Will 340 exhaust system fit 318 (1971 Duster)

[Johnny Dart]

Its been many years since I had the 318 in that car. But I'm pretty sure that's the gasket i ran. Whatever I had, it worked.

 

[str12-340]

here are pics of my two 318s with 68-70 340 manifolds. The blue engine has original 1970 318 heads and uses CSI thick header gaskets. The orange engine has 302 heads and I used Remflex gaskets (see pics for gasket part numbers). I chose relatively thick, compressible gaskets to eliminate the potential problem of leaks and that strategy was successful. The blue motor was last rebuilt in 2013 and these gaskets were installed then. The orange motor was installed in 2021 with those gaskets and I have driven it over 15,000 miles since then.

 

[CRUZE 418]

Yeah, I don't know, these 2 pictures sort of show the difference between the 340 and the 273/318. Mine had air across the bottom of the port with the 340 gasket. Looks like you were able to get away with it. I'll just back out.
Good luck!

 

[Swinger 340]

My 71 Duster is being restored and I want to buy a full dual exhaust system that will match up to the OEM exhaust manifold. I’m currently looking at a stainless steel system at Waldron’s muffler. The OEM 318 was not available (according to employee at Waldron’s) with dual exhaust - so the company has no dual exhaust that is guaranteed to fit my OEM 318 engine/vehicle. FYI - the car has a 3-speed standard on the floor. Can anyone tell me if the OEM exhaust system for a 1971 340 Duster would match up to my 1971 318 exhaust manifold?

The output flanges on the 340 are flat and on the 318 are corned. If you can adapt that, then go for it. For me, it would be two options. Buy a set of 340 exhaust manifolds and will be good to go or buy a set of 340 headers. The headers should give you a little more HP, but take away from the stock look. Going the other way, 340 head to 318 exhausts, will not work due to the lower exhaust port will be open and would need to be blocked off someway.

 

[66fs]

... Going the other way, 340 head to 318 exhausts, will not work due to the lower exhaust port will be open and would need to be blocked off someway.

That is not true. I've run 72 340 J heads on a 273 with Early A-Body exhaust manifolds. There is plenty of meat to seal the 340 exhaust ports. I just blended the top and sides to match the 340 ports. They never leaked,

 

[5868cuda]

I have a 72 Duster with a 318. I have 1970 340 exhaust manifolds so I ordered a 1970 340 exhaust system from Waldrens and it all worked out fine. I had to add the right side muffler hanger for it to work properly. I ordered it with the chrome exhaust tips (which I had). I think in hindsight I would have ordered the stock sounding mufflers, I ordered the medium loud ones and the sound in the car is a bit loud with that drone in the lower RPM's. One more thing, I ordered Aluminized pipes, its now 5 years and still no rust.

 

[Swinger 340]

That is not true. I've run 72 340 J heads on a 273 with Early A-Body exhaust manifolds. There is plenty of meat to seal the 340 exhaust ports. I just blended the top and sides to match the 340 ports. They never leaked,

I have match them up before and I found an 1/8 inch gap at the bottom of the manifold to the exhaust port. The "J" head ports are much the same as the "X" ports. The 273 and 318 both have the smaller exhaust port as well as the smaller manifold to match. Not sure what you mean by "early A-body manifolds". Maybe some early manifolds were larger than the ones I had.

 

[66fs]

I have match them up before and I found an 1/8 inch gap at the bottom of the manifold to the exhaust port. The "J" head ports are much the same as the "X" ports. The 273 and 318 both have the smaller exhaust port as well as the smaller manifold to match. Not sure what you mean by "early A-body manifolds". Maybe some early manifolds were larger than the ones I had.

There is only one set of LA exhaust manifolds for an Early A (1964-1966) and they came on 273 engines. Ran "J" heads for years until the gas wasn't good enough to run 10+ compression ratio. Still have the manifolds, but they are on the car now with 273 heads. I never ran "X" heads on the 273, because of the 2.02 intake valves, 1.88 were close enough at +.040.

 

[Vinny]

Fel-Pro MS90460 ....... No muss no fuss.

View attachment 1716386865

What are the 2 small gaskets in the photo for? I have so many in my stash and have never used one. Thank you.

 

[harrisonm]

We have a repair shop in Topeka that does a lot of work on classic/muscle cars. They have a long and great reputation for not only doing amazing work but taking great care of the cars while they have them. It is about the only place I will leave my Barracuda and pick it up later. They do amazing exhaust work. They could easily do a good job on your car. Maybe you could find a local shop like this one to do your exhaust work.

 

[Johnny Dart]

What are the 2 small gaskets in the photo for? I have so many in my stash and have never used one. Thank you.

Good question. Not really sure, have the same stash as you. Maybe something to do with the Magnum motor ?

 

[66fs]

What are the 2 small gaskets in the photo for? I have so many in my stash and have never used one. Thank you.

They seal the tubes attached for the EGR system that bolted to the exhaust manifolds. I've never used them.