Head flow testing.

One of the better basic guides to engine porting is here. It is intended for car engines but it applies to Nortons also. There is only one rule that always applies and that is "air likes to go straight- when you try to make it turn it becomes very unpredictable"

http://www.popularhotrodding.com/engine ... ewall.html

Ok I've savored that article prior but skipped some stuff on the seats I see now.
Can you test flows with the carb or injector + manifolds installed?

Do you have sense of where most the intake blast goes, ie: collides or glances off chamber dome?

hobot said:

Ok I've savored that article prior but skipped some stuff on the seats I see now.
Can you test flows with the carb or injector + manifolds installed?

Do you have sense of where most the intake blast goes, ie: collides or glances off chamber dome?

Click to expand...

Sure, I have done a lot of testing with the manifolds and carbs and exhaust pipes installed.

The fuel from the intake tends to wet the cylinder head near the plug and the outer cylinder wall. Quite a bit of swirl in a Norton head.

The fuel from the intake tends to wet the cylinder head near the plug and the outer cylinder wall. Quite a bit of swirl in a Norton head.

Click to expand...

Now that's interesting surprise for me to contemplate. The thermal images also surprised me that the outer front of head glowed more than the central area with Norton air ducting. Exhaust flow out would make the outer fronts hotter and likely evaporate the fuel blast too.

Would ya index plug gap to face the exhaust valve or some other angle?

For more contemplation, what would a bigger set of valves in a Combat head set someone back and how big is practical for wide range of rpm operation on aggressive Norris D cam?

Here is the final graph on Kenny's head after playing with a few seat designs. Got a nice improvement. The blue line is Kenny's Fullauto and the white like is Ken's Maney stage 2. Both have the same valve size. The Maney has a big port and the Fullauto has a small port.



And here are a few carb options tested on Kenny's head.

The top line is the same as above- just a velocity stack on the port.
The next line down is a curved Commando manifold with a velocity stack- no carb
The third line down [blue] is a 32mm Mikuni on a straight manifold.
The fourth line down [lt green] is a 34mm Amal MK2 on a Commando curved manifold with a rubber spigot.
The fifth line down [yellow] is the 32mm Mikuni on a curved Commando manifold with a rubber spigot.
The sixth line down [violet] is a 32 mm Amal concentric on the Commando manifold.
The bottom line [red] is what happens to the 32mm Amal when you put a velocity stack with a screen on it.
A velocity stack with no screen on the Amal flows the same as no velocity stack but it may make a difference in how it runs due to the length and the fact that it will contain the standoff.

If a screen does that, what happens with an air filter on the carb?

Glen

worntorn said:

If a screen does that, what happens with an air filter on the carb?

Glen

Click to expand...

An air filter hardly affects the flow- an air filter has a lot more area so the air velocity through the element stays low. A screen causes problems when you try to move the air through it at a high speed. A vortice is created at each wire and plugs the holes. Try holding a window screen out of you car window and going for a drive - it will act just like a piece of plywood when the wind hits it. Jim

Gosh like a small scale 60's space program entertainment. Some Air filters can actually help flow a bit as tends to settle out/smooth the turbulence entering the carb throat. But can a Commandos?

It's hard to beat the flow of an open velocity stack in the shop. On the motorcycle at speed an air filter may beat a velocity stack. It just depends on which way the wind is blowing. Jim

In the porting articles one of them mentions a bit of flow bench improvement with a filter on and the smoother flow as a reason but of course only means that application not that they do universally. I've seen the air flows of complete bike and rider up to 60's mph, the air splits around the engine and slaps back together right where Norton put the carbs mouths and filter box so most the air flow is sideways into the space behind engine and air box not rushing along lengthwise. Then it get blasted out to the sides of oil tank/battery area and chewed up spit out like an explosion by rear wheel spokes/fender. Don't know if could apply to Norton with rear facing intakes but as a youth in small out board with carb facing forward I put my hand in front of it at ~45' angle and got sudden increase in rpm, so taped a playing card there and got a enough rpm/power boost the small boat got most of 10 mph faster and would ride on its prop blades lifting boat out of water screaming like a banshee. Nil grit in air on bodies of water though. This wasn't exactly ram air as no funnel or air box but was more a pressure wave tumbling into the throat. I'll never forget it as allowed me on cheap combo to tease other more powerful boats into embarrassing them. Then there's what happened with I Peel slapped together with small head and single carb and crude intruding gaskets just to get through break in phase before the dual carbs and thin stem CHO head showed back up a year later.

What about shrouding of the 1-5/8" intake valves against a 73mm bore?

Do you have a flow & velocity chart of the Mic Hemmings big valve conversion?

Great information Jim.

I still see roadbikes with just the velociity stack screen as protection from an ingestion of road grit. I guess it's a look some are after, but what a cost to both the engine longevity and, from this information, high rpm performance.

