I am tracking down a hot misfire on my 400 that may be a sticking valve (accompanied by a lifter tick about in time with the misfire), so I need to check valve operation. However, this only happens once the engine has been loaded and worked a bit, so I need to run it a while open.
Do the 400s tend to gush oil all over without the covers or do they keep it in the heads? This is in a van so sprayed oil would be in the interior of the truck.

 

I don't know, but I'm subscribing to see what others say. My guess is that Tim Meyer would know.

 

I cut the tops off of some 302 valve covers one time when adjusting the valves while it was running...old school way...lol, didn't spray to much oil but with no valve covers the problem is the oil draining back down often builds up and runs over the rail, that hitting the manifold/header will make a smoke train!!!

 

Ditto............

 

Yes, oil is going to go everywhere.

 

yep its messy

 

I also cut off the top part of some after market (junk, BTW) valve covers - at the top 4 bolt holes. I then welded the top onto the bottom, making it higher. I had to beat the top part a bit to make it conform to the bottom. I then scuffed the gasket side of the v/c, put some black RTV on it and attached the rubber gasket to it so it would stay on after repeated use.

They worked well until I goosed it a bit - I have roller rockers - they spewed some oil out, but not too bad. I think the oem stamped steel rockers would work better - they have the little oil guard on the bolts.