This is an important issue, because if you do not get adequate airflow across
the intercooler, your charge air temperatures will be higher than experienced
during real-world use. This means that your dyno results will be understated,
and your tune will not be correct. The biggest concern is that the additional
air density from cooler air in real world use could cause a lean condition
if tuned incorrectly on the dyno.
In general, in addition to ensuring that the engine has reached stabilized
operating temperature, the SAE also recommends duplicating the charge air
temperatures seen during actual usage. The EPA actually uses a 100 hp fan
during FTP (federal test procedures) testing, but this is not realistic for
most shops. Testing by ATI has shown that a 25 hp engine (internal combustion
or electric) can produce 60 mph of focused airflow for an area similar to
the size of an intercooler. 60 mph is the standard used by many OEM’s
when duplicating the exact temperature drop is too difficult.
Obviously any air source is better than none, and if this much power is not
available, you can also supplement available airflow with a water mist for
further cooling. Your charge air temperatures can be verified with a super-heat
pyrometer (available from Grainger and other sources for around $145). Remember,
ensuring that the charge air temperatures on the dyno are similar to real-world
use is what matters; how you achieve that temperature drop on the dyno is
up to you.
