5.9L Magnum questions

273 said
Here a manifold header shootout on a stock 4bbl magnum, there's another out there somewhere that has magnums and there basically on par with 340 ones, they found the best combination to be one 340 and one magnum manifold, I forget which ones but was only better by a hp or two.

As for 273 manifolds who knows probably slightly less than 318's, only dyno test I've seen was a set of tti headers gained 10.8 hp on a stock 273 Commando.


Horsepower
RPM318360340SHT1 58tti1 34
2500186185187189187189187
3000223223225226228228226
3500269271272276280281279
4000299301306307314318312
4500311313315321319326321
4600211314315320317327319
5000303304308315312316311
5400281291289295282296289
Legend318:Stock '69 A-Body exhaust manifolds with 24-inch extensions360:Stock '77 360 iron log-style exhaust manifolds with 24-inch extensions340:Stock '70 340hp exhaust manifolds with 24-inch extensionsSHT:Hedman 151/48-inch-tube shorty headers with 24-inch extensions 1 58: Hooker Competition 1 58-inch ceramic-coated header tti: Tube Technologies Inc. 1 58x1 34-inch chrome step header 1 34: Hooker Super Competition 1 34-inch header; bare, uncoated

https://www.motortrend.com/articles/mopp-0307-installing-exhaust-headers-into-300hp-crate-engine/
Click to expand...

That test was pointless. The stock cam doesn't even have lobes (exaggeration, but close) so the exhaust isn't the limiting factor and this didn't show anything. They should have done the test with the 380 HP crate motor not the 300 HP crate motor. Completely worthless test.

If it was me, I would look for a big outlet early PS Magnum manifold and a later 340/360 DS manifold. Generally the '73/74 freeflows are cheaper ($300?) and if you are lucky you can find the magnum manifold for $12 at a Pull and Save. Then compare those costs to the cost of headers. If the manifolds are significantly less, run them and accept whatever HP loss they have.

Note, I am assuming the later freeflow manifold fits the DS of an early A. Maybe that is wrong?