Carb-intake manifold-intake port matching

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Danno

Danno

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Before I assembled the carbs to the motor, I matched the junctions carb-to-manifold and manifold-to-intake port. I was shocked at how mismatched these junctions were. Most of the work was at both ends of the manifolds, although there was a little grinding/sanding/polishing to be done a the carb throats to make everything the same. Was I wasting my time, or will this make it run better, stronger, smoother?
 
Danno said:
Before I assembled the carbs to the motor, I matched the junctions carb-to-manifold and manifold-to-intake port. I was shocked at how mismatched these junctions were. Most of the work was at both ends of the manifolds, although there was a little grinding/sanding/polishing to be done a the carb throats to make everything the same. Was I wasting my time, or will this make it run better, stronger, smoother?
Click to expand...

From what I have seen -up to about 1mm mismatch doesn't seem to make much difference on a 32mm port. Smaller higher velocity ports need a good match. Jim
 
From Roland Pike's notes. Roland was the man who really developed the Gold star for BSA.

Carb-intake manifold-intake port matching
 
Duh yep trip up vortex lip from over size carb on undersize port head was enough to rekindle my interest in Commando as a sport bike teaser instead of lolly gagging poor man's Harley mimic. I don't think of factory Combat as very potent and never contest with mine. When I get around to natural inspired Peel the manifold will slightly expand to over size match, not tapper down smoothly, Might ask comnoz about this. Of course Peel principles does not apply to hardly anyone elses Nortons as we all know a single carb is not as good as two of em being lazy half the time. A slight tapper from head entry to valve pocket is often reccommended with formulas on the % tapper to use. The trip up turbulance wave does not have be formed inside carb or behind it - as had a 25 hp Mercury outboard on whimpy light boat I ran w/o engine cover so carb faced forward and one day reached back and angled hand to semi funnel wind to suddenly hit an angle that made engine rpm jump a few 1000 which made me hurt my ears grinning. Took a playing card and taped it at same angle so excess over rev on tap any time and began hunting down hot rod boaters in Fla. lakes, rock pits, canals and bay. Carb/hand was about 3-4 inches out in front of carb. Was good enough a semi friend with a race boat made deal to use my engine in a long endurance type bay race and did pretty good till he took a bit too much of a short cut close to a small island and hit a piling that frayed hull to smitherines but shallow enough engine didn't submerge.


hehe fun tale with above playing card engine, Fla canals get clogged with sea weed so Army ducks towed metal plows to cut it loose to float up and pile up against a bridge so thick could walk across it but basically nasty concentration of stinky slimmy scum and big city crap, so a few small boats would be semi sagged wtih props tangled so working paddles and hands and poles to inch past the 100-150 ft long clot, when here I come like 40 mph to cut power at seaweed island edge and ski by momentum across it while water pressure lifted prop clear till slow enough prop reentered and back on power never comming off a decent plane, but my spray would cover the poor slow pokes raising fists and yelling stuff I could not hear with the wind in my face.... Dang thing 10 ft long would get almost 50 mph. Oh yeah on the tear drop race hull I tested in prefect flat narrow cannal water it would cycle through 3 phases of planing, 1st lifted to small wedge of rear hull, then lift hull out the water about 3 inches riding on cavitation plate then couple more inches on just decencing prop blades then out the water and instant to fall back on flat hull wedge and repeated spending about a second in each stage. You bet it left a nice rooster tail behind but playing card and duct tape worked at treat.
 
I'm sure that one of the Dominator range came with sleeves pressed in to the inlets as standard.
Dave
 
worntorn said:
From Roland Pike's notes. Roland was the man who really developed the Gold star for BSA.

Carb-intake manifold-intake port matching
Click to expand...

Interesting. Can you elaborate on the positioning of the venturi that was mentioned in the article? Where it was said "behind the carb", does that mean the inlet stub had a constriction in it or a sleeve in the inlet port was shaped into a venturi?
 
As Cash states, my 1962 650ss has steel sleeves in the inlets. These are just a push fit. As I have not run the bike without them I can't say what difference they make. Any thoughts?
 
