Well, as I understand it (as explaind to me by a very reliable source) the MAF is calibrated for a difinitive minimum and maximun flow of air to regulate the fuel injectors fuel flow (among other things). The custom tunes we get for our trucks usulaly extend, or widen, the range of calibration the MAF monitors. It just seems likely to me (IMO and my sources) that putting the MAF behind the charger would increase the volume and pressure of air folw across the MAF beyond it's calibration, resulting in the engine "thinking" it's going faster and or needing more fuel. Hence, the fuel injectors are told to pump more fuel to accomodate the required fuel air ratio. To make it work properly, you would need to get a custom tune that incorporated a clibration for the flow amounts being distributed behind the charger. I (and he) don't know if a tune would suffice or even be capable of calibrating the MAF for the amounts of air flow that would, or could, be passing through it. Hence you will most likely always be running rich. If anyone knows any different, please jump in and give your thoughts.

 

There cannot be (on this planet, anyway) more air coming out of the supercharger than there is air going into it.

 

Sure, but what if you were driving your truck on Uranus?

 

Then why would you put a supercharger on an engine if you don't get more air...isn't that why they call it "Boost"?

The purpose of supercharging an engine is to raise the density of the air charge, before it's delivered to the cylinders. Thus, the increased mass of air trapped and then compressed in each cylinder during each induction and compression stroke makes more oxygen available for combustion than the conventional method of drawing the fresh air charge into the cylinder (naturally aspirated). Consequently, more air and fuel per cycle will be forced into the cylinder, and this can be efficiently burnt during the combustion process to raise the engine power output to higher than would otherwise be possible.

Or you can move to another planet.

 

The supercharger only compresses the air it cannot make more of it, a NA engine acts like a vacuum sucking the air in where as a supercharged engine the supercharger acts like a pump it sucks in much more air and compresses it then forces it into the engine.

 

The same mass of air goes into the inlet of a supercharger comes out of the supercharger. Its pressure/density/temp may be different, but the mass and number of "air" molecules are the same.

"Matter cannot be created nor destroyed, by "non-nuclear" means. There isnt much fission or fusion happing in a supercharger.

peace
Hog

 

Whatever.....I got that (what I wrote) straight from a supercharger site describing the concepts of supercharging.
1: Boost- to increase, raise, make more
2:Supercharge- to charge or load excessively; to over load
3:Supercharger- a blower or compressor to supply air under high pressure

if we weren't forcing air at a maximun capacity, we wouldn't need to change our PCM tune.

 

Yes but now you are sucking in more air and then compressing it and forcing it into the compression chamber under boost. You have to adjust the tune to supply more fuel to be burnt and upgrade the fuel system to supply more fuel or you will be running lean. The rest of the tune is mostly to maximize performance while keeping a margin of safety to protect your investment. The compressor cannot compress air that it does not have so the same amount of air goes through the MAF regardless of whether it is after or before the compressor. Since the IAT sensor in our trucks is in the MAF there are advantages to moving the MAF downstream from the compressor especially if you have an IC to cool the air charge.

If you cannot suck it in (air) you cannot compress it and blow it out! A compressor does not manufacture air it can only compress what it has available to it.

 

A supercharger sucks in MORE air and forces MORE air (than normal) to the cylinders. I see what you are saying about the the position of the MAF...the conditions should be the same at either end as the velocity will be the same.
I stand corrected.

 

OK, I was thinking about this all day yesterday and now I'm really confused.

If the same air flow velocity is going into the charger as that which is being pumped from the charger......why doesn't the MAF work in both locations?