alright round 2 of my composite endevour. made a nice mold out of steel and aluminum this time instead of using the rapid prototype machine.

Curious as to what everyone thinks of the surface finish inside. There are slight machining marks left from the mold (which i think is good) and also slight dimples in a lot of the corners of the weaves.

I think it would be best to leave it as it is but I was wondering if anyone thought a polished finish would be better, or better yet if someone has proof that a part like this flows better polished vs. smooth machined finish. As you'll see the surface is quite smooth as is.





This one show's off the dimples im talking about, not sure if they are significant enough to make a difference just a side effect of the layup process we used.

 

Dimple effect like a golf ball? Myth busters did a test on a car and claimed it would be more fuel efficient with dimples because air wouldn't "stick" to it, so maybe in theory the velocity stack could flow better with dimples... bench flow test?

 

i saw that one too. I understand how/why it works based on the fluid mechanics of it, but i dont know if the indentations on my pieces would be enough to get the same results. i know its a long shot but just curious about everyone input. there is a flow bench at school but not sure if i could have access to it as the prof in charge of it is a bit of a ****.

 

The boundary layer is a very thin layer of air flowing over the surface....the molecules directly touching the surface are virtually motionless...those small dimples can create air tumbling effect and keep the boundary layer on the surface from becoming completely motionless which in turn speeds up each boundary layer above the one on the surface....each layer of molecules within the boundary layer moves faster than the layer that is closer to the surface

 

ya this is known as the "no slip" boundary condition. its a simplification used for most all computation because it is basically true under most circumstances. when the air is tumbling close the surfaces (as the dimples are supposed to do) then the boundary layer can develop quicker into full flow

the picture should illustrate what we're talking about so please, no more basic fluid dynamic discussion. the viscosity is the thickness or technically speaking, the resistance to shear forces in the fluid. to simplify the higher the viscosity the more drag. inviscid means for calculation purposes you can ignore any "friction" as it becomes negligible.

since i guess i wasn't clear enough, im specifically interested in any experience anyone has with dimples this small on the inside of an intake runner.

 

I think Endyn was the only one I saw that put little dimples inside the intake ports of some heads. I thought he had some write up about it on his site..

 

I wish I could tell you if the dimples would work make any sort of difference im sure it will create a some sort of effect but is the effect going to account to anything. Intresting thought, Is this going to be on a top feed set of Itb's? I just ask because if so maybe it could help with atomizing the fuel better??

 

make 2 of those....leave one with dimples and smooth out the other one (sand it) do back to runs on the dyno switching back and forth and you will see if it makes enough of a difference to matter (im guessing it will be a very small difference and not enough for a dyno to pickup)

 

yeah i thought of the dimples used in heads but i believe that is more to help keep the fuel energized.
I agree that a dyno probably won't be able to tell the difference, im thinking like .5% to 2% flow difference and since this is the furthest section from the valve it contributes little, but if there is an extra pony to be gained maybe it is worth the effort.

what i might end up doing is make five, polish one, and then when im tuning i'll swap the polished one and see if i can see a difference on the plug, which im not really expecting to.

its quite smooth inside (apart from the dimples). its comparable to the smoothness of CF when sanded to 600-800

also the size is 61mm to 51mm inside diameter, and the engine will have itbs, but probably not top feed until i can afford a tuning solution which handles 8 inj.

 

you can run 8inj off the stock ecu its not hard to do....you just wont be able to phase between them.

 

very interested in what the difference in #s will be for flow & power (even if it is +1hp)

 

What problems were u having with the rapid prototyping.?

 

wasn't with the RPT itself but the mold release stuff we were putting on wasn't doing its jobs and the parts were a bitch to get off the mold, or all the mold release stuff would stay inside the part and would have to be sanded out.

since i made the new mold out of metal we can use a different release and are having much better luck.

 

I don't get it. Dimples work on golf ***** and cars because they delay flow separation, decrease the size of the wake, and reduce the pressure differential across the ball/car.

If you're concerned with wall wetting in the ports, I'd just leave a slightly rough surface in the last inch or so of the runners. Before that, I'm not seeing a benefit.

 

well the second 2 things are a result of the first. intake runners have interesting characterstics brought on by the fact that the flow is starting and stopping so frequently, even changing direction in some instances.

 

True, but why would that mean adding dimples would improve performance?

 

With inspiration from my B&W's, I inquired about the same thing while at KFI (dimpled ramtubes to simulate a B&W flowport to be exact).

Testing was performed, but with such negligible results, it wasn't persued.

 

which explains why this technology is not applied/used in any major racing sports, whether it be NASCAR, INDY, or NHRA

 

let me also remind you (as good as a discussion this is) there is a difference between air traveling around an object and air traveling through an object. otherwise we would have seen this technology a long time ago on valves and throttle plates