APT 40mm Billet Smart Carb mounted on a 431 Puma. With important mounting notes.

[The_Steve_Man]

I feel like I just stayed at a Holiday in last night!

[SmartCarb]

I was not referring to four stroking (miss-fire) at light loads (small throttle openings) when the RPM is low and the engine is off the pipe    I was referring to the detonation that is inherent with highly developed two-strokes when the RPMs are high and the engine is on the pipe, the throttle opening is low, and the resulting crankcase filling is minimal.  When these three conditions occur simultaneously, short-circuiting of the fresh charge occurs, the cylinder is not scavenged sufficiently, and too much residual exhaust is mixed with the fresh charge.  When enough fresh charge is trapped with the exhaust residuals, the residual exhaust often raises the temperature of the remaining fresh charge to the point that it is prone to detonate during the combustion event.
 
When short-circuiting occurs, HCs are increased even when a combustion event occurs at the end of the current cycle.  HCs are increased even more when a misfire occurs regardless of what caused the misfire.

Gotcha. I must have misinterpreted your earlier statement, it was the "just cruising around" that threw me.

Testing, testing, testing, testing....

 Two stroke engines that have been developed to medium to high levels of power output should not be used for just cruising around because of detonation related issues due to poor scavenging.

Please explain your findings to us a little more in detail of how detonation occurs in a high performance two stroke due to poor scavenging. Being that detonation in a spark-ignition internal combustion engine occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. (WIKI)

 If I'm understanding you correctly you are saying that at high rpm, the throttle is low enough to not adequately fill the crankcase and the pipe is over scavenging the cylinder enough to cause short-circuiting by pulling the bulk of the fresh charge out the pipe? Because the cylinder is unable to completely clear the residual exhaust gases, the temperature of the residual exhaust gases cause the fresh charge to rise to the point of what? Preignition? That is an entirely different animal and according to this logic would be only thing that could potentially occur if there were enough heat energy left in the exhaust gases to overcome the bulk cooling effect of filling the cylinder with fresh charge. In a loop scavenged two stroke the bulk transfer of the intake gases is what begins exhaust movement out of the cylinder and in a good engine the wave front in the pipe will have reached the end of the diffuser section and a strong negative pressure is being exerted on the cylinder to pull out exhaust and haul fresh mix up from the crankcase. Exhaust residuals dilute the fresh charge and could in no way contribute to detonation.

Modern large bore ultra high performance two stroke engines with power valve exhaust do a very good job of charging and recharging the cylinder (scavenging). Its really only when you are off the pipe that any real short-circuiting occurs. Short-cicuiting referring to fresh charge that escapes out the exhaust port due to insufficient back wave to push the charge back in the cylinder just before exhaust port closing. Large bore snowmobile and PWC two strokes often approach 4 hp per cubic inch in factory trim. Piston port or rotary valve GP engines of yesteryear could possibly have had problems with just cruising speeds and low throttle settings to cause detonation due to insufficent bulk flow scavenging, but today's 2t's with state of the art combustion chambers and boost ported cylinders are very efficient and the evidence is clear simply by the incredible power they make and the power they make over a reasonably broad torque curve.

[brewer_brewer]

I like my smartcarb, just saying

[udontknowme]

I have not tested different intake system lengths on the Dyno for the 430.  If the power peak and torque peaks occur at about the same RPM on the 430 as the 250, I would expect the tuned length of the intake system to be similar.  The exhaust pipe has the major influence on the RPM of where the peaks occur.

If you are using a "250" pipe with a larger stinger and larger silencer core, a 250 intake would probably be an improvement.

the well tuned 250 stuff i seen had peak hp at nearly 11k rpm. i imagine a engine of 400+cc would be a fair bit lower, for reliability sake anyways.  one time  hooked  a digital rpm unit on a engine about 500cc. sounded like it was gonna blow up at 10k

[udontknowme]

Large bore snowmobile and PWC two strokes often approach 4 hp per cubic inch in factory trim.

thats not bad, all things considered, and with the new technology theyre using. i have a idea for a twin cylinder engine totalling 500cc. if it ever makes it to fruition i estimate about 4.5 hp per CI or .28 per cc, using gas and a standard keihin or mukini style carb and no fancy electronics of any kind. seems like the size of your wallet is always the determing factor  :highly_amused:

[Jerry Hall]

the well tuned 250 stuff i seen had peak hp at nearly 11k rpm. i imagine a engine of 400+cc would be a fair bit lower, for reliability sake anyways.  one time  hooked  a digital rpm unit on a engine about 500cc. sounded like it was gonna blow up at 10k

You must be looking at 250 shifter kart engines that are being twisted to around 11000 rPM.  The TRX 250 R engines and pipes that we used on the national outdoor and stadium events usually made their peak power at under 9000 RPM.

