Aerochargers are better than (insert compressor)

[Greg Hermann]

At 4:11 PM 10/21/01, lance wrote:
>If it's a restriction at cruise/light load, I'd hate to think what it is
>at WOT.   :-)  Start hating !

You need to understand that the turbine does not really run off of the
pressure in the exhaust gas. The nozzle in the turbine housing turns the
back pressure upstream of it into high gas velocity. The momentum of the
high velocity gas striking the turbine is what produces the turbine's power
output.

The velocity of the exhaust gas coming out of the housing nozzle is usually
in the range of Mach .7 to .9 in the effective operating range of a turbo.
(It cannot exceed Mach 1, which is what is called a "choked flow" condition
in a nozzle.) The _ONLY_ way to get more mass flow of gas through a
"choked" (Mach 1 flow velocity) nozzle is by increasing the density of the
gas upstream of the nozzle.

Say you are running a single turbo with a .70 A/R turbine housing on it.

Say the radius of the turbine is 2.5" Since A/R _means_ Area/Radius, that
means that .70 = A/2.5 , and the Area of the nozzle inside the turbine
housing is equal to 1.75 square inches. (Same area as a  1.5 inch inside
diameter pipe has.)

2.5" is probably a generously  large number for the turbine radius, too,
for the size range of turbos we are talking about here.

Do you really think you will get optimum cruising fuel mileage if you are
exhausting a 200 plus HP engine through a 1.5" diameter single exhaust pipe
??

Perhaps these numbers will put things in perspective for you--

So what is the gas load when an engine capable of 200+ hp is
>only making 15-20 hp?  How is opening the wastegate going to improve
>that?  Won't opening the wastegate contribute to delayed response when
>you do go WOT and have to close the wastegate before the turbo starts to
>spool?

Again, I will say that with the right controller, opening the wastegate at
light engine loads can help efficiency. Oddly enough, McInnes seems to
agree with me.

Greg
>
>Lance


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