273 / 318 Exhaust Manifold Question

superstock64polara said
Has anyone ever tried to port/gasket match a pair of OEM 273/318 A body exhaust manifolds? Any noticeable difference in power?

I have a 67 barracuda with a 273 Commando mill, was wondering if I should gasket match the original exhaust manifolds or install the Flowtech full length headers I have. Ground clearance is an issue, my car sits fairly low at the moment.

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I cleaned up my 66 manifolds a bit before installing. Who knows if it made a difference. I just thought it couldn't hurt. If there was a performance increase I would guess may be a couple horsepower. The 273 manifolds, 2 and 4 barrel for any given year., are the same part numbers. Without getting into specifics, there are different casting numbers for some manifolds between 64 and 69 273's but the differences are because of design changes and not for performance. The 340 manifolds of course have bigger ports and outlets and in 72the manifolds changed again with slightly smaller ports, tubes, and outlets. From what I see in the parts books, 273/318 manifolds weren't used on 318's.
2 barrel exhaust compared to the HP 4 barrel exhaust should make a difference but there again, probably not a huge amount. I have never seen a side by side comparison there so who's to say how much for sure. A free flowing exhaust will make a difference though whether a HP single or 2 1/4" dual. I spent the bucks and put the Accurate LTD 4 barrel single system on my 66, more to be correct than for performance. It runs good but nothing to compare it to.
Same with headers. They may add 20 or more horse or torque on one engine and only 10 on the next. I put Tri Y headers on my 73 Challenger 340 car and it didn't run any faster. I didn't richen the carb or tune for them though.