porting

[mikey]

Got a scrap head and thought id have a go at polishing the ports,
what are you trying to achieve, is it to smooth out the port with out
taking off to much material? and do you do both inlet and exhaust ports?

[Al]

Mikey you need to leave the surface finish rough.
Smooth surface will cause petrol vapour to form a film which dribbles into the cc. Bumpy surface has greater surface area and promotes the formation of droplets.
These droplets can then re-vapourise and can be used beneficially.


AL

[Pigford]

Mikey - This is a real "black art"

The inlet ports are the crutial areas - too smooth & it can reduce power - coz the air/fuel mix won't .... err, MIX properly.

The exhaust ports are less critical and you can polish away

Just matching ports/manifolds/headers is a good start, remove any lumps & bumps & give it a go

[mikey]

Cheers guys have a go at the exhausts as i say its a scrap head
so dont matter if i screw it up

[Al]

http://www.popularhotrodding.com/engine ... index.html

Here's an interesting article Mikey. Not too much on the theory stuff but a practical approach for guidance purposes.

AL

[BShaw]

from memory what I was taught over 30yrs ago was to think air flow and moving volume of air, opening up tapers, removing ridges, and to leave the surface rough because it creates turbulence, there is no point opening up the carb & exhaust ends of the ports if you get this effect >< what you really want is this == if you get what I mean.
While I do agree with what pigford said about matching mating surfaces at inlet and manifold, it is the valve end of the port which is the important end.
I know tapers create pressure but ya can't beat volume/flow.
Don't bother starting with a dremmel either. you will be there for weeks.
Just my tuppence worth.

[02GF74]

wot they say. matching ports is definitely the first stage.

not a Z head butrover V8 as example:
(sorry about the big pics, just sit further back!)
before:

after: