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Is it better? Is that statement based on dyno evidence, your sole opinion, or an opinion of consensus from track testers? We have seen the Cycle World torque graphs of roadster 750's and 850's w/OEM heads quite recently and there are large weak domains above 3500 rpm and too early drops at higher rpms when compared to the contemporary Ducati 750's, for instance. Yes, Jim C. has proven very good breathing of the FA head design, but I have yet to see a torque graph of the FA heads enabling a comparison with the afore mentioned graphs.
-Knut
the first ever tuning notes I ever read were written by John Hudson, who had a preference for not increasing valve head size, but rather improving flow around the standard sized valves. I guess that has stuck with me because that was 43 years ago.
I read in various places says that the re-angling of Commando valves to achieve clearance between moving valve heads and has no other performance benefit in itself. The performance benefits are derived from the larger valves increasing flow with suitably modified ports. There are suggestions that the revised angle can mask the port and reduce flow. Do I personally have 'evidence?...no.
In my naivity I would also expect that if Jim and Ken entered into this project of improvement and thought there was a significant benefit to be had from simply re-angling the valves at standard size they might well have chosen to do so?
The Fullauto ports were designed to work with the standard valves that Ken expected most to use! I am told Mick Hemmings big valved every one he sold, bar mine, and he certainly told me he should do mine! I decided to see how it worked before considering big valves. Nothing has persuaded me I need to change them.
My 750 short stroke has been on a dyno, but some time back and was not run to it's full potential at the time being very fresh. It made respectable RWHP at 6500 with a lot of potential left. Does this prove anything? Not to me, except that in performance terms it is in the ball park with to the 850 I used to have which had a fully hemisphered ex Thruxton shorts stroke head, big valves and Omega pistons, but that unfortunately did tangle it's big vavles at one point!
Is this scientific, no. But the configuration was modeled and none of the feedback from that suggested I was making a big mistake.
On track testing (racing!), it hasn't been out dragged out of a corner by another 750 or 850 Norton, rather the other way really, and the thing has to carry me, and I seem to be a little larger than my competitors! I tend to be beaten by faster riders, but on the right circuits I have been able to stay with 1980s four cylinder 750s, and even 1300s.
I would expect to be out dragged by well developed 920s and 1007s, but in the two cases I have exited a corner near one, I was definitely being out ridden by the pilots, who were lapping me!
