Knuck/Pan Intake Port CMCD "charge motion control dam" DogLeg

[oneuptom]

CMCD is made up, a play on Fords patented CMCV

Can anyone point me to hard data that would disprove my theory? My theory is this dogleg increases velocity and induces
swirl-tumble to the charge. And it would be more beneficial for producing torque than a slower moving less active charge.

I think other than a slight smoothing here (people usually hog the snot out of it for increased CFM), it will hurt VE volumetric efficiency and raise the Max Torque rpm. From what we now know about producing big torque numbers at low rpm those ports are already too big everywhere for a 74 inch motor.

Right at the valve and a 1/2 inch just below the valve into the throat is all you need to touch/focus on unless welding was also involved.

Jerry Branch used to promote this porting for Knucks/Pans (magazine how-to article by him) and I see many others still are... (mostly people selling a porting service) and others who don't understand the fundamentals of what a slow churning 4 stroke wants

[JBinNC]

The only thing I know is that so many of these old heads that have been "ported" have had the guide bosses completely removed. And that gives the already short guide even less area to be anchored to the head. The result is that the guides move relative to the seats, and I also see a lot of loose guides that are spinning in the head (with the attendant oil leak into the port). So, I'm really happy when I get a set of pan heads to work with that still have the guide bosses intact.

As far as the intake port flow goes, air don't like to turn, and that convoluted pan intake port could hardly be worse in that respect.

Jim

[oneuptom]

There's so much BS in the forums and marketing literature about the WHY behind Fords CMCV

This guy nails the real reason for the CMCV and has Dyno chart overlays to demonstrate what it's really doing

https://www.youtube.com/watch?v=FoQnoAQJJg8&ab_channel=FourEyes

[JBinNC]

I looked over that video. Not really applicable to a pan or knuck for a number of reasons.

You are right about the port sizing. S&S said one reason their 98 cu.in. Sidewinder shovels ran so well is that at that displacement the port size is closer to correct. J. Branch also improved the iron XR head by making both the ports and the valves smaller. That increased the velocity and helped power across the whole curve.

For the pan intake, air don't like to turn, and the port shape will reduce velocity because there is friction in each turn, in a manner of speaking. The fast pans of the day did away with the intake manifold altogether and moved the port to the left side of the head, and mounted two carbs. George Smith reportedly did several sets of pan heads this way, with good results (for that time).

Jim

[flatman]

I remember seeing a racing Vincent where the gas tank had a big hole in it where the velocity stack for the front head stuck thru. I think instead of straight out the side for a carb, more toward 45 degrees or more toward straight up and down. Basically as straight inline, and as close with the valve stem as possible. Straighter toward the valve seat the better. remote fuel bowl Amals would work. I think the yamaha virago had such a carb also. (or maybe vmax?) but you were thinking efi?

[oneuptom]

Try to visualize the actual small diameter charge column moving through this port. And keep in mind it's always going to take the shortest distance between any two points. This is also the principle behind extrude hone!!

In the case of the Pan port it's going to narrow considerably in order to do that. Result, the velocity increases considerably. Column to wall friction and turbulence will only help to build boundary layer and straighten the path for the charge column.

The charge column through a straighter, nicer port is going to have a much larger diameter and move at a much lower velocity. You can't think intuitively like a lay person would discussing this subject. Air moving through a port doesn't behave like you would imagine

[JBinNC]

Dude, you need to learn not to talk down to people who are trying to give you help and advice. I'm guessing you are young and VERY inexperienced. But that is no excuse for being rude.

You go ahead and put in the WORK, and then come back and tell us all about it.

Jim

[oneuptom]

I sense a little projection there Bud!.. Anyway, I've never suggested you were a liar like you did to me

[JBinNC]

I sense a little projection there Bud!.. Anyway, I've never suggested you were a liar like you did to me

I don't recall anyone here calling you a liar, least of all me. I think I'm done here.

Jim

[flatman]

oneuptom being you seem to be really into air movement, what are your thoughts on dimples? Or the step waves in porting? 35 degree valve seats vs 45 vs 60 degree valve seats? Also I see some of the vw guys are cutting grooves in their carb venturis (think kinda like a pie crust edge) for improved performance. Thoughts?

[oneuptom]

I don't recall anyone here calling you a liar, least of all me. I think I'm done here.

Jim

No memory either huh?.. Calling my pan acquisition story "made up" is calling me a liar! Thanks for nothing!

[oneuptom]

oneuptom being you seem to be really into air movement, what are your thoughts on dimples? Or the step waves in porting? 35 degree valve seats vs 45 vs 60 degree valve seats? Also I see some of the vw guys are cutting grooves in their carb venturis (think kinda like a pie crust edge) for improved performance. Thoughts?

Depends a lot on the engine. Like this Pan port, I see it as wanting no more than 0.450 lift for good torque and maybe 30 degree seats with a venturi throat to help tip the flow over the valve head. The flow wants to form a tight cone over the valve for optimum flow, and sooner you can make this happen in the lift range the better flow you'll have

[flatman]

I always heard 30 (or 35)degree was good for a flathead performance upgrade (as oppossed to 45 degree) but 45 degree and greater was better for an overhead? Piecrust venturi and dimples and wave port mods?

[oneuptom]

I always heard 30 (or 35)degree was good for a flathead performance upgrade (as oppossed to 45 degree) but 45 degree and greater was better for an overhead? Piecrust venturi and dimples and wave port mods?

The dimples are basically to remove the boundary layer for the last bit of CFM and to also introduce fuel out of suspension back into the flow. I don't think much help in a low speed torque motor.

A 45 degree seat will work nicely in flathead also if you build a asymmetrical venturi just below the seat on the far less active side of the port. 30 degrees exposes more window area to the flow sooner but does't want a lot of lift.

I don't know about piecrust carb venturies. I'll look that up, sounds interesting!

[flatman]

David vizard (or is it visard) has written a book on porting/teaches it at colleges? and videos. Interesting, knows his shit, but I must admit, alot is over my pay grade.