Headers vs. Manifolds

The age old question……. What’s the difference in power between manifolds and headers.
And the age old answer is…….. “it depends”.

I look at it this way……. In terms of the typical ohv v8……The more hp/ci your build makes with headers…….. the higher the % of loss you’ll see with manifolds.

20 or so years ago I dyno tested a friends 396BBC that he’d been running in his 68 Camaro.
The local “396 guru” had given him a “400hp” recipe, and it was underwhelming in the car.
He’d been running it for a few years and was looking for more.

It had ex manifolds on it, and he pulled the head pipes out of the car to use with the manifolds on the dyno.
It made right around 290hp STP.
A set of cheap headers was worth 35-40hp on that day.

It got a cam swap & intake swap, then it made 416hp with the headers…….. and headers went on the car during the re-install.
Huge difference in feel from behind the wheel.