Carb-intake manifold-intake port matching

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Gas turbine engines (jet engines) are not entirely the same thing ?
They consist largely of spinning things forcing airflow anyway...

Does that 'ta' stand for trolls association, seems to be you doing all the trolling ?
 
John 50+ hp out a 500 is remarkable bragging rights on accidental flow trick. For comparsion of lipped intake and 2-1-mega Ms Peel, could leave my 70hp 365lb SV in the dust after 60-70 mph and SV only neck and neck till then d/t two extra lower ratio gears so felt like peddling it. SV could barely register 120 given enough time but that was Peels base line commute rate and didn't even have to tuck down till going rather faster. Btw I also found ya don't need a mis matched lip to get most if not more from the bounary layer enegizer, just a rough chewed fuzzy crude cut gasket that intrudes ~1/16". Just accidental expedient bodge on Peel with single carb - as I still believed the 'common' sense - a single was poor power maker so only wanted to get intial run in done waiting on new Amals to arrive and dissapointed when putting them on.
 
Needing your analogy does not apply to Peel's Drouin impeller or Lake Injector but could use some flow logic on type of water spray nozzel and which way to face the blast to evaporate a good part of it on way to chamber but still have enough dropplets in chamber to continue cooling before dissacoiating to combust too.
 
My take on it would be that it is an acoustic effect not a high/low flow turbulence effect. A huge and usually overlooked condition of the mas flow through an engine in these sort of discussions is that it is not a steady state flow, it stops, starts, and even goes backwards.
 
texasSlick said:
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.

... they found they lost the power gain when they streamlined the carb - manifold - port.
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I believe that BSA did do something to increase airflow into the cylinder. Carbs do have obstructions and won't flow as much as the same diameter port can. The bell-mouth entry will be less than perfect (sometimes a lot less), and there are are other internal obstructions. A GP carb would be better than most, but still won't flow as much as the same diameter port.
Fitting a bigger carb allowed more airflow. I'd think nothing of fitting a carb 5mm bigger than the port diameter.

They lost power when they opened the port to the new carb size. The port then became too big (even for the carb flow), but more importantly they lost port velocity. That not only affects fuel droplet size, but it affects cylinder filling. What keeps the mixture flowing into the cylinder after the piston reaches BDC on the intake stroke? Port velocity and mixture inertia (in the port) does. After BDC, velocity matters more than what the port can flow.

You could do a lot worse than this:
Port diameter (mm) = square root (cylinder size in cc x rpm/2950)
The rpm you use in the formula would be where you want maximum torque to occur.
It won't hurt if the carb is bigger than that
 
hobot said:
John 50+ hp out a 500 is remarkable bragging rights on accidental flow trick. .
Click to expand...


Well I think you will understand that one simple "flow trick" did not take a 500 from a standard 25-28 bhp to 50 bhp rear wheel :)

The bike had a few other modifications as well :)

Most of which I have detailed in this forum before and will therefore not repeat.
 
X-File wrote:

"They lost power when they opened the port to the new carb size. The port then became too big (even for the carb flow), but more importantly they lost port velocity. That not only affects fuel droplet size, but it affects cylinder filling. What keeps the mixture flowing into the cylinder after the piston reaches BDC on the intake stroke? Port velocity and mixture inertia (in the port) does. After BDC, velocity matters more than what the port can flow."

This has merit .... I considered port velocity as an explanation for the BSA effect. The larger carb may have delivered more mass to the cylinder. OTH, others have reported a power increase by sleeving the manifold (implies same carb as original), thus I looked to another factor for the power boost. I would not rule out X-File's explanation as accounting for some (how much?) of the BSA power boost.

Hobot's argument that boundary layer energizing can help flow negotiate turns does not evoke an argument from this aerodynamicist .... I just don't think it explains the BSA results.

Rohan reports that swirling the mix produced power gains, and using ink as an aerosol marker showed fuel does not necessarily wet the walls .... perhaps the idea of a small turbine behind the fuel delivery tube is not so crazy. Hobot and all note: my dime size turbine is not intended to deliver more mass flow, but to deliver fully vaporized fuel to the cylinder, not a mix of vapor and aerosol. It would work by dispersing the spray coming off the fuel delivery tube, and would spin by the air flow. A small screen placed behind the fuel delivery tube might accomplish the same thing without unduly restricting the flow.

