Hi KBlair,

OK, what output characteristic does the MAP sensor have ?

The device I am working on will be customer mapable from a PC.

Would you be better off using a LH MAF which is temp compensated ?

If you are interested in LH MAFs, have a look at the data on my web site <a href="http://www.jdsporsche.com" target="_blank">www.jdsporsche.com</a>

 

</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 KBlair:
<strong>We are hoping to get better flow through the intake by removing that "cork in the bottle", so to speak.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Has anyone actually done any testing to see how restrictive the air vane sensor on the L-Jetronic systemactually is? According to the book "Bosch Fuel Injection & Engine Management", Bosch tests show the air pressure drop at the sensor is only 0.12 kPa (0.017 psi).

 

From the Megasquirt FAQ:

Q: Can the MAP sensor handle overpressures?

A: If you mean will the MAP sensor handle a backfire or similar engine event, then yes. If the target application is a Turbo or Supercharger, then the old 1-bar MAP used in this design (MPX4115) will not work - it will rail out at 110 KPa. All version 2 MegaSquirt systems were delivered with the MPX4250 2.5-bar sensor, so are appropriate for use in all installations from naturally aspirated to boosted up to ~21 psig.

Info on the Megasquirt can be found at:
<a href="http://www.bgsoflex.com/megasquirt.html" target="_blank">http://www.bgsoflex.com/megasquirt.html</a>

We will have to fit a temp sensor in the intake but that doesn't seem to be a problem. Jim and I were talking about airbox designs but decided to use the original as a first run. Once we get the MS working and calibrated correctly, then we can go on to tuning and re-designing for power gain. We have a cohort in Sweden who is almost complete with a Megasquirt in his 79 Euro. He will be providing templates for us to use as a starting point.

Cost is a big factor for use, the total cost for MS parts is around $120 plus probably another $120 if we want to build a stimulator to test off-car. Another factor is the use of standard Bosch OX sensor and not the expensive one. Also looking at Ford Racing high-impedance injectors.

MS is mappable, you can even reprogram in-car with the car running. One modification allows the use of 2 separate maps, user switchable.

The MS replaces the L-jet ECU, but not the ignition computer.

Email me if you want to talk more.

 

I think math got in the way of the explination.

If it's a safe assumption that the spring constant is small, then the torque placed on the flapper is always about the same. If the torque is the same, the pressure diffrence between the two sides of the flap must be the same.

Notice, I said the pressure diffrence between the two sides of the flap, NOT, the pressure of the air.

Also, notice I didn't say the velosity of the air in the intake, BUT the velosity of the air as it passes the gap between the flapper and the far wall.

If the pressure between the two sides of the flap remains constant, and density is increased, the velosity of the air, flowing between the flap and the wall, must decrease. That makes sence, right?

The only way to decrease the velosity of the air at that point, while preventing the a "back up" infrount of the flap is if the flap open up.

Thus for a given flap reading, increaseing density makes the volume go down much faster.

What basicly happens is the flap over reads the air. It moves too far open in relation to the mass passed.

I wish I could pull my MAF off and test the darn thing. This is getting me mad.

Something to rember, the 81-82 have the same MAF as the 83-83 US cars. The MAF clearly was NOT matched to the engine, but has at least some extra capasity. Otherwise there's no point in it also being on the 4.7l engine too.

 

ouch my head hurts from reading all this

Think of the Ljetronic AFM as a mechanical MAF. it just measures mass flow across it. the more mass flow, the more the barn door is deflected and subsequently, the more fuel duration is dictated by this varible voltage to the computer.

Now, what happens on the high pressure side of supercharger system?/ well, you have temperatures to deal with , far in excess of how the AFM was calabrated by the factory.

Ive proven the AFM regulates fuel perfectly up to 300rear wheel hp, but I think this is the limit.

Huntley racing has used the AFM to about 330rear wheel hp, but on the lower pressure side of the turbo.

Mark

 

That is true, but the problem is not the barn door, its the size of the opening. at around 4 square inches, it is a bottle neck. generally we have seen 10hp differences between 5 liter conversion of old CIS systems, vs the same in a AFM model. The AFM is a very capable system and very simple to work on .

