# Intercooler Efficiency... - the MATH again

```In a message dated 97-11-16 20:11:21 EST, you write:

<< Why does'nt everyone just forget the cheasy trick's and worthless single
> pass conversions and just buy a proper intercooler....  Any one that
> tells you otherwise is just yanking your chain

> Later!
>Eric Fletcher S.O.C.
>'87 5KCSTQ with WAY too many toys.....
>>
Lifting from Pressure Frequently under his Diaphram, admittedly almost
Topping out, the rather Dense QSHIPQ still shivering from some Syberian
Physics Seminar , Bypasses his fellow PT's (whacked from shots of "Pressure
Spikes" at last nights Waste Gate party), knowing it's bad PR, but raises his
Pitch as he Props the question:
"...  Er, ah, um, Professor, mind if I borrow the chaulk?"

Let's put this "CLAIM"  in perspective to the math...  "Worthless single pass
conversions?"  Let's start there, some baseline first.  The stock IC in
single pass trim can flow a little better than 400CFM (formulas for that are
available in Corky Bells book, I have a core here in my office that I took
for measure - happy to share the numbers used), has a good baseline
efficiency as far as contruction.  Let's change that over to evaluate it
against a 2.0bar mod, stock k26

CFM fomulas (inserting 80 Volumetric Efficiency for 10vt motor - hey folks
insert what ya want, no posts please)

CI * rpm * .5 * VE/1728 = Baseline CFM
Baseline * Pressure Ratio = Boosted CFM

136 * 5500 * .5 * .80/1728 = 173 CFM
173 * 2.0 = 346CFM

346CFM looks to be WELL within the design parameters of the stock k26 @
2.0bar.  In fact, you can do some VE mods or even go to 2.3 bar (don't with a
stock k26, another discussion), and you still are within the design
parameters of a stock single pass IC.  So, going single pass on a stock IC
core seems like a pretty decent B4B modification to me, hardly cheesy either,
especially those with stock k26 turbos that run 2.0bar mods only.   So, by
definition, let me be the first to "yank your chain" based on the math.
Actually, the "second", since audi already DID this "cheesy" mod to the 20vt
cars.

Bigger turbo?  Ok, change it over.  Increasing the Effective Core size of an
IC?  Great, change it.

CONCLUSION:  A stock single pass IC is a Good mod for a stock k26 operating
in it's designed MAP.  The ease of installation, low relative cost is
attractive.  A read of my IC efficiency post shows that given a baseline IC
your efficiency gains going to a "more" efficient IC has diminishing value as
the baseline increases.

Going ALL OUT for Density?  Ok, btdt, it's only a wallet away.  Want a good
solid k26 turbo car.  Go 2.0bar computer, single pass IC, and do the exhaust
work, cat back.  The gains beyond that B4B increase at a lower rate for more
dollars, btdt2.

"Yanking" without the baseline?  Propwash...  :)

Scott Justusson
'87 5ktqwRS2
'87 5ktq2GO
'86 5ktqw
'84 Urq

```