maf v & maf g/s

Discussion of tuning specific to MAZDASPEED3/MAZDASPEED Axela/Mazda 3 MPS vehicles
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boloteo
Posts: 36
Joined: November 27th, 2011, 4:33 pm

maf v & maf g/s

Post by boloteo »

Hello,

I have a question lets say that we have 2 mps 3 with the stock maf diameter but they have different maf cal...

So the first reads 4.87v and 319g/s and the second reads 4.87v and 349 g/s,lets just say that they read it in the some rpm area .Which car has more hp ??
mituc
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Joined: December 17th, 2011, 2:47 pm
Location: Iasi/Romania

Re: maf v & maf g/s

Post by mituc »

Probably the first one reading 319g/s has more power, but slightly or not at all.
The reason is that the second one runs richer because the same amount of air actually goes through the MAF housing. Running richer means better cylinder cooling but at the same advance timing values and assuming there's no knock and all other conditions are similar (engine coolant temperature and boosted air temperature) the cylinder pressure will be slightly lower resulting in slightly less power.

By slightly I mean 0 to 2 bhp or so :). Depending on the turbo capabilities you may flow more air than another car with similar turbo and similar intake if you have a post-MAF leak :)

JFYI, with my intake I flow 350g/s at 4.758V and I think I'm a bit rich there already as the actual AFR's goes into the low 10's between 345 and 360g/s and I'm commanding 10.5 there. So 350g/s with the stock intake is even less possible.
2008 Cosmic Blue Mazda 3MPS
Built engine + WMI + GTX3071 gen2, ~509BHP @34PSI
2008 Icy Blue Mazda CX7
Stock engine and exhaust (YES!!), JBR3" + GTX2867 gen2 + Autotech HPFP, self-tuned to 330-ish BHP
boloteo
Posts: 36
Joined: November 27th, 2011, 4:33 pm

Re: maf v & maf g/s

Post by boloteo »

Both cars have a cai but with the stock maf diameter......

By your opinion when the maf volts reach their limit 4.99v how many hp do you estimate the car??(for stock maf diameter)
mituc
VersaTuner guru
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Joined: December 17th, 2011, 2:47 pm
Location: Iasi/Romania

Re: maf v & maf g/s

Post by mituc »

Nobody can estimate that man... The MAF g/s alone won't tell you how much power a car does. It also depends on timing, compression, and so on. And even if the mixture is richer and theoretically you can run more timing, there is a limit which you can't pass no matter how much you enrich the mixture.
Also, with the car reading more air you will probably run out of fuel with the stock fueling system before you reach the MAF cut voltage (4.90V).

P.S.: stock MAF housing diameter = stock MAF cal - pretty much, which very small variations depending on what additives and ethanol mixtures the fuel in your area has. So you should consider re-doing the MAF cal on both cars, check them both for post-MAF - pre-turbo leaks or exhaust leaks before the first oxygen sensor, and everything.
2008 Cosmic Blue Mazda 3MPS
Built engine + WMI + GTX3071 gen2, ~509BHP @34PSI
2008 Icy Blue Mazda CX7
Stock engine and exhaust (YES!!), JBR3" + GTX2867 gen2 + Autotech HPFP, self-tuned to 330-ish BHP
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Steve @ VersaTune
Lead tuner
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Joined: March 29th, 2010, 12:58 pm

Re: maf v & maf g/s

Post by Steve @ VersaTune »

MAF Cal is actually more than a MAF calibration as it is used for aftermarket tuning. In addition to the basic calibration for the real air mass flow measurement, it is used to compensate for air small leaks, variations in injector flow due to dirty njectors, oxygen content in fuel, etc. The point is to get the actual AFR to equal desired AFR with as little trim as possible. If you want to compare MAF numbers, you need to compare vehicles with identical intake systems and look at the MAF volts if the calibrations are different.
mrQQ
Posts: 64
Joined: November 25th, 2010, 6:06 pm

Re: maf v & maf g/s

Post by mrQQ »

if you have MAF calibrated too high, eg, ECU thinks it's 300g/s when in fact it is only 250, the car will make less power, because ECU will think that it has already reached requested load, while in fact, it didn't yet. If you drop it back to real number, the ECU will still raise BCS to try and reach requested load.
Kevin
Posts: 129
Joined: November 18th, 2011, 10:09 am

Re: maf v & maf g/s

Post by Kevin »

Also, if its not calibrated properly like Mrqq said and is returning 300 instead of 250 the car would add fuel for that amount of air and run very rich. Also, stock fuel pump is only good for around 275g/s, so without a fuel pump upgrade you are going to starve the car at that amount of airflow and damage your engine


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