MK

</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> </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 KBlair:
<strong>We are hoping to get better flow through the intake by removing that "cork in the bottle", so to speak.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Has anyone actually done any testing to see how restrictive the air vane sensor on the L-Jetronic systemactually is? According to the book "Bosch Fuel Injection & Engine Management", Bosch tests show the air pressure drop at the sensor is only 0.12 kPa (0.017 psi).</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">

 

Open the Air flow sensor lid and increase spring tension (it is adjustable) this will lean mixture. Cost-$0.00.
Can anyone answer question I posed on 2-03-03
"L-Jetronic air flow sensor"?
Joseph

 

Right on Mark, that's what we are thinking. Current discussions are that we want to fab a cylinder that is the size of the round part of the AFM that mates with the intake manifold on the lower end and the airbox on the other end. We just aren't sure about the horn (or flute) that is on the inside of the lower portion of the airbox.

Personally my goal is to get the car to 300 crank hp. I can't do that with just exhaust modifications. There is no chip available. So it's a series of baby steps, 10hp here, 15 there. Remove the smog pump and mechanical fan, gut the cats, Afterburner 16, headers, etc. The MS computer is the final step in that equation. Well, maybe an ignition system to go alomg with it but we'll see.

 

Guys,

The Flapper door has NO means of compensating for air density! This is a simple mass flow calculation. The mass flowrate of the air at any point in the intake system is constant. If the AFM was able to compensate for density, why did they put a temperature sensor inside it? Doesn't temperature alter density as well?

Assume a constant mass flowrate.
Assume a constant diameter

m=pAV

If m is constant (which it will be at any point in time) and A is constant, then raising p...the density (a function of temperature and pressure) will decrease the speed. Trust me on this one, this is correct.

Mass continuity always applies! Bernoulli equation in the form presented above is NOT valid! Bernoulli only applies to invicid, incompressible flow. This is a compressible flow situation.

Think of it this way, if 50 cars (grouped together) travel at 60 MPH, then 50 cars pass a given point in one minute. If 120 cars (grouped together) travel at 30 MPH, then 60 cars pass a given point in one minute. In case two, 10 more cars passed by at 1/2 the velocity! This is the same idea with the air, twice the pressure, same temperature, twice the air mass, reduced velocity.
Intake velocity will slow down under boosted conditions. This phonomenon allows a turbo charged car to use small intake pipes and still pass a large mass of air.

Might the mass of air have some effect on the vane in the meter?, well maybe, but it certainly is not predictable.

I have basically decided to convert the car to a hot wire mass air system.

I will put a hot wire sensor on the intake (normally aspirated) side of the engine, then signal condition this output and send it back to the L-jet brain. Link Electrosystems and Split Second both make excellent and inexpensive programmable digital controllers to do this.

The end result is I will be able to eliminate the band-aid fuel system (piggyback two injector controller) and map a new fuel curve with 200 data points, which can be altered to send a wide range of voltage back to the L-jet brain. Laptop programmable and lots of resolution, just what I need.

I have to commend Callaway on being able to make the system work the way they set it up. However, technology has come a long way in the last 20 years and the Bastard could stand to be freshened up a bit. The hope is to get the fuel map correct, which will increase throttle response and power output, especially down low. The only other option is to go to a stand alone system, which is big bucks and weeks to program.

Think of this as a way to monitor and change voltage signals to the L-jet brain based on a signal sent by a new, very reliable mass air sensor. It will probably be the best money ($550.00) I ever spend on the car.

 

Wrong wrong wrong and more wrong. I can't trust you on this one, and here is why:

First of all, air flow theory is compressible fluid dynamics, not incompressible as you state.

Second, the AFM flapper door is moved by the amount of molecules that pass through it. It is EXREMELY good at adjusting for air density related to driving at higher altitudes, etc, IN FACT, it is so good at this, the temperature sensor was added to fine tune its capability. IN FACT, the accuracy was excellent up to 10,000ft.

