Big bang in a 360
 

We were finishing up a 360 install in a 71 fury pretty stock build edelbrock rpm intake, comp cams mild cam, holley 650 dp carb all timing was set up right for initial start, we got it cranking tried a few times as my buddy turned the key off there was a loud bang and one of the exhaust manifold studs shot out of the head and coolant started coming out of the hole. The only thing i can think of was either a really bad exhaust backfire, or excessive crankcase pressure.... no pcv valve or breather he had put an oil cap on both valve covers. Ive never seen something like this happen before.... any ideas?

Are you sure someone didn't tighten it ?? Are the threads stripped ?
Big bang, 180 deg out of time ?

Crank case pressure will push a gasket out. I would also bet you are 180 off and that bolt was left un tightened as well.

It was a threaded stud that was in there and it stripped everything on the way out, i wouldn't doubt he was 180 off either he didn't even do the thumb compression test. im assuming hes going to have to tap that hole now what would you guys suggest. Diamond bit tap for those cast iron heads? and some nice arp exhaust manifold bolts? And to adjust the timing to where it needs to be?

Never seen that stud come out, Leak yes or brake, never fly out. The valve covers being sealed off had nothing to do with that. Also the only way you could have preassureized the cooling system is a bad head gasket or a cracked head or block.

Im with bad timming also on this, 2nd thats a bad idea running 2 twist on oil caps. You need a PVC valve in one side and a breather in the other side. If you run just a PVC with no breather it will create a vacuum and screw your rings up.

180 out will make it back fire through the exhaust and or also the carb. Are you sure it wasn't a loud metal breaking bang?

i have never heard of such a thing either. bremereric has a point.
the timing is off.
what about the crank timing being off maybe you had valve contact and the head was damaged?