I could make HUGE backfires in my Porsche before I tightened the exhaust.
My Porsche has dual 38mm 2bbl carbs and an MSD electronic ignition.
After the engine got hot, I could be driving, turn ignition off for a few seconds by turning the key to off, stomp on the pedal so it opened the carbs up all the way, and the moving pistons would suck lots of gas into the engine & then out into the exhaust. When I turned the ignition back on, the leaking exhaust manifold gaskets would let enough fresh air into the exhaust & mix with the unburned gas.
Turn on the key ... BANG!!! ... a really loud boom & a flame from the tail pipes.
That was a lot of fun to do in the tunnel at night because it echoed so much and the flame was so visible.
Since I put in new copper gaskets between the heads & the stainless steel manifolds, it doesn't leak air any more & I can't make it backfire.
My dad used to do that with his VW Bus, too ... it was fun to ride with him when he did that as he passed people walking on the side of the road! LOL