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FI build question - MAF and MAP

 
Old 04-26-2018, 11:33 PM
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BURL
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Default 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
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Old 04-27-2018, 08:01 AM
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Turpid porpoise
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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
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Old 04-27-2018, 08:38 AM
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If you go speed density, you also need an IAT sensor in front of the throttle body.
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Old 04-27-2018, 08:39 AM
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Originally Posted by hatewhatownsyou View Post
If you go speed density, you also need an IAT sensor in front of the throttle body.
Good catch, it can also be mounted in the manifold with a little ingenuity.
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Old 04-27-2018, 09:54 AM
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Default MAF,MAP for 15 PSI tune

Originally Posted by Turpid porpoise View Post
Good catch, it can also be mounted in the manifold with a little ingenuity.
OK, let ne make sure I understand. I do not intend to go speed density.

I will need a 2.5 bar MAP and you are saying the stock MAF is good to 15 PSI?
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Old 04-27-2018, 11:05 AM
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Turpid porpoise
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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.
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Old 04-27-2018, 12:12 PM
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Default MAF air flow measuremet at 15 PSI

Originally Posted by Turpid porpoise View Post
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.
Yes I understand the MAP measures pressure. But the MAF has to measure the airflow entering the engine and I did not know the stock MAF could measure the increased air flow at 15 PSI. That's a lot more air than it has to measure normally aspirated - correct?.

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.
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Old 04-27-2018, 01:06 PM
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Turpid porpoise
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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.
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Old 04-27-2018, 01:19 PM
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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.
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Old 04-27-2018, 01:39 PM
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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.
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Old 04-27-2018, 03:30 PM
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Default MAF air flow measuremet at 15 PSI

Originally Posted by TastyBacon View Post
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.
What you have said agrees with what I have read. And closed loop certaily is best for fuel trim. And I know PSI is just a measure of restriction but if you are able to reach 15 PSI I would think it safe to assume you are cramming much more air (and fuel) through the engine unless you've stuffed socks into the intake runners. So back to my original question - does a replacement MAF exist that can read the amount of being passed to support say 650 - 750 horsepower. I don't care about how much restriction we are talking it takes a given amount of air to support that horsepower level. Now if you are wide open you are using MAP tables anyway (right?) but say you are at 3/4 throttle - can the stock MAF read this amount of air or is there a replacement that can? You guys ca tell me all day long I should do speed density but I'm hard headed and I'm gonna try using a MAF if one exists that can read the air. I may be sorry to choose that path but please help me with the MAF question.
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Old 04-27-2018, 03:44 PM
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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.
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Old 04-27-2018, 04:11 PM
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Default MAF vs Speed Density

Originally Posted by Turpid porpoise View Post
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.
I just saw a GM 85 MAF here http://www.speedinc.com/shop-by-vehi...rsion-kit.html. Don't know if this is an upgrade or not.

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.
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Old 04-27-2018, 05:51 PM
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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.
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Old 04-27-2018, 06:30 PM
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Default MAF air flow measuremet at 15 PSI

Originally Posted by TastyBacon View Post
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.
Thanks for your patience and help. Time to decide on a tuner I guess and make contact!
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Old 04-29-2018, 01:46 PM
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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.
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Old 04-29-2018, 03:08 PM
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Originally Posted by always faster View Post
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.
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
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Old 04-30-2018, 02:50 PM
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Originally Posted by TastyBacon View Post
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.
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.
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