent.. direct injection engines because of how the fuel is delivered?

 

that, id love to see info on.

 

The four forces applied to conventional flight is Lift, Gravity, Thrust and Drag. I believe that lift is caused by air flowing over the top of a wing faster than over the bottom causing there to be lower pressure on the top. The wings only cause drag because they protrude from the fuselage, thus drag is a undesirable by-product of thrust. Judging by the picture posted above of the dimpled and smooth golf ball the dimpling helps because of the unconventional shape of the ball. Spherical objects aren't designed to fly. Also, the dimpled golf ball is almost the complete opposite of the inside of a manifold. With the golf ball the air is flowing completely around the sphere whereas a manifold has air flowing thought a tube.

 

does the science of it change with shape?

 

Obviously not, I'm saying that air would act differently in different scenarios. Just because dimpling works well on a sphere flying through the air doesn't mean that it would work just as well for air flowing through a pipe.

 

Tried, tested, cussed, discussed, 20 yrs ago, by some of the hotrod braintrust...AIRC, Hotrod, Carcraft, had published material on this.

 

would you happen to hve an article or know where one is?

 

mythbusters..lol

I don't know about dimples, but have you ever looked at a C&C ported head? it don't have dimples but its not smooth

 

the finer you can get the fuel the better. the more surface area from more droplets, the better the burn the more energy you can extract AND its more complete as far as emissions.

also. this is semi sorta related but in a harley engine. so if you arent interested in my redneck ways stop here.

my dad has a harley with a S&S super G, and one of their intakes. well after observing how horrible the atomization was when i was tuning it and watching rain drop sized fuel droplets entering the intake.. i decided to modify the intake manifold in an attempt to increase atomization post carburetor. the intake tracts are very short, and basically split from the central source (carb) and then run 180 degrees apart (opposite directions to feed each of the cylinders in the Vtwin) to fill each cylinder. i took a sharpie and drew what you would imagine sound waves to look like along the bottom, concave proximal to the inlet, and convex distal to the inlet. and carefully cut grooves on the bottom half of the intake exactly symmetrical on both sides to create a similar effect to what you are describing, using a specific bit that was perfect for the job (i was able to cut at a consistant depth by allowing the mandrel to stop my cutting depth. no damage). and then i cleaned up the rest with an 80 grit sanding roll. (these engines really are pretty disappointing from an "engineered to perform" standpoint.)

in the intangibles, this modification excelled. my dad was/is thrilled. throttle response was better, power was better especially in the midrange (which matches his cams). it used to fall on its face really bad at only 5200 rpm from running out of air, but now it'll pull to nearly 5500. and fuel milage increased just over 2mpg avg. from any other time in its life. pretty cool stuff and welcome results on an engine not known for doing anything all that well except making noise.