Head flow testing.

I'd rather see the comparison between the Axtel and the Full Auto.

I had faith in you, Jim. I knew you would get to it when you could.

However, I think this is the 32 mm port head, and the intake valves are .060" larger than stock. Correct me if I'm wrong. I also had Axe do a 30 mm port head, but I sold that to a guy restoring some factory flat track bikes. Wish I could have sent that one to you also. Axe always said that the 30 mm port worked just as well as the 32 mm, but it would have been nice to compare them. Axe was a real believer in smaller ports and venturi contours at the seat way before they became generally accepted.

I think I've almost run out of heads to send you for your data collection. I do have a short stroke head that Axe did for Ron Wood, with even larger valves than original, that made really good horsepower, but I have to fit new seats and make up some guides and valves for it before I can send it. At my current pace, it might be a while!

Thanks again for making all this flow data available. It's been fascinating seeing the comparisons.

Ken

swooshdave said:

I'd rather see the comparison between the Axtel and the Full Auto.

Click to expand...

The info is all here somewhere in this thread, if you want to compare them. To me, they look very similar. The Fullauto looks like it's velocity numbers are just a bit higher over most of the lift range, and the Axtell looks like it might have a slightly higher flow at max lift, but they are really close. Axe would have loved having the Fullauto head to work with.

Ken

Ken may I remind you that Jim is still an active rider so you merely lucked out to have head returned considering he was blown off freeway into a ditch this year and had two flats at hi speed and who knows what else just missed him w/o him even knowing it. Same for all of us stupid riders. Peel's 750 CHO head didn't give the spunk the 28 mm standard low CR head did, until about 7500 rpm then kicked in like another piston but spining to fast to use it. Hope is the bigger 920 will flow faster for low down spunk then cam or boost makes it flow enough to scare me.
I'd like to try big valves if the small ones don't do it to spank what I want but perfer the smaller ones for heat transfer which is what i think will limit Peel most of all.

I had to pull it back out of the box to see if I missed something. It is definitely stock sized 1.5 inch Black Diamond valves and the ports measure about 31mm at the gasket surface but 30 mm when I use my calipers about 1 inch down the port.

Here is another graph with the Fullauto head added. This head has been cleaned up around the guides. It is Homeslice's head before we did a big valve conversion.



I seem to be missing the velocity graph for Kenny's Fullauto head so I added the plot from the Fullauto head I ported for my own bike. It is about the same up till .300 or .350 lift where Kenny's unported head starts to level off.

hobot said:

Ken may I remind you that Jim is still an active rider so you merely lucked out to have head returned considering he was blown off freeway into a ditch this year and had two flats at hi speed and who knows what else just missed him w/o him even knowing it. Same for all of us stupid riders. Peel's 750 CHO head didn't give the spunk the 28 mm standard low CR head did, until about 7500 rpm then kicked in like another piston but spining to fast to use it. Hope is the bigger 920 will flow faster for low down spunk then cam or boost makes it flow enough to scare me.
I'd like to try big valves if the small ones don't do it to spank what I want but perfer the smaller ones for heat transfer which is what i think will limit Peel most of all.

Click to expand...

Maybe I'm just showing my ignorance here, but I never heard of a Commando 750 head with 28 mm intake ports. All the ones I know about are either 30 mm or 32 mm. Which head did you have?

Ken

comnoz said:

I had to pull it back out of the box to see if I missed something. It is definitely stock sized 1.5 inch Black Diamond valves and the ports measure about 31mm at the gasket surface but 30 mm when I use my calipers about 1 inch down the port.

Click to expand...

Sorry to put you to all that trouble, Jim. When Axe originally did the head, he used his own 1/16" larger intake valves (made from Ford Falcon valves). I eventually used those up, and replaced them with Black Diamond valves. I could have sworn I used their oversize 1.560" valves in it. Shows what happens to your memory when you get old. Anyway, thanks for taking the effort to check.

Ken

Maybe this will clear things up a bit. It looks like I did have some senior moments here. I've gone back and checked my old records, and also measured the other intake valve from this head.

The original Axtell valves in this head were both slightly oversize, 1.532" for the intakes and 1.320" for the exhausts (vs. 1.490"/1.302" stock). When I replaced them with the Black Diamond valves, I used their 1.560" intakes, but cut them down to the smaller size. In fact, I cut them down even a bit smaller. As I recall, it was just a case of taking to big a cut in the lathe, but I decided to use them anyway. I just measured the other intake from the head you have, and it is 1.513". I suspect the other one you have is about the same. That does look a lot more like a 1.500" valve than a 1.560" one, but it isn't. It's a cut down 1.560". There, I think I've got it right this time.

About the head port size, I had Axe do two 750 heads for me, one with 30 mm ports and one with 32 mm ports. My old records say that the 30 mm port head was 30.5 mm at the gasket face, and the other one was 32 mm. It looks like I sold the 32 mm port head, and kept the 30 mm head, the exact opposite of what I thought I had done, since the one I sent you is clearly the 30 mm port head. If Axe was right, it probably doesn't make much difference. He said the flow was limited by the valve seat area, and going from 30 mm to 32 mm ports didn't increase the power output. I think one of the reasons we see the port diameter opened up at the gasket surface is just to have a smoother transition from the larger carb bores used on the race engines.

