Recently dynoed a 500 efi, customer did all engine work himself, i had nothing to do with build or assembly, just flowed and cleaned his injectors, dynoed and tuned it. So heat cycled motor on dyno, started to lean on it, massive amounts of white smoke pouring out exhaust. He refreshed it because it previously had poor ring seal and oil control. We started investigating , found most plugs almost completey fouled with oil. Turns out, when it was rebuilt the previous time somone left intake valley oil heat shield out, in most cases not a real big deal other than getting hot oil on bottom of intake. In THIS case he had factory pcv hooked to plenum, on a 500 efi the pcv pulls directly from center of manifold over the cam, without this shield in place it was literally pumping oil into the intake plenum, as it pumped oil into intake, it caused ring seal to get worse, created more crankcase pressure and forced MORE oil into intake. After we disconnected the pcv and ran it we had oil bubbling from pcv hose and dipstick would push out under a load.
we extended the pcv hose, vented the valve covers, and did a leakdown. Numbers were from 18% to 30%, gave every cylinder a good long shot of brake clean sunday morning, reran it, leakdown dropped to 12% to 18% thru motor, not great but not as bad as it was. Point here, IF you dont have that oil shield in a 500efi, do NOT run factory pcv fwiw or you will have same problem. Thought id mention it so somone else doesnt have this problem.

We saw 505hp and 520 ft lbs tq before tuning it, after putting some timing back in the tune (that somone previously took out) and getting afrs right we saw 563 hp/580 ft lbs tq, no ball of fire for having slightly worked promax heads, no pulleys or acessories on dry dyno headers using j607 but cam was something owner reused that wasnt stock but unknown lift/duration. It DID make most hp on 89 octane vs 93 and did NOT have KR at 34 degrees of total timing on top, tq curve was long and flat from 3600 to 5400 in excess of 550 peaking at about 580 at 4600.

Most all other blue motors have the PCV in the intake also and will get same results you did if the oil shield is removed.

Lots of people have dealt with this on the HP500 motors as this was a more common engine to rebuild with more performance.,

If you lose the shields they are cheap thru GMPerformance.

yes, without the oil shield motor was sucking oil into intake in massive amounts.

This motor had freshly flowed injectors that matched within 4% or so, about 1.5 pts of afr delta on top end with # 1,7 and 8 signifigantly hottest so if your tuning reading plugs look hard at THOSE!

This was with the batch fire injectors firing every revolution (set to double fire vs single fire), if set to single fire like a 502 mpi is stock those deltas are more like 2.5 to 3 pts apart fwiw!

I had similar experience last year. Builder left out the lifter valley tray and we ended up using large amounts of oil. Fast forward we relocated PCV to valve cover. Problem solved.

It it is my understanding that the lifter valley tray has to be removed when using tie bar retro style lifters. These engine originally come with lower profile dog bone lifters. We have been running without the tray for a while with no observed issues. I think the only reason for the tray is because of where mercruiser elected to put the pcv valve. Thanks.

Its there for a reason..........its beyond me why builders dont reinstall it......^^^^^ I ran the valley pan on my 540's with tie bar lifters