I started in Corky Bell's book, Maximum Boost,
to find information on sizing intercoolers.
There are equations offerred but
much easier to use is a chart Corky provides.
Assuming 400 HP (600 CFM), your intercooler needs
to have a charge air face of about 66 square inches.
The charge air face being the inlet side of the
intercooler where the hot compressed air squeezes
through the internal turbulators. If you are moving
700 CFM (~460 HP), the intercooler should have
around 77 square inches of charge air face. Both
calculations assume medium density internal
turbulators (spacing between internal turbulators).
A. Graham Bell, author of Forced Induction Performance
Tuning says to figure on 5 square inches of charge
air face per 100 horsepower with low density turbulators
and about 8 square inches per 100 horsepower with
high density turbulators. Make sure you multiply the
result by 2. 2 to add in the area occupied by non-
flowing surfaces within the intercooler. Using this
method you can see that Corky Bell's sizing is on
the big side.
Both Corky Bell and A. Graham Bell say to favor
intercoolers having more frontal area over thickness,
especially when you have a radiator or A/C condensor
inline with the intercooler.
Neither author goes into detail about
sizing the frontal area of an intercooler.
Since the HY35 has been used on some of the Dodge/
Cummins trucks from the factory, using the dimensions
of the factory intercooler could be considered a
miniumum. I have
a 2003 Dodge/Cummins which has an intercooler sized
at 27. 5" wide by 25" tall. If you can maintain
near the same frontal area of the factory intercooler,
you should be ok. Since you are probably limited on
space, perhaps running two smaller intercoolers would
work out better?
I'd say the 27" by 5. 5" intercooler on ebay is on the
small side.
Hope this is helpful,
Paul Lohr
Attention: TDR Forum Junkies 
