Axing the flapper style mas air meter
#51
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Originally posted by Evil Aviator
The stock AFM measures the airflow prior to the turbocharger heating the air, the intercooler cooling it, and the rest of the intake taking its pressure drop toll. Therefore, the ECU must estimate the temperature and pressure of the air in the manifold. In English, the stock AFM has absolutely no idea what is really happening in the intake manifold.
The stock AFM measures the airflow prior to the turbocharger heating the air, the intercooler cooling it, and the rest of the intake taking its pressure drop toll. Therefore, the ECU must estimate the temperature and pressure of the air in the manifold. In English, the stock AFM has absolutely no idea what is really happening in the intake manifold.
#52
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Originally posted by RexRyder
the temp sensor in TB isnt it for measure temp of coolant flowing thru it? for the 3000rpm rev thing
the temp sensor in TB isnt it for measure temp of coolant flowing thru it? for the 3000rpm rev thing
#53
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Originally posted by Felix Wankel
I thought there was an air temp sensor on the TB elbow anyhow?
I thought there was an air temp sensor on the TB elbow anyhow?
#54
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Originally posted by NZConvertible
As Henrik said, the system is a closed one, so the mass flow cannot change at any point in the system. It's physically impossible.
As Henrik said, the system is a closed one, so the mass flow cannot change at any point in the system. It's physically impossible.
What you are forgetting is that a vehicle intake system has dynamic properties. As the air travels through the system, it will compress and expand in different areas, heat and cool in different areas, get caught and released in different areas, absorb and release moisture in different areas, etc. Just because a given amount of air mass goes through the AFM, it doesn't necessarily mean that the same amount feeds into the rotors at that exact same time.
To be honest, I'm not sure what all the stock ECU measures in regard to engine tuning, or how it weighs different data to make changes to the engine tuning. However, if the AFM were so darn accurate at estimating the mass airflow at the manifold, then there would be no need for an additional temperature sensor on the intake elbow. Think about it.
While looking up something for a friend, I found a passage from Corky Bell's Maximum Boost book which may help explain at least one issue that I seem to have trouble conveying to you folks.
“It is distinctly possible to upset the basic throttle response if an engine is equipped with an airflow meter positioned too far from the throttle body. Opening the throttle causes a low-pressure pulse to be created that travels upstream toward the airflow meter. The time it takes this pulse to reach the flow-meter and cause it to react is indeed the delay in throttle response. Typically, such a pulse must travel from the throttle body to the intercooler, through the intercooler, back to the turbo, then to the flowmeter, in order for the flowmeter to register a response. It is not until the flowmeter receives this pulse that the air/fuel ratio can change to account for new load conditions in the engine.”
Like most of the Corky Bell issues, this is simplified, but hopefully you will begin to understand part of what I am talking about.
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Originally posted by Evil Aviator
The Earth's atmosphere can also be considered a closed system, but I doubt that the air where I am right now has the same properties as the air where you are. IMO it is more accurate for you to calculate the air mass where you live than it is for me to measure the air mass where I live and try to apply it to your location.
What you are forgetting is that a vehicle intake system has dynamic properties. As the air travels through the system, it will compress and expand in different areas, heat and cool in different areas, get caught and released in different areas, absorb and release moisture in different areas, etc. Just because a given amount of air mass goes through the AFM, it doesn't necessarily mean that the same amount feeds into the rotors at that exact same time.
To be honest, I'm not sure what all the stock ECU measures in regard to engine tuning, or how it weighs different data to make changes to the engine tuning. However, if the AFM were so darn accurate at estimating the mass airflow at the manifold, then there would be no need for an additional temperature sensor on the intake elbow. Think about it.
While looking up something for a friend, I found a passage from Corky Bell's Maximum Boost book which may help explain at least one issue that I seem to have trouble conveying to you folks.
