273 / 318 Exhaust Manifold Question

[superstock64polara]

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.

 

[George Jets]

318 with stock cast exhaust manifolds gasket matched with TTI 2.5" dual exhaust, performs nicely.

 

[MOPAROFFICIAL]

• Everything works better when matched. Headers however will scavenge better , something your manifolds don't really do

 

[pishta]

exhaust is under pressure when it leaves the cylinder, lots of it! Itll find its way out even past minor obstacles. Suppose its better to have a larger exhaust port on the manifold side but matched would be better than hogging one side out. Id not mess with 273/318 manifolds if you got headers, especially in a 67+ chassis.

 

[George Jets]

Headers dump a lot of heat and noise up into the engine bay, plus are a pain to work around and leaks are common.

The hot high pressure exhaust gasses exit the cast exhaust manifolds into the large 2.5" Dual Exhaust, that is where the hot gasses go into expanding all the way out to the back. The big 2.5" exhaust system is what does the exhaust scavenging for you, keeping your engine bay clean and your ground clearance high.

Plus you already own the nice A Body cast manifolds. Blast them and high temp paint them silver, will look nice for a long, long time.

This is the good stuff. ^^^

☆☆☆☆☆

 

[superstock64polara]

Headers dump a lot of heat and noise up into the engine bay, plus are a pain to work around and leaks are common.

The hot high pressure exhaust gasses exit the cast exhaust manifolds into the large 2.5" Dual Exhaust, that is where the hot gasses go into expanding all the way out to the back. The big 2.5" exhaust system is what does the exhaust scavenging for you, keeping your engine bay clean and your ground clearance high.

Plus you already own the nice A Body cast manifolds. Blast them and high temp paint them silver, will look nice for a long, long time.

View attachment 1715917238
This is the good stuff. ^^^

☆☆☆☆☆

Thanks George Jets, that's a nice looking mill and engine bay. Some good advice there also, I might just do as you have done, gasket match and paint the manifolds. I'm concerned that the Flowtech headers I have will hang down very low on the driver's side.

 

[George Jets]

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.

View attachment 1715917205

Just looking at your Commando Exhaust Manifolds, looks like they are more like the performance manifolds for the 4 bbl Commando engines vs the smaller port 2 bbl engine exhaust manifolds.

Kind of likes these pictured here for the 273/340 performance engines.

 

[superstock64polara]

Just looking at your Commando Exhaust Manifolds, looks like they are more like the performance manifolds for the 4 bbl Commando engines vs the smaller port 2 bbl engine exhaust manifolds.

Kind of likes these pictured here for the 273/340 performance engines.

View attachment 1715917277

I didn't think there was difference between 273 4BBL and 2BBL exhaust manifolds...

 

[George Jets]

I didn't think there was difference between 273 4BBL and 2BBL exhaust manifolds...

Look at the sweeping flow of your Commando manifold, looks like a Stock 340 performance manifold.

Then look at this standard A Body manifold on this 72 Duster 318, it is not the 340 manifold, just the standard manifold.

The shape and the way your's kicks out looks like it will deliver more performance. So Yeah, you do have some nice Commando manifolds On there.

Any chance you have a better picture of what your passenger side exhaust manifold looks like?

 

[superstock64polara]

Look at the sweeping flow of your Commando manifold, looks like a Stock 340 performance manifold.

Then look at this standard A Body manifold on this 72 Duster 318, it is not the 340 manifold, just the standard manifold.

The shape and the way your's kicks out looks like it will deliver more performance. So Yeah, you do have some nice Commando manifolds On there.

View attachment 1715917320
View attachment 1715917321

Live and learn man, thanks!

 

[George Jets]

Here is a set of 340 performance exhaust manifolds for comparison to what you have on your 273 now.

 

[George Jets]

Just kind of wondering if someone put 340 exhaust manifolds on your 273 4 bbl Commando or if those are the stock 273 4 bbl Commando manifolds?

Don't Know ???

 

[superstock64polara]

Just kind of wondering if someone put 340 exhaust manifolds on your 273 4 bbl Commando or if those are the stock 273 4 bbl Commando manifolds?

Don't Know ???

George Jets, my manifolds aren't the same as the 340 HiPo manifolds. My RHS manifold is somewhat similar, but has smaller ports and the LHS is different to the 340 stuff. Mine are the same as the image below:

 

[George Jets]

George Jets, my manifolds aren't the same as the 340 HiPo manifolds. My RHS manifold is somewhat similar, but has smaller ports and the LHS is different to the 340 stuff. Mine are the same as the image below:

View attachment 1715917461

OK thanks, looks like you have a matched set there, they probably came stock on the 273 Commando 4 bbl.

Being you have the bell fittings for the exhaust pipe instead of the flat flange tells me what you have there.

That last picture I Put up on the 340 manifolds were like 1973 version, so that is one reason the passenger side looks different than yours.

It's all good, just wanted to understand what you have going there.

_______________

My friend's 72 Duster with a '69 Stock Built 318, 9.2:1 compression , newer 302 closed chamber heads and a 340 cam. All mopar parts on the build including the LD4B intake manifold. Has the Edelbrock 1406 4bbl carb.

That big exhaust system is one of the major parts of the build that makes it really perform, with the cast manifolds on too.

Goes like a son of a gun, need to keep both hands on the wheel when you put your foot into it. It Goes . . .

 

[George Jets]

Also just looking, do you still run the passenger side exhaust manifold butterfly? Those can stick and restrict the exhaust flow.

We cut those out and weld the manifold holes shut. Then there is no chance of that restricting the flow.

