Not lookin for speed just more low end. Whats the best prop for my 18hp briggs copperhead? Thanks

Not sure whether you are aware of this, but everything in prop design/selection is a balance/tradeoff.

If the boat is already propped correctly and you go lower pitch, you typically get better low end, but slower top end. If your boat/motor combination is currently overpropped (too high pitch) and you are lugging the engine, it is possible that you could get better performance both on the low end AND high end by going to a lower pitch prop, but ONLY if you are currently overpropped.

Sometimes with a big/heavy boat one can get a better hole shot and load carrying with a larger diameter, but only if the engine has the power to handle the additional diameter. If you go too big in diameter, performance will suffer all the way around. If your prop diameter is too big, you would get more mid range and top end by going down in diameter.

Call Copperhead. They have already tested pretty much every prop size and can both sell you one for what I personally think is a pretty good price or recommend one. You could also call Hopkins which made the original Copperhead propellers (not sure who is making the current ones).