Cylinder Head Question
Discussion
I agree with boosted, smooth them out - no need to go mad though.
Look about half way down this page:www.mez.co.uk/westfield/
This is the porting job my dad done on a pair (It's what he's been doing for last 25 years..).
Valves are standard size, but the seats enlarged a fair amount and the back of the valves cleaned up a bit. Guides have been machined back also.
Eliot
Look about half way down this page:www.mez.co.uk/westfield/
This is the porting job my dad done on a pair (It's what he's been doing for last 25 years..).
Valves are standard size, but the seats enlarged a fair amount and the back of the valves cleaned up a bit. Guides have been machined back also.
Eliot
Boosted LS1 said:
Shouldn't think so, they'll be coked up soon enough.
Boosted.
But i was under the impresion that a nice shiny exhaust port was to reduce the ability of them getting coked up? i know you will never keep it that way but if polishing them helps prevent it longer and aid that airflow then it has to be worth the little extra effort?
Mikey G said:
Shouldn't think so, they'll be coked up soon enough.
Boosted.
But i was under the impresion that a nice shiny exhaust port was to reduce the ability of them getting coked up? i know you will never keep it that way but if polishing them helps prevent it longer and aid that airflow then it has to be worth the little extra effort?
It will delay the build up for a while but s**t sticks as the saying goes. Is the effort worth it, they clog up pretty fast? I'd be happy to see a nice shape.
Boosted.
I reckon to get a good finish on all ports. If your fuel comes out of suspension on the inlet, a rough surface is unlikely to re-emulsify it. If you can have a shiny finish, the 'zorst ports will help in cleaning a lot. Arguably, if you stick to a fine finish, the flow will be more laminar locally, perhaps aiding a 0.000000001 CFM.
I think that factory finishes are just as bare as possible (Minimum work) that goes for head grinders as well. Shiny finish is difficult/tool consuming. If you did a test, there would be very little in it. Rather like using wet/dry finish on a boat. It's ignorant myth.
Why not just bugger around with much coarser elements, like valve size, lift, duration?
I think that factory finishes are just as bare as possible (Minimum work) that goes for head grinders as well. Shiny finish is difficult/tool consuming. If you did a test, there would be very little in it. Rather like using wet/dry finish on a boat. It's ignorant myth.
Why not just bugger around with much coarser elements, like valve size, lift, duration?
chrisj said:
I'm busy port a set of RV8 heads at the moment, and was wondering what sort of finish the exhaust ports require.
I know the inlet ports need to be smoothed but not polished to provide a little turbulence to keep the fuel in suspension, but would polishing benefit the exhaust side?
The surface of the exhaust should not be polished to a shine. The eddies created by the imperfections in the surface help restrict boundary layer flow. If you with to learn more I suggest this page [http://naca.larc.nasa.gov/reports/1937/naca-report-562/index.cgi?page0001.gif]
speedy_thrills said:
I'm busy port a set of RV8 heads at the moment, and was wondering what sort of finish the exhaust ports require.
I know the inlet ports need to be smoothed but not polished to provide a little turbulence to keep the fuel in suspension, but would polishing benefit the exhaust side?
The surface of the exhaust should not be polished to a shine. The eddies created by the imperfections in the surface help restrict boundary layer flow. If you with to learn more I suggest this page [http://naca.larc.nasa.gov/reports/1937/naca-report-562/index.cgi?page0001.gif]
I mucked around with that stuff when I did Chem Eng at university. Nusselt, Prandtl and Reynolds numbers and their associated relationships. Fluid flow is pretty foul even in the most simple systems. One such as an exhaust port is going to be hideously complex. What are the densities, temperatures, viscosities, etc, etc you are dealing with? I can tell you one thing, the turbulence caused by surface roughness are going to be insignificant to the turbulence caused by the valve.
Port flow is hideously complex, but can be skinnied back to the whole "What flow/velocity is optimum" and working back empirically to the most ideal figure. We are talking about real ports here which are about as removed from a sensible mathematical approximation as you can get. I would argue that until I was blue in the face. I would want to see some hard data showing me that my belief was wrong!
dilbert said:
I wonder exactly how rough their plate is?
I don’t suppose it matters really once you have established the principles and mathematical formulae to describe the flow characteristics you are recording. As a physicist once said to me “An elephant who’s mass may be ignored”.
dilbert said:
Sounds like another one of those problems where you need a good computer!
Computer Fluid Dynamic (CFD) programs have their uses but as I understand fluid dynamics (aerodynamics in this example) are still best honed through extensive testing as it tends to be a bit if an unknown quantity and black art.
You'd be interested in the aero engine that JPL were developing a while back.
If the turboject was developed from the turbocharger, what was the pulse jet developed from?
Obviously it doesn't work quite that directly, but JPL had this trial engine. It was basically an array of cylinder heads, and rather than having pistons the cylinders were replaced with long tubes, in which detonation was controlled.
Essentially I think they were controlling the cam speed electronically to prevent nulls occuring in the at the wrong place.
Although very noisy, apparently the engine developed considerably more thrust than an equivalent with a propeller!
If the turboject was developed from the turbocharger, what was the pulse jet developed from?
Obviously it doesn't work quite that directly, but JPL had this trial engine. It was basically an array of cylinder heads, and rather than having pistons the cylinders were replaced with long tubes, in which detonation was controlled.
Essentially I think they were controlling the cam speed electronically to prevent nulls occuring in the at the wrong place.
Although very noisy, apparently the engine developed considerably more thrust than an equivalent with a propeller!
love machine said:
chrisj said:
I'm busy port a set of RV8 heads at the moment, and was wondering what sort of finish the exhaust ports require.
I know the inlet ports need to be smoothed but not polished to provide a little turbulence to keep the fuel in suspension, but would polishing benefit the exhaust side?
The surface of the exhaust should not be polished to a shine. The eddies created by the imperfections in the surface help restrict boundary layer flow. If you with to learn more I suggest this page [<a href="http://naca.larc.nasa.gov/reports/1937/naca-report-562/index.cgi?page0001.gif">http://naca.larc.nasa.gov/reports/1937/naca-report-562/index.cgi?page0001.gif</a>]
I mucked around with that stuff when I did Chem Eng at university. Nusselt, Prandtl and Reynolds numbers and their associated relationships. Fluid flow is pretty foul even in the most simple systems. One such as an exhaust port is going to be hideously complex. What are the densities, temperatures, viscosities, etc, etc you are dealing with? I can tell you one thing, the turbulence caused by surface roughness are going to be insignificant to the turbulence caused by the valve.
Port flow is hideously complex, but can be skinnied back to the whole "What flow/velocity is optimum" and working back empirically to the most ideal figure. We are talking about real ports here which are about as removed from a sensible mathematical approximation as you can get. I would argue that until I was blue in the face. I would want to see some hard data showing me that my belief was wrong!
Excellent point!
Perhaps it would be worth some dynamometer time testing weather having fins to smooth air flow would increase power? I’m sure that the exhaust shape would change dramatically through development also.
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