[Jerry Hall]

thats not bad, all things considered, and with the new technology theyre using. i have a idea for a twin cylinder engine totalling 500cc. if it ever makes it to fruition i estimate about 4.5 hp per CI or .28 per cc, using gas and a standard keihin or mukini style carb and no fancy electronics of any kind. seems like the size of your wallet is always the determing factor  :highly_amused:

Snowmobile engines do not usually have their power over as wide of an RPM range as engines with transmissions.  It is a lot easier to make huge peak power numbers if you do not need it over a wide RPM range.  The CVT can hold the engine at it's peak power.

[udontknowme]

yes i know snomo engines are a different breed because of the transmission system. try riding a snomo type of powerband with a conventional transmission :excitement: :excitement:

[rsss396]

I believe pre-ignition is what starts the chain of events leading to detonation in the cylinder during high rpms and part throttle.
In this situation you are no longer filling the crankcase completely, this will lower the crankcase pressure which means the cylinder gases are more prone to back fill into the transfers and pre-heat the tunnels and fresh mixture. This not as much of a issue at lower rpms because the exhaust port has more time to effectively bleed the pressure down but as rpms increase the time for this to happen shortens.
I do know that Aprilla forbid their racers from doing victory burnouts at the end of the race because of the motors violently detonating and seizing from spinning the tire at high rpms and low throttle positions, these same bikes could run WOT on the dyno and track until the tank would run dry without any issues.
I also owned a 700 arctic cat snowmobile that when in the same type of situation was very prone to siezing, that motor was bullet proof, unless you just cruised at very small throttle postions for a extended period of time, now you could say well it was just lean in that area, but according to guys on the dyno that checked fuel rates they were not really that bad so I suspect the pre-ignition condition stemming from the pre-heated fresh fuel charge was to blame.

[SmartCarb]

Snowmobile engines do not usually have their power over as wide of an RPM range as engines with transmissions.  It is a lot easier to make huge peak power numbers if you do not need it over a wide RPM range.  The CVT can hold the engine at it's peak power.

The CVT is just another transmission, although to your point it does maintain a more or less constant shift speed. However anyone who has ridden a modern snowmobile in the mountains and the tractability new machines offer will recognize immediately new 2t engines do indeed have impressive performance, broad torque curves, and nice stable combustion when you are low in the power band and executing tight maneuvers. Peak RPM typically being around 8200 RPM. Hillclimb and Snowcross racing also show this to be true. Wobbley has been building SC equipped GP twin 2t race engines in New Zealand/Australia for years and we have one in our pikes peak quad. Pikes Peak is now completely paved and the torque necessary to power out of an 11% grade uphill corkscrew at race pace is pretty severe (manual 6 spd). The broad usable power of a state of the art two stroke is certainly an improvement over the hyper light switch engines of years ago. Could these engines once again be made available for on street use and become emissons compliant? Yes. Is there politics against their use? Yes, it's all about emissions, however DFI 2ts and our SF-II engines are showing it is certainly possible. We test at ARB and EPA cert labs several times a year and have our own emissions certifcation laboratory. One thing is clear, the EPA does not care what the operating system of the engine is (2t or 4t) doesn't matter as long as it passes their numbers for emissions and noise. But those numbers are getting much more stringent and harder to meet.

[SmartCarb]

I believe pre-ignition is what starts the chain of events leading to detonation in the cylinder during high rpms and part throttle.
In this situation you are no longer filling the crankcase completely, this will lower the crankcase pressure which means the cylinder gases are more prone to back fill into the transfers and pre-heat the tunnels and fresh mixture. This not as much of a issue at lower rpms because the exhaust port has more time to effectively bleed the pressure down but as rpms increase the time for this to happen shortens.
I do know that Aprilla forbid their racers from doing victory burnouts at the end of the race because of the motors violently detonating and seizing from spinning the tire at high rpms and low throttle positions, these same bikes could run WOT on the dyno and track until the tank would run dry without any issues.
I also owned a 700 arctic cat snowmobile that when in the same type of situation was very prone to siezing, that motor was bullet proof, unless you just cruised at very small throttle postions for a extended period of time, now you could say well it was just lean in that area, but according to guys on the dyno that checked fuel rates they were not really that bad so I suspect the pre-ignition condition stemming from the pre-heated fresh fuel charge was to blame.

