</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by ViribusUnits:
<strong>Also, the engines volume through put is dependent on 3, not 2 factors. Displacement, RPM, AND volumetric efficency. Basicly, it's how full each intake stroke is.

The point behind adding headers, new intake, bigger vales, ported head, wilder cam, etc. etc. etc. is to increase the volumetric efficancy of the engine. IIRC a typical volumetric effiancy value for a 2 valve Detroit engine is like .80, while a typical value for a 4 valve is like .88

As you can see, unless you start adding positive pressure on the intake mannafold, your actualy increaseing the volume the engine uses.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">The volume of air that the engine passes through it is constant, unless it's an engine that shut's down some of the valves during operation or something like that. The amount of air that passes is it's displacement. A 5 liter engine displaces 5 liters of air. What changes is the density of that 5 liters of air. All you have to do is look at a vacuum gauge that's monitoring intake manifold pressure. At idle the engine displaces 5 liters, but the air on the throttle side of the engine is at low pressure/high vacuum, because it's not dense (lower than atmospheric pressure and density).At full throttle the engine is still displacing 5 liters, but the air on the throttle side of the engine is at high pressure/low vacuum because it's dense (close to atmospheric density). Adding new intake, bigger valves, ported heads, wilder cam reduces the pressure drop of the air as it moves through the intake path and into the cylinders. This results in a greater pressure/higher density air getting into the cylinders. If adding that stuff increased the volume that the engine moves, there'd be no need to have higher displacement engines. You wouldn't need to bore and stroke an engine, just put on a really big intake, heads, valves, and cams. It doesn't work that way. Once you get atmospheric pressure/density air into the cylinders on a normally aspirated engine, that's all the air you're going to get going through there, no matter how big your intake, ports, and valves. The exception is tuning of the size of some of the intake tract to utilize pressure pulses to get higher than atmospheric pressure into the cylinders. That's what the S4 and later engines do with the intake resonance flap. In another post somewhere, Marc from Devek mentioned a volumetric efficiency of around 120% on some normally aspirated engines. That's not accomplished by just sticking on parts with big ports.

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva"><strong>Have you used a turbo, or supercharge, with the AFM down stream of the charger</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">The AFM is a flap that the air flowing through it moves against spring tension. The air meter on the CIS system is a flap that the air flowing through it moves against spring tension. The spring tensioned flap below is doing a good job of keeping the mixture consistent with boost blowing through it.

<img src="http://www.928trackcars.com/fausett/images/superchargercomplete.jpg" alt=" - " />

 

"For some reason, you discount the actual success of the AFM in my environment of testing. IE, easlily responding to all possible performance mods and also, keeping ratios constistant in a 23% less dense air environment (ie 7000feet)"

Which wideband O2-sensor unit are you using to datalog and monitor the air-fuel ratios with altitude changes?

"I even increased Displacement by 300ccs and the system fuel air performance was identical!!!!
So, if the AFM only measured volume flow, how would it adjust , perfectly????? Luck??"

Increased displacement and other mods such as exhausts & intakes will increase the flow & volume of air through the engine. This will swing the flapper door open further at the same RPM. This results in higher voltage output, which references a higher load-point on the fuel-maps, meaning more fuel to match the increased flow. Don't confuse flow and volume with density and mass.

To illustrate the altitude-change scenario, imagine you have a fixed volume and mass of air in a small balloon. Size the balloon so that it sticks into the AFM and props open the door halfway. Now take this configuration up to 7000ft and what happens to the balloon? For the same mass of air, it occupies a larger volume and pushes open the flapper door even more than before. This results in a higher-voltage output and a richer mixture. But... since the displacement doesn't change, we have to ingest the same volume at a lower density. For the same flapper door angle, we'll have too much fuel for the actual mass of air that flowed.

And the airplane wing flap example is silly because we're not dealing with Bernoulli effects here. But rather positive-displacement volume measurements. Good example is a flow-bench. Th flow-bench will record a certain CFM say... 150CFM flowing through the AFM at 50% of max opening. Take it up to 7000ft and 150CFM will still open the flapper-door 50%. However, you've got a lot fewer oxygen molecules flowing into the engine up there...

"Next, I have a copy of the pobst book of (everything you want to know about Bosch) and he quotes in his book that the AFM LJet is unresponsive to engine mods, and all they will to is make your engine run lean. However, he is dead wrong."

Where's your data? Numbers? Charts? Procedure used? Independent peer review? How many books have you written?

 

John,
I have studied air flow dynamics as well. I have books on top of books in my study.
This is not an attack, it is just a conversation and a discussion to help you understand the AFM function, from a perspective you may have missed.

