Port and Polish

[chasbmw]

There is very much you can get from an airhead engine, by an integrated package of tuning improvements, and if done well you will get a bike that is more powerful at all rev ranges and will be almost as reliable as stock.
Jim Cray based in the uk did a stage one tune on my bike, which consisted of, twin plugging, porting,adjusting the piston/head clearance so the squish band worked, together with some work on the air intake system. He would call this a stage 1 tune and really changed the way that the bike worked in the real world on the road.

Since that initial work I have continued with other changes such as Dells, seibenrock 1070 kit, but in terms of value for money, that initial stage 1 tune was best.

There are some dynocharts and pictures of modified parts that can be seen on my photobucket site, same username as here.

[vanzen]

I asked Oak, and here is his reply.

I normally do not recommend porting and polishing. There are two chains of thought. A bit roughed up port on the intake is beneficial. It tumbles and swirls the air fuel mixture for more homogeneous preparation prior to combustion chamber use. Porting and polishing works against that benefit.

If it were mine to deal with I would omit the porting and polishing. I have yet to see where it has done any good. More than not, it is likely detrimental and a hype thing from the old days when engine dynamics was not fully understood.

Hope that answers your question..........Oak

Porting, done by a professional who is experienced with airhead BMWs
will change the power delivery characteristics of the engine.
The specific result, how the porting will affect power delivery vs stock,
is entirely dependent upon the specific shape and results of that professional's work.
In a nutshell, a good job of porting will suck more air-fuel mix into the combustion chamber.
More air-fuel mix equals more power.
The specific resultant port shape determines how much fuel mix can be sucked,
how well that fuel mix will be atomized,
and how that fuel mix will be delivered throughout the rpm range.

To deny the fact of this seems foolish to me.
To consider the change unnecessary, not cost effective, not successfully accomplished in some instances,
or not beneficial to the average rider, etc. ...
will be a qualitative opinion and not a quantitative fact.

Oak appears to be lumping two different processes together (porting & polishing)
giving evidence to eschew one of those (polishing)
and then dismissing the other (porting) out of hand and without reason.
Pay attention to how Oak begins his paragraphs:
"I normally do not recommend porting and polishing."
"If it were my mine to deal with ..."

If considering porting, it will be essential to define the power characteristics you desire.
Be assured by the professional, preferably with evidence of past work, flow-bench testing,
and before & after dyno documentation of your heads,
that those characteristics can be / have been achieved.

Conversely, I will agree that polishing is fluff to please the buyer.
Seeing all those shiny surfaces works wonders –
To convince the buyer into believing that something was indeed changed.
Accepted current opinion is as Oak states:
A roughened surface promotes atomization of the fuel mix.

[Major Softie]

I agree, Vanzen. While Oak may have good arguments against porting, he gave none. He argued (reasonably) against polishing and gave no argument against porting except that "he wouldn't."