This is a really dumb question, but I'm asking it anyway...On the inital start up of a fresh re build, (assuming the engine has been pre-lubed etc) is it ok to run the 20-30 minutes of cam break in on open headers? I know its gonna be loud, but having an exhaust hooked is not an option st this time.
Thanks

You are not going to damage anything by running it with open headers. Just make sure you are not running it too lean and it's all good. If you are not sure that the mixture is perfect then a little rich at the outset is better than too lean.

The few times I've done it with friends this was the method of choice, actually. Maybe we all just liked making noise, but also you get a better view of what that new motor is spitting out. Hopefully nothing, it the answer you're looking for on that one- open headers will allow clear sight.

I MUCH prefer doing a startup with full exhaust and mufflers.

It's true there was a day when I preferred the noise, but that was 35 years ago. Today, if the motor is unhappy, I'd rather hear it before I see it. Seeing it generally means it's too late.

As for "stuff coming out" there had better not be any stuff coming out!

I'm with JiM. Back in the day it was tradition to ring in a new motor or out an old one on uncapped headers. Now not so much.

This is a really dumb question, but I'm asking it anyway...On the inital start up of a fresh re build, (assuming the engine has been pre-lubed etc) is it ok to run the 20-30 minutes of cam break in on open headers? I know its gonna be loud, but having an exhaust hooked is not an option st this time.
Thanks

Go for it uncorked.You can still listen for engine noise with the collectors pointed rearward.Muffled would be my choice as stated above..but not something I would sweat.
For fun..the Top Fuel dragster crews break in their builds without mufflers.:D.

i hate to do this with open headers, if you have a problem you certainly wont hear it.

Also if you are using flat tappet cam make sure you get the zinc in there

If you decide to test run with open headers I would suggest that you stuff a rag in the collectors after each run. Even though the chance for any cool air to warp an open valve is remote, it's better to be safe than sorry.

Keith