The one thing that you continue to miss is that the RPM and pressure are variable (via the throttle position or atmosphere), and the volume is constant. Toss out the over used and commonly misunderstood term of "volumetric efficiency". This term is ment to refer to MCFM, not just CFM.
all engines with a given displacement will take a identical CFM (volume) at a given RPM, period. now, is that Volume dense or not that dense?
The more you trick out your car's engine, you get more mass flow, not volume. but to give a term to the auto nuts , the term "volumetric efficiency" was used to take into acount the increase pressure gradient through the engine. a good analogy, would be the barometric pressure listed for denver vs SF. they both would be listed at 29.90 on a normal day, but would be adjusted for altitude. Just like you would do with an airplaine altimeter upon landing and takeoffs. Clearly, this is miss understood to the point that most people would not understand that Denver is really normally 23" of Hg, or 20% less dense.

Again, you speak of the temp sensor. it was used to further refine the efficiency of the sytem. in the bosch book, they said the first afms were good at adjusting for density changes, up to 7000ft. at 10,000 feet , the US emmissions off enough, so that a temp, and barametric sensor was used to refine the output. keep in mind , it doensnt take much to change emmissions. That little air screw can relieve enough pressure from the AFM plate , so that the C0 and NOx can change dramatically, while the mixture is realitively constant. Under WOT conditions, we only care about a device that can handle the changes in density so that at altitude our mixutures are correct. (see my previous posts on confirming emperically, the adaptability of the AFM to changing mass flow)

Yes, is all PV=NRT. thats the reason that the flap moves. it is an aerodynamic device that is very simular to a flap on a wing, or even better said, it is a wing itself.

We changed the Rear wheel HP of the 928 with AFM from 175 rear wheel to 242HP with no changes of the fuel system or AFM. how did it adapt???
yes, if you want to use the term, volumetric efficient, we were more efficient, but what does that mean? it means we were moving more mass flow through the system. If a system is 100% efficient, then it is moving 100% of the potential volume at atmospheric pressure (ambient). if it is less than 100%, then the equivilant mass flow is like there was less volume flowing, at (KEY POINT, at standard
Atmosphere.)

The AFM is not a variable orifice example. the flap is a non impeading factor. in fact, by the bosch book, they rate the pressure drop of the flap by under .08psi. (basically insignificant)
It is does move in response to mass air flow, and density. If you take all of your knowledge of air flow. (and as a mechanical engineer, you had some basic air flow studies) ( I was aero, so we studied it a little deeper) and you look at the proper values for the variables, you will understand more of what i am talking about.

Ive already told you that under pressure, the AFM's calabration will probably be off, but will still respond to changes in mass flow. That said, it should work, but may be off a tick as long as you dont max it out by higher mass flow rates.

I dont mean to turn this into an
arguement, but I do have a clear understanding, based on solid flow theory. (no pun intended)

IM making a post to one other fellow, who is questioning my testing procedures. take a gander at it and respond back.

Mark

 

Z, Ill try and insert my comments below.
Let me try and clarify below: (with the&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by Z:
<strong>[QUOTE]Originally posted by ViribusUnits:
[qb]Also, the engines volume through put is dependent on 3, not 2 factors. Displacement, RPM, AND volumetric efficency. Basicly, it's how full each intake stroke is.
Mark K&gt;&gt;&gt;&gt;&gt;&gt;as I said in my post to John, forget about volumetric efficiency, lets talk about mass flow. 3 factors, I agree, but its RPM, displacemnt and pressure, or density of the intake charge. the more mass you can burn, the more HP. its pretty simple that way. Mass flow, or pressure goes from high to low. outside pressure is higher than in the open intake valved cylinder. there is a pressure gradient from the beginning of the AFM all the way to the piston face. otherwise, the air wouldnt move in!! vacuum does nothing, pressure does everything.&gt;&gt;&gt;

The point behind adding headers, new intake, bigger vales, ported head, wilder cam, etc. etc. etc. is to increase the volumetric efficancy of the engine. IIRC a typical volumetric effiancy value for a 2 valve Detroit engine is like .80, while a typical value for a 4 valve is like .88
&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;Mark K. Yes , but remember, what I said about volumetric efficiency.&gt;&gt;&gt;&gt;&gt;&gt;&gt;

As you can see, unless you start adding positive pressure on the intake mannafold, your actualy increaseing the volume the engine uses.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">The volume of air that the engine passes through it is constant, unless it's an engine that shut's down some of the valves during operation or something like that. The amount of air that passes is it's displacement. A 5 liter engine displaces 5 liters of air. What changes is the density of that 5 liters of air. All you have to do is look at a vacuum gauge that's monitoring intake manifold pressure. At idle the engine displaces 5 liters, but the air on the throttle side of the engine is at low pressure/high vacuum, because it's not dense (lower than atmospheric pressure and density).At full throttle the engine is still displacing 5 liters, but the air on the throttle side of the engine is at high pressure/low vacuum because it's dense (close to atmospheric density).
&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;YES YES YES. YOU GOT IT!!!!!!

