how much boost can a maf take?
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Drifting
Joined: Oct 2005
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From: bakersfield cali
how much boost can a maf take?
how much boost can a maf from a tpi vet take, the car is an 86. I have read else whwere in this forum that 7 to 8 psi max and some other s say that 12 to 15 psi max? The boost will be coming from a rear mounted turbo with alky meth injection.
what do you guys think?
what do you guys think?
Instructor
Joined: Dec 2005
Posts: 197
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From: Woodland California
I dont think it matters as boost is pressure, not flow. A 350 cu in engine can flow 678 cu. ft/ min. at 6000 RPM at 100% efficiency. The supercharger is an air compresser that increases pressure above atmospheric compressing the air thus more o2 per cu. in. The MAF sensor senses flow, not pressure. With boost the mass of air as measured by the MAF will be wrong because it does not take into account the increase in air pressure. This is why you need an FMU, or aftermarket ECM to manage fuel in a boosted engine.
Last edited by TPI; Jan 29, 2006 at 10:19 PM.
Supporting Vendor
Joined: Oct 2004
Posts: 761
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Mass Air Flow
Hey TPI,
You are partially right. I made a similiar post a while back challenging Forum members to answer a question about air flow on a '350' before and after adding a charger (no matter if turbo, centrifugal S/C, Roots, rotary screw, etc.). Let's take your example of a '350' flowing 678 CFM as a normally aspirated engine. Let's also suppose this '350' makes 400 HP @ 6000 RPM (N/A). Now we add the blower and let's say we make 15 pounds of boost at the manifold after cooling the air back down with some kind of intercooler. Let's also say the dyno now says we are now making 800 HP. My question to you is how much air is the engine flowing in CFM? The answer is 678 CFM !!! The engine's volumetric efficiency (airflow) is not changed by adding an air compressor. However if we were to put the air flow meter at the entrance to the compressor we might measure from 1400 to 1500 CFM. We doubled the mass air flow by compressing the air. We went from a charge density of 1 to 2.
The MAF sensor would most certainly measure the difference regardless of whether the sensor is placed at the throttle body (after the compressor) or at the entrance to the compressor (before the compressor). The grams per second would double.
On the earlier L98 Vettes the MAF is used for the fuel calculation but is quickly pegged. The tables can be re-done but they don't relate as easily to fuel flow as the later ECM's like on the LT1/LT4's. That's why it's often easier to add the FMU. Also the early Bosch MAF's used a 'hot wire' sensor. It's a very small gage platinum wire with a constant current supply to it. It measures mass air flow by looking at the current flow thru the wire and comparing it to a known measured temperature. It is very accurate however the tiny wire is subject to breaking - it's fragile. On a blower application I recommend leaving the screens in to extend the life of the sensor wire.
Beginning on the LT1's the MAF is a rugged 'thin film' platinum RTD sensor (RTD = resistance temperature dependent). The sensor itself is virtually indestructable - failure is usually the result of the electronics itself, not the sensor. The 'thin film' platinum RTD took the place of the tiny gage platinum wire in the L98 Bosch MAF sensors.
To conclude, any MAF sensor will measure boost very accurately, as a result of the change in charge density, thus measuring airflow but indirectly and not as CFM but rather as grams per second. The higher airflow in CFM that removes the heat from the sensor (whether 'thin film' or 'hot wire' style) is what results in the measurement. So how much boost a MAF sensor can take is a function of it's calibration and whether the sensor contributes to the final fuel calibration is a function of software. On the L98's, as I said earlier, the MAF sensor calibration is pegged at 255 grams per second. At 800 HP you'd need double this amount or more. Best regards, Greg
You are partially right. I made a similiar post a while back challenging Forum members to answer a question about air flow on a '350' before and after adding a charger (no matter if turbo, centrifugal S/C, Roots, rotary screw, etc.). Let's take your example of a '350' flowing 678 CFM as a normally aspirated engine. Let's also suppose this '350' makes 400 HP @ 6000 RPM (N/A). Now we add the blower and let's say we make 15 pounds of boost at the manifold after cooling the air back down with some kind of intercooler. Let's also say the dyno now says we are now making 800 HP. My question to you is how much air is the engine flowing in CFM? The answer is 678 CFM !!! The engine's volumetric efficiency (airflow) is not changed by adding an air compressor. However if we were to put the air flow meter at the entrance to the compressor we might measure from 1400 to 1500 CFM. We doubled the mass air flow by compressing the air. We went from a charge density of 1 to 2.
