Max lift with stock valve length?

It's time to start putting my '71 340 back together so it will be ready when the body/chassis work is done. Might not make sense but I'm doing an iterative build over time with different cam/head/intake/carb combinations in hopefully increasing levels of HP. I'm retiring and an ongoing project like this will help keep me out of the bars during the winter. I will be doing the majority of the work myself and I hope to learn from success and failure.

I want to start off with the stock 2.02" J-heads that were on the motor. They look to be pretty low mileage but I'll go through them and make sure the guides are good, etc. I'll be porting the heads myself and will freshen up the valve job. It was running a stock 340 cam, but I will be starting out with a solid flat tappet cam that is 242/247 @.050", .540"/.549" lift, and 109 lobe separation. With the correct head prep to lower the seal seats, will the stock length valves support this amount of lift? Springs appropriate for the cam will be purchased, maybe I need to figure out what those are first so I have the setup specs? I'm not against going to a longer valve, but to get the project rolling, I would prefer to use what I have.


Ok, I finally found my Crane catalog.

The part number of the spring for what you want is
99838.

The catalog says it’s good for .690 lift. At 1.650 it’s at 112 pounds and 1.600 it’s at 131. At .600 (1.000) lift it’s 383 pounds. It coil binds at .950 so if you net .600 lift you’d be .050 away from coil bind which is pretty spanky.

It has a spring rate of 438 lbs/inch and an OD of 1.465.

Crane didn’t make their own springs. This is really close to the spring I use that I found from Doug Herbert. Someone made this spring for Crane and I’m sure someone still has it.

You’ll just have to dig around and find them. If Doug Herbert is still up and going I’d try them first.