Adding new intake, bigger valves, ported heads, wilder cam reduces the pressure drop of the air as it moves through the intake path and into the cylinders. This results in a greater pressure/higher density air getting into the cylinders. If adding that stuff increased the volume that the engine moves, there'd be no need to have higher displacement engines. You wouldn't need to bore and stroke an engine, just put on a really big intake, heads, valves, and cams. It doesn't work that way. Once you get atmospheric pressure/density air into the cylinders on a normally aspirated engine, that's all the air you're going to get going through there, no matter how big your intake, ports, and valves. The exception is tuning of the size of some of the intake tract to utilize pressure pulses to get higher than atmospheric pressure into the cylinders. That's what the S4 and later engines do with the intake resonance flap. In another post somewhere, Marc from Devek mentioned a volumetric efficiency of around 120% on some normally aspirated engines. That's not accomplished by just sticking on parts with big ports.
&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;Yes, AGAIN. My mistake on the 5 liter displacement change as part of my argument. those 300CCs would not address what we are talking about. The other mods would . More mass flow, more HP. pretty simple. as far as over 100% volumetric flow, Marc and i have talked about the certain race engines that "self" supercharge by way of pulse tuning the intake. very much above my knowledge level!!

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva"><strong>Have you used a turbo, or supercharge, with the AFM down stream of the charger</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">The AFM is a flap that the air flowing through it moves against spring tension. The air meter on the CIS system is a flap that the air flowing through it moves against spring tension. The spring tensioned flap below is doing a good job of keeping the mixture consistent with boost blowing through it.

 

Danno,

we have calabrated the ARM 1 and new o2 sensor, to be accurate within 10%. (pretty crude) this was done on the dyno. we have run up to 8000feet , over 27% less dense altitude, with no temp, or barametric sensor and had the ratios stay constant. if the AFM didnt work, 27% change in altitude would relate to a 8.8:1 fuel air ratio which would be noticable.(instead of our measured 12.6:1 on the dyno)

Your right as was said earlier about the 300cc increase. that is really not the point here. its the other mods that got us from 175 rear wheel HP to 242rear wheelhp. (300ccs took us to 293hp)

YOU are dead wrong about the balloon analogy. first of all , the mass flow is not fixed!!! it is extremely variable, based on ambient pressure, minus all the pressure drops til the piston face.
volume is fixed, rpm changes, pressure/density changes. Your paragraph is entirely backward. Less mass flow, the flap is deflected less, perfectly metering out the proper fuel. you said "for the same flapper door angle" but the angle wouldnt be the same, now , would it??!!!

you also say, "at half throttle, your at 150cfm" but at 7000feet you would still be at 150cfm, but less dense, so you get richer????? nahhh. think about it. We have done voltage meausrements of the AFM at sea level and at altitude. the voltage is way way down at altitude 7000feet, and so is the power, (equivilant to the drop in pressure) yet the mixuture seemed to be constant.
If what you said was true, our car would have run at 8:1 fuel to air at 8000feet, 27% less dense conditions. however, if anyone has seen what a car does at this ratio, you know it looks like you have a desiel truck engine the smoke is so black!!

The tests mentioned were conducted at the dyno with a Horibra air fuel metering system, to also calabrate the ARM 1 for crude indications. a fellow acomplished Aero engineer with many years of NASA/Lockheed and one of the designers of the F14 jet figther, with no less than 14 patents on that airplane, were assisting with many of my tests and conclusions.

This all gets back to the problem with this industry. people either never studied, learned or trust what they read without question.
\
Examples: Volumetric eff, HP means nothing, torque wins races, I feel 10hp, flywheel or wheel lightening gives a certian measureable hp, underdrive pulleys give measureable hp, premium gas vs regular, AIR FILTERS can improve gas mileage.

All are hogwash that the public is misled into buying products that dont work and dont work for physically obviousl reasons.

enough for now!!

