High CR pistons and squish heads chat…

Son of Siredward

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Yepper - Sir Eddy's is Blue...

SirEddies blue line.jpg

SirEddies%20head%20008_zps0k5khfa9.jpg
 

Son of Siredward

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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

Ken
Ken, do you want to put this on the Rocket to see what we can do next year at Bonneville? Love you brother!
 
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The Norton head fires very late., what else gets near to28degrees.?. I assume that the squish band helps promote this
 
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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".

Glen
 
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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".

Glen
 
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There was an article in I think Classic racer or some such backin the late 80s written either by Dunstallor people who prepared his race bikes...what struck me was that nothing they did was actully covered in the so called tuning manual. ie we advanced the cam something rotten.... Was this a quest for mid range but the norton engine is always fairly torquey even when supertuned. Perhaps the dunstall cam profile had too little dwell -a fault by design..My other thought was that twas an attempt to compensate for bending pushrods...
 
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I suspect that for him the midrange was just something to get thru quickly then remain above.
His racebikes had some great results, can't be denied.

Glen
 

lcrken

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Ken, do you want to put this on the Rocket to see what we can do next year at Bonneville? Love you brother!
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.

parts1.jpg


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.:rolleyes: 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.

Ken
 
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Ken - that compromise bathtub head by Jim Messler looks like the way to go - similar to the Chrysler head below.

Take a good long look at the Chrysler Hemi head below. Oval shaped combustion chamber without crowding or shrouding the valves too much. Note the steep downward angel of the ports and broad radius leading up to the valve seats. An ideal configuration for a 2 valve performance engine. Would work great on a Norton if you could get close to the shape.

191631962_10220941644270467_1625783838488563086_n.jpg


194261101_10220941642550424_7857808112627212630_n.jpg

T
 
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Would that be a modern day Chrysler Hemi or an old-time Hemi such as the 426?

Glen
 
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That is definitely not an original stock Mopar 426 hemi head from the sixties. They were a true hemi ie circular and had only one sparkplug. They also used a high dome piston with sizable valve reliefs to acheive the 10.25:1 compression ratio in the street hemi and an even larger dome 12.50 in the race versions.
When drag racer Don Garlits switched from the earlier fifties 392 hemi to the 426 he found it down on power. He tried everything and in a last ditch blow or go attempt advanced the timing 16 degrees from the 34 degrees used on the 392 to 50 degrees and blew everyone into the weeds. The key to getting the most out of the 426 was a long advance time to get complete burn with the high dome. Here's the story.
 
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Even so-
The new fuel injected
Hemi 5.7 makes about 70 BHP per litre, almost as much as a stock 9 to 1 carbed , aircooled Commando!
An old time naturally aspirated 426 made about 60BHP at 10.25 to 1cr.
Maybe we're doing OK already? :)

Glen
 
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Son of Siredward

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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.:rolleyes: 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.

Ken
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.
Need to get busy on it... Hope to see you their!
 

Son of Siredward

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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?
Hi Jim,
The Blue is Sir Eddy's Head, Green is a stock 750 Head and the upper lines are Kenny and Martiyn's Fullauto heads.
 
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@jseng1
Hi Jim,

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.
 

Son of Siredward

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@jseng1
Hi Jim,

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.
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.
This is a 500cc compared to Kenny's at 750.
WP_20160603_13_24_42_Pro.jpg
WP_20160603_12_15_15_Pro.jpg
 
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Here's Rodgers 500 custom Norton short stroke piston and dyno chart. The chamber was reshaped for more squish and and compression. 57 HP on the dyno.

257917339_10221874047259959_6031230016898923636_n.jpg


259114635_10221874052780097_5806943834729828912_n.jpg
 
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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
Glen
 

lcrken

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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
Glen

I think it does show the correction factors. They are shown as 1.02 for run 017 (red), 1.05 for run 007 (green), and 1.03 for run 010 (blue). Those seem like typical numbers to correct the readings from ambient conditions on a mild day to standard temperature and pressure (STP). I don't see any mention of correction from RWHP to crankshaft HP, so I assume the values are RWHP, as that is what you get from a Dynojet 100 dyno. And that seems like a reasonable amount for a well built and tuned 500 cc Norton twin. I could be wrong, but that's what it looks like to me.

Ken
 
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