Turbo porting is something many dont think about when upgrading turbos but should. Most turbo housings have restrictive and rough cast housing. By porting and polishing you can gain a large amount if flow, especially on the turbine inlet and through the wastegates.
If you're doing a turbo upgrade, I highly suggest asking if you can have the turbos ported. Very small price for and increase in power, spool, wastegate control and egts.

I was in a hurry so I didn't do as good of a job as I typically do for customers. Usually they are very shiny.

 

My turbos are ported by the turbo builder just like in your pictures.. I think it makes a difference to go the extra mile but few do it due to the labor involved. Contrary to popular belief, due to the boundary layer effect, you do not want the walls totally shiny but rater lightly textured for optimum flow.

 

If you really want to do it right, check out Extrude Hone. Had this done on an intake and it was pretty effective.

 

This is true but people like shiny sadly, same with porting heads which I do a fair share off.
The compressor side on these is actually pretty good. Lots of turbos I can expand the volute a ton and increase high pressure flow and decrease air temps exiting. Here is a td04h housing from a billet 20t setup I did for a guy a few weeks ago.

 

I did an Exrudehone on my Stealth Twin Turbos' intake manifold and gained 25whp! This was on stock turbo's too.

 

I'd love to have turbos and heads done!

 

Extrude hone is great for smoothing but it's usually a secondary step. Have to take the bulk out with a die grinder then hone

 

Watch that video, with the right grit it's amazing what it can remove. I've seen the size of the chunks of glitter that come out firsthand. Aerospace companies use it and so do many others particularly when the casting is complex.

 

That is true yes but to take out a large amount in one section and very little in another you can't really do. Extrude hone is a great process but like anything it has its limitations.

 

Extrude Hone takes material from the areas with flow resistance, if it's not removing material it's not a restriction. Certainly CNC or hand porting would be used to change an overall base shape. Also, softer materials like valve guides or thin areas where material shouldn't be removed have to be protected, good operators know this.

When I had an intake manifold done the walls were flawless but somewhat rough as desired and a pretty decent amount of material was removed. I've been told that it's used in aerospace applications and to port turbos to include wheels but I've found no video of that yet.

 

I'll share a relevant example from my time working with jet engines. In order to maximize performance for one test, fan/compressor blades were polished to a mirror finish to eek out a few more pounds of thrust (which they did vs non-polished blades). Nevermind that the mirror finish wouldn't last in practice due to abrasion from air, particulates, etc. ;-)

As an engineer, I've not encountered a situation where higher surface roughness increased flow rate. In fact, we often seek higher surface roughness to slow down flow/increase turbulence in an effort to increase heat transfer (think cooling air fed to hot turbine airfoils).

 

Higher surface roughness does indeed increase flow rate by energizing the boundary layer air. Similar principle as using vortex generators on the upper surface of the wing to energize the boundary layer air in order to decrease stall speed by allowing a higher angle of attack before the onset of airflow separation.

A simpler and well proven analogy is the golf ball. Ever see the episode on Mythbuster where they covered a car with clay? One was smooth and the other dimpled all over like a golfball. The golfball car was more efficient as it had a lower coefficient of drag due to its "rough" dimpled surface. It's also a well known fact that if a golf ball was made with a smooth surface it would not travel nearly as far as it does with a dimple finish.

Ideally this is what you want your porting to be...

[url=https://flic.kr/p/JpKbzo]

 

I'm guessing that's why IPD switched to dimples.

 

Aerodynamic drag is a complex topic and our understanding continues to evolve as better tools become available. Computational fluid dynamics (CFD) has moved things forward, but we're still in the early stages of being able to accurately model fluid flows. The computing power required is significant and calibration (lab testing) is still a critical step.

You're correct that vortex generators "inject" energy into the boundary layer, but their purpose is increasing lift and lift ALWAYS creates drag. They do this by disturbing the flow/boundary layer in order to "restart" the boundary layer, improving the ability of the airflow to stay attached at high angles of attack, as you mention. Nothing in physics is "free", and the cost of tripping the boundary layer is higher drag, which doesn't increase flow rate.

Consider this... If tripping boundary layers on the low pressure side of airfoils decreased friction/increased flow while increasing the critical angle of attack, don't you think every high speed airfoil (supersonic airplane wings, jet engines, turbochargers, boat propellers) would have them? Yet, you find vortex generators on slow, "spam can" personal aircraft - think snoring, boring *** Cessna that putters along at 100mph burning 8 gph getting worse gas mileage than our gas guzzler taxed cars -- because VGs are an effort to improve stall characteristics and, ultimately, minimize the manufacturer's liability risk (and the mfg doesn't pay the fuel bill).

As an aside, most private pilots don't fly regularly enough to stay proficient and need all the help they can get in staying safe. Pilot error is the number one cause of private pilot accidents. Slower stall = slower landing speed = improved survival rate = lower product liability costs.

An example... P-51's have a unique, highly efficient "laminar" flow airfoil -- high performing because it avoided turbulent flow, keeping the boundary layer thin. This is why you see so many successful air racers using 70 year old P-51s or derivative designs. Think about that... Could a 70 year old automobile be competitive at, well, anything? ;-)

Golf ***** are a specialized case that have little in common with the passages in our engines. Because they spin in an uncontrolled, unpredictable fashion, you're stuck with a spherical shape and the options for minimizing friction/drag of a spinning/rotating spherical body are limited. Dimples are used because more effective methods are not available.

The primary source of drag in a golf ball has nothing to do with surface/skin friction (parasitic drag) -- It is driven by the high frontal area that leaves a large "wake" (aerodynamic drag). The dimples reduce this form of drag by inducing turbulence, which reduces the low pressure zone behind the ball at the cost of a negligible increase in surface friction.

I've seen the Mythbusters episode. Their results confirm the "golf ball" effect because frontal area drives most of the drag in automobile bodies. Automobile bodies don't employ dimples because there are more effective means in minimizing frontal area drag (e.g. changing body shape, like steeper slope in the 996 windscreen compared to the 993).

Getting back on topic... We're seeking to minimize the skin friction (parasitic drag) in the passages in our engines. Our passages have very little frontal area/aerodynamic drag, which suggests dimpling will have very little benefit.

Maybe IPD can provide flow test data for intakes that are exactly the same (same casting, processing, etc.), except for the last step... dimpling. Don't want dyno charts -- too many variables. Just isolate on the single variable in question in a highly controlled environment. As long as the dimpling doesn't change the flowpath and effective diameter/flow area, I'll bet $1 the smooth version offers higher flow -- assuming an appreciable difference can be (accurately) measured over such a short distance at a head pressure of ~1.2 bar, similar to our engine conditions.

Fascinating topic...

 

I was always under the impression that the intake side was kept rough to keep the fuel in suspension and not falling out into drops in the bottom of the intake. The exhaust side was always polished as much as possible.

Excellent post above, by the way.

Chris