Intercoolers-does size matter?

[Blown353]

28" x 9" x 3" will support a lot of CFM and still work very well if it's vertical flow as there is quite a bit of cross-sectional area in the charge air flow direction (3" x 28" exposed to charge air.) You get the most temperature drop and the least pressure drop by passing the charge air through a large area of core and most of the heat loss will occur in the first few inches of core height; you can keep adding core height for greater temperature drop but if you were to plot the drop of charge air temp drop vs. core height at a specific ambient air temp the line becomes almost asymptotic; adding core height up to a point will result in greater temperature drop but once you start approaching the ambient temp you have to add LOTS of core height to shed those last few degrees and that added height also means greater pressure drop.

However, if that 28 x 9 x 3 is a horizontal flow core the charge air is only exposed to a 9" x 3" area which is very little surface area and flow path for the charge air. It will not support many CFM without a huge pressure drop and that's probably why the intercooler you are talking about is rated for only 350hp; because that's all the CFM it can flow without a huge pressure drop. If it were a vertical flow core it would flow a LOT more CFM.

Example: Say you have an air inlet temp to the intercooler of 300F and an ambient temp of 90F. With a 6" tall core the outlet temp of the intercooler is 150F. An 8" tall core might drop that to 120F, and a 10" core might drop you to 100F, but a 20" tall might only get you down to 95F. As the outlet temp gets closer to the ambient temp it gets harder and harder to get that last little bit of heat out, so there is no point in going any larger than necessary to get *most* of the heat out. The bigger you go the greater the pumping losses and the more volume to fill which creates more "boost lag."

FYI, when I spoke with Gerhard at Bell Intercoolers earlier this year for design input when I had him build my intercooler (about 750 crank HP) I gave him my size constraints. He recommended a 3" thick, 27" wide, 6" tall vertical flow core for my application as a minimum size (i.e. it would cool enough to make adding an intercooler worthwhile), 8" being his recommended height, and 10" being better still, and 12" tall as being the tallest recommended due to the "diminishing returns" factor starting to take over. That is a vertical flow intercooler (3" x 27" is the charge air direction.) I ended up going with 27" x 3" x 12" for the core because the extra core height fit the nose of the car better and eliminated a tubing bend and also because if/when I build a 400" short block I'll be passing more CFM through it and could use the added cooling capacity.

FYI, here is a pic of my intercooler so you can see what I mean by "vertical flow." Most of the "ebay" intercoolers are horizontal flow which support substantially less CFM.





My suggestion would be to call someone who builds intercoolers (I really like Bell) and ask them for design & size criteria then work up something that will fit your car. Bell is reasonable on the cost IMO, excellent quality, and they had my design built and to my door in 2 weeks. I gave them all the critical dimensions (mounting tabs, inlet & outlet locations, etc) and I left the end tank design up to them-- they fabbed the end tanks with the best shapes and internal baffling per their experience for proper flow distribution and least pressure drop. Excellent guys to work with.