Volumetric Efficiency
09-18-2006, 06:24 PM
#11
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RE: Volumetric Efficiency
Well, it would be alot better to just sticky the article from the MM&FF website because there are a bucnh of charts, pictures, etc. that really help. So I will just wait until next month to see if MM&FF puts it up there or not. If they dont I will submitt this one and see if they will stick it...
09-18-2006, 06:33 PM
#12
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RE: Volumetric Efficiency
Well if anyone wants to read it ... here it is. There might be some words mispelled, I did a spell checker n everything but Im not taking the time to reread 8 pages... I already had to type it! LoL As you can tell.... I had a boring day at work lol
Here it is!
Here it is!
09-18-2006, 06:34 PM
#13
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RE: Volumetric Efficiency
Inside The Black Box (Part 1)
Understanding and Tuning Your Ford EFI System
Sine if us have been there. Others never have. For those who have seen the inside, we realize it’s a scary and confusing place. We slowly found our way around the “safer areas.†than ventured further as we felt more comfortable. Still, years later, there are unknown caverns where we fear to tread. The place we speak of does not exist in the physical world - it’s a virtual one. We’re talking about the world of the Ford Electronic Engine Control system.
Not too many years ago, the means to get inside and reprogram the Ford Electronic Engine Control (or EEC, pronounced eek ) system was reserved to few who possessed the specialized systems and electronic engineering knowledge to read and “reverse engineer†the Ford EEC system. But in this day and age, in addition to several stand-alone electronic engine control systems (that totally replaces the stock system), there are many aftermarket systems available with the ability to reprogram your existing Ford EFI system, either through an add-on chip or by reflashing to stock processor.
In this three-part series, we’ll give you the background info on how the EEC systems work. In part 2 we will discuss simple tuning specifics (as far as the Ford EEC system parameters go), while in Part 3 we’ll go through some actual tuning techniques (again, very much simplified). In the end, you’ll hopefully understand what your hired tuning expert is doing.
THE SIMPLE EXPLANATION
The Electronic Control Unit (ECU, aka Powertrain Control Unit or PCM) is the brain of the entire EEC outfit. It uses various sensors to “see†current running conditions and understand driver demands, then makes decisions and perform calculations based on its internal programming (on board memory). Finally, it sends electronic outputs to a host of actuators which control the fuel and spark delivery for the engine, emissions control systems, coolant fans, automatic transmission functions, and so on. As EEC systems have evolved and continue to do so, the ECU gains control over more and more variables. In this series, we will focus primarily on the fuel and spark control, since they have the greatest influence on engine performance.
FUEL CONTROL BASICS
Before we go into detail on the three different fuel control strategies, you need to understand the fundamental similarities between all EFI systems. That leads us to the electronic fuel injectors and the EFI fuel system. It’s a simple enough concept. For a constant air/fuel (A/F) ratio, as the airflow into the engine increases (from increased rpm, increased throttle opening, or increased boost, for example), the fuel flow must also increase proportionately. But with electronic fuel injectors, the added fuel flow does not come from increasing the flow through the injectors the same way, as say, the throttle valve increased the airflow by opening the passage in the inlet path. Electronic fuel injectors are actually digital (on/off) devices.
An electronic fuel injector is an electrically controlled on/off valve for fuel flow. When it’s on, it flows fuel in proportion to its nozzle size, and fuel pressure. When it’s off, meaning they are opened and closed quite rapidly. If more fuel is needed, the “on†pulse gets longer. The amount of time the injectors are open is termed Pulse Width.
Or the time between successive pulses gets shorter. This is important, since many people don’t understand how you can flow more fuel with a shorter pulse width. The ratio between injector “on time†and on time plus “off time†(total cycle time) is know as the Duty Cycle, DC. For example, if the PW (on time) is 2.5 milliseconds (ms), and there are 5 ms between injections, the DC will be 0.5 or 50 percent.
Injection events can either be done in batch fire mods, where groups (banks) of injectors are fired at the same time (usually once per engine revolution), or in sequential mods, where individual port injectors fire for their cylinder only, normally following the engine firing order (once every second engine revolution for four stroke engines). Sequential EFI (SEFI) systems have some advantages for fuel control over batch systems (like improved emissions and rev limiting ability), and are therefore used on all modern OEM EFI systems.