Manifold step, boundary layer trip lip, wires in the stream, or a mechanical device, can all accomplish better vaporization of the fuel, which should result in more efficient combustion, and hence more power. I do not think these (singly or even in combination) can result in more than a few hp gain. Reports of 50 hp from a 500 are believable (I remember when Ferrari first obtained 300 hp from a normally aspirated 3 L ), but these involve more go-fast mods than this discussion on port matching allows.

I do not think the BSA results have been conclusively explained. The purpose of this discussion is not to win arguments, but to throw out options for all to mull over, weight, and consider, then for those wanting to squeeze a little more out of our venerable machines, to experiment with the options. My days of stop light Gran Prix racing are over, but I am happy to spread whatever knowledge I possess to help others.

Slick
 
Testing shouldn't be too hard for someone with the means.
Make up some turbulence inducing press in sleeves of various configurations and give them a try.

With the right software, I also think that someone could design a pretty trick intake manifold and 3D print it.
 
Golf ball type dimples inside the intake port... That's the answer... Just gotta figure out how to do it...!
 
hobot-ness never capitializies hobot as ain't worth the extra key action.

If ya have followed the mileage masters from the 50's to current day ya find that full vaporization of fuel entering chamber is great for mpg but not mph. Boundary layer 'staggnation' piling up on itself trying to go around a bend > expanding till parts of boundary flow and main stream flow reverse to fill in the lower pressure - is what is being improved on by the flow trippers that does 2 main things [beside minor influence on stirring unevaoporated drops back into main stream], are directing sluggish boudary vortexes into main flow to energize it to flow the herd and thining-speeding up boundary layer by allowing main stream energy to reach closer to inner cruve of bends. For best mpg and efficient power fit a carb that close to 80% the size of intake valve, to get more inefficent race power fit bigger and bigger carbs till no more improvement then back down a tad. Its ancient trick to spary paint or powder like Bon Ami into carb then shut down and see where it colllects and try to modifiy surfaces ahead of the stagnation and blast into surfaces so more of it flows mixed into chamber.

Also if ya can create the right kind of swirl tubulence then its still swirling some in chamber to help spread flame fronts but for most power ya want some unevaporated feul or water to help cool combustion to avoid detonation.

Even though a ported hi CR hot cam engine can benefit more than a stocker to intake and exhaust improvements I've had 2 stcok engines that became as good as race engines by accidental intake trippers and opening up the exhaust. My comparisions were Fla. small hydroplane races and much later Peel taking on inline 4's by out accelerating them as they had to back off d/t wheelies while Peel just lightened front or floated it completely useless to steer with so learned only rear tire steers when the turning if power increasing fast enough with rpms to keep front out of traction effect on severe lean angles.

Texas slick there is an ultrasonic device sold to connect by air hose to the carb that is supposed to shock dropplets smaller for better throttle response and mph gallon to look into to expand you concept. Also can look into Viktor Schauberger as well as truck and air craft flow trippers and vortex generators like Kenny Dreer got into for more insights into flow mysteries. Btw in Texas they call manly foot wear, "Shit Kickers" d/t what cattlement deal with but in Miami we knew them as "cornered roach kickers" or "Porto Rician chain link fence climbers'.
 
Spent some time reading on a forum for Pro Stock drag car racers and builders. In the 70s and 80s it was all "ported and polished" now not so much on the porting and a definite no to the polishing.
The ground surface of the intake port is said to produce better atomization and more power than an identically shaped polished port.
Having polished the occassional port back then, it is clear that sometimes you can work really hard to produce a negative effect.

Glen
 
On the BSA Goldstar example where the lip where the carb joined the manifold increases the engine power, there can be no doubt that the lip did increase the power on these engines.

As hobot points out there can really be no other reason than this lip causes turbulence that mixes the fuel better with the air for better burning. It may be that the BSA really needed this extra turbulence because the carburetor was not providing it as it might on many other machines. The Amal GP carburetor is very smooth inside, not even having the restriction normally provided by the needle on most other carbs. The only restriction on the Amal GP is the extension that carries fuel into the main bore from the needle jet. Even most fuel injected machines have a throttle valve that makes more turbulence than the Amal GP. I think the Amal GP smoothed out the flow too much. If this was not the case then fuel injected race engines would have throttle bodies with a throttle valve that would not still be present in the center of the throttle bore.



