bowie
I've been dipping my toes into the dark magic world of cylinder heads.
Just quickly, I have a 8v cylinder head for a non cross flow engine with a large compression chambers (about 7.5:1) that I want to shave, throw bigger springs and oversize valves, before cleaning up the inlet / exhaust runners (nothing drastic, just removing of crud, and ensuring valve train is tip top top really)
NOW! Lets talk about shiny surfaces.
I've been reading stuff that tells me a rough surface on the inlet runner will actually promote atomization. So some folks claim leaving the longer radius (furthest route into the combustion chamber) rough, as the air flow will be quickest here, rough, that the texture of the surface will help pull the fuel apart.
Are they talking crud or what?
My understanding of watching lakes and streams cut away of banks and shores, and that as engines are air pumps more air wins, You would want to encourage the quickest velocity possible, and not slow it down / trip it up with old trees and canoes?
I suppose I should point out this cylinder head is for a kind-of-volvo that will live at 5-8k rpm for the majority of it's life.
Perhaps the rough surface / atomization thing is a compromise for when a vehicle doesn't live consistently at high inlet speeds.
Similarly for polishing combustion chambers. Some claim it does nothing more then prevent carbon built up (that seems good enough reason really) whilst others claim all sorts of witchcraft about swirls and little tornadoes and all kinds of crap.
But just to break it down,
-Shiny surfaces will prevent carbon built up
-Shiny surfaces sill allow / promote, smoother faster air speeds.
?
carnut1100
A "smooth" surface but not shiny will allow good airflow because there are no lumps and bumps, but the roughness on the surface promotes a turbulent boundary layer which is very small and "breaks" the friction between the main charge and the port walls.
What we are talking about is leaving the surface at 60-80 grit not polishing it.
Definitely smooth it.
This has been proven time and time again both on flow benches and dynos.
There was even a case where a 747 was painted in primer before delivery and they were amazed at the lower fuel consumption, then put the top coat on and it was like normal...
bowie
Now that is interesting.
Thanks for confirming that.
More reading for me to do.
Vee_Que
7.5:1!? Obviously not a b20. There is a lot that can be done to the heads, like decking until you reach 10.8:1 with a good bottom end and tight squish. Porting is perilous, as is valves, I assume you'd put a larger cam in? Basically you need to improve the angle of the flow going in and out on the top wall, with minor work to the lower side.
bowie
no not at all, its for a non Volvo engine build by communists, but I assume air acts like air no matter what your political persuasion.
But yes, smoothest path possible for the column of air/fuel in and out is what I'll be going for eventually. And yes. cam with a silly amount of duration and lift will be added to make use of the time spend polishing / sanding...
eventually.
Vee_Que
Oh, no on the polishing smooth. The turbulence is important.
egads
Yup, golfball dimpling is a good real world example of turbulence improving flow.
bowie
Oh now that's a point. I thought golf balls were dimpled to give them some stability, but I suppose that turbulence is exactly what it is.