You have many of the principles around the AFM function backward and confused.
Mass flow rate is NOT constant. It varies with the throttle position. low mass flow at idle, high mass flow at full throttle. actually, the speed of the mass and volume are constant, determined by the size of the engine. (ie 500cfm for a 4.7liter, at 6000rpm) However, what is the density of that 500cfm at 6000rpm. that depends on throttle position and mass flow (ie Power setting)
BERNOULLI not applying???? better think that one over again. you have some points backwards!

As far as Hot wire conversion, Ive tried this and there is no kit that matches the 5-9 volts needed. the 944 afm uses a 0-5 volt system that matched with the split second, will work (on 944s) to make it work on a 928, lots of work needs to be done!

The AFM is a great device. best of old and new school, at the cost of a reduced inlet diameter of only 4 square " vs the MAF of around 7.

Im only coming down hard on you here because of several of your comments and thoughts put down as FACT, when they are clearly incorrect.

Ask me any specific question about the flow theory through the AFM and Ill try and respond to it as best I can. (if i dont have the answer, someone on my team will have it for sure!!)

Mark

</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 John:
<strong>Guys,

The Flapper door has NO means of compensating for air density! This is a simple mass flow calculation. The mass flowrate of the air at any point in the intake system is constant. If the AFM was able to compensate for density, why did they put a temperature sensor inside it? Doesn't temperature alter density as well?

Assume a constant mass flowrate.
Assume a constant diameter

m=pAV

If m is constant (which it will be at any point in time) and A is constant, then raising p...the density (a function of temperature and pressure) will decrease the speed. Trust me on this one, this is correct.

Mass continuity always applies! Bernoulli equation in the form presented above is NOT valid! Bernoulli only applies to invicid, incompressible flow. This is a compressible flow situation.

Think of it this way, if 50 cars (grouped together) travel at 60 MPH, then 50 cars pass a given point in one minute. If 120 cars (grouped together) travel at 30 MPH, then 60 cars pass a given point in one minute. In case two, 10 more cars passed by at 1/2 the velocity! This is the same idea with the air, twice the pressure, same temperature, twice the air mass, reduced velocity.
Intake velocity will slow down under boosted conditions. This phonomenon allows a turbo charged car to use small intake pipes and still pass a large mass of air.

Might the mass of air have some effect on the vane in the meter?, well maybe, but it certainly is not predictable.

I have basically decided to convert the car to a hot wire mass air system.

I will put a hot wire sensor on the intake (normally aspirated) side of the engine, then signal condition this output and send it back to the L-jet brain. Link Electrosystems and Split Second both make excellent and inexpensive programmable digital controllers to do this.

The end result is I will be able to eliminate the band-aid fuel system (piggyback two injector controller) and map a new fuel curve with 200 data points, which can be altered to send a wide range of voltage back to the L-jet brain. Laptop programmable and lots of resolution, just what I need.

I have to commend Callaway on being able to make the system work the way they set it up. However, technology has come a long way in the last 20 years and the Bastard could stand to be freshened up a bit. The hope is to get the fuel map correct, which will increase throttle response and power output, especially down low. The only other option is to go to a stand alone system, which is big bucks and weeks to program.

Think of this as a way to monitor and change voltage signals to the L-jet brain based on a signal sent by a new, very reliable mass air sensor. It will probably be the best money ($550.00) I ever spend on the car.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">

 

See a couple of inserts&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;
[QUOTE]Originally posted by John:
[QB]Guys,

Mass continuity always applies! Bernoulli equation in the form presented above is NOT valid! Bernoulli only applies to invicid, incompressible flow. This is a compressible flow situation.
&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt; &gt;&gt;you have Bernoulli turning in his grave right now, that his laws dont apply here. I guess Venturis were just a "pipe" dream. (pun intended)
PV/NRT

the more the mass flow through the AFM vain, it moves due to a higher pressure on the front and a lower pressure on the rear of it. sure, there is some venturi priciples in effect, but thats not the reason it moves. The reason that it is so smooth, is there is a kind of counter balance on the opposite side, with a pressure chamber, that resists fast movments of the opposing plate, acting like a air cushion.
So, the more mass flow through the AFM, the more it deflects and the more the potentometer moves to increase voltage to the ECU which then singles more fuel from the injectors via longer duration.