Mark Kibort

QUOTE]Originally posted by Danno:
<strong>"For some reason, you discount the actual success of the AFM in my environment of testing. IE, easlily responding to all possible performance mods and also, keeping ratios constistant in a 23% less dense air environment (ie 7000feet)"

Which wideband O2-sensor unit are you using to datalog and monitor the air-fuel ratios with altitude changes?

"I even increased Displacement by 300ccs and the system fuel air performance was identical!!!!
So, if the AFM only measured volume flow, how would it adjust , perfectly????? Luck??"

Increased displacement and other mods such as exhausts & intakes will increase the flow & volume of air through the engine. This will swing the flapper door open further at the same RPM. This results in higher voltage output, which references a higher load-point on the fuel-maps, meaning more fuel to match the increased flow. Don't confuse flow and volume with density and mass.

To illustrate the altitude-change scenario, imagine you have a fixed volume and mass of air in a small balloon. Size the balloon so that it sticks into the AFM and props open the door halfway. Now take this configuration up to 7000ft and what happens to the balloon? For the same mass of air, it occupies a larger volume and pushes open the flapper door even more than before. This results in a higher-voltage output and a richer mixture. But... since the displacement doesn't change, we have to ingest the same volume at a lower density. For the same flapper door angle, we'll have too much fuel for the actual mass of air that flowed.

And the airplane wing flap example is silly because we're not dealing with Bernoulli effects here. But rather positive-displacement volume measurements. Good example is a flow-bench. Th flow-bench will record a certain CFM say... 150CFM flowing through the AFM at 50% of max opening. Take it up to 7000ft and 150CFM will still open the flapper-door 50%. However, you've got a lot fewer oxygen molecules flowing into the engine up there...

"Next, I have a copy of the pobst book of (everything you want to know about Bosch) and he quotes in his book that the AFM LJet is unresponsive to engine mods, and all they will to is make your engine run lean. However, he is dead wrong."

Where's your data? Numbers? Charts? Procedure used? Independent peer review? How many books have you written?</strong>[/QUOTE]

 

Just found my AFM voltage vs altitude test results on a 240rear wheel hp modified 928S with euro intake , but US FI: (no temp sensor connect)

Conditions: WOT, 4500 to 6000rpm, 60-100mph
Sealevel 75 degrees: 7.7 to 8.4volts, 7.7seconds

7000feet 65degrees: 6.5 to 7.5volts, 12.1 seconds

Mixture was noted as stable at 12.5:1 range

Since the rpms were constant, and the flap was deflected less (i.e. it has to as the voltage was much lower, and it is logrithmic towards the top of the max deflection, so small changes in voltages, mean big changes in fuel metering.)

In fact, if you look at the voltage, its intersting that at 7000feet, the voltage is close to the same at 6000rpm as it is at 4500at sea leve. if you look at the HP of the engine at 4500 vs 6000rpm , you can see its around 25-30 percent less. This makes sense as the mass flow at 7000feet 6000rpm is close to the same as 4500rpm at sea level.

The AFM works well for mass flow changes.

Mk

MK

Mark

 

"we have calabrated the ARM 1 and new o2 sensor, to be accurate within 10%. (pretty crude) this was done on the dyno. "

Well, there's the problem right there! The ARM1 is only accurate to 0.1v and the standard switching flip/flop O2-sensor is very temperature dependent.

At 1300F air-fuel ratios from 10.0-13.0:1 is represented by voltage outputs of 0.97-0.94v and at 1600F, the O2-sensor is putting out 0.88-0.81v. These aren't even close to being accurate! Not to mention that these ranges from way too rich to too lean falls within the resolution of only 1 LED on the ARM1 (1st blue dot when warm, 2nd blue dot when hot).

"Mixture was noted as stable at 12.5:1 range"

This is the last LED on the ARM1. If you have a 12.5:1 mixture or a 10.0:1 mixture, the SAME LED will be lit! If you are relying on data from this ARM1 toy, then all analyses and conclusions derived from it are suspect as well. The only accurate way to monitor air-fuel ratios is with a wideband O2-sensor with an RPM-based datalogger that's accurate to at least 0.01v.

Don't forget that the altitude-sensor is providing data to the computer and the air-fuel ratio is corrected for altitude. This is the real reason you're getting proper air-fuel ratios with your testing. Try disconnecting the altitude sensor next time and you will indeed see that diesel truck exhaust coming out the back of your car at 7000ft.

 

John, here is a link to Murillo Motorsports. <a href="http://murillomotorsports.com/" target="_blank">http://murillomotorsports.com/</a> I know Mike and he is VERY capable of handling any turbo engine management needs. I don't know what your budget is for this project but a Speed Pro management system and MSD ignition can do ANYTHING you need done. Mike is an ace on both.

