Valve angles and 90 degree throats

[superbike]

A particular brand of race bike head i work on seems to have 90 degree or near enougth throats then a 45 then a 30 allmost like they are ported right out to the valve seat edge.

The road going version of the same heads seem to be the same but have a very very slim 75 cut added as well.

When i fit oversize inlet valves to the road version of these i just rougth out the whole throat with a 70 do the 45 at 1mm then the 30 blended into the combustion chamber with a 2mm oversize penny on the stick valve. So in effect the seat looks like a splayed out flower where as the race version is just a straight drop into the port . i leave the port size pretty much stock as they seem to be big enougth up to 12mm lift anyway, race bikes go to 14-16mm lift.

The gains from 6-12mm are very good but lower lifts staying the same. With my new tools turning up soon im wondering wether or not to try opening out more with a more steeper angle like the race bike version.

Has anyone here tried using say 85 -90 degree throats i guess it could sacrifice low lift flow for high lift ?

I also read in this old porting book that for ultimate flow parallel throats were the way to go.

[Guy Croft]

It would be too easy to say 'oh, yes, you want angles X,Y,Z'. But the unfortunate answer is that the style that works on your Ducati heads, Phil, may not be common to anything else and I certainly have no direct experience with them.

If you publish a really good shot of a Ducati port and seat region - better still a cross section from a head cut in half - then I'll give it my best shot!
I've done a lot of head work and dyno too and so might just hit on the answer without you're having to spend months on it. But you will not really be satisfied until you spend those months experimenting. Even then you'll never be quite sure! You could read what I have written in GC V/W and that may be a good guide:

http://guy-croft.com/viewforum.php?f=2

GC