[Blown353]

If it's a centrifugal supercharger application you want mount your bypass BEFORE the intercooler. That way you aren't moving a large volume of heated bypass air through the intercooler under non-boost conditions, which will heat up the intercooler. At low speeds (low airflow) this can quickly heatsoak an air/air intercooler.

This isn't a real concern with turbos as the airflow is in proportion to engine load and not RPM, so at low load you aren't moving a ton of "unused" hot air through the intercooler and the heatload issue won't be as pronounced.

The ideal spot for the bypass valve is just prior to the point of restriction (i.e. the throttle blade) that way there is no flow-reversal in the piping when the throttle plates close-- but it isn't as big of a deal as everyone makes it out to be. Put it where you like it... but in the case of centrifugal supercharging it's beneficial to take the cruising heatload off the intercooler by putting the bypass before the intercooler.

Moving the bypass valve from after to before the intercooler on a centrifugally supercharged car with a water/air intercooler that I helped configure & tune was worth about a 15 degree drop in intercooler water temps at a steady 60mph cruise. With the bypass moved to before the intercooler the hot air from the supercharger was no longer constantly moving through the intercooler at cruise.