How much HP gain do headers have compared to HP manifolds?
440 6 Pack with MP purple cam .468 lift. The drives side header is touching the power steering gear box. I wonder if that causes the seal to leak? I'm thinking about going back to HP cast iron manifolds. Thanks Don

Depends on the HP level and the size of the header tubes IMO. Why not clearance the header tube? On a stock headed engine with a small cam I would say no more than 15hp difference. Low speed and midrange torque may be down a bit as well.

Not much difference with cast iron heads and a cast iron intake manifold. Maybe a few HP at peak depending on the rest of the exhaust system. For a car like that I'd probably go back to the original cast iron exhaust manifolds as long as you still have them.

Seems to me the header will rotate away from the steering box under acceleration, so the options are:

Clearance the tube
Shim the engine mounts upward (maybe the trans mount too)
Change headers
Swap to OEM manifolds

All good comments. Clearancing the header might be my choice.
I should have said it has 906 heads ported with MP porting templates.
It has about 420 horsepower. Aluminum Edelbrock 6 Pack manifold.
I don't have the original ci manifolds. Thanks

I saw 30 HP gain on a low compression 426 Max wedge pump gas motor going from the stock M.W. exhaust manifolds to a set of Hooker A body fenderwell 1 7/8 primary pipe headers with 3.5 inch collectors on a DTS engine dyno years ago

What are the rest of the cam specs? In short, less duration/overlap will see less power loss with manifolds. In your case I’d guess 15 hp, plus or minus 5.

Andy the exhaust is 2.5" with tailpipes and delta flow Flow master mufflers. The headers are 1-7/8 tubes with 3" collectors.
Thank you for your expertise and Merry Christmas.
Don

I did a low deck 440 a few years back. 906 heads with bigger valves, Comp XE262 hyd flat tappet (guy wanted smooth idle with AC on), Edel Performer RPM intake and 91 octane pump gas. Made 450 HP with 1-7/8 headers and went 425 hp with non HP manifolds from 1973 charger.

Here is a really old article from the tech archives. My old stroker that made 550 hp with cast iron manifolds. That was a good combo.

http://www.moparts.org/Tech/Archive/bb/550hp.html

How much airgap do you think I should have between the steering box and the header tube?
Thanks, Don

Not touching, paint it silver, and use any size inline fluid cooler with cool air access/flow.

Andy thank you that's a very good article. Plus it shows me how the ci manifolds would look on my engine. Spark plugs are definitely easier to access. I like the head pipes, I would make them 2.5" to match my exhaust. I have a bung after the collector.

That's close to my combo, no ac. Thanks for the info.
Don

Thanks I will do a little heating and beating then mock ups. Then see how much gap I can get.
Don

Mopars have enough play/slop in the mounts to scoot it a little also.

Nick's Garage has done a few videos of engine dyno sessions with header versus manifolds on different combos.

My Super Bee