For a given injector size, at a fixed fuel pressure, the fuel flow rate will increase directly proportionally to the duty cycle. That is, until you reach 100 percent DC. At that point, the injectors are theoretically open all the time, and fuel flow can’t increase unless the fuel pressure is increased - we’ll get to that in a minute. If you get to the point of saturating the injectors (100 percent DC), you’re a/F ratio will go lean if additional air flows into the engine. Hence the reason to install larger flow injectors. In practice, you typically don’t want to exceed 85 percent, since the injectors can overheat from all the applied current. Also at high DC the injector pulse width can become unstable, and with some injectors, less fuel will actually flow at high DC’s.
So maximum fuel flow will then be limited by the size of your injector, right? Not totally. The other variable is the fuel pressure acting across the injector (from the supply side to the intake manifold side). For a given nozzle size, you can push more flow through with a higher fuel pressure. This is why injectors are flow rated at a specific fuel pressure. It is also why you can get away with smaller injectors when using a Fuel Management Unit (FMU) that’s included in many supercharger kits. The FMU basically cranks the fuel pressure way up under boost to force more fuel through the smaller injectors. It’s really a Band-Aid solution to having properly sized injectors, because the high pressure can shorten the life of your injectors and your fuel pump.
So for a given injector size, we now have two variables to control our fuel flow: DC and Fuel Pressure (FP). To make life easier for the Ecu to control the fuel flow precisely, we’d like to have only one variable, so the FP is fixed at a constant value, typically 39 psi for most stock EFI fords. But if we want constant fuel pressure, why do we regulate it with manifold vacuum in order to maintain a constant pressure across the injector? As intake manifold vacuum increases, the intake pressure decreases, therefore we reduce the fuel rail pressure the same amount to maintain the constant pressure drop across the injector. For boosted applications, we need to do the same thing in the other direction, i.e., as boost increases manifold pressure, we need to similarly increase the fuel pressure (although most stock fuel pressure regulators will not do this). The confusing part is we normally talk about manifold vacuum in units of inches of Mercury (in. Hg), while boost and fuel pressure are usually measured in pounds per square inch (psi). If you do the units conversion, at 15 in. Hg manifold vacuum (idle with a mild cam), we should reduce fuel pressure by about 7psi.
On the earlier EEC cars, the fuel system was a return-style system, where the electric fuel pump in the tank simply pumped fuel at full flow all the time. The (manifold vacuum modulated) fuel pressure regulator then bypasses the excess fuel back into the tank. With the newer returnless fuel systems, it gets a bit more complicated. Now the ECU senses fuel pressure in the fuel rails and relative to the manifold vacuum, and controls the fuel pressure across the injector by pulsing the pump voltage. With this system, fuel is not needlessly pumped around and around, heating up in the process. But it requires a special pump to work with pulsed voltage.
Now that you understand the basics of fuel delivery, you need to understand how t
Understanding and Tuning Your Ford EFI System
Sine if us have been there. Others never have. For those who have seen the inside, we realize it’s a scary and confusing place. We slowly found our way around the “safer areas.†than ventured further as we felt more comfortable. Still, years later, there are unknown caverns where we fear to tread. The place we speak of does not exist in the physical world - it’s a virtual one. We’re talking about the world of the Ford Electronic Engine Control system.
Not too many years ago, the means to get inside and reprogram the Ford Electronic Engine Control (or EEC, pronounced eek ) system was reserved to few who possessed the specialized systems and electronic engineering knowledge to read and “reverse engineer†the Ford EEC system. But in this day and age, in addition to several stand-alone electronic engine control systems (that totally replaces the stock system), there are many aftermarket systems available with the ability to reprogram your existing Ford EFI system, either through an add-on chip or by reflashing to stock processor.
In this three-part series, we’ll give you the background info on how the EEC systems work. In part 2 we will discuss simple tuning specifics (as far as the Ford EEC system parameters go), while in Part 3 we’ll go through some actual tuning techniques (again, very much simplified). In the end, you’ll hopefully understand what your hired tuning expert is doing.
THE SIMPLE EXPLANATION
The Electronic Control Unit (ECU, aka Powertrain Control Unit or PCM) is the brain of the entire EEC outfit. It uses various sensors to “see†current running conditions and understand driver demands, then makes decisions and perform calculations based on its internal programming (on board memory). Finally, it sends electronic outputs to a host of actuators which control the fuel and spark delivery for the engine, emissions control systems, coolant fans, automatic transmission functions, and so on. As EEC systems have evolved and continue to do so, the ECU gains control over more and more variables. In this series, we will focus primarily on the fuel and spark control, since they have the greatest influence on engine performance.
