FI build question - MAF and MAP
#1
Pro
Thread Starter
FI build question - MAF and MAP
I ot a mechanic or tuner but from what I yhave read it appears that the C5 uses either MAF or MAP to run engine depending upon the load, acceleration etc. I plan on doing a FI build that I do not intend to go over 15 PSI boost. I assume I will need a two bar MAF.
Do I also need to upgrade the MAP?
And can you suggest a source which ever of these are needed?
Thanks
Do I also need to upgrade the MAP?
And can you suggest a source which ever of these are needed?
Thanks
#2
Melting Slicks
You will need a 2.5 bar MAP, not MAF. A 2 bar MAP will only read to about 14.5 PSI, the 2.5 bar will read to about 21. You don't want to be sitting right on the edge of the MAP sensor range so get the 2.5 over the 2 bar.
The MAF can be removed if you plan to tune via Speed Density.
http://www.dpecorvettes.com/gpage4.html
The MAF can be removed if you plan to tune via Speed Density.
http://www.dpecorvettes.com/gpage4.html
#4
Melting Slicks
#5
Pro
Thread Starter
#6
Melting Slicks
MAF(Mass Air Flow) does not measure PSI, the MAP(Manifold Absolute Pressure) does.
Why don't you want to go speed density? It is definitely the way to go at 15 psi, just make sure it is properly tuned and you won't have an issue.
Why don't you want to go speed density? It is definitely the way to go at 15 psi, just make sure it is properly tuned and you won't have an issue.
#7
Pro
Thread Starter
MAF air flow measuremet at 15 PSI
I'm going to stick with a MAF tune for mileage ad I think better air flow measurement at lower RPM and engine load. Obviously I only know what I have read at this point and it seems for every person that says go speed density someone else says MAF is better.
#8
Melting Slicks
PSI is just a measure of restriction, it doesn’t give an accurate depiction of how much airflow you will have. 15 psi on a stock LS6 and a YSi is much more air than 15 psi on a stock LS6 and a Si. At 15 PSI I would venture to guess that you will be well beyond the limits of the stock MAF and should be tuning speed density.
#9
Melting Slicks
most tuners disable the maf or scale around the MAF anyway, and only use it for the IAT reading under boost. to answer the question. the MAP sensor is what you'll need to upgrade. see which one your tuner recommends, as they're the one who'll have to make it work.
#10
Ah, the age-old MAP vs. MAF debate. Take this all with a grain of salt because I haven't finished my build yet, but I can summarize the research I've done and tell you why I came to the conclusion I did based on others' experience. I started out thinking that I really wanted to keep the MAF, because GM designed the PCM to use it, and I don't have super high horsepower goals. Also, a lot of guys go open-loop and speed-density at the same time, so I kind of tied the two together in my mind. I definitely don't want open-loop, I want to keep using my front O2 sensors to trim AFRs when my right foot is not on the floor, for gas mileage etc. like you were saying. The rear O2 sensors can go in the garbage can, though
Well, after a little more reading, turns out plenty of people are running speed density in closed-loop, and it works just fine. CLSD gets you the benefits of eliminating the MAF while maintaining closed-loop AFR control. Getting rid of the MAF simplifies the intact tract--you can use fewer pipes and couplers and you don't have to worry about designing your intake to maintain straight, smooth airflow to keep the MAF signal from getting turbulent and noisy. My favorite part is that it really simplifies PCV and breather plumbing because you no longer have to worry about unmetered air. The only catch, as far as I know, is that you need to have a good tuner who is willing to spend the time to dial in your VE table 100%. Without the MAF to directly measure airflow, you need that table to be accurate in order for the speed density calculations to be correct.
Well, after a little more reading, turns out plenty of people are running speed density in closed-loop, and it works just fine. CLSD gets you the benefits of eliminating the MAF while maintaining closed-loop AFR control. Getting rid of the MAF simplifies the intact tract--you can use fewer pipes and couplers and you don't have to worry about designing your intake to maintain straight, smooth airflow to keep the MAF signal from getting turbulent and noisy. My favorite part is that it really simplifies PCV and breather plumbing because you no longer have to worry about unmetered air. The only catch, as far as I know, is that you need to have a good tuner who is willing to spend the time to dial in your VE table 100%. Without the MAF to directly measure airflow, you need that table to be accurate in order for the speed density calculations to be correct.
#11
Pro
Thread Starter
MAF air flow measuremet at 15 PSI
Ah, the age-old MAP vs. MAF debate. Take this all with a grain of salt because I haven't finished my build yet, but I can summarize the research I've done and tell you why I came to the conclusion I did based on others' experience. I started out thinking that I really wanted to keep the MAF, because GM designed the PCM to use it, and I don't have super high horsepower goals. Also, a lot of guys go open-loop and speed-density at the same time, so I kind of tied the two together in my mind. I definitely don't want open-loop, I want to keep using my front O2 sensors to trim AFRs when my right foot is not on the floor, for gas mileage etc. like you were saying. The rear O2 sensors can go in the garbage can, though
Well, after a little more reading, turns out plenty of people are running speed density in closed-loop, and it works just fine. CLSD gets you the benefits of eliminating the MAF while maintaining closed-loop AFR control. Getting rid of the MAF simplifies the intact tract--you can use fewer pipes and couplers and you don't have to worry about designing your intake to maintain straight, smooth airflow to keep the MAF signal from getting turbulent and noisy. My favorite part is that it really simplifies PCV and breather plumbing because you no longer have to worry about unmetered air. The only catch, as far as I know, is that you need to have a good tuner who is willing to spend the time to dial in your VE table 100%. Without the MAF to directly measure airflow, you need that table to be accurate in order for the speed density calculations to be correct.