[quote="daveh"

Interesting. Can you elaborate on the positioning of the venturi that was mentioned in the article? Where it was said "behind the carb", does that mean the inlet stub had a constriction in it or a sleeve in the inlet port was shaped into a venturi?[/quote]

Dave, I take it to mean the venturi was placed on the inlet side of the Carb same as one might mount a bellmouth .

He doesn't give any more info about either mod other than what is in the quote above. The non matched square shouldered Carb to Carb stub fitting has been used by many (including me) and seems to work. The Venturi type inlet stack is something I have not seen in use, perhaps some of the racers here have?

Glen
 
I am thinking "behind the carb" refers to somewhere between the carb and the port, I.e. in the manifold.

I am also thinking the increase in power may be attributed to aerodynamic turbulence dispersing and atomizing the fuel droplets. Increased turbulence would occur with a step in the ports as first found with the oversized carb. I have no explanation how the Venturi could accomplish the same effect.

Another way to create aerodynamic turbulence in the manifold, should this be the desired mechanism to develop more power, would be to place fine wires across the flow.

Slick
 
Matchless said:
As Cash states, my 1962 650ss has steel sleeves in the inlets. These are just a push fit. As I have not run the bike without them I can't say what difference they make. Any thoughts?
Click to expand...

There was a Featherbed Norton enthusiast, Beng, who posted on this forum up until a few years back. Interesting guy, who didn't suffer fools gladly! I miss his contributions. I can't remember if he ran his 650SS without the sleeves, but you could search his posts. And you have the opportunity to experiment with yours, and report back!

Glen, Slick, thanks for those explanations. I would like some visual on that venturi!

Dave
 
I remember Beng all too vividly. Some of us fools didn't suffer him all that gladly either. I sometimes read the NOC site, he was removed from that one as well.
But you are correct, he had quite a lot of info on Dommies, not so much on Commandos, which he considered inferior along with late model Dommies like my 1968 650SS.

I have followed Roland Pikes interesting finding with my special, I used 41 mm carbs shouldering onto a 38 mm intake stub and intake port for that. Unfortunately I cannot report as to any net effect because I have not done dyno testing nor have any other setup to try on there. That is why dyno work like Nigel is doing is valuable, there isn't much of this kind of info and it really does take out the guesswork.

I had the carbs off the 650ss long ago before reading Roland's autobiography. Late model 650 ss bikes used larger carbs (30 mm) than earlier models did. I suspect there is a shoulder present either between the Carb and spacer or spacer and head. Later specs are sometimes quoted at 52 HP vs 49 for early. I wonder if this is due to a Roland Pike Gold star effect?
Might pull a Carb off for a look see.

Glen
 
Its not just any ole turbulence that can both mix mixture and energize boundary layer to flow around bends better so wires across flow add more resistance than assistance. Flat streamlined vanes help gases flow around some bends better and straighten flow not stir it. It does not take much of a trip lip or grooves, demiples, rifling or ridges to energize boundary layer as too much makes flow choke up with too many gas molecules not moving in desired direction. Velocity stacks both help draw air from larger opening but also smooth flow as too much swirl also allows too many molecules not moving as directly into chamber as possible. Trial and error, errors and trials is how most of this discovered. Comnoz left a big clue on intakes with his flow bend of various tubes but did not follow it up.
 
Closely spaced wires in both directions, placed in the air stream would be a screen, and would restrict flow more than help fuel atomization as Hobot has said. I am thinking 11 fine (0.005) wires spaced in one direction, either horizontal or vertical (makes no difference if the flow channel is straight). If the tube radius is R, start with one wire at radius = 0, then 5 more at radius = 0.10R, 0.20R, 0.35R, 0.50R and 0.65R, and 5 others similarly 180 degrees opposite. There is nothing scientific about this spread except for avoiding the boundary layer flow at radius > 0.8R where the fluid velocity is too slow to generate strong vortices, and since the fuel is admitted in the tube center (radius = 0), I am concentrating the wires nearer the center where the fuel droplets are concentrated.
The distance distal (downstream) from the fuel admittance point will be a factor in the optimal wire spacing.

