[s-cars] FMIC Alternatives - 1 or 2

[Djdawson2 at aol.com]

In a message dated 2/26/04 9:10:30 AM Mountain Standard Time, 
charlie at elektro.cmhnet.org writes:

> Two in series will lower the temperature more (which is what you want).


Hmmm... based on what logic?

> 
> Two in parallel will present less restriction to the air, ie: less of
>  a pressure drop across the IC's.  The temperature at the IC-out side 
>  will (roughly) be the same as the temperature in between the series
>  IC's (IC-out side of the first IC).

This is a faulty assumption.  You are basically stating that the area of 2 
ICs will only accomplish the heat transfer of one.  The enemy of a series setup 
is unacceptable pressure drop and restriction.  Based on simple 
thermodynamics, this isn't a good approach.  The enemy of the typical FMIC (long rows, end 
to end) is a low cfm rating.  Note that intercooler core flow is typically 
rated at 10psi.  Anyone on this list running 10psi?  290 cfm is the rating of the 
current core that ASW is using in their FMIC kit.  Again, do some numbers... 
this isn't theoretically adequate, even though it seems to work well in 
practice.

Back to the parallel concept.  A couple of things determine the effectiveness 
of heat transfer.  One is the surface area in the IC core.  Another is the 
type of tubes... you want "rub" if you will, air to the tube.  This "rub" is a 
balance however... too little "rub" = minimal heat transfer.  Too much "rub" = 
excessive restriction and excessive pressure drop across the IC... no good.  
Last is the charge velocity.  The faster the air travels through the IC, the 
less time there is for heat transfer to take place.  So a core rated at a higher 
cfm is a good thing.  One rated below the actual volume used by the engine at 
max rpm is not optimal.

So, if we have 2 ICs in parallel, a couple of things SHOULD be accomplished.  
For simplicity, let's assume 2 ICs of the exact same spec.  First, we have a 
dramatically increased cfm capability... two thumbs up.  Second, we have cut 
the charge velocity through the ICs in half, allowing twice the time for heat 
transfer to take place... again, 2 thumbs up.  Last, air acting as a fluid in 
this circumstance, will travel down the path of least resistance.  This means 
that the flow through each intercooler will always balance, assuming there are 
no extremely dramatic bends in the path to one IC versus the other.  To me, 
the whole concept looks like a win-win.

> 
> If they are large enough to present minimal restriction to air, with a
>  minimal pressure drop, two IS's in series will be better because of 
>  the lower final output air temperature.
> 

I seriously doubt it... but I won't know until it's tried.  Good theory often 
gets slapped in the face on the dyno...  However, a parallel setup is exactly 
what I'm going to be trying on my car... for all of the reasons stated above. 
 I will be doing baseline tests with the stock IC, then with a parallel 
setup, and finally a typical FMIC if one can be borrowed... just for the sake of 
coming up with some real data, and real answers.
Dave in CO