The MAF sensor would most certainly measure the difference regardless of whether the sensor is placed at the throttle body (after the compressor) or at the entrance to the compressor (before the compressor). The grams per second would double.
On the earlier L98 Vettes the MAF is used for the fuel calculation but is quickly pegged. The tables can be re-done but they don't relate as easily to fuel flow as the later ECM's like on the LT1/LT4's. That's why it's often easier to add the FMU. Also the early Bosch MAF's used a 'hot wire' sensor. It's a very small gage platinum wire with a constant current supply to it. It measures mass air flow by looking at the current flow thru the wire and comparing it to a known measured temperature. It is very accurate however the tiny wire is subject to breaking - it's fragile. On a blower application I recommend leaving the screens in to extend the life of the sensor wire.
Beginning on the LT1's the MAF is a rugged 'thin film' platinum RTD sensor (RTD = resistance temperature dependent). The sensor itself is virtually indestructable - failure is usually the result of the electronics itself, not the sensor. The 'thin film' platinum RTD took the place of the tiny gage platinum wire in the L98 Bosch MAF sensors.
To conclude, any MAF sensor will measure boost very accurately, as a result of the change in charge density, thus measuring airflow but indirectly and not as CFM but rather as grams per second. The higher airflow in CFM that removes the heat from the sensor (whether 'thin film' or 'hot wire' style) is what results in the measurement. So how much boost a MAF sensor can take is a function of it's calibration and whether the sensor contributes to the final fuel calibration is a function of software. On the L98's, as I said earlier, the MAF sensor calibration is pegged at 255 grams per second. At 800 HP you'd need double this amount or more. Best regards, Greg
Instructor
Joined: Aug 2004
Posts: 117
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From: MIRA LOMA CA
Hi Greg! Its Good To Hear From You! Could This Be Why My Lt1 Seems To Be Running Rich After The Procharger Was Installed? Well I Should Say I Never Checked It Before The Procharger, Never Had A Reason To Check,but This Points Out How Important It Is To Run Base Lines Before Mods 
COULD THIS EXTRA VOLUME THROUGH THE MAS SENSOR CAUSE THE INJECTORS TO RUN RICHER? AT ALL LOADS & SPEEDS.SORRY FOR THE HYJACKING OF THIS THREAD :o
COULD THIS EXTRA VOLUME THROUGH THE MAS SENSOR CAUSE THE INJECTORS TO RUN RICHER? AT ALL LOADS & SPEEDS.SORRY FOR THE HYJACKING OF THIS THREAD :o
Instructor
Joined: Dec 2005
Posts: 197
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From: Woodland California
Originally Posted by BlowerWorks
Hey TPI,
You are partially right. I made a similiar post a while back challenging Forum members to answer a question about air flow on a '350' before and after adding a charger (no matter if turbo, centrifugal S/C, Roots, rotary screw, etc.). Let's take your example of a '350' flowing 678 CFM as a normally aspirated engine. Let's also suppose this '350' makes 400 HP @ 6000 RPM (N/A). Now we add the blower and let's say we make 15 pounds of boost at the manifold after cooling the air back down with some kind of intercooler. Let's also say the dyno now says we are now making 800 HP. My question to you is how much air is the engine flowing in CFM? The answer is 678 CFM !!! The engine's volumetric efficiency (airflow) is not changed by adding an air compressor. However if we were to put the air flow meter at the entrance to the compressor we might measure from 1400 to 1500 CFM. We doubled the mass air flow by compressing the air. We went from a charge density of 1 to 2.
