My '03 Trailblazer 400 won't accept the Aaen or HPD exhaust, the head pipe on '03 to large. The main jet was a 240 and needle raised all the way stock. Lower clutch rpm engagement than my '00 had and friends '02 400 Scramble. The exhaust pipe inside is about 1/2 inch larger than the other years. This quad ran a lot better than the '00-'02 models. Anyone know all the changes for '03 400 2-stroke engines.

 

I wonder if they put bigger ports in the piston to handle more air flow and had to make the exhaust port bigger ?

 

And I wonder if you put a 600cc triple Polaris in your Aaen quad?