Large bore engines have all kinds of ways to create localized hot spots and plenty of time for detonation to occur. Pre-ignition and detonation are two completely different things. Pre-igntion- being auto ignition, where the mixture torches off before the plug has a chance to light it. Detonation being a separate combustion event occuring as the initial flame front (lit by the spark plug) pre heats the end gases in front of it to the point of auto ignition (active radical combustion) and the two or more flame fronts collide and produce the characteristic knock of detonation. I think just hung up on terminology and to be fair I'm sure your thoughts are fairly correct in the context to which you are referring. Anyway back to the carburetor.

Looks like Lectron runs power jets on their carbs.

http://www.lectronfuelsystems.com/carburetor/



I wonder if one could be adapted to the smart carb?

This is from their FAQ:

"Should I have a power jet carburetor or not?

This is a must for a two stroke engine. We prefer to have them on all types of engines two or four stroke.
The power jet carburetor can give you a wider range on tuning and also helps you fine tune top end power on all types of engines."

"What does the power jet do for tuning?

The power jet is for high speed tuning only. The power will kick in about 3/4 from top RPM First get the motor running good at idle and mid-range then work on the power jet.
The power jet will not effect the tuning of idle, mid-range, or response on the carburetor."

The SC does not need a power-jet. The float bowl pressurization circuit is a much more effective way to control top end fueling and provides the same very fine atomization as the rest of the range. At the very top end of RPM's the pressure being exerted against the fuel in the float bowl begins to move from static pressure into dynamic liquid flow and fuel is being squirted up the nozzle by the 200+ MPH air pressure being rammed into the scoop. The real beauty is that the forces driving the fuel are exactly proportional to the air pressure flowing into the engine. Same applies for adding boost.

[rsss396]

I have read the the definitions of pre-ignition and detonation and understand they are different, but I have always suspected that you get to a point where one leads to the other but occur in separate strokes, meaning the pre-ignition probably builds enough heat in the piston, cylinder and combustion chamber to create local hot spots that may start detonation on the next compression stroke. Whether it continues to detonate I am not sure but if the conditions are ripe for pre-ignition to happen then it just may go back to lighting off the fuel before the spark.

So since you do not feel a powerjet is needed because of the float bowl pressurization circuit and a compound angle needle is not needed to fix a lean condition on the top end how are you going to increase the fuel on the topend without over richening the bottomend mixture

[SmartCarb]

I have read the the definitions of pre-ignition and detonation and understand they are different, but I have always suspected that you get to a point where one leads to the other but occur in separate strokes, meaning the pre-ignition probably builds enough heat in the piston, cylinder and combustion chamber to create local hot spots that may start detonation on the next compression stroke. Whether it continues to detonate I am not sure but if the conditions are ripe for pre-ignition to happen then it just may go back to lighting off the fuel before the spark.

Completely agree, there will forever be nuances that escape our attention and like my Dad always used to say, nobody's ever been inside one while it's running. Probability suggests that yes the two phenomena could certainly overlap and this may very well be the reason a lot of people are confused by the differences.

So since you do not feel a powerjet is needed because of the float bowl pressurization circuit and a compound angle needle is not needed to fix a lean condition on the top end how are you going to increase the fuel on the topend without over richening the bottomend mixture

Exactly the way we do it now, run a steeper grind on the metering rod to add fuel mid to top, then set the clicker in a slightly lower setting than the leaner rod you just took out, to hit your target idle/tip-in mixture values. Then ride it like you stole it.

EDIT: The SC is almost completely signal based and in a lot of cases is fairly indifferent to the metering rod as long as it's not critically too lean. The range of metering rods we have ever used in the 36,38 and 40mm carbs, with exception of alcohol, nitro, boosted and a few odd applications, amounts to four sizes. All the same grind length, (we did toy with some shorter rods (same grinds) when the cast 38s came out, but results were not as favorable as we hoped and we resorted back to the longer rods which are the same as the billets). 082", .080", .078" and .076" tip thickness - 2.357" grind on a 3.583" metering rod.