The MAF sensor would most certainly measure the difference regardless of whether the sensor is placed at the throttle body (after the compressor) or at the entrance to the compressor (before the compressor). The grams per second would double.
On the earlier L98 Vettes the MAF is used for the fuel calculation but is quickly pegged. The tables can be re-done but they don't relate as easily to fuel flow as the later ECM's like on the LT1/LT4's. That's why it's often easier to add the FMU. Also the early Bosch MAF's used a 'hot wire' sensor. It's a very small gage platinum wire with a constant current supply to it. It measures mass air flow by looking at the current flow thru the wire and comparing it to a known measured temperature. It is very accurate however the tiny wire is subject to breaking - it's fragile. On a blower application I recommend leaving the screens in to extend the life of the sensor wire.
Beginning on the LT1's the MAF is a rugged 'thin film' platinum RTD sensor (RTD = resistance temperature dependent). The sensor itself is virtually indestructable - failure is usually the result of the electronics itself, not the sensor. The 'thin film' platinum RTD took the place of the tiny gage platinum wire in the L98 Bosch MAF sensors.
To conclude, any MAF sensor will measure boost very accurately, as a result of the change in charge density, thus measuring airflow but indirectly and not as CFM but rather as grams per second. The higher airflow in CFM that removes the heat from the sensor (whether 'thin film' or 'hot wire' style) is what results in the measurement. So how much boost a MAF sensor can take is a function of it's calibration and whether the sensor contributes to the final fuel calibration is a function of software. On the L98's, as I said earlier, the MAF sensor calibration is pegged at 255 grams per second. At 800 HP you'd need double this amount or more. Best regards, Greg
You are partially right. I made a similiar post a while back challenging Forum members to answer a question about air flow on a '350' before and after adding a charger (no matter if turbo, centrifugal S/C, Roots, rotary screw, etc.). Let's take your example of a '350' flowing 678 CFM as a normally aspirated engine. Let's also suppose this '350' makes 400 HP @ 6000 RPM (N/A). Now we add the blower and let's say we make 15 pounds of boost at the manifold after cooling the air back down with some kind of intercooler. Let's also say the dyno now says we are now making 800 HP. My question to you is how much air is the engine flowing in CFM? The answer is 678 CFM !!! The engine's volumetric efficiency (airflow) is not changed by adding an air compressor. However if we were to put the air flow meter at the entrance to the compressor we might measure from 1400 to 1500 CFM. We doubled the mass air flow by compressing the air. We went from a charge density of 1 to 2.
The MAF sensor would most certainly measure the difference regardless of whether the sensor is placed at the throttle body (after the compressor) or at the entrance to the compressor (before the compressor). The grams per second would double.
On the earlier L98 Vettes the MAF is used for the fuel calculation but is quickly pegged. The tables can be re-done but they don't relate as easily to fuel flow as the later ECM's like on the LT1/LT4's. That's why it's often easier to add the FMU. Also the early Bosch MAF's used a 'hot wire' sensor. It's a very small gage platinum wire with a constant current supply to it. It measures mass air flow by looking at the current flow thru the wire and comparing it to a known measured temperature. It is very accurate however the tiny wire is subject to breaking - it's fragile. On a blower application I recommend leaving the screens in to extend the life of the sensor wire.
Beginning on the LT1's the MAF is a rugged 'thin film' platinum RTD sensor (RTD = resistance temperature dependent). The sensor itself is virtually indestructable - failure is usually the result of the electronics itself, not the sensor. The 'thin film' platinum RTD took the place of the tiny gage platinum wire in the L98 Bosch MAF sensors.
