Thread: Turbo Porting & Polishing

It isn't a poor mans version as you stated because extrude hone leaves a polished finish while working it with a die grinder/Dremel does not it leaves a rougher surface.

Many argue that the rougher finish like that of a ported head atomizes fuel better then a extrude honed in regards to heads/intake manifolds. There are many ways that both are better and/or worst depends on the application and location of what is being worked.
I brought up ECM because it's another means of removing material etc

the "rough" finish on a head port that you say helps atomize fuel better is not correct either.

Yes they argue, but thats all they do..nnobody has proven a rough surface will guarantee better flow in a head, where a polished surface will prevent (to an extent) carbon build up which will at least maintain flow as opposed to preventing it like the jagged non-uniform build up that a rough surface would induce.

The theory and only arguable reason behind a rough finish is to maintain laminar flow by allowing the flowfield's boundary layer to remain attached to the surface/s. When boundary layers detatch, transitional and turbulent flow ensues and are obviously less favorable for atomization and "good" mixing... At the approximate value of Reynolds Numer (Re) that the common cylinder head port sees its not going to make a difference thats why alot of people port AND polish and the results arent much different from a basic port job initially but over time, the polished head will flow beter becasue it has less or at least a uniform build up of gunk. The carbon build up and other gunk that will ensue over time will provide enough "roughness not to mention that surface will never be perfectly flat.


Now onto the turbine housing. a rough surface on the turbine wont be very beneficial. A smooth/polished surface is beneficial because it will prevent carbon build up, whereas a rough surface essentially promulgates said build ups. The boundary layer in a hot-ass turbine housing with a huge rotational blade/wheel mass spinning at 10-20,000 rpm or higher will create a horrible swirling vortex of entropy-like environment throughout lol, not to mention the exhaust flow is most likely already turbulent or transitional at best from the combustion process and all of the crap it has to pass through to get to the turbine wheel.....

so...rough surface/smooth surface not really a big deal...thats why OEMs like Borg Warner and Honeywell just cast them and pump them out. If you want to convince yourself read up on the basics of Fluid Mechanics and Thermodynamics. A fundamental understanding of these subjects and some examples will allow you to see that in such a harsh and dynamic environment the surface finish doesnt make huge differences in relation to flow imporvement.

Some people reported a couple hundred RPM of better throttle response from the Extrude Hone process but whats 300 RPM, really...lol I had my turbine done and didnt notice a difference on my GT30R, but I know it has much less carbon build up than if i didnt polish it...

The only thing that can change from removing (a maeasureable amount) material from the turbine housing is a change the Aspect Ratio (A/R) which can have some noticeable affects....

Im curious to why you think a rough surface will enhance atomization, or why it will improve the flow in a turbine housing please explain?

again, to clarify...

Extrude Hone will leave a smooth finish (not perfect, but close). This will prevent carbon build up. The potential to have improved flow exists, but most likely wont happen LOL

The Die Grinder effect (agree w/ vadim that a dremel will just knock surface rust off cast iron and not do much real work) leaves a somewhat "rougher" and non-uniform finish depending on how good you are with it. If you just use it to deburr and get rid of flashing etc, that will certainly improve flow by eliminating unecessary obstacles the flow must pass and "bend" around. But if you create an uneven surface by leaving behind measureble strokes and grinderpaths, you just introduced more small obstacles and essentially did nothing... the rough surface will not do much to prevent carbon build up...

So technically, this isnt even the poor mans extrude hone, so you're right about that lol.
If done correctly, at best a deflash, deburr and maybe a filleting of the turbine inlet may help a little, but I doubt it would ave any real noticeable effects especially as time goes on and carbon builds up...

I did not say a rough finish on the exhaust side was beneficial , a smooth finish will allow the exhaust gases to flow
Now intake side a smooth finish as extrude hone will not atomizeruel like a hand port would due to the smoothness not allowing a mixture but instead a puddling effect and not atomizing. Now injector placement plays a factor as if the injector sprays directly to the back side of the valve it makes no difference.
A proper set up with the injector set up further up the runner away from the head along with a hand port and airflow will atomize the fuel more then say the same set up extruded.
Also extrude hone is like a blind guy porting. Porting as a lot to do with radius, bowl, etc. extrude hone just takes away it isn't controlled.

