Building a 5.3, S488 turbo, I have the 862 heads and was going to port them and have 2.00 in intake valves installed. Heads are in great shape, low mileage and they've been setting at the machine shop for 6 mths waiting on the machining for the bigger valves. My question is, with the small bore, how much will I pick up HP wise with the bigger valves? I'm going to need the engine together to get everything set up in my car and I'm tired of waiting. How much HP, estimate, have people made with these heads with nice port work and stock valve size boosted? I was going to pick up some 243's and use them but they want $400 for for them and I think that's a little steep.

 

The gains you will see from the bigger valves can be offset with a pound or two of boost easily. Just saying.