[jcs003]

The Lectron and the SmartCarb are each a very fine example stemming from the original Edmonston designed single circuit flat slide carburetor. The distinctions however between the Lectron and the SmartCarb span nearly 45 years of development with no less than five other varieties in between. These less known iterations include the EI Blue Magnum, the Daytona Quicksilver I and Quicksilver II's, Edelbrock Quicksilver, AFT and finally theSmartCarb.

William H. "Red" Edmonston and I were partners at the time of his passing and most of the development work for the SmartCarb took place at the University of Wyoming in our 2 stroke research and development laboratories. Red clearly understood the limitations of a single circuit system and the fundamental flaw imposed by a more or less round throat venturi. The trough or valley at the bottom of an Edmonston designed venturi was quite well understood by this time and it can be found on a Lectron. It is this feature that led to what was really the beginning of our understanding the importance of concentrating and accelerating as much of the actual airflow through the venturi, right at the base of the metering rod and nozzle interface as possible, at all throttle positions. In a more or less round venturi, the rate of throttle opening from idle to half open is exponentially divergent, meaning it’s getting much larger, faster, the farther you open it. From half to wide open, however, the lines of the circle are converging and the rate of opening is slowing even though you are now almost wide open. This causes the pressures through the venturi to swing wildly as you move the throttle slide bottom to top and vice versa, which in turn causes the signal to the metering rod to fluctuate, and unless corrections are made by altering the angle of the metering rod crisp throttling and consistent fueling suffers.

(Signal referred to here is the negative value created by the piston displacing air as the engine cycles, creating a pressure drop within the venturi as air rushes in, thus allowing atmosphere to push fuel up through the nozzle, past the surface of the metering rod and into the intake airstream. In the case of a metering rod carburetor this signal is also read by the flat of the metering rod which creates another secondary low pressure zone.)

The difficulty of putting very accurate changes in angle along a 1/8” surface of a metering rod is maddening and is Lectron’s biggest challenge. This is one reason Lectrons are most noted as a drag racing carburetor and was a place they were found to work really well. Today I do believe they have made tremendous progress in metering rod development and the addition of a power-jet has made their job a little easier. IF all the angles are correct, for the right engine, and the PJ is set correctly they work really well through the whole range much better than a conventional carburetor.

Red felt the better solution was to shape the venturi as such that we could maintain an even pressure against the metering rod through the whole range of throttling. The question was how to do that without giving up a lot of flow and limit the carb’s full potential size for size. He understood laminar flow very well and we did a lot of experimenting with lead in curves to control airflow and get the carburetor to gulp a lot of air, even though the neck of the venturi was unconventionally restrictive. We also added a nose to the slide to further direct and compress airflow leading into the metering rod. What really tipped the scales technology wise though is the ambient air density correction circuit and how it interrelates to the venturi. Most people understand this to be the altitude correction circuit, which it is, but it is really much more. It provides an instantaneous dynamic balance between the pressures the throat of the carburetor is actually seeing and the ambient air pressure against the top of the fuel in the float bowl in all conditions. Perhaps a more familiar term people recognize for this effect is Manifold Absolute Pressure and is something that all modern closed loop EFI systems rely on for correcting air/fuel ratios with changes in ambient air density. Apart from the venturi shape this feature alone is what allows the SmartCarb to only need a single angle grind metering rod, and in most cases a common grind across a very large variety of products and applications.   This circuit also acts much like a power jet at the very top end when the static pressure being applied to the fuel in the float bowl also becomes dynamic and liquid flow lift ensues, hammering fuel up the nozzle directly proportional to total flow through the venturi. This is actually much superior to a power jet in that it remains finely atomized, because it is after all still using the main (and only) circuit, whereas a power-jet is literally throwing fuel on the fire and is emitted as almost pure liquid when it enters high into the air stream. This isn’t the worst thing, however it does dramatically affect Lectron’s full potential for fuel economy gains, altitude compensation and emissions reductions and it effectively makes it yet another multi circuit carburetor.

The drawback to the SmartCarb air density correction circuit is lack of a float bowl overflow and the necessity of tip over valves, along with the additional problems they create. The performance benefits the system offers are more than worth the effort though and the tip over valves, along with additional functionality to further protect our patents for the scoop and venting system, offer a very desirable side benefit in that now the carburetori s completely sealed. Certification testing shows the SC to be the lowest evaporative emissions carburetors ever test. Plus there is no raw fuel spillage on the ground and it fits very conveniently into the new epa tip over ruling for motorcycles. Who’d of known they were about to implement that? We are continuing to improve the system and are implementing changes to eliminate sticking issues.

