LS7 Maf questions/issues...anybody else running one on a 3800? Or in a 4" housing?

[ZephTheChef]

So now that I have the turbo up and going, I have been playing with my LS7 MAF (100mm housing) and the numbers just aren't adding up. I have been scaling back my injector size in the tune as well as the MAF chart to get some more resolution (since originally it was maxxing out the values in the maf chart at around 9,000hz) and so far, I have been able to hit right around 10,000hz. I have gotten pretty close to getting the 67.7 max allowed value right at the 11,500hz max position in the table.

My issue/question now relates to things not adding up. Even looking at a stock LS7 tune in HP Tuners, 10,000hz is maxxed out at over 67.7 lb/min airflow. Let alone in the bigger housing I have. The car is not making anywhere near the power that would equate to. I mean it's pulling pretty good, but I think we're in the low 400hp range right now...it does not quite pull like my S600 @ approximately 600 crank hp, and they should be a similar weight. BWs matchbot calculator has me between 400-500hp depending on what intercooler efficiency value I put in (my chiller loop is not running right now, but the intercoolers are still full of water so will pull some heat out of the charge anyway). Which jives with my butt dyno. So what's up? Why am I getting so close to maxxing out this MAF at half the HP I thought it would be capable of measuring? Any ideas or experience?

The car runs smooth even at idle, the maf operation appears to be smooth and consistent, it idles nice and low so I am pretty sure I don't have any vacuum/boost leaks. It does still have honeycomb and is maybe 4" from my intercooler outlet and has a good 6" of straight pipe off the backside. I haven't gotten the car leaned out yet to be able to accurately calculate what kind of power it is making from IDC and wideband reading, but I am pretty sure it's not in the 650+HP range that an airflow that high would indicate. Any experience with this LS7 maf or ideas why I am running out of maf?

[ZephTheChef]

I am somewhat wondering if going from 3.5" intercooler outlet to 4" MAF housing is defeating the purpose of running a 4" MAF housing? I could certainly pull the intercooler and cut and weld a 4" outlet end tank...but I don't want to go through the trouble if I'm not pretty sure that's the problem. It would be a huge pain to pull that intercooler since the fittings and lines and intake pipes are all really crammed in there and would have to be removed and re-installed.

If all else fails, I understand that these MAFs will read up to 15,000hz, is that correct? I have a MAFT pro that I can use to scale as necessary to get that all working...but if this MAF is really only giving me half the airflow capability I thought then it still may not be enough for higher boost. I'm only around 17psi right now and my turbo should push 30+ to redline turned up.

[ElecTech]

It's only as capable as the PCM it's connected to and if its anything like the 0411 pcm, I'm guessing the MAF table is only capable of 512 g/sec. Which means, the PCM will only fuel to the 512 g/s limit, regardless of the frequency so what you will likely have to do is scale the injector value in half a (or .75 or whatever) and the airflow table in half to try and pick up some headroom. This, of course, will change the reported airflow value to half of actual, but theoretically would allow nearly 1000 hp worth of airflow, as long as the sensor frequency range is there. You can search in the v8 section on scaling for more information, but every table that references airflow will like have to be scaled by the same amount.

[ZephTheChef]

Yeah, I know about the hard limit in the computer. But my point was that that hard limit should equate to approximately 670hp...and the car is making roughly 400 based on fuel flow, so why is my maf approaching that limit in the computer already? Anyway, I did pressure test and determine I have a fairly sizeable boost/vacuum leak, despite not having any idle issues...so I am going to work on getting that sealed up and hopefully it is the reason my MAF is reporting so high as compared to what it should be reading for my current HP level. Thanks for the input!

[ElecTech]

Injector model accuracy can cause a false shift in the airflow model, and also a fuel flow/pressure issue will cause you to falsely compensate the fueling by increasing MAF table values. Un-metered air is also possible. I would suspect one or more of these.

[ZephTheChef]

You are certainly correct about the fuel and airflow model inaccuracies feeding back into each other. My fuel side is correct, I believe but has now been skewed to bandaid the air metering inaccuracy. It definitely acts like a boost leak, it just doesn't seem to be contributing to idle issues like those usually do, in my experience. I have flow tested my pumps up to about 20psi more pressure than they should see in operation and they still flow plenty for my injectors. I also can see the fuel pressure gauge under power and am not seeing any dips, it rises as expected. I am banking on the big boost leak, but I won't tear the car down until it snows or something, lol.