Dramon_Killer

Ok so i'm getting ready to port match my upper and lower intake manifolds. When porting the upper how far should i go up when making the intake runners bigger. Secondly my friend said that the side walls need to be rough for proper fuel atomization. How would i go about getting that roughness, would just leaving the walls how they are after i finish using my dremel be ok? Also he said that if you polish the tops or something like that of the intake runners it creates a swirl effect which helps combustion or something like that he wasnt too sure on it though. Any thoughts on that?



Thanks.

mazdaspeed7

Turbo motor, right? I would only port match the runners to the gasket. The runners narrow down some at the flanges, but its pointless to go any bigger than the actual runner diameter. Also, you only need to worry abotu a slightly rough surface below the fuel injectors. Above that, polished is best. Polished flows best, but fuel tends to cling to the walls. Some texture is worth the losses(very minor) because it makes up for it with a more consistent fuel mixture. As for texture, 60-80 grit sanding rolls are generally adequate for below the fuel injectors.

Dramon_Killer

So basically it doesnt matter how smooth the UIM is even though you see old gas and crap all along the walls of it?

mazdaspeed7

Think about that for a minute. If the air/fuel charge is flowing backwards up the intake towards the tb, dont think you have problems slightly bigger than fuel clinging to the runner walls?

Dramon_Killer

Maybe its carbon buildup? I dunno but the n/a i used to have was kinda dirty where the UIM was too with gas and stuff. It's not too bad but its just a really light and very slgihtly damp coating.

j9fd3s

you need to think 4th dimensionally, why is it carboned up higher than the injectors?

mazdaspeed7

All engines that Ive seen will have carbon in the intake manifold, regardless of where the injectors are. A good example is most modern piston engines, where the injector sits right at the head, and sprays almost directly at the valves. Its pretty safe to assume that fuel wont really be traveling backwards up the runner if the engine is in good working order. Yet there is still carbon buildup. While I dont have a good explanation as to why it happens, and im too lazy to go look it up, I am still confident that polishing the manifold above the injectors will have no ill effects.

pengaru

think ping-pong effect, what do those pulses carry small quantities of? fuel? exhaust? blowby? oil?



hrm, i'm thinking a bit of everything, over time your runners get buildup of junk.



It's actually somewhat surprising how much is pumped out of the chamber through the intake port before it starts sucking a/f in, you need to hold your hand over the bore of a individual throttle body setup and feel the pulses to realise how much there is, in a plenum setup those pulses are interacting with eachother.

mazdaspeed7

Penguru, its still beside the point. While there are instances when exhaust blowby, oil, etc are carried back up the runner, it has no relevance to polished runner walls and fuel clinging to said polished runner walls. Therefore, having a slightly rough surface only matters below the injectors, where air and fuel will be flowing the majority of the time, ESPECIALLY under WOT, which is where the fuel clinging problem manifests itself the most.

pengaru

It's a tangent, I agree. But you indicated if you have fuel and crap going upstream you have bigger problems, I don't exactly agree with that because there are forces at play that do bring **** back up the runner that you wouldnt expect.



As far as polishing the runner goes, this can be and has been debated to no end as far as I've seen.