Project 6-71 340 Demon

Mad Dart said
I disagree. That block will take 8PSI Easily without any 4 Bolt caps. If the 4bolt caps are Aftermarket it will actually weaken the block in those areas when you drill for them. A Girdle is also a Myth though it may make you feel better, it does almost nothing on a SBM. Most of the big engine builders "YES even the ones on this site" do not drill their blocks for 4 bolt mains or use a girdle on their radical small block builds.

I know of a guy that built a SBM with over 20psi, stock block & Crank that wound it up to over 7K and made over 900HP at the wheels. It lived no problem for a very long time. It is all in the tune.

Use studs on the mains. Studs on the heads with Cometic gaskets and you will be good to go. If you get worried about Detonation throw a Meth Injection kit on it. That blower would probably love some cool mist sprayed through it!:D

The boost isn't the problem, it's the 600 ft pounds of torque and the stress from the blower that will cause the mains to fail. You talk to anyone that has built a blower motor, and they'll almost all say the same thing, a girtle is a must with a small block with that much torque.

Coyote Jack said
I've never used studs in an engine before. One of the things I heard is if you go to studs you have to get the mains align bored to match them. It didn't make sense to me as the bolts or studs don't actually touch the caps on the sides only on the vertical. Hope that makes sense.

Jack

Unfortunately, you shouldn't of had it line bored, or any machine work done till you had everything needed for the build. Studs and a girdle is something that I wouldn't leave out if you want the engine to last, and if the girdle is installed correctly, you'll need to have the top of the caps machined to match so you can pre load them when the girdle and main caps are torqued down.

There is a lot more to a blower motor than people realize, you'll find yourself redoing some things as you go.

One other thing you'll have issues with is cooling, an Edlebrock water pump and a set of aluminum heads will be the best money you can spend.