Well, after a little more reading, turns out plenty of people are running speed density in closed-loop, and it works just fine. CLSD gets you the benefits of eliminating the MAF while maintaining closed-loop AFR control. Getting rid of the MAF simplifies the intact tract--you can use fewer pipes and couplers and you don't have to worry about designing your intake to maintain straight, smooth airflow to keep the MAF signal from getting turbulent and noisy. My favorite part is that it really simplifies PCV and breather plumbing because you no longer have to worry about unmetered air. The only catch, as far as I know, is that you need to have a good tuner who is willing to spend the time to dial in your VE table 100%. Without the MAF to directly measure airflow, you need that table to be accurate in order for the speed density calculations to be correct.
#12
Melting Slicks
I believe the issue also lies in the tables in the stock PCM. Dont quote me on this but I believe the PCM will not read over 12mHz. I think the OEM maf tops off at something like 460g/s(12mHz). Based on this information and my limited understanding of MAF tuning via the stock PCM you would need a MAF that is large enough that the calculated airflow doesn’t top a value equivalent of 12mHz(you have to scale the MAF table in the PCM for the new MAF). I know LPE sold a 100mm MAF but I dont know if it’s still available or even an option for this platform. I went speed density the second I went FI and never looked back.
Last edited by Turpid porpoise; 04-27-2018 at 03:46 PM.
#13
Pro
Thread Starter
MAF vs Speed Density
I believe the issue also lies in the tables in the stock PCM. Dont quote me on this but I believe the PCM will not read over 12mHz. I think the OEM maf tops off at something like 460g/s(12mHz). Based on this information and my limited understanding of MAF tuning via the stock PCM you would need a MAF that is large enough that the calculated airflow doesn’t top a value equivalent of 12mHz(you have to scale the MAF table in the PCM for the new MAF). I know LPE sold a 100mm MAF but I dont know if it’s still available or even an option for this platform. I went speed density the second I went FI and never looked back.
What bothers my mind about the Speed Density tune is that much of the fueling info must be derived from calculations based on pressure of air. Of course the IAT is known so using gas law calculations can yield how much air is actually going into the engine. But, I will do a lot of light throttle cruising and I live in an area with frequent elevation changes. Also I have wondered about the water vapor content of the air and how speed density handles that. I certainly am probably wrong but it just seems MAF would be more accurate at anything less than Wide Open Throttle.
#14
That Speed Inc. link is for the same MAF your car should already have come from the factory with. You can use an LS3/LS7 card-style MAF in a larger diameter pipe to lower the frequency at a given airflow, which gives you more headroom under the 12,000 Hz limit.
Reaching the edge of my knowledge here (hopefully someone who has actually done this can chime in), but there is also a 512g/s airflow limit that you may need to scale the fuel injectors to stay below.
I know you have already made your mind up, but the bane of MAF setups is noise. Fueling calculations based on a noisy MAF signal are going to be much worse than speed density calculations.
Reaching the edge of my knowledge here (hopefully someone who has actually done this can chime in), but there is also a 512g/s airflow limit that you may need to scale the fuel injectors to stay below.
I know you have already made your mind up, but the bane of MAF setups is noise. Fueling calculations based on a noisy MAF signal are going to be much worse than speed density calculations.
The following 2 users liked this post by TastyBacon:
BURL (04-27-2018),
Turpid porpoise (04-28-2018)
#15
Pro
Thread Starter
MAF air flow measuremet at 15 PSI
That Speed Inc. link is for the same MAF your car should already have come from the factory with. You can use an LS3/LS7 card-style MAF in a larger diameter pipe to lower the frequency at a given airflow, which gives you more headroom under the 12,000 Hz limit.
Reaching the edge of my knowledge here (hopefully someone who has actually done this can chime in), but there is also a 512g/s airflow limit that you may need to scale the fuel injectors to stay below.
I know you have already made your mind up, but the bane of MAF setups is noise. Fueling calculations based on a noisy MAF signal are going to be much worse than speed density calculations.
Reaching the edge of my knowledge here (hopefully someone who has actually done this can chime in), but there is also a 512g/s airflow limit that you may need to scale the fuel injectors to stay below.
I know you have already made your mind up, but the bane of MAF setups is noise. Fueling calculations based on a noisy MAF signal are going to be much worse than speed density calculations.
#16
Burning Brakes
Contact Bret (BLOWNBLUEZ06) and he will make you a kit that will keep your maf fully fonctionnal.
Will be over 1000hp , will run a ls3 card style maf and Bret setup.
Perfect for the street.
Will be over 1000hp , will run a ls3 card style maf and Bret setup.
Perfect for the street.
The following users liked this post:
BURL (04-29-2018)
#17
Pro
Thread Starter
Have been intending to touch base with Brent. I have heard many good things about him. Just been trying to understand as much of this stuff as I can before going to a tuner. I hate to be at the mercy of others decisions because I don't understand the issue at hand. I'm a good distance from him but I may arrange for him to do my tune. Heard great things about his street tunes
#18
Correct. An LS3 card style MAF in a 3.5" tube gives a 10,600Hz signal at 68#/min on my car. This would give you lots of measurement range under the 12kHz input limit, but you will still need to scale the calibration for MAF, g/cyl, and injector flow. No big deal since you are probably using injectors that flow more than 8.0g/s, so you'd need to scale for them anyway.