Possible exhuast issue?

[SinisterSilverado]

A couple months ago I acquired my grandpas '85 C10. I somehow didn't notice this until today, but it has a SI/DO Magnaflow muffler with one of the exhaust holes welded shut. The muffler also runs right next to the gas tank. He never noticed it either. I figure this is a pretty big issue, but I'm asking here just to be sure. I never take this one on the highway, but the one time I did I had the symptoms of vapor lock and now I think this was probably why. Should I get this fixed pretty soon? Here are pics.

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[towman]

the exhaust on the square bodies runs by the gas tank like the picture, as far as the one outlet being blocked off it would depend on the muffler design if it restricitng flow or not, i would assume not since the truck still runs

 

[SinisterSilverado]

I didn't know it came stock by the gas tank. As for the blocked off end, I figure it would be blocking some flow since Magnaflow advertises that straight through design. The truck also has some pretty crappy performance for having a 305 with a 700R4 transmission.

 

[Toms94z71]

I didn't know it came stock by the gas tank. As for the blocked off end, I figure it would be blocking some flow since Magnaflow advertises that straight through design. The truck also has some pretty crappy performance for having a 305 with a 700R4 transmission.

pretty crappy performance is pretty typical for mid 80's small block truck if it is still all factory, I mean how the crap to make 130hp v8s granted from what I'm reading that year with a 4bbl is rated some where around 160.