Nigel
 
I agree we All comprehend that the smaller textures of *non-polished* surfaces helps power by breaking up thin boundary layer to re-mix condensed fuel liquid back into the main flow. But this small texture in not enough to affect main flow that a lip can so lips main benefit is streamlining flow around bends. Similar to vortex generators on wings and roofs of hi mileage seekers. Tapering down intake paths to chambers can help flow ***but*** its a very slight ~ 1.5 degree slope *so* just blending inter faces may often choke flow resistance converting speed into pressure where its not wanted - as comnoz found on his tube tapper tests - he did not follow up on the *non-intutive* alternative hobot will. I am BIG pipe organ semi-trained to know pipes tuned by bumping trip plates in front of air slots or curling metal lips more or less till suddenly pipe resonating loud perfect pitch. Also know pressure and port size flow if a bit too much can over-blow a pipe ruining its tune but turbulence.

see what sense ya can make of these sites

https://www.google.com/?gws_rd=ssl#q=vo ... reamlining
 
tricatcent said:
As hobot points out there can really be no other reason than this lip causes turbulence that mixes the fuel better with the air for better burning. l
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Hobots next post then goes on to (partly) deny this !

As he then shifts focus to, the lip may be producing a standing wave in the gas flow pattern, that may produce better steering around corners and entry into the combustion chamber - so it may well be better flow that is producing more power in that BSA engine.

Tuners have long noted that it can be the lumps or bumps near the inlet valve guide that ultimately determines an engines' power output.
That gas flow pattern into the engine is EVERYTHING to producing good power.
And BSA never got near the manx power output/litre, where the manx's pulse tuning of inlet and exhaust was to become THE classic example of what this could achieve.
 
Rohan said:
And BSA never got near the manx power output/litre, where the manx's pulse tuning of inlet and exhaust was to become THE classic example of what this could achieve.
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According to Roland Pike the BSA Goldstar Factory racebikes did get very close to Manx power levels , quite surprising given that the Manx is OHC and is a pure race engine. Even the road going Goldstars sold to the public were in the 40 -42 hp range with dyno sheets to prove.

Glen
 
Yes, have the Goldstar book with some of those dyno sheets.

Thats a fair bit behind the later short stroke manxs though, with 50+ hp on tap.
Even the old long stroke manxs were in the 40-42 hp area.

Note that all these are engine dynamometer tested though, not rolling road at the back wheel...
(??).
 
Yep Rohan: *both* standing waves created to show up at throat openings *AND*OR*Also* a step or lips deeper inside to help tumble flow around bends better are both known ways to gain power for essentially nothing by luck or smarts. In Peels case various things combined to make beeline front lifting leaps boring relaxing compared to sideways wheelie off peg scaping toe smacking angles no fatso tire rigid frame cycle seem able to hook up regardless of their computerized intake and exhaust flow valving action with staggered 4 valves to assi None of the above expected by just a bit of surface roughening. Plow rows of ridges, grooves or projections somewhat before bends in ports or slopes of car roofs or wings has been applied a long time, so catch up before spouting disparagement w/o knowing what ya missing out on.
 
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?

Tex, I suggest the specific horse power of a Triumph 750 twin with hi-comp pistons is always less than that of a Commando 750. If you lift the head off a Triumph, the piston is always coked up on the side away from the plug, unless the head has been modified to centralise the plug. In that situation, more fuel doesn't necessarily mean more horsepower. If the inlet tract flows better and the fuel is better mixed with the air - that gives more power if the combustion process was previously wasteful. I wouldn't leave a step in the inlet tract, I've tapered my ports to get laminar flow, and rely on the head to create good combustion conditions - thus I would never remove the squish band.

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...
 
"Tuners have long noted that it can be the lumps or bumps near the inlet valve guide that ultimately determines an engines' power output."

hobot said:
Plow rows of ridges, grooves or projections somewhat before bends in ports or slopes of car roofs or wings has been applied a long time, so catch up before spouting disparagement w/o knowing what ya missing out on.
Click to expand...

Isn't that part of what I said. ?
You seem to have taken to shootin from the hip, apparently without aiming at anything in particular ??

A famous example of inlet manifold problems was the very 1st version of Nortons dominator, circa 1949.
A long bifurcated inlet manifold, from the pen of Mr Hopwood hisself, failed to produce performance as expected.
A short stubby 1 into 2 alloy manifold bolted on restored the performance.
Inlet gas flow is not always obvious or as expected...

Engines that make serious hp don't generally have too many twists or turns along the (Inlet path)way though...
 
Its fairly easy to mimic some of my Ms Peels intake by crafting an intruding rough edged gasket at head, all the way around or more or less of a crescent. Of course if something else in chamber or exhaust does not allow much more flow then may not work as advertised.
 
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