MAP clamping

[dont_blink]

So my mas has realized its limits and my ve table runs out at 215kPa, about 60kPa lower than my max boost. So naturally when the mas goes squirly and the car tries to revert back to the VE table, the car goes lean and knocks like an SOB. I know I can modify the MAP signal to effectively rescale the VE and timing tables. Is a simple MAP clamp like the homemade ones the SRT4 guys run going to effectively cut the MAP signal down to raise the amount of boost I can tune for or is it just going to stop the table where I set the clamp and not modify anything below that point?

[fast98]

So you are flowing more than 512 g/s? or you are over 11,100 hz? If so there are other ways around it with the stock pcm, unless you have modified the correct table the pcm stops looking at the ve table by 5800rpm on just about every stock tune I have seen. Post up a log and tune file so we can help and also MAF is the accepted abbreviation for mass airflow sensor. lol

[dont_blink]

Yes but in real terms MAS = Mass Airflow Sensor while MAF = Mass Air Flow. The Saturns use a different sensor that peaks out at 11,500Hz and it's in a bigger housing than the Cobalt. The problem is I think it's going bad and even at light throttle stuff the car will revert back to the VE table for fueling 100%, even with dynamic airflow crossed over at 1500rpm instead of the original 5800rpm. It seems at about 9900Hz is where the MAS goes loopy and the car runs super lean real quick, I assume this is from reverting to the VE table for fueling. I have pegged over 11,000Hz before and had the MAS throw a high circuit performance CEL. The VE table is by far more accurate for fueling anyhow. I'd just much rather use that if I can. Think we can get a custom 3bar OS for these cars going? :-)

[black06g85]

never ran into that issue with my car, when I started pegging the maf, I just went to a bigger housing, problem solved (well at least WOT full boost high rpm lol). PCM is hardcoded nothing we can do

[dont_blink]

The MAS is no way to make power though. The thing gets a little dirty and it throws everything off. I tried clamping the MAP, but no such luck. To do this right I would need to add a secondary 3bar MAP sensor and keep the stock MAPT sensor in place for IAT2 readings and the difference in scaling between the stock 2.5bar and the 3bar should put the whole VE table lower, giving me more accurate fueling. We'll see how it goes I guess. That or finding a way to cut the stock MAP signal down proportionatly throughout the rpms. I'm going to be experimenting with this. One thing you have to remember though is that a turbo car has a much lower BSFC than a supercharged one and therefore won't use as much of the MAS. You have to think that if I lay down 360whp, I am losing like 50bhp just to spin that blower. That extra power needs more air and fuel, which the MAS still reads.

I guess I could trick the PCM though and tell it that 5V from the MAP isn't actually 300kPa on a 3bar MAP. 5V could be 215kPa, so when the car is actually running 25psi, the PCM thinks it's only at like 190kPa instead of like 270kPa, giving me full control at a slightly lower resolution. Anybody ever tried this?

[ChevyHighPerformance]

So my mas has realized its limits and my ve table runs out at 215kPa, about 60kPa lower than my max boost. So naturally when the mas goes squirly and the car tries to revert back to the VE table, the car goes lean and knocks like an SOB. I know I can modify the MAP signal to effectively rescale the VE and timing tables. Is a simple MAP clamp like the homemade ones the SRT4 guys run going to effectively cut the MAP signal down to raise the amount of boost I can tune for or is it just going to stop the table where I set the clamp and not modify anything below that point?

The simple solution for you is to use a new re-calibrated MAF from West Automotive Performance Engineering. You will get a new MAF calibration curve with the new MAF. This MAF can sense a much higher air flow rate than the stock MAF.

You can modify your MAF to sense a higher flow rate but that is for the more experienced tuners.

[dont_blink]

I don't think you are understanding the problem. The car is reverting back to the VE table, which is only good to 17psi. Even with dynamic airflow crossover set really low, the car is still referencing the VE table. If the MAS fails altogether at anything higher than that and the car needs to run on pure VE it will go lean and I will have a problem.

[ChevyHighPerformance]

I don't think you are understanding the problem. The car is reverting back to the VE table, which is only good to 17psi. Even with dynamic airflow crossover set really low, the car is still referencing the VE table. If the MAS fails altogether at anything higher than that and the car needs to run on pure VE it will go lean and I will have a problem.

So having a MAF that has been rescaled to read to a higher airflow, be within ECM limits, and comes with a new calibration curve won't help you.

[dont_blink]

Okay, so. The PCM is hardcoded to 11,100Hz, which I have already hit a few times. The MAS itself is in a 3.25" housing. Sure I could put it in a bigger housing, but then it has to bottle neck back down to 3" anyhow. I mean, that's great if you can find a MAS for my car that reads to 15,000Hz and 512g/sec, but if the PCM can't see past 11,100Hz then what is the point?

Are you seriously trying to tell me that MAF based fueling is better than MAP based fueling? You need to rethink that statement. Obviously you are not contributing to this thread, you are trying to keep me on a road that I have already been down.

[ChevyHighPerformance]

Okay, so. The PCM is hardcoded to 11,100Hz, which I have already hit a few times. The MAS itself is in a 3.25" housing. Sure I could put it in a bigger housing, but then it has to bottle neck back down to 3" anyhow. I mean, that's great if you can find a MAS for my car that reads to 15,000Hz and 512g/sec, but if the PCM can't see past 11,100Hz then what is the point?

Are you seriously trying to tell me that MAF based fueling is better than MAP based fueling? You need to rethink that statement. Obviously you are not contributing to this thread, you are trying to keep me on a road that I have already been down.

You started this thread saying that your MAS has reached its limits. I'm trying to tell you that there is a re-calibrated MAF that may read 500 g/s and outputs 8,000 Hz where the stock MAF may read 300 g/s and outputs 8,000 Hz (these are made up numbers to illustrate the difference). The new MAF comes with a calibration curve that you use to convert the new MAF output to actual g/s.

You can also perform a similar mod to your existing MAF to read a higher range of g/s and not exceed the PCM's max MAF Hz.

"Are you seriously trying to tell me that MAF based fueling is better than MAP based fueling? You need to rethink that statement." Why did you start this thread with your MAS has reach its limit then accuse me saying that MAF based fueling is better than MAP based fueling? Why are you still using your MAF is you think MAP based fueling is better?

Clearly, plainly, obviously, this is technically beyond you. You are not the first person with this problem. There are many peoples' engines that pump more air through their PCV system than you do through your entire engine. Your mom's calling you - put your helmet on, go downstairs, and eat your happy meal before it get cold.

[dont_blink]

Lol okay buddy. The MAS was created to make mass production of cars easier. It is also the best way to point out a lazy tuner. I was using it because the VE table had reached its limits, no other reason. Now that I found a way around it, I won't be using it any more again. Go read some more books and how-to's on tuning so you can e-thug the experienced people some more. A bigger MAS is an easy way to say: I'm too lazy to properly tune my car. When the throttle is closed, the MAS stops reading all the air. The MAP, however, can still meter all the air after the throttle body. Thereby being a more reliable way to calculate fueling.

[black06g85]

so all the guys running maf based 500+whp cars are lazy tuners lol.
sure guy.

we are stuck with a shitty ve table to base off of, rescale cut resolution problem solved. if you insist on using that to tune your car

now I tune my rx-7 standalone in speed density, doesn't make me a "better" tuner.