With all of that said, I have just one more thing. Make no mistake, Lectron is not our competition. Our competition is all modern fuel systems worldwide, electronic or mechanical. Here’s why; any emissions reduction strategy requires a fuel system that is able to two things very well. Finely atomize fuel and maintain extremely accurate air/fuel ratios. TheSmartCarb simply does those two things better than anything else we currently know of period, and it does it without electronics. For instance we are in the second leg of EPA Tier II and ARB on road emissions certification for Zaeta’s TM powered 530 DT motorcycle (google it). This is TM’s open enduro race 4t engine they have attempted to prior certify in North America themselves. They have tried twice , both times using two precious metal catalysts and a race TMXX Mikuni downdraft, both times unsuccessful. APT is actually touching on Euro III numbers with this bike and is passing EPA and ARB easily with just our new 40mm side pull FCR replacement carburetor and no cats. In fact we are under Tier II CO emissions by nearly 90% and HC and Nox 38% and 16% respectively all this with a 28% gain in fuel economy. This is no joke and these aren’t the types of things you are hearing about in the forums and possibly in a lot of people’s minds on a performance related forum  this may not seem like a big deal at all. But actually it is everything.

Hi smartcarb.  i am impressed by your technology. however,  can you elaborate on your mentors understanding of laminar flow.  reason i ask is, laminar flow has no place within the intake of an internal combustion engine.  hi velocity and/or turbulent flow is what makes a typical carb atomize the way it does.  is it your way to promote pressurization of the fuel flow that compensates for this?  maybe within my query is the patented info.lol

john

[SmartCarb]

Hi smartcarb.  i am impressed by your technology. however,  can you elaborate on your mentors understanding of laminar flow.  reason i ask is, laminar flow has no place within the intake of an internal combustion engine.  hi velocity and/or turbulent flow is what makes a typical carb atomize the way it does.  is it your way to promote pressurization of the fuel flow that compensates for this?  maybe within my query is the patented info.lol

john

And therein lies the fundamental difference between the SC and every other predecessor. You need to understand Mikuni, Keihin and many others learned a lot of what we take for granted from Mr. Edmonston. He lived the remainder of his life competing against his own technology. Story goes though he's on a jet leaving Detroit shortly after selling Lectron to GM. It was raining with fog, he was watching the leading edge of the wing and of course with vapor we all can see laminar flow form as the airstream straightens itself and accerates over the leading edge and curve of the wing. Same thing with hearding the air into the throat of an SC, and years later we put it into practice. If you look closely you will see a decided curve leading into the venturi, this accelerates, straightens and begins to compress the air and greatly helps our cause to stuff more air through an otherwise fairly constrictive throat. Naturally, with any carburetor true to Bernoulli the idea is to create as high of a compression zone as possible without choking flow and causing stall, thereby increasing flow to maximum velocity and achieve the strongest venturi vacuum you can. Ok we all get that. To answer your question, it has always been understood that you want to create turbulence (mixture motion) along the intake to aid atomization and fuel suspension. This is only true however after the fuel has been introduced into the airstream and some surface roughness (not wall uneveness) helps keep everything mixing.

With the SmartCarb, we promote laminar flow as a means to create very high velocity and compression under the slide so that we can utilize a single fueling circuit. The atomization in an SC is created by the metering rod and not pre-emulsion through a pilot jet at idle and further emulsion though the nozzle at wide open, as it is with a conventional carburetor. In these carburetors any extra turbulence is welcome because they are so poor at atomization. With an SC because the fuel is delivered from the metering rod above the airstream, the fuel is carried as a vapor plume into the engine and doesn't need a lot of assistance to maintain suspension. Great news is this allows you to hog more air through your engine with an SC or run a slightly larger venturi and not suffer the all too easy consequences of flow stall, causing fuel to fall out of suspension. To a certain degree of course this happens in all engines, but the farther you can carry the bulk mix into the combustion chamber, the closer the actual trapped air/fuel ratios are to those as delivered by the carburetor. Then you really begin to narrow the gap with Direct fuel injection and the goal of minimizing fuel consumption is best served. Combine that with Kadenecy effect bulk transfer of the mix in modern two strokes and you see where this is all headed. Move further along with Sonic-Flow Engine tech with variable geometry plumbing and things really begin to look pretty bright and a new lease on uncomplicated 2t's may be coming along.