Anyhow, my apologies for once again spreading confusion.

Ken

Early Commando heads (up to 1970 I think) have 28,5 mm inlet ports and manifolds that taper from 30 mm to 28,5 mm.

From DynoDaves site :
The BIRCO symbol and 23166 are both easily identified by the positives in the casting of this early ATLAS head. These heads have the late style re-angled exhaust ports at 80º included angle or 40º each from straight forward. It has carried over 28.5mm intake ports from the previous heads. The head bolts have been unfortunately down sized to 5/16-26cei.The spigot relief machining is 75mm.Oiling is top feed.


Peel's BIRCO was fed by a 34 Miki so the 32 mm manifold exits left a couple mm lips at narrower port faces and then a rubbery gasket untrimmed intruding another mm into the air flow. Some day will try the combo again on a Combat as out did my 6 speed 365 lb 70 rwhp SV650 especially after 60-70 and then like 15 mph faster top end. I had to prep before throttle snaps so the turbulizer effect still bugs the sheet out of me to explore more.

Thanks, JT. That's news to me. The earliest Commando head I have info on is the RH1, which had 30 mm ports. It was used up until '72 or so, but I have no info on when it was first introduced.

Ken

Good info, hobot. I'd forgotten about Dyno Daves info. It seems that the RH1 head had 28.5 mm ports after all. I got my info years ago from a factory listing that showed it as 30 mm, but apparently that just meant it was intended for use with 30 mm carbs.

Always something new left to learn.

Ken

As far as I know all the non-combat 750 heads were called a 30 mm port but measured 28.5 until they went to the 32mm port in the later years. I think the only port that measured a true 30 mm was the RH10 head. Jim

Interesting. So the one I sent you must have started out at 28.5 mm, and Axe opened it up to 30 mm. That sounds reasonable.

Ken

Since I couldn't find the velocity map for a stock fullauto head and I hadn't tested a new one for a while anyway I though maybe I would do so. I pulled a fresh head out of the box and dropped a pair of Black Diamond valves in it and set it up exactly like the Axtel head I just did. Here are the results. I knew there was something I liked about the Axtel head.

Green is fullauto, blue is Axtel, white is the cleaned up RH4



Here is the velocity chart

Blue is the fullauto, red is Axtel and white is the RH4

They really are similar, aren't they. Great minds think alike, and all that sort of thing? The impressive part is that the fullauto head is that good out of the box. It took a lot of labor hours to get the Axtell head to that level. Axe built his own flow bench back in the '60s to do his "internal aerodynamics" work, and put together a very accurate Heenan-Froude brake dyno to do his development with. No digital data logging systems back then, so his dyno runs took longer and had fewer data points. The first time I ran my bike on his dyno, he had me stand beside him while he worked the load control and watched the tach, and I watched the scale showing the load. When the tach hit each 500 rpm increment, he would swivel his foot sideways to tap mine, and I was supposed to write down the scale reading. He used a sling psychrometer to get the humidity and temperature for using standard correction factor tables to convert the HP readings back to standard temperature and pressure figures. Might also have used a barometer for pressure, but I don't recall all the details. It took maybe a couple minutes at full load to get a run. A dyno run now takes seconds instead of minutes, and a computer program does all the calcs instantly.

Ken

Yes, computers are great for comparing and verifying the results. The hard part is knowing what you want. I sure burned a lot of gasoline and tires trying to figure out what worked before I stumbled onto a good combination. Jim

lcrken said:

The impressive part is that the fullauto head is that good out of the box. Ken

Click to expand...

hobot said:

The BIRCO symbol and 23166 are both easily identified by the positives in the casting of this early ATLAS head. These heads have the late style re-angled exhaust ports at 80º included angle or 40º each from straight forward. It has carried over 28.5mm intake ports from the previous heads.

Click to expand...

What is impressive to me is that Axtell got near "Fullauto" like flow and velocity numbers using the stock casting and no added material to "D" or raise the port floors, so maybe he did something that still no one else has done yet?

As for the 23166 casting, in 1962 Norton was selling 500, 650 and 750cc motorcycles all with that same casting, it just had to have different machining to fit the 750. The 23166 head was discontinued in the 60s and replaced with the 25319 casting for all the Dominators. The new Commando in 1968 got a new casting with the number 06-0380, the best I can make it out anyway, not as clean a casting as some of the 23166 heads.

All three 750 castings used in the 60s had the same size valves in them, maybe someday someone who lives to be 130 years old will measure their ports to see if when the casting number was changed the shape or size of the ports were changed also.....

The Axtell head is a nice piece of work but I wouldn't say it is something new. What it is, is a well balanced piece of work. One where the port shape has been optimized without being made larger. The bowl is the correct shape to make the small intake valve flow to it's potential. There has been no material removed from the floor of the port so the short side radius is all it can be. The port is also widened in the area of the valve guide. If you look down the intake it does have the beginnings of a D shape. Jim

I was fortunate enough to have Ken Canaga loan me a port mold of an Axtell head back in my racing days. I still use & refer to those measurements in my race manual. And my old racing buddy Chris Scott let me ride his bike with Axtell head and Axtell #3 cam using "hot" 102 degree lobe centers. I remember being very impressed with how hard it pulled for a 750. That was the best combo of the day and still hard to beat.