Headers Vs. Exhaust Manifolds

[BB 70 Challenger]

A friend of mine and a regular member here had his 489 cid (4.28" x 4.25") B Wedge dynoed both with the stock Magnum cast iron exhaust manifolds and also with headers. The engine is a very much stock looking pump gas engine.


The power numbers were:

- stock exhaust manifolds + full exhaust: 458hp/5000rpm & 520t.lbs/3700rpm torque http://3.bp.blogspot.com/_1utFs2uOvMs/SbaF6q1AD-I/AAAAAAAACj0/oq-LLmIiTEc/s1600-h/valusarjat.jpg
- 1 3/4-3" headers + full exhaust:          484hp/5100rpm & 531ft.lbs/3400rpm torque http://4.bp.blogspot.com/_1utFs2uOvMs/SbaJAY768CI/AAAAAAAACkE/amYKdT1oH2g/s1600-h/peltisarjat.jpg

So, the difference in power is something like less than 30hp and about 10ft.lbs torque in peak numbers. That is not too much? I understand that in even bigger and more powerful engine the difference is likely more, though.

[Aussie Challenger]

MOPAR did do some home work on the cast iron manifolds but headers usually give more, notice that peak torque is lower and peak HP slightly higher, sometimes a little tweaking of the jets is needed when going to headers also which can give slightly bigger numbers.

[Marquis_Rex]

The above shows a dyno powercurve under taken at Chrsyler Engineering in the mid sixties during the development of the original Gen 2 Hemi engine. The power curve is shown with and without tuned length headers (vs C body and B Body style log manifolds). Appologies- that the engine rpm axis has been cut off- but it should go from 1200 rpm to 6400 rpm which most of the original testing was done with. As you can see this changes makes quite a difference in power AND torque. A much bigger difference than some of the modern 32 valve V8 engines I've been involved with.