Different MAF (g/s) readings on different intakes, despite making same power.

[brandon19]

Hey all, I was just curious if anyone would understand why this happens, or if there is something I am not understanding here. So bare with me.

Essentially I have a 3" intake inlet pipe with a 3" intake MAF sensor housing on the end. I was flowing around 350g/s at 6500rpm at 21psi. I got curious and got a 4" intake MAF sensor housing made to see any differences. I took off my 3" MAF sensor housing and replaced it with the 4" one, keep in mind I am still on the 3" intake inlet pipe. I adjusted the MAF calibration once again so actual and desired AFRs matched, except this time, at the same boost and similar rpm point, it was flowing around 380-390g/s according to the log, but I can tell you it 100% didn't feel any different to when I had the 3" intake MAF sensor on. IDCs were still the same as before despite flowing 30-40g/s more and power on VD was still fairly similar, so why the higher airflow readings? Normally I would say the MAF calibration was wrong, but the AFRs are on point, so I can't see where it went wrong.

It isn't really an issue at the moment, I have just switched back to the 3" intake MAF sensor housing for the time being, but was wondering if someone was able to explain why this was the case. Does it have something to do with the lower MAF voltage readings? Normally around 4.5-4.7v on the 3", on the 4" it was around 3.6v, but again I wouldn't of thought that would matter.

 

[Enki]

Simple; trims.
After the first pull (in a genwon at least), the ECU will compensate for fueling/mafcal being off, and come back down to expected levels. Also, these cars tend to get more power from timing rather than fueling, like in most PI applications, so perhaps you either have flat timing or are hitting higher loads which is pulling timing, thus more drastically removing power vs the increases you'd see from the extra airflow.

Ideally, this is a conversation you should be having with your tuner, as it may need a touch up tune on the new intake.

 

[brandon19]

Sorry, I wasn't so obvious on it but I tune this car myself. I had adjusted the MAF calibration according to the intake change (was almost a 25-30% increase across the board from 3" to 4"). There wasn't really a problem I was facing, I was just trying to understand why it calculated much higher airflow readings, despite not actually flowing more air.

Timing was not flat and not being pulled either, they were almost identical runs at the same boost level (similar temps) except the 4" intake was reading 30-40g/s more than usual and Virtual Dyno showed same power output aswell.

I have since just switched back to the 3" intake anyways, it responds better and is easier to get consistent AFRs.

I do appreciate your knowledge and help though.

 

[Crazycanadian]

Sorry, I wasn't so obvious on it but I tune this car myself. I had adjusted the MAF calibration according to the intake change (was almost a 25-30% increase across the board from 3" to 4"). There wasn't really a problem I was facing, I was just trying to understand why it calculated much higher airflow readings, despite not actually flowing more air.

Timing was not flat and not being pulled either, they were almost identical runs at the same boost level (similar temps) except the 4" intake was reading 30-40g/s more than usual and Virtual Dyno showed same power output aswell.

I have since just switched back to the 3" intake anyways, it responds better and is easier to get consistent AFRs.

I do appreciate your knowledge and help though.

Here's the thing.... You aren't actually "Calibrating" the MAF curve.. In order to do that properly you'd put it on a flow bench and measure the airflow and voltages with the intake assembled. From there you'd change things with in the ECUs internal math to get your AFR's in line..

What you're look at, is the variations you get from tuning a MAF the way we generally do it.. The 4" is also experiencing more turbulence causing your inconsistencies

 

[Enki]

Anything 3.5" or bigger should probably have a honeycomb straightener in it IMO.

 

[brandon19]

Yeah okay sweet guys, I appreciate your help.

On a side note, I was wondering if there was a general rule of thumb with IDCs (yes I see it has been discussed a lot and Enki has done a lot of work with showing the different injection windows and all that jazz, which I still can’t understand). At what IDCs do you recommend to NOT go for more airflow and what are the symptoms if you increase IDCs too far? Leaning out, misfiring, engine boom.. lol?

I accidentally ran to 107% on one pull, but everything seemed to still be in order AND the car made 420whp on VD with DynoJet CF.. yayy?! Currently I am pushing around 96% and seems to settle around 370ish whp mark on the same CF as before. Not sure if it helps but I have had the injectors flow tested and cleaned.

Thanks again.

 

[Enki]

Keep it at/below 100 so there's room.

 

[brandon19]

Keep it at/below 100 so there's room.

Okay easy, AFR targets are 11.5 at the moment on octane 98 pump gas. Car has forged billet pistons, otherwise I would normally run a bit richer. Do you think there is much point running any leaner, or maybe 11.5 is on the leaner side already? Should add I am revving to 7000rpm.