The AFM plate is a kind of a flap on an airplane, without the flow over the top of it. so, the flow on the face side is greater than the rear, so thats the pressure differential that moves it. the more the pressure , the farther it is deflected until it is maxed out. The force to move it is neglegible in the overall picture. (2nd or 3rd order)

Someone mentioned that the bypass idle port can adjust mixure, as it can, but at full throttle, that port is so small that even completely open, it wouldnt effect air mass flow. even if it could,it would be false air and would have to be matched by increased fuel pressure or an additional injector ( Ive often thought of getting a large false air port and a separate injector for this kind of 10-20hp possible gain.

There is a great description of the AFM in one of the Carrol racing books, and in the Bosch Injection manuals.

Hope that helps.

Mark

 

Mark - </font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva"><a href="http://www.splitsec.com/products/psc1/PSC1009.htm" target="_blank">The PSC1-009 Programmable Signal Calibrator</a> is designed specifically to perform an air flow meter (AFM) to mass air flow (MAF) conversion on vehicles that use an AFM with a greater than 5V output. Such AFMs start near 0V at a light load and increase in voltage to above 5V as load increases.</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Has anyone figured out if the Mustang MAF will fit?

 

I still dont think this will work. I could be wrong here. as the voltage of the 928 starts at 4.5 at a limping idle to around 5volts, and never anyting less. top voltage when the flappy is open is around 8volts. I think this is the model I used and it does work on the 944, but not on the 928. Its been awhile and the folks at Huntly racing did a lot of work to help me out with the piggy back computer, but the PSC1 didnt work. Now, there could be a new model that is directly used for the 928 system, i havent seen it yet. Can anyone confirm??

If they are available, you will need a MAF to AFM conversion tube so that the euro intake air box (was designed for the 928 with MAF for the euro 2 valve) will work with the 4.7 US existing "U". I have this finely machined part. The MAF is then a Mustang MAF and it is 3.5" down to 3" diameter. a rubber adapter tube joins it to the air box and it to the custom metal adapter tube that fits snuggly in the "o" ringed "U" opening.
To do all this, the |MAF , signal generator and custom tube cost me around $1000. I sent it all back, except the tube. let me know if anyone wants it. I have the two critical components.
1. the euro air box
2. the custom adapter tube for a MAF to the stock US intake "U" leading to the Throttle body.

Installation is a piece of cake with all this work done, but my problem was with the signal generator not having the proper voltage to the stock US ECU.

MK

Mk

 

Mark - do you remember which model PSC1 you had?

Was it a -004 0-5v (vs. -009 0-8v)?

Also which Mustang MAF did you try?

I was asking about this one, a 73mm, for a 94-95 Mustang GT 5.0L.

<img src="http://boards.rennlist.com/upload/95MustangGTMAF.jpg" alt=" - " />

Unfortunately I don't know the dimensions of the flange.

 

Mark,

I'd hate to burst your throry wide open, but the Bernoulli equation can not be used with compressible flow, that is a proven and documented fact. Any person who has studied Fluid Mechanics knows this. For Bernoulli to apply, 4 assumptions must be made:

1. Viscous effects are assumed to be negligable
2. The flow is assumed to be steady
3. The flow is assumed to be incompressible
4. The equation is applicable along a streamline

Should you not agree, please see the Engineering Text; Fundamantals of Fluid Mechanics, by Munson, Young and Okiishi. Page 112 to be precise. Trust me, two very tough fluid mechanics courses tought me this.

Air Mass flowrate through the engine at any given time is constant. So let's say at 4000 rpm, the motor is pulling 500 cfm. The temperature, pressure and intake cross sectional area on the intake side dictate the velocity of the air there.

Go past the turbos, the temperature has increased and the pressure has increased, thus the density has changed...substantially, it is much, much higher. The mass flow at this point is still the same, but the pressure and temperature have changed and so has the velocity.

As for the AFM being able to detect this, I still don't buy it. Perhaps it can compensate for a barometric pressure change, such as up to 10,000 feet altitude, but this is far less than the pressure change my meter is seeing.