[200q20v] RS2 & 3B - Fueling Around

Bernie Benz b.m.benz at prodigy.net
Mon Jan 21 12:35:33 EST 2002

Right on, Wolff!

If you plot your opperating points on the compressor characteristics map you
will find different compressors operate at different efficiencies at any one
point, selection always being a compermise.  But further, if you look at the
difference in efficiencies between the two compressors in the area of this
discussion's interest, high flow rates at high boost, you find that:

1. The larger compressor is more efficient, but that this difference in
efficiency contributes a very small percentage to the final charge
temperature over the fixed heat of compression.  Intercooling is the only
way to remove this unavoidable heat of compression.

2. Over the full operating range of a broad performance engine, street, not
exclusively full race application, the smaller turbo is operating at higher
efficiencies over a broader range than is the larger turbo.  Again,
selection is always a compermise, pick your poison.  Mine is maximum torque
in the 2 to 5K range.


> From: Wolff <wolff at turboquattro.com>
> Date: Mon, 21 Jan 2002 08:31:16 -0800
> To: 200q20v at audifans.com
> Subject: Re: [200q20v] RS2 & 3B - Fueling Around
> How does all of this compute if you measure mass of air per time unit? I
> think the reality of the situation is that different turbos are more
> efficient at different boost levels at delivering air that is not warmed
> above the temperature of the compression alone. In other words, a bad turbo
> design will add a lot of heat beyond just the heat made by compressing the
> air. Hot air is less dense, so less air mass (molecules) of air will
> actually be put into the motor at a given pressure.
> $.02
> Wolff
> "Nobody can forget the sound." - Michele Mouton
> ----- Original Message -----
> From: "Bernie Benz" <b.m.benz at prodigy.net>
> To: "TM" <t44tq at mindspring.com>
> Cc: "200q20V mailing list" <200q20v at audifans.com>
> Sent: Sunday, January 20, 2002 9:44 PM
> Subject: Re: [200q20v] RS2 & 3B - Fueling Around
>>> From: "TM" <t44tq at mindspring.com>
>>> Date: Sun, 20 Jan 2002 21:34:20 -0500
>>> To: "'Bernie Benz'" <b.m.benz at prodigy.net>
>>> Cc: "'200q20V mailing list'" <200q20v at audifans.com>
>>> Subject: RE: [200q20v] RS2 & 3B - Fueling Around
>>> If your statement is true, how do you explain the
>>> driveability problems of those individuals who played
>>> mix n' match with RS2 components?
>> I can usually and eventually explain problems caused by my misjudgements,
>> but not those of others.
>>> Simple fact that RS2 injectors are designed to run at
>>> a different pressure than 3B injectors- without a
>>> matching FPR, how are you going to obtain the right
>>> amount of fuel? It will either be too rich or too lean
>>> based on the same electrical input.
>> This statement points to the fact that apparently you don't understand the
>> closed loop characteristics of the FI system.  The electrical input would
>> not be the same!
>>> You're changing the situation if you're implying that
>>> I am only talking about a max boost situation where the
>>> fuel system is running closed-loop-
>> It's always running closed loop!
>>> I'm talking about
>>> all across the board, as we don't run our engines at
>>> max throttle/boost all the time, do we?
>> Under those limited circumstances what is the need for upgrade?
>>> I don't really understand what you're talking about in
>>> terms of flow being the same at a fixed boost level- how
>>> would a larger turbo produce the same amount of boost
>>> w/o more airflow?
>> Under any given scenero, in which you define boost and RPM, you have fixed
>> mass air flow, totally independent of the boost provider.
>>> I thought that you would have more airflow
>>> through the larger turbo, causing the effect that you would
>>> have more air physically flowing into the intake at the same
>>> boost level as the compressor would be able to compress more
>>> air at the same pressure due to the larger size.
>> In simplistic terms, P x V = a Constant, when feeding a constant
>> displacement machine.  You have fixed P, so therefore V is likewise fixed,
>> independent of the hardware providing the pressure.
>>> If turbo boost
>>> is measured as absolute airflow through the intake manifold
>>> (which I think you're saying),
>> Wrong, you are mixing up terms.  Boost is a pressure measurement, air flow
>> is a volume per unit time, quanity measurement.
>> Bernie
>>> then that makes sense to me and
>>> I'm totally wrong about turbocharger operation and I stand
>>> corrected.
>>> I don't want to spread misinformation, sorry if I did.
>>> Taka
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