“It is distinctly possible to upset the basic throttle response if an engine is equipped with an airflow meter positioned too far from the throttle body. Opening the throttle causes a low-pressure pulse to be created that travels upstream toward the airflow meter. The time it takes this pulse to reach the flow-meter and cause it to react is indeed the delay in throttle response. Typically, such a pulse must travel from the throttle body to the intercooler, through the intercooler, back to the turbo, then to the flowmeter, in order for the flowmeter to register a response. It is not until the flowmeter receives this pulse that the air/fuel ratio can change to account for new load conditions in the engine.”
Like most of the Corky Bell issues, this is simplified, but hopefully you will begin to understand part of what I am talking about.
The Earth's atmosphere can also be considered a closed system, but I doubt that the air where I am right now has the same properties as the air where you are. IMO it is more accurate for you to calculate the air mass where you live than it is for me to measure the air mass where I live and try to apply it to your location.
What you are forgetting is that a vehicle intake system has dynamic properties. As the air travels through the system, it will compress and expand in different areas, heat and cool in different areas, get caught and released in different areas, absorb and release moisture in different areas, etc. Just because a given amount of air mass goes through the AFM, it doesn't necessarily mean that the same amount feeds into the rotors at that exact same time.
To be honest, I'm not sure what all the stock ECU measures in regard to engine tuning, or how it weighs different data to make changes to the engine tuning. However, if the AFM were so darn accurate at estimating the mass airflow at the manifold, then there would be no need for an additional temperature sensor on the intake elbow. Think about it.
While looking up something for a friend, I found a passage from Corky Bell's Maximum Boost book which may help explain at least one issue that I seem to have trouble conveying to you folks.
“It is distinctly possible to upset the basic throttle response if an engine is equipped with an airflow meter positioned too far from the throttle body. Opening the throttle causes a low-pressure pulse to be created that travels upstream toward the airflow meter. The time it takes this pulse to reach the flow-meter and cause it to react is indeed the delay in throttle response. Typically, such a pulse must travel from the throttle body to the intercooler, through the intercooler, back to the turbo, then to the flowmeter, in order for the flowmeter to register a response. It is not until the flowmeter receives this pulse that the air/fuel ratio can change to account for new load conditions in the engine.”
Like most of the Corky Bell issues, this is simplified, but hopefully you will begin to understand part of what I am talking about.
The only point I was trying to make is that what an AFM, a T sensor and an atmospheric pressure sensor you can calculate the mass entering the system, you had indicated that this was not possible. With a speed density system you need a model for the VE of the engine, the T sensor, atmospheric pressure and MAP sensors.
To cover the pros/cons of each system is a completely different discussion.
Henrik
87TII
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Originally posted by Evil Aviator
Opening the throttle causes a low-pressure pulse to be created that travels upstream toward the airflow meter. The time it takes this pulse to reach the flow-meter and cause it to react is indeed the delay in throttle response. Typically, such a pulse must travel from the throttle body to the intercooler, through the intercooler, back to the turbo, then to the flowmeter, in order for the flowmeter to register a response. It is not until the flowmeter receives this pulse that the air/fuel ratio can change to account for new load conditions in the engine.
Opening the throttle causes a low-pressure pulse to be created that travels upstream toward the airflow meter. The time it takes this pulse to reach the flow-meter and cause it to react is indeed the delay in throttle response. Typically, such a pulse must travel from the throttle body to the intercooler, through the intercooler, back to the turbo, then to the flowmeter, in order for the flowmeter to register a response. It is not until the flowmeter receives this pulse that the air/fuel ratio can change to account for new load conditions in the engine.
Originally posted by Henrik
I think you'de agree that after the system has stabilized from a rapid throttle change, the AFM will give a reasonably accurate measurement.
I think you'de agree that after the system has stabilized from a rapid throttle change, the AFM will give a reasonably accurate measurement.
Last edited by NZConvertible; 01-10-03 at 02:09 AM.
#59
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Originally posted by RexRyder
wouldnt the flapper thing go all the way open under boost?
wouldnt the flapper thing go all the way open under boost?
Brad
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The AFM is calibrated for use at atmospheric pressure. The flapper door will open proportional to the mass of the air and the square of the velocity of the airflow. When you pressurize the flow, the mass remains the same but the flow decreases so the AFM will measure progressively lean as boost rises. You can probably do the change, but you need to fix the fuel problem.
