[vettestr]

I have run many blown engines over the years with great results. You can get away with many less than ideal engine component combinations at low boost. By get away I mean the engine will run and stay together in most cases. Low boost to me is 6 to 8 pounds with 10 LBS getting less reliable and 14 LBS will break stock parts sooner than latter.

In very general terms you can run 6 - 8 LBS with bone stock everything but need to keep fuel ratios on the richer side. You need to control the engine basics and keep your RPM down to about 5K max. Never let engine rattle or pre-ignite from hot spots, lean condition and keep ignition advance down to 24 to 28 degree ballpark. Again I think these conservative ballpark numbers can all be pushed as engine hard parts are improved.

Positive manifold pressure starts to require higher valve spring pressures, hydraulic cams and overlap are not ideal. Sealing the cylinder pressure will push head gaskets out without better clamping and gasket material. Cast pistons seem to go before a cast crank or rods fail but higher boost will find the weak link. Pre-ignition for any reason is kiss of death on high dollar parts and forget stock components.

In HS. I worked in my Dads machine shop so used engines were almost free. A stock SBC will take 8 pounds of boost all day long without a problem if you simply don't rev beyond 5K or allow any of the things that cause pre-ignition. At 12 PSI you are going to hang a valve open sooner or later if you don't run a solid cam and springs. At 14 to 15 PSI you will push the head gaskets if other stock parts don't get ya so O-ring the heads. At 20 PSI with a forged crank and second keyway added, pink rods,forged pistons, O-ringed alum heads I pushed my roller cam through the bottom of the blower and saved the left valve cover but it was cracked. I also broke the input shaft on the tranny and never knew what part broke first.