Review on Doug Thorley Headers THY 343Y C Exhaust by Roy Bush

They have been on my 1997 Express since 2013. Previously, the stock 3" twin tailpipe was added a small cam, L31 marine inlet, high flow motors and dual 3"/single 4" muffler and 4" tailpipe. I also had a 0411. Bolting on the headers provided a nice torque boost. I managed to get a little more after reconfiguring the headers. I used to have short headers that were already giving some power gain over headers that broke at 70,000 miles. The move from short to three-seat models and corresponding tuning changes increased torque at the wheels to 47 ft-lbs. It has increased from a peak of 278 rwtq to 304 rwtq, but in some areas it has increased even more. At 2700 rpm it gained 43 ft/lb. Same headers on new 383 aluminum head. Headers still in great shape. Fuel consumption was about the same before and after, but with my high 3.73 gears, the tendency to downshift to 3rd on long interstate climbs was almost completely eliminated.