To conclude, any MAF sensor will measure boost very accurately, as a result of the change in charge density, thus measuring airflow but indirectly and not as CFM but rather as grams per second. The higher airflow in CFM that removes the heat from the sensor (whether 'thin film' or 'hot wire' style) is what results in the measurement. So how much boost a MAF sensor can take is a function of it's calibration and whether the sensor contributes to the final fuel calibration is a function of software. On the L98's, as I said earlier, the MAF sensor calibration is pegged at 255 grams per second. At 800 HP you'd need double this amount or more. Best regards, Greg
Supporting Vendor
Joined: Oct 2004
Posts: 761
Likes: 68
Maf
Hi TPI,
I re-read my post to you and it's certainly not clear towards the end. My apologies to you and anyone else who is now confused by my confusing answer. Spontaneous answers sometimes leave something to be desired !!!
Anyhow, the MAF sensor measures mass air flow. When the supercharger sucks up 1400 CFM and compresses it down to say 700 CFM the charge density (weight of the air) increases. The compressor is not 100% efficient so it also raises the air temperature of the compressed air, which as you say affects the charge density. You can run the air thru an intercooler and/or inject water and/or alcohol to cool the charge back down and thus further increase the charge density.
Regardless of whether you "intercool" or not the air leaving the compressor is denser, has more mass, i.e., grams per second. It has nothing to do with the sensor itself. The MAF sensor does not cause a change in charge density or pressure. Of course the MAF sensor has a pressure drop thru it just like any piece of pipe or tubing but it's inconsequential and has nothing to do with its' ability to measure mass air flow. These MAF's are extremely accurate and responsive to changes in air flow and/or air flow density.
The MAF measures mass by the cooling effect the air has on the sensor. The sensor is a platinum wire (85-89) or a platinum thin film sensor (94 & newer). Platinum has a very specific resistance vs. temperature. The MAF sensor passes a constant current thru the platinum wire/film causing it to get very hot, particularly if no air flow is present. The MAF sensor constantly measures the resistance of the platinum wire/film. The more air (CFM) or the denser the air is as it passes thru the barrell of the sensor the greater the cooling effect on the sensor. So the temperature of the heated sensor changes with air flow. Because the platinum sensor is so accurate and because the constant current is a known, a calculation can be made as to mass flow. The calculation requires the actual air temperature as well. Consequently in the sensor is a second platinum 'RTD' sensor (resistance temperature dependent) used to measure the actual air temperature. The MAF then outputs a signal (85-89 is a 1-5vdc while 94 & up output a frequency) proportional to mass air flow. In the computer this signal can be scaled and/or skcewed to whatever flow you want it to be. That's how tuners on a dyno can use the MAF signal for adjusting your air/fuel mixture.
Now VetteNut94 - you need to look at your fuel trims at idle etc. On some ProCharger kits the surge valve is too close to the MAF and the pulsating air at idle 'fools' the MAF sensor. Easiest way to see on '94 & newer (don't do on 85-89) is to disconnect the MAF sensor. The PCM will switch to a speed/density calculation. If the trims radically change at idle you need to relocate the MAF sensor or surge valve entry point.
Best regards to all, Greg
I re-read my post to you and it's certainly not clear towards the end. My apologies to you and anyone else who is now confused by my confusing answer. Spontaneous answers sometimes leave something to be desired !!!
Anyhow, the MAF sensor measures mass air flow. When the supercharger sucks up 1400 CFM and compresses it down to say 700 CFM the charge density (weight of the air) increases. The compressor is not 100% efficient so it also raises the air temperature of the compressed air, which as you say affects the charge density. You can run the air thru an intercooler and/or inject water and/or alcohol to cool the charge back down and thus further increase the charge density.
