- Nov 4, 2012
Yepper - Sir Eddy's is Blue...
Ken, do you want to put this on the Rocket to see what we can do next year at Bonneville? Love you brother!Thanks for the response, Christian, and the welding suggestions. I'll have to pull out my junk test head and see if I can improve my results.
Also, thanks for the interesting combustion chamber pictures. Maybe getting a little OT, but it's a subject that's historically been of great interest here on the forum, so no fault.
As you said, some of the best known specialists back in the day had serious disagreements on the best way to improve efficiency in Norton heads (as well as others). I had the opportunity to hear Axtell's (firmly held) opinions on Jerry Branch's technique, and to observe examples of both. I chose to follow Axtell's advice in this area, for a number of reasons, and was very grateful for it, but that's another story. And neither of them followed Paul Dunstall's principles. Jim Messler, one of the factory Norton tuners had his own ideas on the best mods for Commando heads, also very different from the above experts. I have one of his short stroke 750 heads with giant valves in a full hemi chamber, but fairly small ports. It worked extremely well for me for many years on a 920 race bike. I've also seen one of the bathtub chambers he was doing later in his career. I don't have pictures of it, but as I recall, it looked a lot like the ones produced by George at MEZ Porting, shown below, but with a more oval bathtub shape. I recall once talking on the phone to eccentric tuner Kenny Augustine about his ideas on Norton heads, but I don't recall the details, except that he had some interesting things he wanted to try. I don't know if he ever got the chance to do so and see the results. I'm pretty sure the other Norton tuners back then (Leo Goff, etc.) all had their own take on the best way to go, but I don't have any experience with them or any info on their methods. More recent (at least relatively) specialists like Steve Maney and at least a couple of European tuners, have also experimented with trying to improve on the original Norton head design. And there's always our own Jim Comstock, who has had his way with many a Norton cylinder head, and Jim Schmidt, who has put a lot of time and energy into applying the Harley XR750 port design philosophy to the Norton head. And how could I leave out Canadian Norton wizard Herb Becker, whose work has been explored on this forum several times. There's clearly more than one way to successfully set up a Norton twin. It fascinates me that research is still going strong on such an old design, and the availability of new, improved Commando heads, originally from Fullauto, and soon to be from John Snead, offers another resource for experimentation. Good time to be a Norton lunatic.
View attachment 82834
That's true, a lot of bikes require much more advance. The standard Vincent was at 38 degrees. The BSA A 10 is around 34 degrees.
The 1360 TP Vincent fires at 24 degrees. Big squish bands and twin plugs helping there. Also high compression dials it back a bit.
I reread the Dunstall tuning guides last night to see if I could glean anything useful for increasing midrange.
There was no mention of midrange as every modification was aimed at increasing top end, most at the expense of the middle.
This makes sense for racing, the tach doesn't spend much time below 5 k rpm.
Dunstalls first statement is " The Norton Commando head is a very good design".
Hi Paul. If you're referring to the bathtub head picture I included, it's not one I possess. The picture is from the MEZ web site. The only bathtub head Norton I've owned was the Commonwealth Norton, which I eventually sold to Fred Eiker. It ran over 150 mph at Bonneville before his crash, but I don't think he ever had it dynoed. The only picture I have of that head, which was done by Jim Messler, is really poor quality, but I'm attaching it anyhow. You can just barely see the oval combustion chamber shape, if you look carefully. It's a bit more conservative than some of the other bathtub shapes in this thread.Ken, do you want to put this on the Rocket to see what we can do next year at Bonneville? Love you brother!
Hopefully I will make it this year, most likely my last time as well... Plan is to put the motor back together with the old cam and setup when we set the records in 2016.Hi Paul. If you're referring to the bathtub head picture I included, it's not one I possess. The picture is from the MEZ web site. The only bathtub head Norton I've owned was the Commonwealth Norton, which I eventually sold to Fred Eiker. It ran over 150 mph at Bonneville before his crash, but I don't think he ever had it dynoed. The only picture I have of that head, which was done by Jim Messler, is really poor quality, but I'm attaching it anyhow. You can just barely see the oval combustion chamber shape, if you look carefully. It's a bit more conservative than some of the other bathtub shapes in this thread.
View attachment 82848
I'm hoping to make it to Bonneville next year with the ultra short stroke 750 that we had so much trouble with at the 2019 meet. I think I've fixed all the issues, but there's only one way to find out. Hope to see you there. Maybe this time I can get the pit location right. I'm still planning to run it at El Mirage first to make sure it's sorted properly. This could be my last year for Bonneville, so I'd like to do it up properly.
Hi Jim,Its hard to read but it looks like the red line is a full auto head and the light blue/green line at the bottom is a stock 750 head but what is the green line at the top?
One would have to assume, the best dyno run Jim Comstock and I had on the Rocket was 51.9 HP at 9400 RPM before falling off.@jseng1
That is fwiw know even a picture of the old "new hemi" head.
The newer one has to my knowledge (would have to look in a book) already conical or hemispherical squish areas and ports with even better coefficients of discharge.
Kind regards Christian
PS: @Son of Siredward
So given the numbers one could assume that Kenny has aboutish +70-77horses on the engine.
Just a note to the above-
The chart above does say " corrected horsepower" although it doesn't say what cf is used.
If it is SAE J1349, the most common correction then it is RWHP + 15% + or - weather corrections. Other CF standards use even higher mechanical correction factors.
This is why it is impossible to compare dyno to dyno results.
We rarely are told if the chart is corrected HP or not, and even when we are, as above, there is no indication of what CF was used.
The chart from Jim Comstock's dyno does show the CF as STP.
It would be great if all dyno operators listed the Correction standard