HRD I am going to build a high compression 11 to 1 340 for my challenger, but I am not comfortable building something with compression on the ragged edge for an 27 foot rv that I will be towing a car through the mountains. I am building it to run on cheap swill, with a backup plan to run premium if required at times. If it wasn't for the sodium valves, quench, and center located spark plug in the heads am not sure I would even push it to 9 to 1.

Reliable no trouble service is first goal, then followed by mileage and increased torque. Full time premium costs just don't add up to savings at any rate. Bumping compression a point or even two from 9 to 10 or 11 to one is not going to net 30% increase in fuel mileage, but it will cost 30% more (minus whatever increased efficiency realized is) at the pump.

Those 413 heads flowed enough to make 445 ft lbs at 2000 rpm in factory trim. That with a compression ratio that in reality is less than 7 to 1. You may very well be correct about the ports, but I am going to find out what this combo is capable of doing. No comparison between the 413 water pump and cooling capacity and the regular 440 stuff.

With your 318 you mentioned, any idea what compression ratio you wound up at with those mods? Guessing it was at 11 to 1 with the block decked and heads cut that much.