This didn't get a single response on ESE, (even though it directly related to a Wobbly post). Not even a derogatory slur.
The ESE Focus is obviously in a different direction at the moment.
Perhaps the Learned Gentlemen that visit here, might have some experience, information, feedback, comment.
cheers, Daryl
Well I've learned that you don't mirror finish inlet ports as it will actually reduce flow...For max flow, there should be a boundary layer. A finish equivalent to a light hone or bead blasting is sufficient to give the boundary layer something to form on. How this would equate to a high velocity, high temp exhaust which will have a lot of energetic tumbling motion entrapped in it, i really can't guess.
Irving, as always, had something to say about exhaust ports - a thin layer of carbon is a good insulator....
MY take is, how often are you going to re polish this duct? I can't see it staying shiny for very long at all.
Neil
I read something years ago about NASA researching what you might call variable texture surface corrugations, trying to match optimum boundary sheer profiles with actual flow velocity.
Sounded far too advanced for any technology I could imagine at the time, but one of the research strings involved dolphins. Their subcutaneous fat ripples as they swim, and the ripples apparently very closely resemble the perfect pitch/texture to minimise drag at any given speed.
There's been at least one elastomeric tube developed in an attempt to mimic that effect.
Go soothingly on the grease mud, as there lurks the skid demon
I don't know about the exhaust surface finish, I have always made the inside of the model engines in the 400 to 600 grit finish range, so quite smooth but not shiny. Anyway's many years ago, a guy in Hamilton a Ferrari that they decided to polish the insides of the inlet ports when they did some work on the heads and valves. It went noticeably worse due to the polish work they did. I am not sure if they got the inlets lightly sand blasted again or not. Somewhere on here at KiwiBiker, was mention of a 400 grit surface finish for inlet ports. Can't remember who said it though.
Neil
i was meaning from the look of the basic use spec sheet
it has Si and Ni is that what makes it harder to machine or does it tool harden?
shark skin as in the swimers togs to replicate a sharks skin.
http://www.symscape.com/blog/swimsui...hnology-doping
http://theconversation.com/fast-suit...n-records-7960
Golf balls is another. although a little more complicated.
http://www.aerospaceweb.org/question...cs/q0215.shtml
I polish exhaust ports on 2ts as i can;t be arsed removing carbon later.
dremel finish flatted off with 400 git is perfect according to Jan? i think.
nice find.Ricardo was years ahead of himself even with tapering of ports as well as 4v and squish turbulence too
But in modern terms #The coolant temp should not be allowed to get anyhere near 100C on a competition engine esp a two stroke.
The only positive story I know about mirror finishing inlet ports relates to the Suzuki GSXR750J. It was supposed to be the ultimate in that family, shorter stroke, bigger valves, bigger ports...
Flowbench and dyno work showed that the inlet ports in the casting were too big. AMA rules said you couldn't add material..
By mirror finishing the inlets a turbulent boundary layer formed. Apparently the mirror finish gives a sort of grip and release effect on air passing which makes for a turbulent layer.
The thick turbulent layer had the effect of reducing the cross sectional area of the port...job done.
That head has become a favourite of the US drag racers for fitting to the old air cooled GSX1100, bolts straight on , just block the oil drains.
Oh aye. Well it's almost all carbon steel, even mild steel has a bit, just not enough to harden.
Anything with Si is hard on tools, which nowadays usually means carbides, which often means compromising tool profiles. High Ni content steels tend to high sheer strengths, which means they tear easily. Well, not easily, in fact it takes a bit of grunt but it seems to like bonding to the tool surface, so it tears rather than sheering nice and cleanly. So without razor sharp edges, a nice rigid setup and a decent coolant you get jagged finishes, especially screwcutting and similar.
High manganese stuff can be a pain too but my favourite thing to bitch about having to machine is AB2. I took some castings to a local who had a big fuckoff Toss horizontal borer, ('cause I didn't want to spend forever doing the job on my universal). His machine wouldn't think anything of driving an 80mm 6 tip face cutter at 10mm x .5 cuts in 316, but the best he could do on that stuff was 2mm x .2. He's been deeply suspicious of every job I've taken there ever since.
Go soothingly on the grease mud, as there lurks the skid demon
Not too concerned about flow,at the moment. (Seems like every discussion about this subject, out there, is always about the Flow)
Limiting/minimising heat transfer, into (and out of) the exhaust port walls, is the goal. Whatever works best, be it silver mirrors, refractory ceramic or carbon crust.
Perhaps a little bit of high school Physics.
Of these 3, Forced Convection is the source of our heat energy (in the port & header).
IR Radiation: (Waves not particles)
Dull surfaces are good absorbers and emitters of infrared radiation.
Shiny surfaces are poor absorbers and emitters (but they are good reflectors of infrared radiation)
Conclusion: Dull, Matt surfaces are best at taking heat from the exhaust gas AND transferring that heat to the cooler fresh charge.
Conduction: (Fast molecules smashing into Slower molecules )
A vacuum is the best conductive insulation, no particles to transfer the energy.
Air gap is an alternative. The High Temp surface coatings consist of hollow ceramic nano balls, to provide the air gaps.
Conclusion: A shiny smooth reflective surface finish with insulating ceramic nano balls might be a good way to avoid taking heat from the exhaust gas and NOT transferring that heat to the cooler fresh charge. Maybe???
And this might be why simply a polished surface OR a ceramic coated one are (reportedly) not, on their own, notably effective.
The result of combining the two might be greater than the sum of the parts. (like a Vacuum Flask)
Cheers, Daryl.
My understanding of that model was it was fine on the road and gave more power then the previous model but when modified and used with longer duration cams then the std road ones the package never worked as good as the old motor did when modified. it was a bridge to far.
Pretty sure the later suzukis sprads with improved heads and tech went back to the same short stroke bore stroke ratio years later with no issues.
Your comment made me think of when Muzzy got pinged one year in the Scott russell/Gobert WSB era for running a device that made the FCR41 into 39mm carbs.
They had got away with it all year, as they designed them to stay attached to the intake manifold this was allowed but one day at tech inspection they came appart with the carbs.
so they had to fidlle them back in.
I think they used them at almost all tracks. likely for the same reason the Suzuki never worked properly.
I think the rules then were std carbs and gearbox and rod material which was why the OWO1 and the ZXR750RR had the CR box and slide carbs and the Ti rods.
That said it must mean the the RC30 won all its races on race kitted CV carbs because thats what they had std so thats pretty impressive in hindsight.
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