Turbo Bypass

[Greg Hermann]

>Jason,
>
>It's not a drop in boost through the intercooler, it's a drop in
>boost at the outlet of the compressor.  The cooling effect of the
>intercooler greatly increases the density of the air going into the
>engine, and thus increases the mass air flow capacity of the engine.
>To reach the same boost level compressor flow capacity must be
>correspondingly increased, either with a larger compressor or by
>spinning the same compressor faster.
>	The effect is a lot more noticeable on supercharger equipped cars
>than on turbo's, since the supercharger compressor turns at a fixed
>rate relative to the crankshaft.  On a turbo the increased flow
>capability of the engine results in a correspondingly increased
>exhaust flow through the turbine, which spins the turbo faster and
>partially compensates.
>
>Zack
>
>> ECMnut at aol.com wrote:
>>
>> > In a message dated 8/21/98 10:55:03 PM Eastern Daylight Time,
>> > bearbvd at sni.net
>> > writes:
>> >
>> > > You bet. an intercooler with a Vortech would work just fine. Just
>> > don't
>> > >  forget to correct the pulley ratio for the higher mass flow you're
>> > going to
>> > >  see through the engine if intercooled at the same boost.
>> > (otherwise, you'll
>> > >  lose some boost)
>> > >   Regards, Greg
>> > >
>> > Greg, I was trying to explain that to someone on the Syphoon
>> >  list a while ago, and they siad I was out to lunch...
>> > That may be true, but Is there a formula or someting
>> > for calculatinge the additional flow needed for intercooled vs. non
>> > IC?
>>
>> If the intercooler doesnt create a pressure drop or act as a flow
>> restriction why would you experience a boost drop through the
>> intercooler?
>>
>> --
>> Jason Weir
>> 88 Wrangler - 258 Chevy TBI
>> Fayetteville, North Carolina
>> home.att.net/~jweir/tbi.inject.htm  --- TBI Installation Page
>> mailto:jweir at worldnet.att.net
>>
>>
>>
You've got to start out with the volume flow which the engine will accept
at a given speed (RPM). This is equal to displacement times RPM times 1/2
(for a four stroke) times volumetric efficiency. Be aware that VE for an
engine drops somewhat with increasing density (increasing manifold absolute
pressure and/or decreasing manifold absolute temperature) , since pressure
loss in a fluid flowing through a passage (ports, etc.) increases directly
with increasing fluid density. Next, you've got to convert the volume flow
through the engine to mass flow (using gas laws, manifold absolute
pressure, and manifold absolute temperature. Next, you.ve got to determine
how big a compressor, operating at what speed, efficiency, and pressure
ratio (with or without an intercooler) will produce the assumed manifold
pressure/temperature conditions. Both the inlet conditions to the
compressor (air filter losses, duct losses, and duct inlet absolute
temperature and absolute pressure (altitude and/or barometric pressure and
the compressor outlet conditions (duct friction losses and intercooler
friction losses) have a direct bearing on the pressure ratio at which the
compressor must operate in order to generate the assumed manifold absolute
pressure. The one common constant at any point in the
compressor/intercooler/engine/header/turbine/exhaust system is the mass
flow (with the one exception that the mass flow increases by about 8% at
the point where the carburetor/injectors add the fuel to the flow stream. A
very powerful arguement in favor of adding the fuel downstream of the
compressor (which I first saw articulated by McInnes) is that doing so
saves the compressor work involved in compressing the fuel vapor.
Regards, Greg