May be one area for you to simply gain some more power out of your 273.

 

[superstock64polara]

OK thanks, looks like you have a matched set there, they probably came stock on the 273 Commando 4 bbl.

Being you have the bell fittings for the exhaust pipe instead of the flat flange tells me what you have there.

That last picture I Put up on the 340 manifolds were like 1973 version, so that is one reason the passenger side looks different than yours.

It's all good, just wanted to understand what you have going there.

_______________

My friend's 72 Duster with a '69 Stock Built 318, 9.2:1 compression , newer 302 closed chamber heads and a 340 cam. All mopar parts on the build including the LD4B intake manifold. Has the Edelbrock 1406 4bbl carb.

That big exhaust system is one of the major parts of the build that makes it really perform, with the cast manifolds on too.

Goes like a son of a gun, need to keep both hands on the wheel when you put your foot into it. It Goes . . .

View attachment 1715917464

Okay, now you've really peaked my interest. I love the 273 Commando in my Barracuda, however it's a little soft on torque. The hot ticket apparently, is to use a 318 short motor and transfer all the 273 HiPo top end over to the 318. The 273 heads are 920 which are closed chamber and similar to 302's, and I'm running a Comp XE262H camshaft. I'm hoping something like this would run as well as your buddy's 318.

 

[George Jets]

What do you have for wheels and rear gears?

8 3/4 rear end also?

 

[George Jets]

Looks like you have a good combination of parts there on your 273 build. That should be a good performance package the way you have it set up.

Looks like an Edelbrock or Carter carb you have on there and the factory single plane 4 bbl intake manifold.

 

[George Jets]

The good 318 short blocks were '68 and '69 that had the factory 9.2:1 compression ratio, with the flat top valve relief pistons on full floating rods.

Getting hard to find them anymore that don't need a bore job. Those factory flat top pistons sit. 040 ths in the hole.

Other 318s are the low compression engines, hard to get the good kick out of them.

Think you have a good combo there with your 273, couple things you can do to bring the whole car around yet.

 

[superstock64polara]

Looks like you have a good combination of parts there on your 273 build. That should be a good performance package the way you have it set up.

Looks like an Edelbrock or Carter carb you have on there and the factory single plane 4 bbl intake manifold.

I would like to keep it stock appearing with the exception of the intake manifold. While the low rise single-plane is cool, I have an Eddie Performer dual-plane which will work better. My Barracuda's a Formula S 4 speed car with a 3.23 geared 8-3/4" sure grip rear

 

[George Jets]

OK the 3.23 gears in the 8 3/4 are a good snappy gear set for running around town, yet still get up to speed out on the highways. So that's good.

Single plane intakes are not real good on low end torque, dual planes are better for low end.

Here is the thing with your 273 and heads. Intake manifold bolts go in at a different angle than the newer aluminum intakes and newer 318 heads.. Then you have port runner size most of them large port. So then you get a miss match at your head ports.

Your single plane is port matched to your heads now and bolts up properly. So I would think I would stay with your factory port matched single plane for the smooth port flow that is already established with those parts.

The LD4B intakes are perfect for the 318s but the bolt hole angles are off for the 273.

Maybe a little carburetor Increase would give you a little more fuel or just re-jet it. And some different Springs in the distributor to help the timing to come on sooner may help too.

Still running a points distributor? Those are fine, just want the points clean and set right.

Do you have mechanical valve train, if so that needs to be adjusted again, that can give you a power boost.

 

[George Jets]

Here is an area of the car that you can gain some pickup and performance that most people don't think about.

It's the rotating mass of the wheels. Steel wheels are heavy, aluminum wheels are quite a bit lighter and the Torq Thrust II wheels are super light.

The thing is there can be almost 20 pounds difference in weight between Steel and Aluminum wheels. Take that times 4 and you have 80 pounds of rotating mass to spin up every yime you take off from a stop light and 80 pounds to slow down when you want to stop.

Noticed this huge difference in performance on my '69 Satellite when I switched over from the factory steel wheels to the Aluminum Torq Thrust II wheels, powered by a 1969, 318, 4bbl, 727 auto and 2.94 gears.

That B Body scooted around just fine with that stock 318 powering it. The light wheels helped to make it all happen.

Had these Aluminum Slots on my '67 Dart.

Cragar chrome 5 spoke wheel are real heavy wheels.

Maybe a lighter wheel package can help you get over the performance hump?

 

[furrystump]

So I realized an improvement port/gasket matching the 340 manifolds. My heads are pretty close to full tilt effort porting, so there was a step down to the manifold. Ceramic coating helps keep the heat out of the engine compartment. The stock port shape is “challenged” so an even transition is important.

 

[George Jets]

Just studying you car build on what came stock on the '67 273 4 bbl Commando, in your '67 Barracuda S.

Thinking that should have been a factory 10:1 compression ratio engine with 273 closed chamber heads.

Unless of course you changed the pistons at the time of your rebuild?

Also wondering if you installed the new cam straight up, or did the 4° advanced thing?

'67s came with a larger Single exhaust, muffler and resonator. 50 year old system. Thinking you could improve greatly with a full dual exhaust?

 

[toolmanmike]

Just looking at your Commando Exhaust Manifolds, looks like they are more like the performance manifolds for the 4 bbl Commando engines vs the smaller port 2 bbl engine exhaust manifolds.

Kind of likes these pictured here for the 273/340 performance engines.

View attachment 1715917277

For 273's there is no "performance manifolds". The 2 and 4 barrel manifolds are the same.