I've tried a number of methods to remedy this problem; covering areas of ingress, additional air vents etc. No real improvement. I've concluded that the principle cause is the engine exhaust being too close to the main landing gear strut openings.

 The lower pressure caused by the fuselage shape and the closed canopy is sucking the smoke, and probably dangerous CO2, in like a vacuum.

 I'm thinking that an exhaust extention of 10"-12" will do the trick. Just need to get that exhaust a bit further away from the fuselage, below & behind the strut openings. This leads me to my question about modifying my exhaust pipe.

 What is the best way to go about this? My exhaust is 3.00" dia steel. Have other members simply welded on a sleeved section? Maybe a butt welded section? Are there appropriate automotive applications for this? I'm not comfortable with a simple bolt on or band clamp attachment. Also, there is the issue of adequate exhaust pipe support due to the increase in weight & arm. Perhaps this would be negligable?

 I'd like to hear how other members have dealt with this.