Race Engine Forum UK

Sorry Guy, I'm having trouble working out which two profiles to compare. Is it the blue and light blue?

Iain

What I gather from Vizards writings and using common sense, is that the more difference you have between the ports, the more swirl you will get. Just inducing a tiny bit of swirl will probably not make a measurable difference. As you stated yourself, a lot of other factors could be inducing swirl as well and the significance of just a tiny bit of swirl will probably be less than that of all the other factors combined. I'm not saying you should add serious swirling properties to the head, because that can be too much. Just that tuning for "just a smidge" will most likely not be noticeable. If any, I personally would tune the heads to compensate for the imperfect inlet manifold in this case.

To replace swirl, in 4V chambers, the inlet ports are inclined to induce tumble. The down side of this is, that once the piston moves up again, tumble will be stopped, while swirl continues happily at that moment. You'd have to see what effect these have on each other if you use both. You need to see if you are already optimized on the tumble side of the equation too, if you want to be able to claim anything scientifically.

I think that Vizards designs and testing was done primarily on existing designs. If those would be lacking the proper amount of mixing fuel and air, or otherwise be impeded, adding swirl would probably help. However, it could very well be that experimenting with the angle and placement of the valves in the head would yield equal or even higher gains. Since I don't see anyone doing that research and publishing about it, this is just a hypothesis I can not back up. I do think it is something that should be researched tho, before claiming that swirl in 4V chambers is a superior or inferior solution. Just improving on a imperfect setup and claiming that your solution is superior is taking shortcuts. You have to test and dismiss the alternatives as well.

guys, sorry (and this is not professional pride), you must not discuss Vizard's researches here any more!

If he has a forum do it there.

GC

Post-script: I have been asked why and my answer is that DV has no right of reply (he obviously isn't a member) so in my view as a matter of respect discussing his stuff is not appropriate here. No offence to anyone intended, it just happens to be my forum and that's how I run the ship..