Physics of MAF's (?)

[Cali]

Hi
New to the board, and a novice on s/c powerplants, but a few things that I don't understand....

I have searched, and found a few people that use a "draw-through" meter as a "blow-through" with success, but my question is this:

Physics tells us that "vaccuum" doesn't exist in an internal combustion engine, only "low pressure". No engine "pulls" air through a MAF, it's atmospheric pressure forcing (pushing) air into the engine- through the MAF and TB and anything else in the route. So what is it about, for example, the lighning 90mm MAF, that makes it different from a standard style? Why does the 14 pounds (+/-) of atmosphere have to be handled differently than that of 14 pounds of atmosphere + 6 pounds of paxton?

[Cali]

Someone has to have input on this-
I'll be more than happy to share my datalogs once it's up and running.

[james redman]

Cali,

My engine is Normally Aspirated by OEM design. I use the NA Hot Wire MAF in blow through mode with no problems.

I have visited sites where the engine developer tried blow through and then reverted to draw through. Supposedly giving a smother idle or some such. I tried to find a link but no luck...may turn it up later.

With regard to the physics all I can say is that the MAF will need need an air temp. measurement from the air stream entering the MAF to help the computer work out the mass flow.

Pressure x Vol. Flow Rate = Mass Flow Rate x R x Temp.

[Michael]

I don't have any direct experience with the MAF found on the Ford Lightening, but other than maybe it's physical size or (possibly) it's calibration, I don't think there is any difference between it and a "regular" MAF found on other Ford F150s.

I can tell you the SN89 kit for my car didn't come with a MAF. However, the install calls for me to reuse the stock GM MAF my car came equipped with. It installs between the blower's output and the throttle body's inlet. This tells me the MAF is capable of registering the amount of flow to the engine when on boost. Obviously, once the supercharger is installed the ECM will need a custom tune so it will know how to handle the added fuel requirements at the higher flow rates, but ultimately, the MAF itself is unchanged from stock.

Not really sure that answers your question though.

[Cali]

Thanks, both replies shed more light on this (atleast from my perspective).


I know from experience with my twEECer R/T that a good tune can take a lifetime to develop on your own, perhaps too many people simply run what they read about versus trying different combinations.

I'm guessing my hot wire MAF will behave totally different after the temperature difference of the S/C's charge is introduced. The only thing I can think of is that the Lightning's MAF takes into account the temperature difference in design (maybe a smaller/larger sampling orifice, for it's diameter/injector combo when compared to a draw-through design, to compensate for the temperature difference and still have a 0-5v output covering the total CFM range of the engine)

[james redman]

I think that newer MAF's (and MAP's) have built in Inlet Air temp. sensors. My engine OEM design has a remote IAT positioned about 500mm ahead of the MAF.

I changed to Blow Through the MAF with the IAT about 100mm ahead of the MAF meter. Both the MAF and IAT are after the intercooler so the Temp. is SC delivery minus Intercooling (+ or - small losses and gains on route)

To me the temperature rise accross the SC is irrelevant so long as the IAT sensor is measuring the same temp. air stream as the MAF is seeing.