[Christ]

I don't believe propane is detrimental to oil films, so it's probably a safer bet to inject it pre-boost, using a boost reference to calculate actual injection pressure/duration.

Vaporization isn't really an issue, as propane is gaseous at room temperature, and the likelihood of your post-boost air being anything short of 100degF is just moot.

To inject after the turbo, you'd be looking into higher injection pressures and longer injection durations, and you'd need everything under a high enough pressure as to keep the propane liquid until it was injected into the intake stream. You probably don't want to vaporize the fuel until it's been injected, due to the pressures you're likely to be working with in the intake stream.

You won't really need to run a vaporizer except on cold days, and it doesn't seem like you'll be wanting to run this thing in the winter anyway.

I think you'll probably get the best efficiency from a direct injection sort of setup, using the propane as though it were a diesel-type fuel, and varying the injection duration. It would allow you to go throttleless, and since you've got a custom ECM, you should have no problem tuning for it.