2 1/2" Exhaust Manifolds

[00fxd]

Lets get this tech section going! I have a question. Who has an opinion of how well the original 2 1/2" outlet exhaust manifolds flow? Would they be sufficient for a mild 350 that may occationally see 6500rpm or should I go with the heddman headers for side pipes?

 

[LEEJANDZ]

What year?

Are you using AIR manifolds and subject to smog laws?



JASON *** BRAND NEW MAGNECOR WIRES FOR SALE!!! *** 1979 L-82

 

[00fxd]

I don't have the manifolds yet. I'm just wondering which to buy. I wasn't aware that 2 1/2" manifolds were available in a.i.r. configuration. The The car is a '65 with a later 350.

 

[Tom Bryant]

The 2 1/2 inch rams horns are very good flowing manifolds. If you want to improve them a little polish the inside of them and have them Jet Hot coated just on the inside for flow (if stock looks is important). I have used them for years on small blocks and they will perform well on a mild small block.

Back in the '60s when we couldn't afford high dollar headers we bought the 2 1/2 inch manifolds from Chevrolet for around $25. each and added a pipe that dropped down and curved out to the side. A lot of budget bracket racers run these. And yes they will go to 7000rpm. I had a '62 Impala with a hot 283 that I shifted at 7 grand regularly. You might have a little more resistance as you increase cubes but for a street engine with mufflers I think you will be happy.

I also have them on my '59 with the '62 Fuelie front pipes and the off road exhaust system.

Tom

 

[00fxd]

I think LEE is refering to bb exhaust manifolds. Thats what I should be workin' on.
Thanks Tom, Sounds good. I would do some port matching and clean up. Those old exhaust manifolds can be tough to grind after all the heat and all the years! The last set I ground on were bb and they were real hard in places.

Any other experiences?

 

[LEEJANDZ]

00fxd -- I'm just wondering which to buy. I wasn't aware that 2 1/2" manifolds were available in a.i.r. configuration. The The car is a '65 with a later 350.

The smog manifolds with the AIR tubes found on emission controlled VETTES.
Thats what I was referencing, since you said you had a later model 350.

True dual exhaust with a X pipe would flow better than the sidepipes.
But I am actually going to dicth my dual exhaust and put side pipes on my 79.
I like the look better!

 

[Mikey1]

327 cars do have that kinda "X-pipe" going through the intake.

On later model 350s without the crossover in the intake an external X-pipe was added in the exhaust. Yet the solution might be more efficient.....nothing to add to the sound of a sidepipe car !

 

[00fxd]

Hey LEE, your right I did mention 350. I thought I left that out. I've never seen 2 1/2s with a.i.r. fittings. Do you think they flow as well or should I stay away from them?
Of course dual exhaust with a crossover or better yet an X pipe is the best, but a lot of us don't always do the right thing when it comes to stuff like side pipes. I actually did consider a crossover pipe with the side pipes for about a nano second .

 

[LEEJANDZ]

00fxd

I actually dont know if they made the 2 1/2's with AIR.
My 79 came with AIR fittings but I dont know the size of the exhaust manifold.

I think you should go with a good set of headers and go true duals with no cats and a X pipe.
I believe that will be the best "flow" setup.

I am unaware of anyone able to use a X pipe on a sidepipe exhaust.

 

[JohnZ]

00fxd

I actually dont know if they made the 2 1/2's with AIR.
My 79 came with AIR fittings but I dont know the size of the exhaust manifold.

I think you should go with a good set of headers and go true duals with no cats and a X pipe.
I believe that will be the best "flow" setup.

I am unaware of anyone able to use a X pipe on a sidepipe exhaust.

The 2-1/2" manifolds were last used in 1965 - none were ever made with A.I.R. fittings; all Corvette SBC manifolds from 1966 through 1982 had 2" outlets. The 2-1/2" ram's horn manifolds flow VERY well. Personally, I'd use the 2-1/2" manifolds instead of all the never-ending hassle with headers - you'd never feel the performance difference unless your engine was HIGHLY modified.

 

[00fxd]

Thanks John. That's what I was hoping you'd say. Who needs leaky gaskets and hot tubes if you don't hafta?