FUEL CONTROL BASICS
Before we go into detail on the three different fuel control strategies, you need to understand the fundamental similarities between all EFI systems. That leads us to the electronic fuel injectors and the EFI fuel system. It’s a simple enough concept. For a constant air/fuel (A/F) ratio, as the airflow into the engine increases (from increased rpm, increased throttle opening, or increased boost, for example), the fuel flow must also increase proportionately. But with electronic fuel injectors, the added fuel flow does not come from increasing the flow through the injectors the same way, as say, the throttle valve increased the airflow by opening the passage in the inlet path. Electronic fuel injectors are actually digital (on/off) devices.
An electronic fuel injector is an electrically controlled on/off valve for fuel flow. When it’s on, it flows fuel in proportion to its nozzle size, and fuel pressure. When it’s off, meaning they are opened and closed quite rapidly. If more fuel is needed, the “on†pulse gets longer. The amount of time the injectors are open is termed Pulse Width.
Or the time between successive pulses gets shorter. This is important, since many people don’t understand how you can flow more fuel with a shorter pulse width. The ratio between injector “on time†and on time plus “off time†(total cycle time) is know as the Duty Cycle, DC. For example, if the PW (on time) is 2.5 milliseconds (ms), and there are 5 ms between injections, the DC will be 0.5 or 50 percent.
Injection events can either be done in batch fire mods, where groups (banks) of injectors are fired at the same time (usually once per engine revolution), or in sequential mods, where individual port injectors fire for their cylinder only, normally following the engine firing order (once every second engine revolution for four stroke engines). Sequential EFI (SEFI) systems have some advantages for fuel control over batch systems (like improved emissions and rev limiting ability), and are therefore used on all modern OEM EFI systems.
For a given injector size, at a fixed fuel pressure, the fuel flow rate will increase directly proportionally to the duty cycle. That is, until you reach 100 percent DC. At that point, the injectors are theoretically open all the time, and fuel flow can’t increase unless the fuel pressure is increased - we’ll get to that in a minute. If you get to the point of saturating the injectors (100 percent DC), you’re a/F ratio will go lean if additional air flows into the engine. Hence the reason to install larger flow injectors. In practice, you typically don’t want to exceed 85 percent, since the injectors can overheat from all the applied current. Also at high DC the injector pulse width can become unstable, and with some injectors, less fuel will actually flow at high DC’s.
So maximum fuel flow will then be limited by the size of your injector, right? Not totally. The other variable is the fuel pressure acting across the injector (from the supply side to the intake manifold side). For a given nozzle size, you can push more flow through with a higher fuel pressure. This is why injectors are flow rated at a specific fuel pressure. It is also why you can get away with smaller injectors when using a Fuel Management Unit (FMU) that’s included in many supercharger kits. The FMU basically cranks the fuel pressure way up under boost to force more fuel through the smaller injectors. It’s really a Band-Aid solution to having properly sized injectors, because the high pressure can shorten the life of your injectors and your fuel pump.
So for a given injector size, we now have two variables to control our fuel flow: DC and Fuel Pressure (FP). To make life easier for the Ecu to control the fuel flow precisely, we’d like to have only one variable, so the FP is fixed at a constant value, typically 39 psi for most stock EFI fords. But if we want constant fuel pressure, why do we regulate it with manifold vacuum in order to maintain a constant pressure across the injector? As intake manifold vacuum increases, the intake pressure decreases, therefore we reduce the fuel rail pressure the same amount to maintain the constant pressure drop across the injector. For boosted applications, we need to do the same thing in the other direction, i.e., as boost increases manifold pressure, we need to similarly increase the fuel pressure (although most stock fuel pressure regulators will not do this). The confusing part is we normally talk about manifold vacuum in units of inches of Mercury (in. Hg), while boost and fuel pressure are usually measured in pounds per square inch (psi). If you do the units conversion, at 15 in. Hg manifold vacuum (idle with a mild cam), we should reduce fuel pressure by about 7psi.
