[s-cars] DahlBack Racing BYpass Valve, why not two.

[mlp qwest]

Trevor -

I'm making some guesses here, but in that @3.5 x 12 ='s @ 42 "gross" sq
inches you will (? should) have @ 15 x 24" charge air passages?  Yes/No?

By that measure, you're probably running, at least in the "gross" numbers
sense (sorry Hap), the biggest side to side (24" IC flow path) IC that I
know of on the lists.  Most of the competing side to side FMIC's I know of
are using either a 3", to a 3.5" to a 4" thick x 10" maximum height cores,
all of which end up working out, IIRC to roughly 12 charge air passage ways
crammed in that 10" height limit for, take your pick, either 30, 35 or 40
square gross square inches of flow face.

At @ 4"x 10" Hap's going to be close, but he's down 3 charge air tubes to
your configuration.  OTOH, IIRC Hap's sized core, which was originally a 12"
tall unit, possessed of 15 charge air tubes, was, based on Garrett's IC
specification sheet, supposed to support 520 bhp with less than a 1.5 psi
pressure drop across the core.  Garrett's 3.5"x12"x24" cores were spec'd for
either 480 or 500 bhp, @, I think < 1.5 psi loss.  I don't recall exactly.

Just using Garrett's numbers for a 15 charge rows x 4" thick x 24" long very
densely internally "turbulated" core construction, my guess is Hap's should
have 12/15ths of 520 bhp with less than a 1.5 psi loss across the IC, or
breathing capacity for a minimum of 416 bhp @ < 1.5 psi loss, before he
starts to push a 4" IC's flow capacity past the 1.5 psi law of diminishing
returns ROT ("Rule of Thumbs.")

I think the Garrett 3.5" x 12" x 24" cores were/are rated for @ 500 bhp at <
1.5 psi loss.  My guess is I doubt you should be pushing 3 psi of pressure
losses with a 15 row 2.3x12x24" core, .... unless you think you're making a
lot more than 500 bhp.  Of course that's only a bald ass guess on my part
as, as I'm sure you or some one else will point out, all of the above is a
circle jerk numbers game since there are so many core construction
variations, even with in the same general intercooler core types, e.g. bar &
plate vs. extruded tube etc.

OTOH, the only way you or anyone else can ever really know is if you can get
a differential pressure gauge & readings across the IC core(s).  I've tried
to plumb and get some raw data off a stock IC, but for some reason unknown
to me, it may be a matter of locating the pressure point pickups in some
feng shui violation, the magnahelic differential pressure gauge refused to
give me a differential pressure reading across the core.  I.e., no matter
which way the high/low side pressure feed were connected to the gauge, the
needle would attempt to move to the "left", which was off the 0 - 80 inches
of H20 scale.

You aren't by any chance running a davtron or similar gauge to track your
temperature drop &/or max  temp vs. ambient readings under heavy boost are
you?

I don't understand where you would be going with putting a pressure relief
valve on the throttle body side of the IC.  Seems to me that if the car's
gone through the work of pushing the charge air through the IC, suffering
the 3 or whatever # psi pumping loss one thinks the IC has cost the process,
the last thing you want to do is release that cooled air to atmosphere.  If
you're going to try to release some pressure in the system to avoid IC
pumping losses, wouldn't you want to do it with the hot air before pushing
it through the IC?

Mike

~-----Original Message-----
~From: s-car-list On Behalf Of Trevor Frank
~
~I was wondering with all of these bohemouth FMIC, mine is 3.5 x 12 x 24,
~and unfortunately side to side.  I suspect there is nearly a 3psi
~pressure drop or so acroos it at redline, so what about placing one
~bypass valve on the other side of the intercooler?  I was thinking about
~maybe even two, adding complexity. Possably one the "throttle body side"
~set with enough spring pressure as to only open after xx psi, nearly a
~safety valve more than a bypass.  I suspect it could even vent to
~atmosphere withought causing issues.  It may even be a feature, to
~richen up if boost get's to high.  It may also cause lots of problems.
~Any thoughts.
~