The turbulence that comes off cylinders (wires) in a flow stream is small scale, high frequency vortices which do not rob the flow of a great deal of energy, as does a step. The high frequency should be a positive factor in fuel dispersal. An example of the frequency is the Aeolian tones that are heard when the wind blows thru the power lines.

As Hobot said, trial and error is the best way to deal with the details, and a dyno helps.

Slick
 
Slick your taunt wiring scheme makes me wonder if we can go by ear getting em right or wrong, though nothing I know about fluid flows supports your concepts > if wire fine enough not to resist flow significantly then also not likely enough turbulence to effect re-mix of fuel drops back in the flow of things. What would make a felt difference is a flat plate behind the round slides about 1/3 the way off bottom so lower throttle flow does not tend to curl back on itself in more throat area than it needs. As throttle opens more it basically disappears to flow interference and may still help some. Miki carbs already have this option also with UFO to smooth bottom of slide flow.
 
@Hobot

Ultimately, if more power was the result of the step in the BSA experiments, it had to be the result of burning more fuel. Power only comes from burning fuel.

Burning more fuel can result from an increased mass of fuel/air introduced into the cylinder, or from burning the fuel in a given amount of fuel/ air mix more efficiently.

Given that the BSA folks did not change anything to increase the fuel/ air mass (they did put on a larger carb, but when they removed the step, they lost what they gained), they must have gained power by the latter factor of burning it more efficiently. Also, the presence of the step and the resulting turbulence, might actually reduce the mass flow, pointing more to the latter factor.

How then did the step result in greater burn efficiency? I theorize (hell, I don't know for sure, but I cannot come up with anything better, and so far no one else has) the step induced turbulence dispersed the fuel droplets and helped atomize them. This would result in faster burn rates in the cylinder, higher mean effective pressure, especially at optimal crank angles, and less fuel to be burned late in the cycle, or only to be exhausted to finish burning in the pipes.

Now, IF that is the proper scenario, how can we better disburse and atomize the fuel? The step generates large scale turbulence, that is, large swirls. Such large swirls carry the fuel droplets more in toto, rather than fragment them into finer droplets which is the desired action. I am not saying such large swirls do not help fragment and disperse, just saying I am looking for a better way.

A cylinder placed across a stream generates turbulent eddies on a scale about twice the cylinder caliber with the eddies in opposing rotation, the opposing rotation should in theory, better fragment the droplets. I grant you your point that a small caliber may not affect a large area, but by experiment, the caliber and spacing may be optimized. I also think (don't know for sure) the high frequency of the vortex shedding will whip the fuel drops better than the step.

The crux of your points are that flow streamlining is the objective. Not per the BSA experiments ... they found they lost the power gain when they streamlined the carb - manifold - port.

As I said, there is nothing scientific about my proposed wire caliber and spacing ... it is a place to start for anyone disposed to experimenting .... mostly, it is Slick's guts .... but I do have a PhD in aerodynamics, and my doctoral thesis was a theoretical analysis of step-induced boundary layer separation.

You are the Forum's Premier Experimenter ... why not look into better fuel atomization?

This may sound crazy, but perhaps a small turbine wheel (about a dimes diameter) placed behind the fuel tube might blast the fuel drops to atoms better than anything so esoteric as aerodynamics, or such a turbine might only sling the fuel to form a wet ring around the carb periphery .... only an experiment will tell ...

Slick
 
Hm slick you are tempting me to think on my own, oh oh. I do not think step tubullizing fuel droplets is the lip/step main power factor, as BSA race crew would of already had carb mixture set up well w/o the step, so if step just vaoprized feul better then it would be expected to be too rich for best power and bore wear. My semi study of this implies the power help comes from faster flow around the port bend so rams more well mixed mixture in. in some long past discussion on this i lleft a bunch of URLs on forms, sizes, placement and features of
lumps bumps hollows ridges dimples and lips. The fan like things sold to spin aire into carbs do not work as advertised. Peel gets turbo fan mixing ramming of 40 mm down to 32 mm trading velocity suddenly into chamber pressure. This of course leads to stepped headers principles and application.
 
texasSlick said:
This may sound crazy, but perhaps a small turbine wheel (about a dimes diameter) placed behind the fuel tube might blast the fuel drops to atoms better than anything so esoteric as aerodynamics, or such a turbine might only sling the fuel to form a wet ring around the carb periphery .... only an experiment will tell ...
Click to expand...

