1) Breathers that don't bottom out on the baffles.

2) Hoses OFF of the pan evac valves just vented to the bottom of the eng compartment.

If you're rings are sealed up, then the majority of the issue is that pan evac with muffs. Even the slightest amount of back pressure will cause the symptoms that you're describing.

Do you miss the old 12 second motor yet??....LOL!!