Like the title says I was curious if a strong back fire might blow a good head gasket. on initial start up I had a couple plug wires backwards and so I got a pretty loud backfire. When I pulled the themostat cap off the coolant was foamy at the top and while it was running the exhaust did seem a little white. Havent had time to do compression check yet to be sure but it worries me. Its a freshly built engine.

Is it a 4cyl? 2.8? Is it possible you have a head gasket on wrong since this is rebuilt?

Its a 3.4 I had running for awhile in the past and put about 1000 miles on it.

checked compression this morning and that is all good. Probably just got foamy from the air in the system.

If possible, i would do a leakdown test. It is your best indicator of any issue. If there was a problem with a gasket, you would see bubbles in the cooling system
troy

A direct answer to your headline question is 'NO'. A backfire is heard when fuel ignites with the exhaust ( or intake ) valve open....or ignition outside of the combustion chamber. In both cases the peak pressure will be a LOT lower than normal ignition.....with the valves closed.

[This message has been edited by Gall757 (edited 08-29-2014).]

It can open a muffler up though.