I am currently in the process of rebuilding a '69 350 olds engine. I want as much power as I can get without having to rev the engine too high. This is going to be in a street car although not a daily driver.
My main question so far is should I have the engine shop put bigger valves in the #5 heads? I read somewhere that this might hurt bottom end power.
What do you guys think? Thanks for any info.

 

Short answer: Yes.

Long answer: Heck, yes. The valve size won't hurt bottom end. Valve curtain area (the circular area between the perimeter of the valve and the valve seat as the valve is opened) is always the restriction in flow. Increasing curtain area (by increasing valve diameter) is a good thing up until the valve gets too close to the cylinder wall. Given that the bore of a 350 is larger than the bore of any Olds 400, 2.070/1.625 valves can be used with no problems. W-31s used 2.000/1.625.

 

But putting in bigger valves without opening up the bowl area underneath is a waste of time and money. If done right it can add power and torque. If not then you just threw good money after bad.