exhaust backfire

OK this is a "Brain Tease" trying to figure this one out.

A 2 beer problem . . .

So to start with you probably have a performance solid lifter cam with adjustable roller rockers. A performance cam that comes on at 2500 rpm and peaks at 7500.

Giving you have a lope at idle, which means that intake and exhaust valves are open at idle waiting for you to rev it up to 2500 rpm so the flow through the cylinder can work efficiently then.

Starting my second beer now . . .

So if this is the case the open valves at idle present the opportunity to introduce unburnt fuel air mixture into the exhaust. This is half of the Bang Backfire equation.

OK next it is only happening on the passenger side, same side as the leaky header at the head mount flange.

As the pulse of the expanding gasses make it past the header flange down the tube to the collector 2,4,6,8; 2,4,6,8 . . . This creates a suction (or vacuum) at the headpipe flange area where the leak is allowing atmospheric air to get sucked in to meet up with the hot expelling exhaust gasses.

Just the right conditions and it produces a Bang, burns all the unburnt gases out of the downwind exhaust. Then 5 -15 seconds later the fuel air mixture in the exhaust builds up again and Bang ! Backfire again, repeat, repeat, until the rpms pick up and the cylinders and the cam start burning more efficiently.

Like one of the guys was saying the header flange leak is allowing air into the exhaust creating a flashpoint for the exhaust gasses to go Bang, instead of sending them down the exhaust pipe out the back like the driver's side is doing.

Willing to bet you do not have an H-Pipe or X-Pipe exhaust, this straight through dual exhaust allows each side of the exhaust to work independent of the other.

Hope this helps.

Dang I need a beer . . .