Before I put the current 409 in our car we had a decent 400 SBC in the car. When I put the car together I used some older Thorley long tune headers. After so many years they rusted out and I bought a set of Sanderson cast iron manifolds which all my buddies said were as good as the old long tube headers. Well after making the new pipes I took the car out for a test run and boy was I disappointed. The car had much less top end power and the car ran a little warmer then before with the headers. The car was quieter with the manifolds, but since I was going to put in the 409 I didn't get another set of headers. The only engine I have ever seen that manifolds work well on are LS engines, not sure why but my best friend's 2000 Camaro ran 12.36@108mph, with Kooks headers he ran 12.0@114mph, but low 12's with manifolds and a dinky y-pipe is pretty impressive. This year after the rear end swap I am taking off the 409 center dump manifolds and putting on the Doug's headers we have. I miss the extra power and you will too if you run the short ones.