500hp 408 with Hi-Po 340 Manifolds?

Bill Dedman said
I don't know how many of you read the article I posted the link to, but I was surprised at the small differences in the horseower the test showed for the different cast manifolds.

318 manifolds................... 311 horsepower
360 manifolds.................. 314 horsepower
early (1968) 340 manifolds 315 horsepower

TTI headers........................327 horsepower

403 ft pounds 318 manifolds
407 ft pounds 360 manifolds
408 ft pounds 340 manifolds (1968)
435 ft pounds TTI Headers

Here's the link... http://tinyurl.com/pemfp5m

Looks like those '68 manifolds aren't worth much over 360s on a mild engine.The software is turning that eight in nineteen sixty-eight into a smiley face... that's not me.

For a relatively stock engine , the losses will be far less than one that has been leaned on. Allow me to reiterate.......engines are air pumps.
To make power , you need air in and out. More = more.
A FAST engine with headers and tuned for them would pick up a ton compared to slapping tubes on a 2 bbl. 318.
Now , should we get into efficiency ?
YMMV , but you will see an increase in fuel mileage with headers......if you can keep your big fat foot out of it. :D
Think of headers as Wheat Thins.........a lot of people hate them , but some think they are really good for you.