I experienced what Greg mentioned about big headers on the dyno. I quit drag racing in 1980 and went dirt track racing. I had a 358" methanol burning, Hilborn injected engine on Carroll Caudle's dyno, and tried a set of his 2" dyno headers just for grins. My thinking was if my 292" C/SM Camaro liked 2" headers (It did. Thanks Garly), so this 358" should. On the dyno it did, it was up everywhere, as much as 40 ft lbs. Bought a set for the car. It was just plain lazy. My driver said it felt like he was towing something. Finally listened to him and put the smaller ones back on it and it stepped right back up.
Guess we don't race dynos, right?