Facatory exhaust size

[Mike1973]

1984 GMC 3/4 ton 2 WD 454 c.i.

What is the factory exhaust size, 2 1/4 or 2 1/2?

[zieg85]

 Pretty sure it is 2.5 to the muffler and 2.25 tailpipe, at least that what mine appears on my 85 C20 with factory dual exhaust (original)

[Mike1973]

Think there would be any reason why I couldn't do 2.5 all the way back?  I mean it's a stock 454, it's not like it requires some kind of precision or anything.

[zieg85]

Think there would be any reason why I couldn't do 2.5 all the way back?  I mean it's a stock 454, it's not like it requires some kind of precision or anything.

I am going to do it when I get my 85 back on the road

[Captkaos]

No reason not to at all.

[bake74]

     You will not have any back pressure running 2.5" all the way back, it might help your truck run a little better, not much but some.