Leak Down Findings

Before you take that 340 apart, think. Most of the leakage seemed to be coming from the intake valves. Sounds like a valve grind is needed. Almost every motor will have some noise coming from the crankcase during a leakdown test. That's where most of the leakage is at, the rings. If it was mine........I'd pull the heads and get them checked and maybe a touchup on the valve grind will put you back in business. You probably won't notice much of a difference in power in a cylinder that leaks 20% versus 5%. I've seen engines that leaked 25% that were rebuilt professionally and only pickec up a tenth or two. A lot of money and time for a little gain. Maybe a $200 valve job will be a better bang for the buck.