Heck, if I had a $ for every version of the 'turbulator' or 'swirlulator' that has appeared on the market,
I could probably shout the bar from now to eternity....
Notice too how turbo engines are getting stronger and stronger these days ?
The ultimate example of this line of thinking ?

Back in the early 1950s, Jack Williams (Chief Race Engineer at AMC)(and father of Peter Williams, yes the racer) was playing around
with the airflow into the 7R race engine on the flow bench (350cc ohc single race iron, the Boy Racer).
He found, using ink injected into the airstream, that if he could swirl the fuel/air mix into the cylinder WITHOUT the ink going onto the walls
that he could gain 10% to 15% to 20% more power, nothing else required. This lifted the hp eventually from low 30's to high 30s bhp,
and made it quite competitive against most of the opposition at the time (before the 4's really got into the game).
Downdraft and offset inlet ports became more common after that...
Just one of the many tricks of getting more go from the machinery.
 
texasSlick said:
@Hobot

Ultimately, if more power was the result of the step in the BSA experiments, it had to be the result of burning more fuel. Power only comes from burning fuel.

Burning more fuel can result from an increased mass of fuel/air introduced into the cylinder, or from burning the fuel in a given amount of fuel/ air mix more efficiently.

Given that the BSA folks did not change anything to increase the fuel/ air mass (they did put on a larger carb, but when they removed the step, they lost what they gained), they must have gained power by the latter factor of burning it more efficiently. Also, the presence of the step and the resulting turbulence, might actually reduce the mass flow, pointing more to the latter factor.

How then did the step result in greater burn efficiency? I theorize (hell, I don't know for sure, but I cannot come up with anything better, and so far no one else has) the step induced turbulence dispersed the fuel droplets and helped atomize them. This would result in faster burn rates in the cylinder, higher mean effective pressure, especially at optimal crank angles, and less fuel to be burned late in the cycle, or only to be exhausted to finish burning in the pipes.

Now, IF that is the proper scenario, how can we better disburse and atomize the fuel? The step generates large scale turbulence, that is, large swirls. Such large swirls carry the fuel droplets more in toto, rather than fragment them into finer droplets which is the desired action. I am not saying such large swirls do not help fragment and disperse, just saying I am looking for a better way.

A cylinder placed across a stream generates turbulent eddies on a scale about twice the cylinder caliber with the eddies in opposing rotation, the opposing rotation should in theory, better fragment the droplets. I grant you your point that a small caliber may not affect a large area, but by experiment, the caliber and spacing may be optimized. I also think (don't know for sure) the high frequency of the vortex shedding will whip the fuel drops better than the step.

The crux of your points are that flow streamlining is the objective. Not per the BSA experiments ... they found they lost the power gain when they streamlined the carb - manifold - port.

As I said, there is nothing scientific about my proposed wire caliber and spacing ... it is a place to start for anyone disposed to experimenting .... mostly, it is Slick's guts .... but I do have a PhD in aerodynamics, and my doctoral thesis was a theoretical analysis of step-induced boundary layer separation.

You are the Forum's Premier Experimenter ... why not look into better fuel atomization?

This may sound crazy, but perhaps a small turbine wheel (about a dimes diameter) placed behind the fuel tube might blast the fuel drops to atoms better than anything so esoteric as aerodynamics, or such a turbine might only sling the fuel to form a wet ring around the carb periphery .... only an experiment will tell ...

Slick
Click to expand...

I also found the BSA article many years ago.

When I was experimenting on the dyno with intact lenghts on my 500 Dominator I made several different fixed tubes and joined them with a Mikuni type mounting fitting. This left a step in the inlet tract which I intended to correct when I decided on the final length.

However given the BSA article, the Jack Williams experiments and given my 500 made over 50 bhp on pump gas on the dyno I left it in there !

Im sure it can be improved but that was all the time I had available back then.

John
 
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