 

Guys,

This discussions WAS NOT about the density change of the air once it entered the combustion chamber. It is obvious that the air that is drawn into the combustion chamber will occupy the entire volume of the chamber, once the valves are closed. Any simpleton can apply the gas law here to figure that out.

This discussion WAS about flowrates through an AFM vs a MAF on the INTAKE (READ UPSTREAM OF THE THROTTLE PLATE) side of a piston engine. That also means it really never sees vacuum conditions, like the intake manifold sees.

Furthermore, this discussion WAS about the specific flaws associated with placing a vane door AFM on the pressurized side (READ STILL UPSTREAM OF THE THROTTLE PLATE) of a turbocharged system.

I have never seen an airflow meter downstream of a throttle plate, so this discussion about intake vacuum is meaningless here. You want to know why? Because the AFM was designed to work at a constant pressure.

As I stated before the conservation of mass equation can be used to determine the relationship between air velocity on the intake and discharge side of a turbocharger system. This is where placing the AFM on the discharge side of the turbocharger system gets very fuzzy.

pAV=constant (assuming a given engine load)

so pAV (intake of turbocharger system)=pAV (discharge turbocharger system)

Assume Area at each location is constant.
p is a function of temp and pressure, but most of the time, the "charge" of air on the outlet side of the turbocharger system will have a greater density than on the intake (assumeing boost is being generated).

Hold A (area) constant, increase p (density) and V (velocity) will go down. So, there you have the fatal flaw of this setup...

There can be more air flowing through the AFM at a decreased velocity.

Now to further make my point, one needs to look at the drag force on this AFM flapper plate. I think we all would agree that the AFM force is generated by the drag force on this plate (just like it is on an aircraft flap).

So the Drag Force on this plate is a function of many factors, but the basics are the coeficient of drag, air density, air velovity and area. In its simple form this eqaution is as follows:

Df=Cd*.5p*U^2*A

Where Cd=coefficient of drag
p=air density
U=air velocity
A=frontal area.

So for simple analysis, to see how drag force is altered with velovity and density. Lets assume a fixed coefficient of drag, and a fixed area. In other words, the plate is at a fixed position, this will simply this analysis.

Going back to pAV, lets say we have two conditions on the intake side of the engine, one before and one after the turbocharger.

On the intake side, assume p=1, A=2, and V=6
(we can use any number we want because the equations govern the units).

So Mdot (mass flowrate) is 1*2*6, or 12

Lets assume that Cd=1.0 and is fixed
Lets assume Area is 2 and is fixed

So in this case (before the turbos), the drag force on the plate is:
1*(.5*1)*6^2*2, this =36

Now, assume density has doubled on the intake side of the engine (after the turbos), to become 2. Mdot is held constant, because we are assuming a constant load (i.e. 400 RPM going up a hill). So Mdot is still 12, but density has doubled to 2. We solve for V and get 3. So double the density, and the velocity is cut in half to 3.

Now,go back to the Drag force equation and refigure drag on the plate (under boost).

Df=1*(0.5*2)*3^2*2=18

The drag force on the plate has been cut in half, even though Mot has remained constant.

Now, obviously the plate inside the AFM will deflect to a given position for either of these circumstances, because of the spring. As this happens, the coefficient of drag is also changing.

The main point is that the drag force is a function of the density (i.e. linear) and a function of the velocity squared. Df=f(p,V^2), and the density is a function of the pressure and temperature of the air.

I think I have just documented the following:

Keeping Mdot constant (one load point for the engine)

Keeping Area constant (inlet and outlet diameter feed pipes for the turbo intake system)

Doubling the density results in 1/2 the velocity (conservation of mass at a given engine speed)

Doubling the density results in 1/2 the drag force on the AFM plate (assuming Cd is constant....not totally true).

So in conclsion it can be seen that the force on a flat plate (i.e. AFM plate) is a function of the velocity squared and the density, and when the density of the air doubles (assume Mdot and all other factors are constant), the force on this flat plate is cut in half. This is only true for comparing the meter on the inlet and discharge sides of the turbocharging system.

Now I ask you all, would this not deflect an AFM plate to a different position if the unit was placed on the intake side of the turbocharger system vs. the discharge side of the turbocharger system?

I do beleive this model explains why the AFM is designed to work at one pressure and on the draw through side only.

