The question came after reading Aggressive Ted's "setup for torque and mileage" on the Engine Build Matrix. How many of you are milling the head,porting,polishing and gasket matching but keeping the stock size valves? The oversize valves are something like 5% larger so is this a modification that pays off mainly at higher rpm and is possibly better suited at the drag strip? What would be the HP difference between identically prepared heads the only variable being the larger valves? Thanks, Wayne.

i have worked with both,the question is money, if you are going to do a complete head job you will see the benefit with bigger valve and a bigger than stock cam. whether you go with stock or larger valves a 3 angle job and pocket porting and gasket matching is a must. i like to take as much off the block to increase compression rather than the head surface. as for hp improvements it be alone while but when i went from stock to over size valves my car went from 15.0ets to 14.7ets 1/4mile.

Thanks TLJ, I am trying to do this right the first time! I have much more experience with V-8's but the slant six has really caught my interest and has helped me get through this winter that seems to never end!!

The big benefit with the o/s valves that they give you the chance to rase the seat higher into the chamber.
Over time and after a few valve grinds, the valve seat recedes into the port pocket and that hurts flow. Using oversize valves gives you the opportunity to get the valve seat out of the pocket and back to the edge of the chamber roof.

Valves that are 'standing high' in the combustion chamber also reduces the chamber's cc volume, which bumps up the engine's static compression ratio.
In my mind, if you have to buy replacement valves, you may as well spend a few extra $$ and install the oversize valves.
DD

Doc, I would like an advance copy of your new book, "Everything You Always Wanted to Know About the Slant Six" *But Were Afraid to Ask.