A common rear end in early Mustangs

--Joe

 

That isn't entirely true. Boost is a measure of how well a motor flows air.

Take 2 Lightning motors for example:

1-stock heads, exhaust, cams, pistons, valves and a 4# lower........say it makes 12 psi.

2-ported heads, full exhaust, aftermarket pistons/valves and a 4# lower.........say it makes 10psi.

Ya follow brutha...........oh and I still don't know what the 8.8 is

--Joe

 

HAHHAHAHAHAHHAHAHAHAHHAA

8.8 IS a mustang rear end. Man i feel stupid.

Oh and yes boost is determined by other things too, i meant in general, but touche.

 

Coldie is half right, its a little more involved. The temp of the air coming out of the intercooler is not ambient. So its not as dense as the air a NA engine of coldie's equations would be sucking in.
Lets take a 6lb for example:
(14.7+8+6)/14.7 = 1.95 thats the absolute pressure of the manifold. That puts us at 5.4L * 1.95 = 10.53L

Through the magic of physics we get that the temp of the air after the intercooler is about 145 degrees on a 80 degree day. The density of the air is (460+80)/(460+145)=.89

So we get an equivalent displacement of *drum roll*
9.37L

Soap,
An NA car could have better flowing heads, cams, etc to increase power without increasing displacement. This is all things being equal.

 

Why wouldn't you do a volumetric efficiency analysis? Measure the volumetric efficiency of the stock 5.4. Then measure it again with the supercharger and use the result to extrapolate the effective displacement? I'm no engineer, but it seems like this would give a reliable number.

 

Obviously. The per-PSI power increase sucks for all pullies. It is far from linear. As you noted below, the difference is density and temperature.

 

Which is why you have not doubled the displacement until 14.7 PSI, even in a perfect world.

 

Thats just displacement x pressure ratio, since:
pressure ratio = (SC displacement * sc rpm * sc VE)/(engine displacement * engine rpm * engine VE)

It still doesn't take into account the density of the air.

 

The real question is: what is the point?

We can keep adding terms to get "more correct" but even then, it doesn't really matter.

The easiest thing to do would be to simply measure the MAF reading at an RPM and poof, you've got a theoretical displacement...

Still not sure what we are trying to figure out though.

Thanks to Sublime for throwing in the temperature info.

Coldie

 

i was just curious what sort of displacement your looking at after boost in theory. thats all, sorry it got all super technical.

And yeah i didnt even think about tempertature, that messes everything up.

 

Your atmospheric pressure will change things as well...

Coldie

 

yeah but i was considering it to be basically sea level at ambient 80 or so, but the thing thats important to work past is the temperature creating during compression, plus the temperature cooled by the intercooler, everything gets too complicated,

 

I heard 15psi effectively doubles your discplacement. 3.0 with 15psi=6.0