Flowmaster was started in 1983, so I guess right around there. It was started by Ray Flugger, originally to make California Sprint car mufflers with low noise and backpressure. I'll assume they had 40s not long after, because I remember as a kid, having uncles bringing their hotrods to family parties with Flowmaster stickers on them.
Actually several Flowmaster 40'S were left behind by Aliens after they
finished doing some crop circles in a remote corn field in Kansas in 1951.
They were not welded on properly and fell off thier craft after lift off.
The extreame noise of thier open pipes could be heard for miles.