I had different results. Didn't have it on a dyno but on track results. I had Hooker Super Comp 1 5/8 headers on my 340. Went to the TTI 1 5/8 x 1 3/4 and it was a tenth and 1 mph faster.
Interesting. I’m not 100% sure the 1 5/8 headers are Hookers. I can’t see a number stamped on the flange, but the only headers of that era I know of that had the collector flanges welded on were Hookers.
They may be something other than Hookers.
I would like to test a set of Doug’s 1 5/8 headers next time and a set of 1 7/8 TTI’s.