If you look at the governing equations, you will see that the AFM will, in fact deflect less at altitude in its given design position (draw through side only). (This is the same reason an aircraft is more sluggish at altitude). But remember, the plate drag coefficient is also changing as this happens. In addition, the velocity of the air on the intake side of the engine is not changed by increasing the density (engine is sucking it in at the same velocity, but at a different atmospheric density). The turbocharged model is very different, since the velocity is wildly fluctuating with density changes.

Mark, I think this is where you are stating the AFM can compensate for density changes at altitude. This is somewhat true, but only because the AFM is still on the draw through side of the system. There will still be a variation because of the change in the drag coefficient of the plate at it deflects less at altitude. This is why there is an altitude compensation circuit built into the system.

So in short, the altitude compensation device helps to "correct" the AFM signal to the computer when the car is at altitude. Yes, the AFM will deflect less at altitude, but this is not directly correlated to the exact air being passed, so the altitude compansation circuit makes up the difference in the L-jet.

I have to be honest, I am nw fully aware of why my system is a wacky as it is. The challenging comments sent me back to the books to do some studying on this topic.

 

I gotta ask you John, where is the altitude compensation circut located?

It's not in the wireing 83 928 diagrams, so that leaves as part of the MAF, or part of the ECU.

My understanding of the MAF is limited, but I don't think there's a pressure sensor in there.

The ECU?

I'm just curious, I'm looking to see if I could test it, as part of the whole, "lets-test-everything-in-the-system" deal I'm doing right now.

 

John - thanks for the Jaguar link, I learned/confirmed a few things. (<a href="http://www.jagweb.com/jagworld/42efi/index.html" target="_blank">Link: Fuel injection and the Jaguar XJ6 4.2 Series 3</a>)

I have already grounded the 02 sensor wire, disconnected the idle switch, removed the vacuum limiter, and adjusted the AFM.

I'm going to replace the full throttle switch with a vacuum switch, (which I was planning on trying anyway) the Jag L-Jet article shows that the european ECUs had this already. This will give enrichment at part throttle, high load, conditions.

I have a couple of vacuum switches from mid seventies Cadillacs, which used the vacuum switch for an 'Economy' light.

A reference to L-Jet 'maps' was mentioned in another L-Jet thread. There are no fuel maps, there are addition and subtraction (discreet) electronic circuits, affected by the various switches, and sensors.

<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

 

Danno, Let me re state my calabration term. You are taking it way to the extreme. we only used it to verify that we were not getting any leaner at altitude. sure , the votage of the O2 sensor, (since that is all the Arm1 is is a voltage sensor with LEDs) is limited to a narrow band of readings, especially beyond 12.5:1 and above 16:1.

So, we also remove the altitude and temp sensors for this test. it didnt run rich, and certainly was not smoking like a diesel. you have to remember that even John is now understanding the aerodynamics of the flap, except for one point that I will discuss later. (drag of the spring loaded vain)

since the air is less dense and the volume is the same whether you are at altitude or at sea level, the mass flow is changing proportionate to the altitude (and so is the reduction of power) . So, at 7000feet ,the air is 23% less dense. YOU also forgot we were taking AFM voltage readings. they were much lower at 4500 and 6000rpms at full throttle. How would you explain this , if the AFM flap was not deflected less ???? even if the temp or attide sensor was sending corrective values, they would not infuence the votage output of the AFM.

we also have done this voltage test at sea level
with the different mods. and, for every 25-50 hp set of mods, we saw more voltage up to close to its max, giving a range of adaptibilty from 175 rear wheel HP to 242rear wheel hp. and then , we added the 300ccs of displacement for even more gains, all while our fuel air ratios were kept CONSTANT, and thats not the ARM1, thats the dyno Horibra or equiv.

The AFM adapts for mass flow changes, however, I have to look at the books to see what John is talking about as far as being used in a vacuum environment. he may be right there!!! John has been doing some homework.

Mark

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Danno:
<strong>"we have calabrated the ARM 1 and new o2 sensor, to be accurate within 10%. (pretty crude) this was done on the dyno. "

Well, there's the problem right there! The ARM1 is only accurate to 0.1v and the standard switching flip/flop O2-sensor is very temperature dependent.

At 1300F air-fuel ratios from 10.0-13.0:1 is represented by voltage outputs of 0.97-0.94v and at 1600F, the O2-sensor is putting out 0.88-0.81v. These aren't even close to being accurate! Not to mention that these ranges from way too rich to too lean falls within the resolution of only 1 LED on the ARM1 (1st blue dot when warm, 2nd blue dot when hot).

