80tq drag racing- Intercooler reevaluation [long]

[Robert Deis]

On Wed, 29 Aug 2001, Bernard Littau wrote:
> >
> > Interesting- much of that heat can't be helped, but I've got to wonder if
> > the turbo upgrade is really the right answer- if it's heat-soaking that
> > badly I think to probably are outside the turbo's efficient range.
>
> My understanding is that the harder the turbo must work for a given boost
> level and volume, the more it heat soaks.

Compressing a gas heats it by nature. Laws of thermo, that sort of thing.
That heat can't be helped, and it's the reason you need an intercooler.
The temperature increase depends only upon the pressure difference

Compressors, however, aren't ideal, and so add some heat of their own to
the mix becasue they're not 100% efficient.  How much additional heat they
add depends on how efficient they are- and any given turbo becomes very
inefficient very quickly if you're trying to outflow it's design
capacity.  Which means a bunch of extra useless heat.

In this case, upgrading to a larger turbo that is still
efficient at the higher flow rate that you want will do more to solve the
problem than a bigger IC would.

"Heak-Soak" refers to overrunning the IC's capacity to dissipate heat.
Once the IC is heak-soaked, it may as well not exist until it has a chance
to cool down.  If the flow rate is withing the compressor's efficient
range, then upgrading the IC is your best bet.

> > You're sure there's no knock?
>
> The Audi ECU has an input charge temperature sensor.  When the temperature
> of the charge goes up, the ECU drops the boost (and perhaps the timing) even
> before there is detonation.

Ah, I didn't know that.

> can't tell if my percieved better intercooler performance is due to
> single-pass nature, or to the addition of the bypass valve,

Former.  Bypass valve doesn't help the IC performance, just helps spool
time between shifts. (And general wear and tear on the intake in
general..)

-- 
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  Rob Deis                  "Let the people know beforehand what the law
  MiB3347                      is and what they are to expect."
  rdeis at io.com                              -- 18th Congress, Rec. 75