Regardless of whether you "intercool" or not the air leaving the compressor is denser, has more mass, i.e., grams per second. It has nothing to do with the sensor itself. The MAF sensor does not cause a change in charge density or pressure. Of course the MAF sensor has a pressure drop thru it just like any piece of pipe or tubing but it's inconsequential and has nothing to do with its' ability to measure mass air flow. These MAF's are extremely accurate and responsive to changes in air flow and/or air flow density.
The MAF measures mass by the cooling effect the air has on the sensor. The sensor is a platinum wire (85-89) or a platinum thin film sensor (94 & newer). Platinum has a very specific resistance vs. temperature. The MAF sensor passes a constant current thru the platinum wire/film causing it to get very hot, particularly if no air flow is present. The MAF sensor constantly measures the resistance of the platinum wire/film. The more air (CFM) or the denser the air is as it passes thru the barrell of the sensor the greater the cooling effect on the sensor. So the temperature of the heated sensor changes with air flow. Because the platinum sensor is so accurate and because the constant current is a known, a calculation can be made as to mass flow. The calculation requires the actual air temperature as well. Consequently in the sensor is a second platinum 'RTD' sensor (resistance temperature dependent) used to measure the actual air temperature. The MAF then outputs a signal (85-89 is a 1-5vdc while 94 & up output a frequency) proportional to mass air flow. In the computer this signal can be scaled and/or skcewed to whatever flow you want it to be. That's how tuners on a dyno can use the MAF signal for adjusting your air/fuel mixture.
Now VetteNut94 - you need to look at your fuel trims at idle etc. On some ProCharger kits the surge valve is too close to the MAF and the pulsating air at idle 'fools' the MAF sensor. Easiest way to see on '94 & newer (don't do on 85-89) is to disconnect the MAF sensor. The PCM will switch to a speed/density calculation. If the trims radically change at idle you need to relocate the MAF sensor or surge valve entry point.
Best regards to all, Greg
Instructor
Joined: Aug 2004
Posts: 117
Likes: 0
From: MIRA LOMA CA
Thanks Greg for the info, I had talked to on the phone some 6 months ago & you had me unplug the maf, this did stop the surge & stalling at idle so I installed a pipe in the surge return hose that redirects the returned air as high up the air stream as possible, right to the supercharger inlet. this helped the stalling & surge but my fuel trims seem to be around 108 most of the time. if 128 blms is considered 0 adjustment to the fuel trim then i think at 108 this would mean the cpu is sutracting fuel if this is the case what would I need to change to bring the fuel trims to 128? I have tunercat & datamaster but dont know what to CHANGE IN THE TABLES next to reflash the cpu.THANKS & BEST REGARDS, DAVE.
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Instructor
Joined: Dec 2005
Posts: 197
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From: Woodland California
Originally Posted by BlowerWorks
Hi TPI,
I re-read my post to you and it's certainly not clear towards the end. My apologies to you and anyone else who is now confused by my confusing answer. Spontaneous answers sometimes leave something to be desired !!!
Anyhow, the MAF sensor measures mass air flow. When the supercharger sucks up 1400 CFM and compresses it down to say 700 CFM the charge density (weight of the air) increases. The compressor is not 100% efficient so it also raises the air temperature of the compressed air, which as you say affects the charge density. You can run the air thru an intercooler and/or inject water and/or alcohol to cool the charge back down and thus further increase the charge density.
Regardless of whether you "intercool" or not the air leaving the compressor is denser, has more mass, i.e., grams per second. It has nothing to do with the sensor itself. The MAF sensor does not cause a change in charge density or pressure. Of course the MAF sensor has a pressure drop thru it just like any piece of pipe or tubing but it's inconsequential and has nothing to do with its' ability to measure mass air flow. These MAF's are extremely accurate and responsive to changes in air flow and/or air flow density.