Glen

Clearly what we need is a direct-injection system, a large volume airbox and a velocity stack on the port! DI works at the rpm most Nortons run, and it cools the charge in the cylinder (hello, higher compression), all without crowding out any oxygen molecules in the port, since the fuel doesn't have to share room traveling into the chamber. Get with it, would you?!

Such great information here. I guess I am fortunate that I am not "burdened" by fancy porting, exotic valve jobs, high compression, long-rod kits, etc.!

But it does make me want to build a special to go alongside the stocker.
Mark

There's hardly any room in chamber w/o over head components in the way to install even a compression release so would be very difficult for direct injector, but dual plug Norton heads exists so maybe possible. Air box size to matter would also take some creativity in shape and location.

jseng1 said:

What about shrouding of the 1-5/8" intake valves against a 73mm bore?

Do you have a flow & velocity chart of the Mic Hemmings big valve conversion?

Click to expand...

I do not have a graph of the Mick Hemmings conversion- but if you have one laying around I will be glad to flowtest it.

Shrouding is more of a concern on a big exhaust valve than an intake. It is the short side of the port that is near the cylinder wall and the intake really does not flow that much on the short side anyway. I have tested some heads that actually had the air flowing backward on the short side. Ducati singles were bad about that.

Cylinder wall shrouding of the exhaust may be why I have seen little or no improvement from going to a larger exhaust valve. I usually go up 1.5mm on the exhaust in a big motor mainly because the exhaust seat works better with a bigger valve.

Whitworth Ranch said:

Clearly what we need is a direct-injection system, a large volume airbox and a velocity stack on the port! DI works at the rpm most Nortons run, and it cools the charge in the cylinder (hello, higher compression), all without crowding out any oxygen molecules in the port, since the fuel doesn't have to share room traveling into the chamber. Get with it, would you?!

Such great information here. I guess I am fortunate that I am not "burdened" by fancy porting, exotic valve jobs, high compression, long-rod kits, etc.!

But it does make me want to build a special to go alongside the stocker.
Mark

Click to expand...

Mark, All you need to do is send me a big pile of money and I will get a motor coming your way. Jim

It looks like you guys have gotten into some pretty radical alterations of the Norton head. The Harley XR-750 head looks similar in shape and size but seems to produce big power with less radical surgery. Does it have some not so obvious advantages? Have any of you flowed a XR-750 head?

In some of the earlier posts it looked like there was a limit to straightening out the ports because of the valve spring pockets. Could this be cured with some reshaped rockers and longer valves to mount the springs higher?

kentvander said:

It looks like you guys have gotten into some pretty radical alterations of the Norton head. The Harley XR-750 head looks similar in shape and size but seems to produce big power with less radical surgery. Does it have some not so obvious advantages? Have any of you flowed a XR-750 head?

In some of the earlier posts it looked like there was a limit to straightening out the ports because of the valve spring pockets. Could this be cured with some reshaped rockers and longer valves to mount the springs higher?

Click to expand...

I have not flowtested an xr750 head but a friend showed me one after he looked at what I was doing on the Norton head. They were similar but the XR head has the advantage of a little more height and a bit less curve to the port. The Norton head casting would need to be taller to get much more straightening in the port. I have done a weld buildup in the intake spring area and then moved the spring as high as I could get it on the valve stem so I could raise the port. It was a lot of work for the small improvement I got. You are still limited in valve size in the small Norton bore.

The XR750 also has a better bore to stroke ratio for horsepower. That long Norton stroke eats the horsepower when the RPM increases. Your better off flaunting the weight advantage of a Norton and using the good midrange torque available. It makes them more fun to ride anyway. Jim

comnoz said:

The Norton head casting would need to be taller to get much more straightening in the port. I have done a weld buildup in the intake spring area and then moved the spring as high as I could get it on the valve stem so I could raise the port.

Click to expand...

I have been wanting to achieve this by starting with a 28mm port head, welding & filling in the combustion chamber, adding a fin and re-machining the combustion chamber for longer valves, re-angle & re-port . I might actually do it if I was still racing. But its just an idea. It would be more likely if someone had a CNC program to copy the combustion chamber. I have seen photos somewhere in this forum of a CNC Norton head made from billet (with the manifold bolts arranged vertically).

Jim S

comnoz said:

The Norton head casting would need to be taller to get much more straightening in the port. I have done a weld buildup in the intake spring area and then moved the spring as high as I could get it on the valve stem so I could raise the port. It was a lot of work for the small improvement I got. You are still limited in valve size in the small Norton bore.

Click to expand...

Jim, if you can code it, we can build it.

Below are screen captures of some 3D work I did for the Norton ultra short stroke; just ran out of resources before executing. A little bit of oblong goes a long way in raising the port floor.