| outside that matters......." :) But in the case of the upper plenum I am inclined to say it wont produce any measurable gains in performance of any kind. Thing is, the casting finish of the plenum on the inside is actually pretty smooth. The "core" that is used in the casting process is a bonded sand medium, typically a finer sand and the space between grains is filled with the binder. This produces a much smoother finish on the inside of the part. The outside of the part, our plenums specifically, appear that they were using a lower grain compacted molding medium - such as blue diamond or some other water bonded sand. The inside surface is a good bit smoother. Additionally, it isn't until you get down into the lower plenum and intake ports of the cylinder head that you really need to concern yourself with surface finish. The upper and lower plenum funnel down in cross section from the inlet of the runner at the upper plenum all the way down to the intake valves. This funneling, the reduction of cross-sectional area, produces an increasing flow velocity as the gases approach the intake valves. The greater the flow velocity, the more important the duct's wall finish becomes as this dictates how thick the boundary layer is. "Boundary Layer": this is the thin "film" of air at the immediate surface of the duct which does not "flow". Think of it like washing an engine part clean of all oil - there still remains a thin film of water on the part. The water is sticking to the part - just a thin layer, but it is there. Even if you take an air tip to blow it off, you will see that it doesn't just jump off the part - you'll blow it around on the surface of the part, chasing it....... AIR does the same thing, you just cant see it. It "sticks" to the surface of the intake runners. This thin layer of air that sticks does actually flow with the air moving through the runner, but not at the same speed. At the microscopic level, atomic level, atoms of air are stuck permanently for the most part, the atoms just above them are a little more free to move, and atoms above that layer a little more than the previous.... and so on and so forth.. So what you have is a gradient of flow from the immediate surface of the runner. The smoothness of the runner will dictate this gradient; the rougher the finish, the thicker the boundary layer. This boundary layer produces flow losses as it effectively reduces the cross-sectional area of the runner.... which in turn will reduce flow. The theory of it all can be used rather easily to support or debunk the benefit of E.H. when conversing with someone untrained in fluid dynamics. There have been no back to back dyno tests or flowbench tests to empirically determine the benefit. Additionally, there have been no computational fluid dynamic simulations performed on this either. This being the case, there is no way to definitively answer your question. Adding to that, even if it were to add 5HP, the question of if it is worth it solely depends on how badly one wants that 5HP and whether they have the money for it or will spend it. If you were trying to break the highest documented horsepower record and come up 4 horsepower short, by that time I would imagine you have ample financial resources to have the E.H. process done as well as the motivation to do it - no holds barred, right? :) In my opinion, just off the cuff from my understanding of the dynamics involved, extrude honing the upper plenum will be a waste of your money. Focus on the lower plenum first to get the technique, and then go to the heads. You can do the most amount of productive work in the intake and exhaust ports as this area has the largest restriction to flow. The turbine housings are a different story. You are dealing with a small flow area even at the inlet of the housing and this funnels down literally to a near-zero area at the nozzle. The exhaust gases are expanding as they exit the cylinder - they are moving to lower pressure. As these gases expand into the exhaust manifold they are taking up more volume and the flow is accelerating as they enter the turbine housing. The snail-shaped scroll of the turbine housing further reduces in area which results in greater gas velocity and the finish within these cast housings, especially at the nozzle, is horrific. There is ZERO cleanup of this area in the housings when they shake them out of the sand mold. In most all of the turbos I have built for customers, the turbos come apart and special attention is paid to this area. A small 1/4" ball carbide burr works great to clean up the parting line casting flash left in this area. It is also a good idea to carve out the sharp corners at the nozzle wall as this is typically where cracks in the housing will start. If you extrude hone the turbine housings, you will still want to go in there with some carbide burrs to get at least the parting line flash out of there and even out the surface. The E.H. process will typically take the surface down equally in all places, so be sure to remove the big high spots first. But again, I have done no back to back dyno testing, CFD simulations, or flowbench testing to back up my suggestion to do this. I will say that E.H. the turbine housings will add greater benefit than doing this to the plenum, but to what exact benefit I cannot say. But for those going no-holds-barred, definately do it.. Do both, do the exhaust manifolds, do the coolant pipes..... Heck, do the throttle cable so you can slap the throttle to WO a couple of milliseconds quicker. :)
Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the
tailor.
Albert Einstein
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18:02:53 01/12/12
