Intake manifold and port

jseng1 · Sep 27, 2023

A customer sent me an interesting photo of an intake manifold and port. The small hole is the balance tube.

Fast Eddie · Sep 28, 2023

Looks nice !

Schwany · Sep 28, 2023

It's clean. Is the port mismatch part of the smaller is better campaign?

jseng1 · Sep 28, 2023

I didn't realize what was in the photo when I posted it. I just saw it again on FB and found out that there is a port reduction sleeve in there reducing the port from 32mm to 30mm - in other words - converting an RH4 head to a RD10 head. You can see the taper and the thin edge on the inserted reduction sleeve.

Schwany · Sep 28, 2023

jseng1 said:
I didn't realize what was in the photo when I posted it. I just saw it again on FB and found out that there is a port reduction sleeve in there reducing the port from 32mm to 30mm - in other words - converting an RH4 head to a RD10 head. You can see the taper and the thin edge on the inserted reduction sleeve.

I'm working on an early 750 Commando head I bought new in the 90's for grins. No clue what the R number is. Intake ports are 28mm. I plan to open it up some, but not a lot. Doing other shaping things to it using hints from your race manual and some of my own ideas to improve oil flow into the pushrod tunnels for the tappets and also back into the crank case. Not sure I'll ever use it, but just in case it will be ready.

jseng1 · Sep 29, 2023

28mm port heads are the best to start with. Use the Axtell port diagram in the race manual. Don't lower the floor. Go high and then wider around the guide (eyebrows). Try not to enlarge intake beyond 30mm for the street. Raise the port at the manifold and move the manifold upward to match (elongate manifold holes).

Schwany said:
I'm working on an early 750 Commando head I bought new in the 90's for grins. No clue what the R number is. Intake ports are 28mm. I plan to open it up some, but not a lot. Doing other shaping things to it using hints from your race manual and some of my own ideas to improve oil flow into the pushrod tunnels for the tappets and also back into the crank case. Not sure I'll ever use it, but just in case it will be ready.

28mm port heads are the best to start with. Use the Axtell port diagram in the race manual. Don't lower the floor. Go high and then wider around the guides (eyebrows) as shown in the diagram. Try not to enlarge intake beyond 30mm for the street. Raise the port at the manifold and move the manifold upward to match (elongate manifold holes if necessary). Never go too far or too big. Run it and test it first to make sure you haven't lost too much low end and mid range. You can always touch it up later - but once you're gone to far you're screwed.

Schwany · Sep 29, 2023

jseng1 said:
28mm port heads are the best to start with. Use the Axtell port diagram in the race manual. Don't lower the floor. Go high and then wider around the guides (eyebrows) as shown in the diagram. Try not to enlarge intake beyond 30mm for the street. Raise the port at the manifold and move the manifold upward to match (elongate manifold holes if necessary). Never go too far or too big. Run it and test it first to make sure you haven't lost too much low end and mid range. You can always touch it up later - but once you're gone to far you're screwed.

I don't have any plans to do anything in excess and will probably do less material removal than what is in your Axtell port diagram. Baby steps really. Ports are now 30mm right at the entrance then blended into the smaller existing diameter. Most of what I'm doing is using the fickle fingers of fate and emery cloth around the guides.

Anybody ever raise the intake floor with JB Weld and live to tell about it?

prince of darkness · Sep 29, 2023

jseng1 said:
28mm port heads are the best to start with. Use the Axtell port diagram in the race manual. Don't lower the floor. Go high and then wider around the guide (eyebrows). Try not to enlarge intake beyond 30mm for the street. Raise the port at the manifold and move the manifold upward to match (elongate manifold holes).

28mm port heads are the best to start with. Use the Axtell port diagram in the race manual. Don't lower the floor. Go high and then wider around the guides (eyebrows) as shown in the diagram. Try not to enlarge intake beyond 30mm for the street. Raise the port at the manifold and move the manifold upward to match (elongate manifold holes if necessary). Never go too far or too big. Run it and test it first to make sure you haven't lost too much low end and mid range. You can always touch it up later - but once you're gone to far you're screwed.

Would it be possible to incorporate Axtell profile on your intake sleeves ?

Schwany · Sep 29, 2023

Only thing I am currently working on (very slowly) is getting the oval like shape around and a little past the guide that is mentioned in your race manual. I have not done any material removal on the floor. I'm adding to the floor further into the venturi and raising the roof if necessary to meet the spec. I may or may not bring the intake manifolds up via a slotted mount.

I did change the radius at the floor where it drops into the seat. It was too flat to me. More later if I ever actually get around to testing it. I have a Fred Barlow ported head on my one and only Norton engine now that works well enough, so this porting exercise is just something to play around with.

Thanks Jim

mean gene · Sep 29, 2023

Have you cut down the diameter of the exposed valve guide in the port area? Looked at some Jap intake guides and they have flats machined on the sides for maximum flow. 6mm valve stems would definitely improve flow. IMHO

Schwany · Sep 30, 2023

mean gene said:
Have you cut down the diameter of the exposed valve guide in the port area? Looked at some Jap intake guides and they have flats machined on the sides for maximum flow. 6mm valve stems would definitely improve flow. IMHO

I have not done anything to the guide OD's yet. I'll see what I can do with my magic fingers and emery cloth. Head still has old iron guides in it with nice tapers on them. I'd get bronze guides installed in there, but don't trust anyone around here to work on a Norton head and am not about to ship my head to Europe. Probably be cheaper to buy an STS head.

