Hey guys,

Just changed my air filter today as it has been in for 10k and looks pretty minging. Had the laptop in the car so thought I would do a bit of logging to see if the MAF readings change with the new filter.

With the old filter, the maximum reading I got was 154.6 g/s at 5160RPM. I would have gone higher, but I ran out of runway lol.

With the new filter, the maximum readings was 152.4 g/s at 5120RPM. I was quite surprised. I was expecting a tiny but more airflow, but the reading was slightly less. I guess the new filter didn't make enough difference for the MAF to sense it, and that the MAF doesn't measure that precisely either.

Doing a rough calculation, divinding the MAF readings by 0.82, it would appear that I lose just under 3 HP with the new filter, which could be down to heatsoak. The intake temperatures got to 53 C. Both runs were in 3rd gear with my foot hard down, reaching just over 70 MPH on the same stretch of road. Boost was practically the same on both runs (2040 vs 2050 mbar, just over 15 PSI with 0.12 PSI difference.)

So there we have it. Based on a quick, inaccurate test, changing a filter at 10k is too early, and doesn't seem to make much difference to the performance of the car.

Both filters were the same OEM ones both made by MANN. Different filters may produce different numbers, so your results may vary. Next time I'm going to try it at 15k and see what happens.

Very interesting! Thanks for posting the info.

I wonder if anyone has done such a test before/after fitting an induction system.

that would be an interesting test as I have a NEUSPEED induction kit with heat shield and would love to know if I am gaining or losing Altho I could do with a front cold air feed as the stock might not be quite so good

Very interesting post ,

Certainly food for thought. As I only do a low annual mileage I tend to change filters about the same milage as you do.

Looking forward to your next test run on the airfield .

You mention "heatsoak", does that apply to overheated air + fuel causing a weaker mix??.

The reason I ask is, mine seems to run better on hot days (normal traffic speeds).

if i`m not mistaking, you should multiple your maf readings with 1.25 factor, not divide it with 0.8.

Second thing what is strange your max maf readings vs rpm are low, the max figure should be around 5800-5900rpm, where this engine produces max bhp :wonder: :wonder:

Ouch 53 intake temp? My highest has been 43 whilst stuck in traffic, does that mean the cai actually works?

Sent from my GT-I9100. Not a Crapple!

this topic is funny

when did you do the first reading with the old filter?what was the outside temperature?humidity?atmosferic pressure?

when did you do it with the new filter? what was the outside temperature?humidity?atmosferic pressure?

so manny variables and only 2 grammes difference

Very interesting post ,

Certainly food for thought. As I only do a low annual mileage I tend to change filters about the same milage as you do.

Looking forward to your next test run on the airfield .

You mention "heatsoak", does that apply to overheated air + fuel causing a weaker mix??.

The reason I ask is, mine seems to run better on hot days (normal traffic speeds).

Heatsoak is where the intercooler gets too hot so can't cool down the air from the turbo enough. This makes the air less dense, so the ECU injects less fuel to keep the ratio correct, but you drop on power. I think that the intercooler was hot from the first test and affected the second test, hence the slightly lower airflow readings.

if i`m not mistaking, you should multiple your maf readings with 1.25 factor, not divide it with 0.8.

Second thing what is strange your max maf readings vs rpm are low, the max figure should be around 5800-5900rpm, where this engine produces max bhp :wonder: :wonder:

I ran out of tarmac, so couldn't rev it any higher. Where I live, it's a lot of country roads, so there isn't anywhere to fully open it up. It's quite slippery where I did the test and 2nd caused a bit of wheel spin, so 3rd it had to be.

And there's a few ways of determinig HP - divide by 0.8, divide by 0.82, multiply by 1.25. All give similar readings, but aren't accurate anyway.

Did it again tonight in 2nd and got a max MAF reading of 174.6 g/s at 6400 RPM. After that, it dropped off and I bottled it at 7300RPM lol. That gives me 218 HP, whcih I'm happy with.

Ouch 53 intake temp? My highest has been 43 whilst stuck in traffic, does that mean the cai actually works?

Yeah, that surprised me too. Only goes that high on boost though. Driving around beforehand, it hovered about 35-40.

Maybe time for an FMIC? I need to think how to persuade SWMBO lol.

this topic is funny

when did you do the first reading with the old filter?what was the outside temperature?humidity?atmosferic pressure?

when did you do it with the new filter? what was the outside temperature?humidity?atmosferic pressure?

so manny variables and only 2 grammes difference

The readings were taken about 35 seconds apart from each other, so humidity, temp, pressure was all exactly the same. Like I said though, it is NOT a definitive test. I had the laptop and my VCDS cable, so thought I'd do a bit of an experiment. Did it with the old filter, stopped, put new one in, did it again.

Just goes to show that MAF readings are not perfect, and there are far better ways to measure and engines performance.

Edited 30 May, 201214 yr by rk696

Hmm if it goes that high only on boost it shows that my ebay special fmic really does work as it would go from the 40s to the mid 20s on boost.

Sent from my GT-I9100. Not a Crapple!

I need to check my figures on this with my Carbonio and see what it comes out with.

According to Torque my usual intake temperature is around the 30 mark on full boost. If I give it hell for a bit longer it can go nearer 40. In a queue today it was up to 45 degrees which makes sense as it was a good 40 minutes sat getting hot.

MAF wise I will have to have a play!