modern motorcycle 4 valve head porting 1

[jk12r]

I have a bmw k1200r and am looking to get the head optimized. I have a spare head and looking at it the casting is pretty good already.

Valve angles are tight at 11 and 10 degrees, exhaust and intake.

The "short side" radius is nearly straight and flat into the combustion chamber.

You can see the obvious "production" nature of the head with a distinct transition between the machined valve and the cast runner, but other than that, I don't see much can be done.

The combustion chamber has sharp edges that probably should be softened and maybe a little unshrouding.

Am I wasting my time and money? Are modern motorcycle heads pretty much "maxed out" without spending thousands.

I see head porters advertising outrageous claims for head porting that I just can't believe.

 

[evelrod]

Very well put, Rob. I've had some pretty heated arguments over intake flow rates and intake port sizes lately. What works well on a four valve is crap on my two valve Lotus head. Even the carb sizes are in question. I'm using 45mm with 36 chokes and thinking of dropping to suitably modded 40's with 36 chokes to increase intake speed with very little loss of volume. Working out new data on these very old heads is difficult since most of the "experts" are schooled on four valve heads. Particularly the exhaust side of the equation.

Rod

 

[Rob45]

Rod:
That's interesting: it seems not so long ago that nobody knew anything about porting 4-valve heads.

A friend of mine had both a small engine dyno and a home-made flow bench, and using them we learned that almost everything that people *knew* about porting was wrong.

Especially for showroom stock engines, with modest valve lifts, the most important thing we could do was to match the valve face contour to that of the cylinder head seating surface, so that, viewed in cross-section, when the valve was near the seat the flow passage looked like a venturi. That and matching the inlet runners and outlet pipes to the ports were the two most important things we could do.