As an analogy, think of a garden hose. Turn the water on to a fixed rate (fixed mass flow) and imagine spraying the flapper. Now pinch off the hose opening and spray again. In which case does the flapper open more - the second one of course. In both cases you've got basically the same mass flow but your readings are way different due to the change in velocity. For a turbo system the intake velocity will be greater before the turbo than after; ie the flapper will open more before the turbo than if placed after.
Edit: I haven't tried moving the AFM and the above is just based on my understanding of the physics involved.
Henrik
87TII
As an analogy, think of a garden hose. Turn the water on to a fixed rate (fixed mass flow) and imagine spraying the flapper. Now pinch off the hose opening and spray again. In which case does the flapper open more - the second one of course. In both cases you've got basically the same mass flow but your readings are way different due to the change in velocity. For a turbo system the intake velocity will be greater before the turbo than after; ie the flapper will open more before the turbo than if placed after.
Edit: I haven't tried moving the AFM and the above is just based on my understanding of the physics involved.
Henrik
87TII
Last edited by Henrik; 01-11-03 at 02:48 AM.
#61
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Someone shoudl do some tests on this... if it would work well just before the TB this would be a veru good mod to aid throttle response and allow proper atmo vented BOV operation.
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Originally posted by astrochild7
alright we need a gini pig who's up???
alright we need a gini pig who's up???
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Originally posted by RexRyder
daym yo lets do this shyt then
daym yo lets do this shyt then
Web viewing isn't so great, but I think you can read the stats on the Bonneville RX-7 if you download the picture to your computer and read it with one of your graphics programs. Note that it had a whole lot of HKS EMS add-ons in addition to the modified AFM. It would be much easier and cheaper to use a standalone EMS, which was not available at the time this RX-7 was built.
http://www.geocities.com/evilaviator/bonneville
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hi guys
just reading your posts through quickly
just wanted to note that on my E15ET i successfully fitted an FJ20ET AFM on it. Worked fine, but i had to adjust the spring though.
On another note, someone said something about the AFM open all the way on WOT, if relocated behind the IC. It was discovered by those at n12turbo.com that the E15ET's AFM flap is fully open at 3000rpm. I would suspect it would be similar on the rx-7s.
Also does any of these US computers, (haltech, wolf, motec) have cold air idle sensors? I'm currently running microtech, it does the job, but quite embarassing stalling while getting out of the parking lot!
just reading your posts through quickly
just wanted to note that on my E15ET i successfully fitted an FJ20ET AFM on it. Worked fine, but i had to adjust the spring though.
On another note, someone said something about the AFM open all the way on WOT, if relocated behind the IC. It was discovered by those at n12turbo.com that the E15ET's AFM flap is fully open at 3000rpm. I would suspect it would be similar on the rx-7s.
Also does any of these US computers, (haltech, wolf, motec) have cold air idle sensors? I'm currently running microtech, it does the job, but quite embarassing stalling while getting out of the parking lot!
#67
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Originally posted by [YMMIJ]
It was discovered by those at n12turbo.com that the E15ET's AFM flap is fully open at 3000rpm.
It was discovered by those at n12turbo.com that the E15ET's AFM flap is fully open at 3000rpm.
Originally posted by [YMMIJ]
Also does any of these US computers, (haltech, wolf, motec) have cold air idle sensors? I'm currently running microtech, it does the job, but quite embarassing stalling while getting out of the parking lot!
Also does any of these US computers, (haltech, wolf, motec) have cold air idle sensors? I'm currently running microtech, it does the job, but quite embarassing stalling while getting out of the parking lot!
The Wolf3D 4.0 has an idle speed control solenoid PWM lead, as well as water temperature correction (similar to a carb choke). I'm sure that the other latest and greatest EMS products on the market also have similar functions (Haltech E11, TEC3, etc.). You may also want to check into the new Microtech LTX series of EMS products to see if they may function better than what you currently have.
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