Dual MAF?

[DrX]

Anyone run dual MAF sensors?

[GMPX]

How? The PCM only has only MAF input.

[DrX]

That's what I would like to know. A professional tuner asked me why I wanted to run an SD tune when I could run dual MAF sensors. I have dual ETC throttle bodies and have been running SD for years. I guess it would be possible to build a box to average the value from the 2 sensors, but I have not heard of anyone doing this before with a GM vehicle.

[Gregs]

what makes it more tricky is that you have to average the frequency of both sensors, and not voltage. I've never thought about this but it sounds like something like that might work.

[L31Sleeper]

I've seen it done on imports, but I have no idea how they did it.

-Justin

[swingtan]

You could do it, but it depends on how you were going to plumb the intakes. If you just wanted a bigger volume of air, you could just use a bigger MAF, this would work easily. If on the other hand you wanted to use a "MAF per bank" then you could interpolate the signals from each MAF and pass the result to the single MAF input on the ECM. Making it very basic, you take the two frequency signals from the MAFs, pass them through a converters to give two voltage signals, then average the two voltages before passing the resultant signal through a voltage to frequency converter. The final signal is then fed to the ECM. You aren't going to get individual bank control though.

In fact, you would probably get a better result if you just used a single MAF signal on one side and doubled the calibration figures. It would simplify the whole thing and give pretty much the same result. You will miss any "issues" that may arise with the unmeasured bank though.....

If you are doing it for Power, it's probably a waste of time. If you are doing it to extend the range of the MAF or because you want a custom split intake, then it may work.

Simon

[DrX]

I would use the freq>voltage>averager>voltage>freq method if it was me. As mentioned by Simon, I also read where some are just using a dummy Maf on 1 side and assuming equal flow on both. My intake uses a common plenum for the 2 blowers but different flow paths for each throttle body.

The tuner I spoke with did not seem too keen on SD and recommended dual MAFs instead.

My only issue with SD has been heat-soaked restarts requiring a major increase in Desired Airflow to keep it running for the first minute or so. My IAT sensor is right inside the lower intake below the IC core and centered between intake ports 1 & 2. I'm currently toying with B3633 to see if it helps.

[L31Sleeper]

I watched your vid, that is a pretty unusual setup, it looks like a Whipple marine setup.
Why wouldn't you just go with a big Whipple ? Like the 305AX

http://www.whipplesuperchargers.com/Images/productimages/ls1_b.jpg

[DrX]

[QUOTE=L31Sleeper;149280]I watched your vid, that is a pretty unusual setup, it looks like a Whipple marine setup.
Why wouldn't you just go with a big Whipple ? Like the 305AX

Those marine setups are for big blocks. My setup is custom fabricated using 2 Magnuson TVS 1900 units which have pretty decent performance maps. At the time I did look at the bigger Whipples but even on a custom intake for my LS7 style heads, the throttle body would have ended up somewhere inside my dash as the rear part of the engine is tucked under the cowl on the trucks. KB now has a 4.2L unit that might fit. Haven't seen any efficiency data for them though.

[swingtan]

Looking at the setup, I'd be more inclined to bring the intakes to a single large MAF, if you are that set on a MAF tune. Personally I'd problem stay with SD for a setup like that and ensure the IAT corrections are set up right. Boost and inaccurate fueling are a recipe for disaster, if you're worried about the banks not matching, averaging the two is just going to make sure that neither bank is getting the correct signal. I'm assuming that the two blowers feed a common plenum, in this case the MAP sensor will be reading the combined pressure and would be more accurate than running dual MAF's.

Simon

[DrX]

Yes, the blowers feed into a common plenum. I did not intend to go back to a MAF tune. Some newer cars do not even come with a MAF sensor.

[L31Sleeper]

Throttle Body in the dash now that's custom !!! LOL
I have to ask why all this for an Avalanche ???

-Justin

[GMPX]

Yes, the blowers feed into a common plenum. I did not intend to go back to a MAF tune. Some newer cars do not even come with a MAF sensor.
GM stick with MAF's, I 'think' Chrysler don't use a MAF.

[DrX]

Throttle Body in the dash now that's custom !!! LOL
I have to ask why all this for an Avalanche ???

-Justin

Just felt that if GM was factory equipping 3000lb cars with 500hp, then a 6000lb truck should have come with at least 1000hp rather than 300hp. LOL

[scdyne]

A MAF is just a sensor that measures air flow. How it's calibrated is key to the accuracy of that sensor. With many imports the MAF sensor element is an integral part of the whole MAF box or MAF tube. (Like older GM MAFs too) When that is the case dual MAF's would be used to sum the Mass flow. HOWEVER GM has MAF sensors that go into a tube that can be of varying diameter with pre and post MAF sensor bends and changes that impact the way the element measures a signal.

If you want to use a MAF, build a single intake tube and have the MAF with the tube flow benched to produce a new Fq curve. Since they are PD blowers and enter the same intake chamber (post boost) the %error on the sum of the MAF will be negligible. The only caution is that if your intake tube is too large of diameter the MAF will not measure air flow correctly, also if you don't have a good pre and post tube run length it may show pressure fluctuations from the lobes of the blowers and skew the readings.
I haven't seen what the intake of a TVS looks like, but on other PD blowers if you are too close to the opening the MAF will show signs of the inverse pressure waves that are produced from the lobe passing across the opening of the blower.. Though averaging in the GM MAF may hide this all the same, I have seen it with other fluid systems and PD pumps using higher sampling rate flow meters. It's the inverse of the incoming pressure at the rate of the rotors rpm x 4 (because TVS has 4 lobes) or something like that.