The MAF measures mass by the cooling effect the air has on the sensor. The sensor is a platinum wire (85-89) or a platinum thin film sensor (94 & newer). Platinum has a very specific resistance vs. temperature. The MAF sensor passes a constant current thru the platinum wire/film causing it to get very hot, particularly if no air flow is present. The MAF sensor constantly measures the resistance of the platinum wire/film. The more air (CFM) or the denser the air is as it passes thru the barrell of the sensor the greater the cooling effect on the sensor. So the temperature of the heated sensor changes with air flow. Because the platinum sensor is so accurate and because the constant current is a known, a calculation can be made as to mass flow. The calculation requires the actual air temperature as well. Consequently in the sensor is a second platinum 'RTD' sensor (resistance temperature dependent) used to measure the actual air temperature. The MAF then outputs a signal (85-89 is a 1-5vdc while 94 & up output a frequency) proportional to mass air flow. In the computer this signal can be scaled and/or skcewed to whatever flow you want it to be. That's how tuners on a dyno can use the MAF signal for adjusting your air/fuel mixture.
Now VetteNut94 - you need to look at your fuel trims at idle etc. On some ProCharger kits the surge valve is too close to the MAF and the pulsating air at idle 'fools' the MAF sensor. Easiest way to see on '94 & newer (don't do on 85-89) is to disconnect the MAF sensor. The PCM will switch to a speed/density calculation. If the trims radically change at idle you need to relocate the MAF sensor or surge valve entry point.
Best regards to all, Greg
I re-read my post to you and it's certainly not clear towards the end. My apologies to you and anyone else who is now confused by my confusing answer. Spontaneous answers sometimes leave something to be desired !!!
Anyhow, the MAF sensor measures mass air flow. When the supercharger sucks up 1400 CFM and compresses it down to say 700 CFM the charge density (weight of the air) increases. The compressor is not 100% efficient so it also raises the air temperature of the compressed air, which as you say affects the charge density. You can run the air thru an intercooler and/or inject water and/or alcohol to cool the charge back down and thus further increase the charge density.
Regardless of whether you "intercool" or not the air leaving the compressor is denser, has more mass, i.e., grams per second. It has nothing to do with the sensor itself. The MAF sensor does not cause a change in charge density or pressure. Of course the MAF sensor has a pressure drop thru it just like any piece of pipe or tubing but it's inconsequential and has nothing to do with its' ability to measure mass air flow. These MAF's are extremely accurate and responsive to changes in air flow and/or air flow density.
The MAF measures mass by the cooling effect the air has on the sensor. The sensor is a platinum wire (85-89) or a platinum thin film sensor (94 & newer). Platinum has a very specific resistance vs. temperature. The MAF sensor passes a constant current thru the platinum wire/film causing it to get very hot, particularly if no air flow is present. The MAF sensor constantly measures the resistance of the platinum wire/film. The more air (CFM) or the denser the air is as it passes thru the barrell of the sensor the greater the cooling effect on the sensor. So the temperature of the heated sensor changes with air flow. Because the platinum sensor is so accurate and because the constant current is a known, a calculation can be made as to mass flow. The calculation requires the actual air temperature as well. Consequently in the sensor is a second platinum 'RTD' sensor (resistance temperature dependent) used to measure the actual air temperature. The MAF then outputs a signal (85-89 is a 1-5vdc while 94 & up output a frequency) proportional to mass air flow. In the computer this signal can be scaled and/or skcewed to whatever flow you want it to be. That's how tuners on a dyno can use the MAF signal for adjusting your air/fuel mixture.
Now VetteNut94 - you need to look at your fuel trims at idle etc. On some ProCharger kits the surge valve is too close to the MAF and the pulsating air at idle 'fools' the MAF sensor. Easiest way to see on '94 & newer (don't do on 85-89) is to disconnect the MAF sensor. The PCM will switch to a speed/density calculation. If the trims radically change at idle you need to relocate the MAF sensor or surge valve entry point.
Best regards to all, Greg
If I am under standing this corectly, The MAF measures mass( grams) directly not volume (CFM), and corrects for temperature. Do I get it?