A ideal set up when I can will be a full port intake side by hand with injectors up the runner then extrude the exhaust side.

Hope that clears up any confusion

Now I plan on using the carbide burr to even out the surfaces and casting marks on the exhaust manifold and Jpipe. But after I probably will use the dremel to get it to somewhat mirror smooth finish. This is a ton easier on our heads since they are aluminum, cast iron is a harder beast (literally).

there is no confusion. I want a proper explanation of how surface finish affects atomization, not just saying smooth = bad, rough = good.

Atomization and uniform mixture is primarily dominated by the fluid it is being mixed into not the material it is surrounded by. Your just making general statements and not backing them up with real science.

you are saying surface finish = atomization effect. Explain

BTW, I'm not trying to make this a pissing contest or have anything against you, but I think you have misunderstood certain principles and how certain aspects of fluid mechanics really work and are unintentionally passing along incorrect info

jRod, he is correct about the intake side needing a rough texture to help atomization. Look up any any tutorials, they all say the same thing. Only exception to the rule is direct injection, and we all know why...

you are saying surface roughness DIRECTLY affects atomization, correct?

Even though this thread was initially about turbine housings, there is no atomization going on in there, so why the rough finish? lol...I think that point is moot by now... It seemed like the other guy was defending the dremel/grinder method as being better than Extrude Hone for a turbine housing. Since bringing up the head port surface finish, that kind of answered itself, didnt it?

What I dont like is that you guys are just blindly stating that a rough surface = better atomization because tutorials say so or thats just the way it is. That is a very shallow statement. Its like saying gas makes a car move...youre skipping a few steps, right?

surface conditions will affect flow only! atomization is a different process which takes place within the flowfield. so the characteristics of the flow field are what dominate the atomization process. The major ones being: pressure, temperature, velocity and density. Yes the surface finish can affect flow if it causes any disruptions such as causing the boundary layer to dettach, but the idea of leaving a slightly rough uniform finish, rests solely on the hopes that the port can help the flow remain closer to a laminar state as opposed to completely turbulent by attaching or "energizing" the boundary layer. That is why better mixing will occur. Not just simply because alot of people say so LMAO.
It is possible to have a smooth inlet surface (ports) and still get good mixing, but other factors will usually be less reliable. This "roughness" of a finish we are discussing is very localized. Its less than what a dremel would leave. leaving this slightly rough surface is a safety hunch over leaving a mirrored surface. We know that the flow will be turning as it enters the port therefore has the potential to lose energy. without adding energy at the point the flow will go turbulent as the boundary layer will separate...if the surface is too rough or lacks uniformity the flow will go turbulent.

so back to the original point of this thread taking a die grinder to your turbine housing for anything more than flashing removall/deburring is a bad idea unless you plan to clean it up and get it as close to polished as you can like Vadim mentioned he would attempt with a dremel, etc...


If you want to port your intake and leave it "rough" it doesnt necessarily have to be rough, just not a mirror-like finish for the purpose and hopes of boundary layer/flow manipulation.

I think part of our problem is that we're talking about many different things in this thread, and no one is differentiating between them.

Port matching
Wastegate porting
General porting
Polishing

To sum up:
All of these things are good to do to a turbine housing when applied properly.
A Dremel and grinding tool is not aggressive enough to port anything cast iron (but can be used to polish).
A proper die grinder is really a necessity to port cast iron.
Extrude Hone is a great way to slightly port, and mostly polish a turbine housing.
Apparently there are other methods to polish as well, including chemical processes.
Porting and especially port matching is always desirable even if you have to leave things with a rough finish.

jRod, from what I understand a rough surface on the intake side post injectors helps catch the fuel molecules and hold them there while the air flows through and pics them up. By having a mirror smooth finish means the fuel molecules would run down and puddle at the valves, then just drip into the cylinder, instead of properly mixing with air.

On my intake side I left 40 grit marks with dremel, even then I think that might be too fine. I don't think I'm getting too good of atomization because of that, resulting in poorer fuel economy. On another note I also have Thermoblok spacers, which are keeping the lower runners from direct head heat and also move the injectors back. I think the lack of heat, might be reducing the fuel evaporation, which could also be at fault for poor fuel economy.



Lower intake runners are mirror polished




Exhaust side is also mirror polished, though I could have spent more time getting rid of the marks