[ponchjoe]

Hi guys,

I am wanting to put 389 valve covers on my 73 400 heads. I am reading that you have to use a spacer for it to work. I don’t have an old set of heads around to compare so what is the difference on stock rocker arm heads that they aren’t interchangeable?

Thanks

[tom s]

depending on rockers.I have a set of 63421 HO valve covers on a set of 96 heads.Roller rockers could be a issue but I believe the 5/16 thick gaskets will help it.Tom

[ponchjoe]

Originally Posted by tom s

depending on rockers.I have a set of 63421 HO valve covers on a set of 96 heads.Roller rockers could be a issue but I believe the 5/16 thick gaskets will help it.Tom

What’s the difference in the the 421 HO covers over the standards?? I’ve read that somewhere to.

[tom s]

They have stacks for push on breathers.Same cover as a reg 63 except for them.Tom

[Sirrotica]

Between 1966, and 1967, the heads were redesigned and the valve angle inclination was changed. To keep geometry correct, the valve and pushrods were lengthened raising the position of the rocker arms in relation to the head surface to the block.

Putting the early 389 valve covers on a later set of heads will interfere with the top edge of the rocker arms, as they were designed for a lower position on the early heads. If you don't get enough height/clearance when using the early valve covers on the late heads, you'll be rewarded with a nice set of 16 dimples along the upper edge of the valve covers made from the rocker arms pushing against the inside of the sheet metal as they lift to open the valves.

I put a set of brand new chrome covers from a 65 GTO on a set of 69, 428 heads, on a 65 389, and ruined them back in 1970. That's called learning an expensive lesson the hard way.

Also be aware that if you run the late heads on an early block the scallops in the early pistons aren't large enough, or at the correct angle to clear the valves with a cam that has more lift than a factory stock cam. You will run into piston to valve interference if you try to run a cam with much more lift than .450. That can also be an expensive lesson to learn.

I'm not sure what your combination is, but that's the problems you could run into swapping early and late heads, and short blocks around. The 66-67 years being when they changed the head design. So it's not the rocker arms causing the clearance problem, it's their positioning design change.

[ponchjoe]

Originally Posted by Sirrotica

Between 1966, and 1967, the heads were redesigned and the valve angle inclination was changed. To keep geometry correct, the valve and pushrods were lengthened raising the position of the rocker arms in relation to the head surface to the block.

Putting the early 389 valve covers on a later set of heads will interfere with the top edge of the rocker arms, as they were designed for a lower position on the early heads. If you don't get enough height/clearance when using the early valve covers on the late heads, you'll be rewarded with a nice set of 16 dimples along the upper edge of the valve covers made from the rocker arms pushing against the inside of the sheet metal as they lift to open the valves.

I put a set of brand new chrome covers from a 65 GTO on a set of 69, 428 heads, on a 65 389, and ruined them back in 1970. That's called learning an expensive lesson the hard way.

Also be aware that if you run the late heads on an early block the scallops in the early pistons aren't large enough, or at the correct angle to clear the valves with a cam that has more lift than a factory stock cam. You will run into piston to valve interference if you try to run a cam with much more lift than .450. That can also be an expensive lesson to learn.

I'm not sure what your combination is, but that's the problems you could run into swapping early and late heads, and short blocks around. The 66-67 years being when they changed the head design. So it's not the rocker arms causing the clearance problem, it's their positioning design change.

Thanks Brad. It’s a 400 but I want it to look like a 389/421 as it’s going in my 62 GMC Stepside.
I have the thick reusable VC gaskets but don’t know if that’s enough

[b-man]

I’d err on the safe side and run some 3/8” spacers. Paint them the same color as the heads so they blend in.

[Gary H]

I've used the 389 style valve covers on 67' and later heads many times., even with roller rockers. Just use the 5/16" valve cover gaskets and you shouldn't have any issues.

[Tom Vaught]

I have not run the factory chrome vale covers on my 64 GTO engine for many years.
I ran the Mickey Thompson early ribbed valve covers.
Those aluminum valve covers have been on the 64 389 engine, a 68 400 engine, and a
engine with Edelbrock aluminum heads without any issues. I do run the 5/16" cork gaskets
when I can find them. They seem to seal better vs the rubber one made in later years.

Tom V.