Exhaust manifold gasket for a 340

[elan71]

Hi
I need a new exhaust system for my 71 'Cuda 340. I'll go to a stock system with manifold.
Now I need new manifold gaskets and don't know which one is correct. There are different dimension like 1.30"x 1.80" or 1.00" x 1.60".
Engine cast code is 2780930-340-3, manifold will be 3418621 and 3418623.
Which one is correct?

Daniel

[Skdmark]

Most likely you need the larger ones. Measure the exhaust openings on your heads to be sure.

If the mounting surfaces of your exhaust manifolds and heads are clean and flat, go without a gasket.
From the factory there was no gasket used

[Cudajason]

Most likely you need the larger ones. Measure the exhaust openings on your heads to be sure.

If the mounting surfaces of your exhaust manifolds and heads are clean and flat, go without a gasket.
From the factory there was no gasket used

agreed!  I used a skim coat or Copper RTV and have not had a leak in 2 years!

Jason

[Chryco Psycho]

I agree no gaskets unless you like changing them . just a thin coat of Ultra Copper RTV

[1 Wild R/T]

340 actually used a heat shield on the drivers side...

https://www.buymoparpartsonline.com/oem-parts/mopar-shield-340-exhaust-manifold-p2946105?origin=pla&gclid=Cj0KCQiAnKeCBhDPARIsAFDTLTLNHeY7un46GsElobFCD4OmsMsik1z1vXCVtXbxE4D4J7KGmUspmwMaAl1sEALw_wcB

[Skdmark]

340 actually used a heat shield on the drivers side...

https://www.buymoparpartsonline.com/oem-parts/mopar-shield-340-exhaust-manifold-p2946105?origin=pla&gclid=Cj0KCQiAnKeCBhDPARIsAFDTLTLNHeY7un46GsElobFCD4OmsMsik1z1vXCVtXbxE4D4J7KGmUspmwMaAl1sEALw_wcB

Didn't think the heat shield was used on the 71 and up manifolds like OP referenced.
Wasn't the driver's side heat shield for the earlier HP manifold to save your plug wires and not really meant to be a gasket?

[1 Wild R/T]

340 actually used a heat shield on the drivers side...

https://www.buymoparpartsonline.com/oem-parts/mopar-shield-340-exhaust-manifold-p2946105?origin=pla&gclid=Cj0KCQiAnKeCBhDPARIsAFDTLTLNHeY7un46GsElobFCD4OmsMsik1z1vXCVtXbxE4D4J7KGmUspmwMaAl1sEALw_wcB

Didn't think the heat shield was used on the 71 and up manifolds like OP referenced.
Wasn't the driver's side heat shield for the earlier HP manifold to save your plug wires and not really meant to be a gasket?

Yup.. Missed the 71 part...

[elan71]

Thank you for all the replays.
Without gasket, well, I learned it the other way with European classics, but, hey, your are the expert and have the experience. Let me try it.
How tight are the screws then tightened with the sealant?

Daniel

[Skdmark]

According to the FSM it looks like 20 ft/lbs. If you have not done it already,  download the service and parts manuals from the resources section of this site. Always handy to have.

If you are swapping them out I would highly recommend installing with new hardware . It is a combination of studs and screws. Studs are used where water passages are located and should have sealant on them.

https://www.rosevillemoparts.com/product/exhaust-manifold-hardware-kit-70-74-318-360-71-73-340-v8/

[anlauto]

I always use the Fel-Pro exhaust manifold gaskets that come with the engine rebuild kits (or sold separately)....but I always trim the excess off to make three separate gaskets instead of one long ugly one....Haven't had any complaints about them leaking...

[elan71]

Thank you for the feeback Skdmark.
Yes, I have the FSM. I have to read it, for the next time.... 

Thank you anlauto, will check it.

[Skdmark]

 

[340challconvert]

I always use the Fel-Pro exhaust manifold gaskets that come with the engine rebuild kits (or sold separately)....but I always trim the excess off to make three separate gaskets instead of one long ugly one....Haven't had any complaints about them leaking...

I used the nos heat shield on the drivers side and trimmed the gasket as you suggested on the right

[Chryco Psycho]

I never use gaskets with manifolds as they always blow thru eventually , with the exception of the 68-70 340 left side that protects the spark plug leads