Correct type gas cap for vapor system.

[MerlinsMopars]

My challenger only has the filler neck vapor line but being a 71, I assumed it originally had the vapor saver system and was changed out because of the 2 lines going to the front. 1 was fuel supply and other was the vapor line so, I installed the 4 nipple fuel tank and vapor tube which detmatt hooked me up with.
My concern is which fuel cap do I use? I have this type in the pics. Can I use it or do I need a certain type for the vapor system?
Getting real close to finishing this black beauty and whenever I am unsure of something, I always reach out here to know what is correct. Even if it's just the gas cap. Lol
Replies are appreciated!

 

[Chryco Psycho]

In 71 most used a 2 line system from the tank , one supplies the fuel & the second was connected to the valve cover breather & the gas fumes were burned through the PCV system so the cap should be non vented .
The pictures you show are I believe is a vented cap for 70 which allows air in & out through the cap in the first picture & the second is a locking version fuel cap which could be for 70 [vented] or 71 [non vented]

 

[MerlinsMopars]

In 71 most used a 2 line system from the tank , one supplies the fuel & the second was connected to the valve cover breather & the gas fumes were burned through the PCV system so the cap should be non vented .
The pictures you show are I believe is a vented cap for 70 which allows air in & out through the cap in the first picture & the second is a locking version fuel cap which could be for 70 [vented] or 71 [non vented]

It's actually the same cap. Just pics of both sides. I was thinking of just grabbing a non vented cap from the auto parts store. I assume that is the correct kind then. The rubber grommet was dry rotted and I looked for another cap like it but people listing them are asking crazy prices 500$-1000$. No way am I paying that for a gas cap. I do have the chrome fuel door also, but not the one with the seal and spring. I did put the spring type with seal on my 68 barracuda and no issues there.
I assume 71 should be a non vented cap. Please correct me if I am wrong, and thanks for the reply.

 

[EV2RTSE]

It looks like you have the right cap for a 71. They're stamped 'Pressure Vacuum' in 71 and 'Not Vented' for 70. Check with NAPA or your local auto parts store and see if you can locate a Balkamp 703-1110 cap, take the gasket from it and use it on your original.

 

[MerlinsMopars]

It looks like you have the right cap for a 71. They're stamped 'Pressure Vacuum' in 71 and 'Not Vented' for 70. Check with NAPA or your local auto parts store and see if you can locate a Balkamp 703-1110 cap, take the gasket from it and use it on your original.

View attachment 106595

Very nice info. Thanks for that info.

 

[Challenge360]

My'70 California car, with ECS has a pressure vacuum cap that is original to the car. I think you're good to go.

 

[Steve340]

You definitely need the pressure/vacuum cap.
With the Vapor Saver system the fuel tank needs to allow air in and pressure build up out.
When you remove the cap any kind of venting or hissing going in or out would point to a faulty cap.

 

[PGio]

GREAT INFO GUYS! THANKS! How do we test whether the "Pressure/Vacuum" cap is working or not?
We could have "the right cap" but if it is not functioning properly and doing its job, it's probably the same as having the wrong cap on it.