Intake Temp Analysis – Dyno vs Road [Archive] - SaabCentral Forums

: Intake Temp Analysis – Dyno vs Road

15th August 2004, 06:23 PM
The common complaint with a turbocharged car on a dyno is that horsepower will be lower than on the road due to heat soak of the intake air. Of course every dyno has some fans to put in front of the intercooler but it doesn’t compare to the airflow at 40-100 mph. I’ve always wondered what the intake temps looked like on a dyno and now I finally have the data to compare it.

Using OBD2 port I connected my laptop to my Saab and logged the intake temps and pressures for a road test and a dyno test. Below is a graph I made of the two different intake temperature tests.

There is a lot of information on the graph so it takes a minute to understand it all. The first things to look at are purple and orange lines, they are in the intake temps for the road and dyno respectively. First off the road temp starts much higher than the dyno intake temp. Before the dyno my Saab Started out cold, I let the engine idle just long enough to bring the coolant temps up to normal. But despite the 35 C temp difference the intake temps on the dyno surpassed the road temps by 15 C. On the dyno intake temps rose by a total of 50 C, with no signs of cooling.

Because the dyno fans are not very effective the intercooler is acting as a heat sink and not a heat exchanger. It might better for intake temps to pack the intercooler with ice to help mimic road driving temps. The only problem with this is the dyno owner’s getting angry with puddles of water on their dyno.

The graph also shows the different pressure curves of the Viggen and Aero turbos. The only difference between these two turbos is the size of the exhaust housing. Initial spool up in not comparable due to different starting rpm, but it is clear that the Viggen turbo spools up quicker but fads faster than the Aero turbo.