Bingo - allowing full flow will cool much better. I’ve seen this problem before - if both engines have the same symptom, I believe you’ve found the root cause.
While the wrong thermostat will create the same symptoms, I’m wondering if the engine builder used the wrong head gasket twice? Gasket material blocking the cooling ports will generate those run away temps.
I have a fresh built 383, that I bumped up to a 496, with a little help from 440 source...
Hello everyone, yes I’m another new member. I’ve got a 1970 Challenger S.E. I’ve been working on. I put the project on hold during Covid, and I’m planning on pulling the car out of storage later this year.