polished cylinder head! EAK!

[ibizacupra]

http://forums.vwvortex.com/zerothread?id=2370351

 

[jase750]

I didn't think that it made any differance if it was shiney ? the porting was the important thing, the rough finish helped to promote swirll ?

 

[ibizacupra]

I didn't think that it made any differance if it was shiney ? the porting was the important thing, the rough finish helped to promote swirll ?

exhaust ports polished mirror, combustion chamber too..
intake is rougher deliberately.

not too sure about the combustion chamber being so polished.... no hot spots likely I guess.

 

[DPJ]

That's a lovely bit of work.

 

[techie]

I didn't think that it made any differance if it was shiney ? the porting was the important thing, the rough finish helped to promote swirll ?

That was my understanding aswell, and a rough surface has more suface area to disapate heat better.

 

[Fl@pper]

i was always told smooth not polished

waaaay too much time on his hands lol

love to see it after a 1000 miles

 

[RobDon]

Looks awesome, hope he posts up some results after fitting.

 

[max_torque]

Looks awesome, hope he posts up some results after fitting.

You want the intake surface finish to be that left by 120grit flap wheel, so probably a maximum crest to trough amplitude of say 0.05mm or so. This will allow the fuel puddle mass a suffuicient surface area to evaporate rapidly and not just slide into the cylinder as a puddle, it's also not to rough to limit flow velocity. (and as mentioned it may actually help flow as you get a thin turbulent boundary layer formation, although personnaly i have never been able to measure this!)

The in cylinder area can be polished smooth, minimising surface area and hence heat transfer to the cylinder head, and limiting the formation of thick carbon build up which can overheat and lead to detonation in localised areas, (also allows you to maintain close squish tollerances) The 1.8T also suffers from a lack of charge motion (little tumble and little squish area due to 5v layout) so polishing the ports is actually gonna have a negative effect on burn rate and move MBT away from TDC.

The exhaust ports are completely unaffected by surface finish! (within reason, dead rats or birds nests in there will probably not help lol!) As the majority or the exhaust blow down occurs during sonically choked flow between valve and seat, (downstream pressure wave cannot travel upstream and effect flow) also the lower temp of the walls will lead to rapid thick carbon build up (as anyone knows who's taken an run engine apart. This is why most engines are very insensitive to exhaust port size and geometery.

so all in all, look nice, but not much effect!
my recommendation, spend a bit more time on getting the intake port shape and squish zones optimised and less time making it look lovely!

 

[RobDon]

Yeha I heard that polished intake can results in the fuel beading rather than atomising, not good!