[steve@tru-built.net]

I'm currently rebuilding the engine in my 68 Pontiac Firebird. The car has been in my family since 1972. My grandfather purchased it from his boss who purchase it new. It's mostly original with 68K miles and numbers matching. It's a 320 HP 350 H.O. with 4-speed car. I'm thinking about upgrading the exhaust manifolds. I don't want to go with header if possible. I'm thinking about installing a set of Ram Air III manifolds. I found a set on Ebay, but they're for 68 and 69 GTO. Does anyone know if these will work on a Firebird without issues?

Thanks,

[b-man]

They’re the wrong manifolds and won’t fit the early Firebirds.

You need the long branch style that fit the first-gen Firebirds and 1965-1970 big Pontiacs.

[68tpls400]

Look at RAM air restoration manifolds. Just like new, only better.
Google them.

[Cammer-6]

will need the oil filter adapter too

interesting car please provide more details

[Donovan]

I installed the longbranch manifolds on my 68 350HO like you are considering. The oil filter adapter is odd and will weep oil but overall a great upgrade. Dual exhaust with 2.5 inch headpipes will be a great fit and make the upgrade worth it. They also look awesome when you pop the hood. These make room for future upgrades to shine, like cam updates.

The A body manifolds don't fit and make less power in any case.

[Donovan]

https://www.ramairrestoration.com/po...c-coating.html

they also have less expensive uncoated units available.

[b-man]

The Ram Air/HO manifolds might buy you 8 to 10 horsepower at the most on a stock or near stock engine.

They’re a nice upgrade (and really mostly eye candy) but once you’re done you’re into them close to a grand once you buy the manifolds, filter adapter and the down pipes that are compatible.

Simply upgrading your exhaust to 2-1/2” and keeping the original log style manifolds might make more sense economically and will provide a nice boost in performance. PYPES exhaust sells some 2-1/2” down pipes that neck down the first few inches to 2-1/4” to match up with the manifold outlets.

The 350, 400 and 455 engines all used the same standard exhaust manifolds so it follows that the 350 would see the most flow and least restriction from them cubic inch wise.

So the same 2-1/2” exhaust system using both manifold styles might have a 5 horsepower difference. The standard log manifolds really aren’t as bad as most people think. The GTO style and long branch style are very close in performance, there isn’t a big difference it’s just whatever fits your chassis.

[rdl]

Originally Posted by Donovan

... The oil filter adapter is odd and will weep oil but overall a great upgrade...

I discovered the same thing the first time I installed the adapter. The solution was to torque the interior bolt to 60 ft/lbs (instead of the recommended 30) and use a good gasket sealant. No leaks or weeping.

[JLMounce]

Originally Posted by b-man

The Ram Air/HO manifolds might buy you 8 to 10 horsepower at the most on a stock or near stock engine.

They’re a nice upgrade (and really mostly eye candy) but once you’re done you’re into them close to a grand once you buy the manifolds, filter adapter and the down pipes that are compatible.

Simply upgrading your exhaust to 2-1/2” and keeping the original log style manifolds might make more sense economically and will provide a nice boost in performance. PYPES exhaust sells some 2-1/2” down pipes that neck down the first few inches to 2-1/4” to match up with the manifold outlets.

The 350, 400 and 455 engines all used the same standard exhaust manifolds so it follows that the 350 would see the most flow and least restriction from them cubic inch wise.

So the same 2-1/2” exhaust system using both manifold styles might have a 5 horsepower difference. The standard log manifolds really aren’t as bad as most people think. The GTO style and long branch style are very close in performance, there isn’t a big difference it’s just whatever fits your chassis.

I agree with this. It's probably not worth it on a mostly stock 350 to upgrade to the long branch manifolds.

Another thing to consider that hasn't been brought up here is IF you can get a set of long branch manifolds. RARE hasn't had a complete set available for years. I tried for about 4 years straight to get a set and was always told, "we're having more cast, should be about 6 months."

[tom s]

I think RARE is shipping D port long branch pretty good now.Its the round ports that are missing.Tom