6mm valve stems: Based on a quick google search, this has come up before and one of probably several conclusions is that 6mm valve stems alone don't make enough difference to pursue the conversion. I did not read the threads. I've got other things to do.

What I don't care much for is the pocket cut around the guide in the roof of the bowl. Looks to me like something that should be filled in. It must cause some excessive turbulence. Then again maybe it prevents it. I'm not an engine designer, just a parts changer with funny ideas.

mean gene · Sep 30, 2023

I made a cutter to radius the bowl area, After this experiment on a junk head, I found an article where it supossed to be only 1/4 to 5/16 deep. I think it has to flow better then the "ramp" that is in the head. Of course you have to replace the guide after this. The drilled hole was to give me an idea of the depth of material I had to work with. I play alot! LOL

jseng1 · Sep 30, 2023

mean green - cutting flats on the sides of the guides does help but not much. I usually gring a little off the sides of the guide with a sanding roll if I'm doing some port work with the guides in place.

Schwany - be careful about removing material near the valve seat. You want to keep a broad radius leading up to the seat (not a sharp curve). JB weld is a maybe cause it can come loose. Better to add an aluminum shoe with a small alum screw threaded through the bottom of the head as well as glue it down with JB weld then do the port work.

Prince of darkness - The port sleeves are too thin to reshape but you can open up the area high and to the sides of the guides 1 or 2mm max for more flow. See illustration below showing where to remove material. You would want to cut and blend into the sleeve a little bit with an eyebrow shape. This redirects for a more downward directed gas flow and that helps.

Schwany · Sep 30, 2023

jseng1 said:
Schwany - be careful about removing material near the valve seat. You want to keep a broad radius leading up to the seat (not a sharp curve). JB weld is a maybe cause it can come loose. Better to add an aluminum shoe with a small alum screw threaded through the bottom of the head as well as glue it down with JB weld then do the port work.

Understood.

I'm not removing material near the valve seats. I'm adding a small layer of material and reshaping the added material so that it is a smooth transition. Only original material in the ports being removed is around the valve guides like defined in your race manual.

jseng1 · Oct 1, 2023

Schwany said:
Understood.

I'm not removing material near the valve seats. I'm adding a small layer of material and reshaping the added material so that it is a smooth transition. Only original material in the ports being removed is around the valve guides like defined in your race manual.

Check the cross section at its small point. 28mm is too small and will choke down performance above 1/2 throttle with twin carbs. Go higher and wider where you can. When I ported my first head from 28+mm to 30+ I was amazed at the performance increase.

Schwany · Oct 1, 2023

jseng1 said:
Check the cross section at its small point. 28mm is too small and will choke down performance above 1/2 throttle with twin carbs. Go higher and wider where you can. When I ported my first head from 28mm to 30+ I was amazed at the performance increase.

I noticed this:

At the end of the venturi there is choke point with a very easy to see machine edge just before the bowl. I'm smoothing that edge down at the end of the venturi and not disturbing the bowl. Sort of a straighter smoother shot into the bowl without a bump in it. Smoothing that edge off widens the port at little.

My ports will end up 31mm right at the manifold entrance and venturi down to 29mm at the bowl entrance, maybe a little more at the sides inline with the base of the guide.

I'm going to pull my carburetors and intakes to take some measurements of the Barlow port to see how he shaped the venturi section and bowl entrance. It is impressive above 3/4 throttle. Also works fine in town as long as I don't try to ride at 15mph in 3rd.

acadian · Oct 2, 2023

Schwany said:
Anybody ever raise the intake floor with JB Weld and live to tell about it?

Some BSA guys have done this, following commando head porting logic AFAIK

Schwany · Oct 23, 2023

Not in a big hurry. I still have another .2mm to go on the sides of the venturi section in both intake ports. The end result will be sightly oval in shape inside the venturi. The ports will still appear round at the manifold mount with the naked eye. I decided to stop at 30.3mm on the port entrances. I'm doing what I think should be an improvement. Very mild like a Stage .5 unless I ruin them. Then it will be a Stage -5, and a paper weight.

The embarrassing truth is I'm doing it all with my fingers using emery cloth, and sandpaper. Very minor burr work at the entrance to get things started. Tedious, but satisfying. Particularly if it works.

jseng1 · Oct 23, 2023

Take the widening/raising all the way around/past the guides and part way into the bowl.

Schwany · Oct 24, 2023

jseng1 said:
Take the widening/raising all the way around/past the guides and part way into the bowl.

Yeah, was afraid of that. I have been sort of pussy footing around the guides. I should remove them, but can't find a valve guide removal tool I know I could use with minimal destruction. Norton used to sell a nice one, but nobody carries them anymore. Beating them out with a hammer and drift is not the way I want to do it.

Anyway, enough of my whining. Raising the roof is gonna require sand paper cones on a stick for the Dremel. I tried for about 2 hours to do it with my fingers and small pieces of emery cloth and it's futile.

Fortunately, I don't need to actually use the head, so I have a lot of time to fool with it.

Thanks Jim

Intake manifold and port

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