On the earlier EEC cars, the fuel system was a return-style system, where the electric fuel pump in the tank simply pumped fuel at full flow all the time. The (manifold vacuum modulated) fuel pressure regulator then bypasses the excess fuel back into the tank. With the newer returnless fuel systems, it gets a bit more complicated. Now the ECU senses fuel pressure in the fuel rails and relative to the manifold vacuum, and controls the fuel pressure across the injector by pulsing the pump voltage. With this system, fuel is not needlessly pumped around and around, heating up in the process. But it requires a special pump to work with pulsed voltage.
Now that you understand the basics of fuel delivery, you need to understand how t
09-18-2006, 09:33 PM
#14
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Location: South Carolina
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09-19-2006, 01:17 AM
#15
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Join Date: Feb 2006
Location: Seattle, WA
Posts: 1,375
RE: Volumetric Efficiency
88BlueGT -
You are my Hero for the day.
I hope you won't be too upset when I tell you that my issue of MM&FF had arrived when I got home.
I am sure many will like to read it though.
Pretty good article.
I like the formulas provided for SD fuel calculations.
That will end up in my notes for sure.
jason
You are my Hero for the day.
I hope you won't be too upset when I tell you that my issue of MM&FF had arrived when I got home.
I am sure many will like to read it though.
Pretty good article.
I like the formulas provided for SD fuel calculations.
That will end up in my notes for sure.
jason
09-19-2006, 01:21 AM
#16
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Thread Starter
Join Date: Sep 2005
Location: Hamilton, NJ
Posts: 15,042
RE: Volumetric Efficiency
^^ I cant be your hero for like a week or something ? Just a day?!? LOL
I was actually very suprised because I am not good when it comes to getting into details with EFI systems but this REALLY helped clear alot of things up... thats why I posted it because its definetly a VERY informative article. The biggest thing now is getting people to read all of that lol It literally took my like a whole day to read it because I had to read each paragraph like three times to understand it and than I would go back and refer to other things, etc. lol But I get it now.... sort of
I was actually very suprised because I am not good when it comes to getting into details with EFI systems but this REALLY helped clear alot of things up... thats why I posted it because its definetly a VERY informative article. The biggest thing now is getting people to read all of that lol It literally took my like a whole day to read it because I had to read each paragraph like three times to understand it and than I would go back and refer to other things, etc. lol But I get it now.... sort of
09-19-2006, 04:41 PM
#18
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Join Date: Feb 2006
Location: Seattle, WA
Posts: 1,375
RE: Volumetric Efficiency
ORIGINAL: 88BlueGT
^^ I cant be your hero for like a week or something ? Just a day?!? LOL
I was actually very suprised because I am not good when it comes to getting into details with EFI systems but this REALLY helped clear alot of things up... thats why I posted it because its definetly a VERY informative article. The biggest thing now is getting people to read all of that lol It literally took my like a whole day to read it because I had to read each paragraph like three times to understand it and than I would go back and refer to other things, etc. lol But I get it now.... sort of
^^ I cant be your hero for like a week or something ? Just a day?!? LOL
I was actually very suprised because I am not good when it comes to getting into details with EFI systems but this REALLY helped clear alot of things up... thats why I posted it because its definetly a VERY informative article. The biggest thing now is getting people to read all of that lol It literally took my like a whole day to read it because I had to read each paragraph like three times to understand it and than I would go back and refer to other things, etc. lol But I get it now.... sort of
LOL
You should have seen me the first time I tried to read the TwEECer manual.
It took a few tries, but eventually the stuff sinks in.
Really it isn't that complicated, it's just not something that is given any thought, so it feels pretty foreign when you just get started.
I hope MANY people read this series.
I am looking forward to the next 2 articles.
jason
09-19-2006, 04:43 PM
#19
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Location: Hamilton, NJ
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RE: Volumetric Efficiency
Yea me too... I cant wait until they come out with the next one. Im just kind of pissed though because the third article is going to be real tuning and they are doing it on an 03 Cobra.... why not a 93 Stang ? 
09-19-2006, 04:57 PM
#20
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Join Date: Feb 2006
Location: Seattle, WA
Posts: 1,375
RE: Volumetric Efficiency
We have to admit to the fact that fox mustangs are dying out.
The mags are going to ignore us in favor of the newer stuff.
A real pisser if you ask me.
We need a TRUE 5.0 mag.
Even if it was bi-monthly, it would be very nice.
The mags are going to ignore us in favor of the newer stuff.
A real pisser if you ask me.
We need a TRUE 5.0 mag.
Even if it was bi-monthly, it would be very nice.