Subject: Re: [s-cars] A/C

[Bruce]

Taka and I did an interesting comparison on the way back from the track last
week.

Strictly unscientific in many ways, but with following results.

He estimates his car at ~280HP, I estimate my car at ~310HP. Now mine has
bigger turbo, with more lag, and better (I hope for all the friggin money I
spent) top end.

Both of us in 4th gear, 3K RPM, steady throttle showing 0 vacuum on boost
gauge, right next to each other on highway.

We are both on the cellphone (OK, we're idiots, I admit it), and hit the gas
at as close to the same time as possible. With A/C on in both cars, I pull
away slightly as the RPMs increase, sort of a steady pull. Same test with
Taka turning off his A/C, and the cars are dead even.

So that tells me maybe A/C saps more than 5HP?

Bruce

p.s. Did I mention that the V1 in my car saved our ASS*S twice on the way
back. Geez...my license flashed before my eyes.
----- Original Message -----
From: "Wayne Dohnal" <dohnal at hevanet.com>
To: "S-car list" <s-car-list at audifans.com>; <pizzoman at yahoo.com>
Sent: Wednesday, June 26, 2002 9:33 PM
Subject: Subject: Re: [s-cars] A/C


> I'll dust off the rusty engineering skills and take a crack at answering
why
> the A/C is run off of a belt.  I've heard that the A/C takes about 5 HP
from
> the engine.  Starting with this assumption, that means an electric motor
> would need 3730 watts, which at 14 volts is about 266 amps.  But since the
> motor won't be 100% efficient, it would draw over 300 amps.  IF we had an
> alternator that could handle this draw, it would just transfer the drain
on
> the engine from the A/C pulley to the alternator pulley, but require more
> engine power because of the losses in the alternator and wiring.  To
counter
> this, the system could use a hermetically sealed compressor like most
> electrically-driven refrigeration units, which would give us a huge
increase
> in reliability and I'd assume a more efficient system.  A car A/C system
is
> considerably more powerful than a typical window A/C because of the
> tremendous amount of solar heating through the windows.
>
> Wayne Dohnal
> 1994 S4
>
>
> <parts of post snipped>
> >My next question is that since our compressors
> >are so ancient and will probably need to be replaced
> >anyway, has anyone come up with a solution that is
> >less power draining than having it run off a belt?  I
> >was thinking of an electrical source rather than a
> >pulley, being drawn from the alternator?  Just a bit
> >of curiosity here and frustration at losing some
> >performance when at WOT on hot days...which I probably
> >shouldn't do before I load up on a nice big
> >intercooler, anyway.  Anyone BTDT?  There is the space
> >in our bay, but can it be done?
>
>
>
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