Back east we called them cut-outs, they used the cable ones from JC Whitney, which sometimes leaked or even screw on pipe caps. I use a machined cap with a wood stove rope o ring gasket on my wheel well headers, one ss nut on each side and my blown Hemi comes alive !
In Ky. in the 60's we called them short pipes, or short plugs. The full length pipes we called lake pipes.
Out west we called 'em sneaker pipes or lakes pipes. Generally we used finned aluminum lakes caps on them. I had a functional pair on my old 56 Pontiac 'till I dragged one off on a speed bump at the DesMoines fairgrounds at the first Heartland Goodguys. DOH!
In the middle 60's my mom asked me what I wanted for Christmas. I told her "DUMPS" and she could buy them at a local speed shop one town over from us. Simon's Speed Shop in Woburn had them in his front window, the straight short ones with the 2 bolt caps, all in chrome. After Christmas I had ARC WELDING in Waltham cut into my front pipes and weld them on for a $5.00 bill. Drove home to show them to my mom, with the caps off, running open and loud on, on my '57 Fuelie and very cammy Bel Air hardtop. I was sooo happy and proud. Mom heard me from a block away. She came tearing out of the house demanding to know. "Is that what I bought you for Christmas?" She turned dark purple, turned and stormed back into the house, slamming the door behind her. I capped them up immediately.
Lakes pipes were the fancy ones with finned block off plates around here. Full length on customs, also shorties that stopped mid rocker panel and dumps that exited right behind front wheel. I had cutouts on my 48 Ford Convertible. An old guy in a nearby town welded on a section of gas filler neck with cap on each side. Simply twist off gas cap and instant noise. Charged me 6 bucks including necks and caps. Damn were those caps hot!
We called them "Dumps" also. We made them from old chevy 6 oil filter cannisters with the cap and bolt that screwed in it. Welded them on right ahead of the curve from the exh pipe, Yes they were loud.