"Mixture was noted as stable at 12.5:1 range"

This is the last LED on the ARM1. If you have a 12.5:1 mixture or a 10.0:1 mixture, the SAME LED will be lit! If you are relying on data from this ARM1 toy, then all analyses and conclusions derived from it are suspect as well. The only accurate way to monitor air-fuel ratios is with a wideband O2-sensor with an RPM-based datalogger that's accurate to at least 0.01v.

Don't forget that the altitude-sensor is providing data to the computer and the air-fuel ratio is corrected for altitude. This is the real reason you're getting proper air-fuel ratios with your testing. Try disconnecting the altitude sensor next time and you will indeed see that diesel truck exhaust coming out the back of your car at 7000ft.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">

 

Hi John,

I cant, with any certainty, predict on how the AFM would react in a Vaccum environment. I think I need to look closely at the old books to determine that one. However, I would think that the system is designed to react at normal atmospheric pressure, and not operate in a "vacuum" (as they say, so pun intended)

the AFM would probably be working in a vaccum equivilant to 30k feet, so im sure it wouldnt work properly. However, under WOT, it could.

Like I said, the AFM was very good at metering out mass flow, but certainly had some limitations compared to a Hot wire, or "true " mass flow metering device.

dont get too carried away with the drag characteristics of the Flap Vain. Its impeadence in the air stream is 2nd or 3rd order. is restriction is so low, it is hardly measureable. it is literally flying on the air stream, with very little drag. In fact, the only restriction of the AFM itself is caused by the size of the opening. Bosch rates the restiction of the spring loaded plate as an almost neglegible, .08psi. (I cant remember the exact figure, but it is low) If it as a fixed plate, your formulas were correct. however, since it is flying and not a fixed flap, like on an airplane. (where it can instantly increase the effective angle of attack, and the cord length and wing
NACA number) In otherwords, the flaps will change the effective shape of the entire wing when it drops. The cord now is from the trailing edge of the flap, to the center of the leading edge. the AFM is entirely different. It flys with respect to the mass flow in front of it. More the mass flow, the more it is deflected. The spring is progressive as well, but takes very little force in respect to the air mass moving though the AFM.

MK

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by John:
<strong>Guys,

This discussions WAS NOT about the density change of the air once it entered the combustion chamber. It is obvious that the air that is drawn into the combustion chamber will occupy the entire volume of the chamber, once the valves are closed. Any simpleton can apply the gas law here to figure that out.

This discussion WAS about flowrates through an AFM vs a MAF on the INTAKE (READ UPSTREAM OF THE THROTTLE PLATE) side of a piston engine. That also means it really never sees vacuum conditions, like the intake manifold sees.

Furthermore, this discussion WAS about the specific flaws associated with placing a vane door AFM on the pressurized side (READ STILL UPSTREAM OF THE THROTTLE PLATE) of a turbocharged system.

I have never seen an airflow meter downstream of a throttle plate, so this discussion about intake vacuum is meaningless here. You want to know why? Because the AFM was designed to work at a constant pressure.

As I stated before the conservation of mass equation can be used to determine the relationship between air velocity on the intake and discharge side of a turbocharger system. This is where placing the AFM on the discharge side of the turbocharger system gets very fuzzy.

pAV=constant (assuming a given engine load)

so pAV (intake of turbocharger system)=pAV (discharge turbocharger system)

Assume Area at each location is constant.
p is a function of temp and pressure, but most of the time, the "charge" of air on the outlet side of the turbocharger system will have a greater density than on the intake (assumeing boost is being generated).

Hold A (area) constant, increase p (density) and V (velocity) will go down. So, there you have the fatal flaw of this setup...

There can be more air flowing through the AFM at a decreased velocity.

Now to further make my point, one needs to look at the drag force on this AFM flapper plate. I think we all would agree that the AFM force is generated by the drag force on this plate (just like it is on an aircraft flap).

So the Drag Force on this plate is a function of many factors, but the basics are the coeficient of drag, air density, air velovity and area. In its simple form this eqaution is as follows:

Df=Cd*.5p*U^2*A

Where Cd=coefficient of drag
p=air density
U=air velocity
A=frontal area.

So for simple analysis, to see how drag force is altered with velovity and density. Lets assume a fixed coefficient of drag, and a fixed area. In other words, the plate is at a fixed position, this will simply this analysis.

Going back to pAV, lets say we have two conditions on the intake side of the engine, one before and one after the turbocharger.

On the intake side, assume p=1, A=2, and V=6
(we can use any number we want because the equations govern the units).

