Cause of fumes entering the car is due to the position of the exit pipe with the car body.Had this with a Tvr and after adjusting the exit pipe it stopped it happening. On another point , if you are interested in having a switchable exhaust on the 3.7, Krazy Horse dealership have just completed testing their 3.7 which i have driven .
This prompted a memory. I've seen a similar situation transformed simply by expending the exhaust pipe a couple of inches.
