I just bought an 89 IROC with a 400sbc.
It has high lift cam, roller rockers, angle plug heads and a TPIS mini ram II intake system. The problem is the stock valve covers are too small, and this creates a knock.(the rockers hit the valve covers)
That is not the only noise, a couple people have listened to it, one said maybe a busted valve or a busted valve spring. Someone else said possibly a rod bearing. It doesn't miss and it runs ok except for the knock. Any advice or other info on 400's will be welcomed.

 

There's no difference between a 400 and any other small block, as far as the valve train is concerned. So whatever you know about small blocks will apply to the 400 as well.

Find out where the sound is coming from. Use a piece of heater hose, stick it in your ear, and probe around with the other end. If it's something to do with the parts of the valve train on top of the heads (rockers, retainers, push rods, etc.) it should be pretty easy to spot that way.

A possibility is that the slots in the heads for the push rods aren't long enough, so one or more push rods are hitting the head casting. Usually that will cause the end of the push rod or its seat in the rocker or both to wipe out.

One thing that very often happens with 400s is the crank hitting the oil pan.

BTW I have stock 85 or 86 L98 valve covers (with the drippers mostly ground off) on my 400 with double-hump heads, a .540-something lift roller cam, and Comp 1102 stainless roller rockers; the valve covers are about ¼" too short, so I use the real thick gaskets. I think the VCs are still smashed against the Poly-Locks.

That thing you've got ought to haul some major a$$ once you get it sorted out...

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"So many Mustangs, so little time..."
ICON Motorsports

 

Take off the valve covers and run it with those oil splash caps on the rockers. See whatcha got when it's running with no covers, and look at the valve covers for interference marks.

 

What alot of people forget is that the stock L98 heads (both perimeter and center-bolt style) have raised valve cover rails. If you use earlier Chevy heads and some after market along with the stock valve covers and roller rocker arms...your roller rockers will hit the valve covers. You will need to go with a tall valve cover.
Roller rockers on the L98 heads will not hit the valve covers because of the extra height given by the raised valve cover rails on the heads.
Hope this helps...

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N/A 406, TPIS Miniram, 58mm TB, 30lbs injectors, Custom Ground Elgin Cam, Ported TFS heads, SLP 1-3/4", & DFI computer.
11.70@117mph

 

Also, if that motor was ran with the rocker arms hitting the valve cover, you will experience damage to your valve train.
If I were you, I'd remove the valve covers and inspect the valve train. Look for bent pushrods, broken springs and retainers, etc. Have someone rotate the engine by hand and look for binding.

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N/A 406, TPIS Miniram, 58mm TB, 30lbs injectors, Custom Ground Elgin Cam, Ported TFS heads, SLP 1-3/4", & DFI computer.
11.70@117mph

 

Fast, on mine, the rockers themselves clear; however the Poly-Locks are so tall that the VCs sit down onto them before they reach the gasket rails. Although, before I ground the drippers down, certain of the rockers did hit them, but not all since the top of those particular VCs isn't straight. And you're right about the rails being raised; I wish I could somehow artificially do that to my heads! Maybe I could make some spacers out of 3/8" aluminum or something.

However, I think that the concept of valve cover obstruction causing valve train damage is a bit overly pessimistic: some little piece of sheet metal, or even cast aluminum, will be blown away a long time before the (far more beefy) valve train parts will be affected.

Also, the most common site of interference between rockers and VCs, is on the side of the VC near where the push rod seat in the rocker is. The valve covers sort of "tilt" inward there, and if the rocker is large in that area it may scrape the inside surface of the VC. This is a problem especially with low ratio rockers, since higher ratio ones have the seat moved inward toward the stud and therefore away from the VC.

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"So many Mustangs, so little time..."
ICON Motorsports