So Mdot (mass flowrate) is 1*2*6, or 12

Lets assume that Cd=1.0 and is fixed
Lets assume Area is 2 and is fixed

So in this case (before the turbos), the drag force on the plate is:
1*(.5*1)*6^2*2, this =36

Now, assume density has doubled on the intake side of the engine (after the turbos), to become 2. Mdot is held constant, because we are assuming a constant load (i.e. 400 RPM going up a hill). So Mdot is still 12, but density has doubled to 2. We solve for V and get 3. So double the density, and the velocity is cut in half to 3.

Now,go back to the Drag force equation and refigure drag on the plate (under boost).

Df=1*(0.5*2)*3^2*2=18

The drag force on the plate has been cut in half, even though Mot has remained constant.

Now, obviously the plate inside the AFM will deflect to a given position for either of these circumstances, because of the spring. As this happens, the coefficient of drag is also changing.

The main point is that the drag force is a function of the density (i.e. linear) and a function of the velocity squared. Df=f(p,V^2), and the density is a function of the pressure and temperature of the air.

I think I have just documented the following:

Keeping Mdot constant (one load point for the engine)

Keeping Area constant (inlet and outlet diameter feed pipes for the turbo intake system)

Doubling the density results in 1/2 the velocity (conservation of mass at a given engine speed)

Doubling the density results in 1/2 the drag force on the AFM plate (assuming Cd is constant....not totally true).

So in conclsion it can be seen that the force on a flat plate (i.e. AFM plate) is a function of the velocity squared and the density, and when the density of the air doubles (assume Mdot and all other factors are constant), the force on this flat plate is cut in half. This is only true for comparing the meter on the inlet and discharge sides of the turbocharging system.

Now I ask you all, would this not deflect an AFM plate to a different position if the unit was placed on the intake side of the turbocharger system vs. the discharge side of the turbocharger system?

I do beleive this model explains why the AFM is designed to work at one pressure and on the draw through side only.

If you look at the governing equations, you will see that the AFM will, in fact deflect less at altitude in its given design position (draw through side only). (This is the same reason an aircraft is more sluggish at altitude). But remember, the plate drag coefficient is also changing as this happens. In addition, the velocity of the air on the intake side of the engine is not changed by increasing the density (engine is sucking it in at the same velocity, but at a different atmospheric density). The turbocharged model is very different, since the velocity is wildly fluctuating with density changes.

Mark, I think this is where you are stating the AFM can compensate for density changes at altitude. This is somewhat true, but only because the AFM is still on the draw through side of the system. There will still be a variation because of the change in the drag coefficient of the plate at it deflects less at altitude. This is why there is an altitude compensation circuit built into the system.

So in short, the altitude compensation device helps to "correct" the AFM signal to the computer when the car is at altitude. Yes, the AFM will deflect less at altitude, but this is not directly correlated to the exact air being passed, so the altitude compansation circuit makes up the difference in the L-jet.

I have to be honest, I am nw fully aware of why my system is a wacky as it is. The challenging comments sent me back to the books to do some studying on this topic.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">

 

Could we all join together in a coalition to stop the tyranny of the <img src="http://forums.rennlist.com/forums/quote_ubb6.gif" alt=" - " /> button? </font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"><strong>I often enjoy the scope of the Aerodynamic/AFM/Emissions/Los EBay Desperados/Styling/Tires discussions, but couldn't we all work towards responding By Reference versus By Value?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">And if the <img src="http://forums.rennlist.com/forums/quote_ubb6.gif" alt=" - " /> button cannot be disarmed, we must remove it!

 

I'm sure my analysis is correct, because my car leaves rather large clouds of black smoke at the first onset of boost, then it cleans up. My fuel curve is a wild approximation of what it needs to be.

So to simplify all of this crap about AFM vs MAF, it is true that the AFM plate will deflect less at higher altitudes and more at lower altitudes (as a function of density).

However, this relationsip with density (i.e. force as a function of p and V^2) only holds true for the AFM being on the intake side of a pressurized system. In short, for the AFM to deflect less or more, it has to be seeing the same velocity of air at those different density levels.

You place it on the pressurized side, the velocity fluctuates with boost pressure (conservation of mass) and the density also changes. So in short, yes, you do have density changes, but your velocity is not a constant, because it dropped as density went up (as compared to what it would be on the intake side of the AFM).

I should also point out the AFM at higher altitudes only approximates the proper signal for fuel (deflection relationship is differnet than the actual AFM deflection vs. voltage curve). This is why there is altitude and temperature compensation on the more modern AFM equipped Motronic cars.

Mark, have we finally agreed? I hope so, but thanks for challenging me nonetheless because forcing me through the books made me learn more.