Why on earth are the big block aftermarket head valve cover bolt hole locations not standardized? You can see that between the EZ Heads and the TF270 there is a 0.070" difference in one set of holes! That's crazy! WTH?

These are actual numbers from the manufacturers (I have verified 2 of the 3 and the 3rd looks to be accurate also). I would like to thank each vendor for providing the information - it helped me a lot in getting my valve covers to fit.

So ever wonder why valve cover bolt holes are so big?

Not only are the locations different, but you also need to be aware that factory heads have the holes at an angle toward the intake side of the head. That means the bolt/ nut surface of some covers are not correct for some heads, as the spot-face is (or can be) at an angle not compatible for some heads.

It might have started with the OEM's refusal to share print specs, and the situation that most of the old prints are difficult to read to say the least.

Folks had to figure that out on their own, so everyone does it differently.

Thanks for sharing the info.
Together with the original factory angle, it can make things ugly.

This worked on my B1 heads

Nice to know.
From the original poster, the offset of the corner bolt holes:
Indy 0.299"
TF 0.350"
B1 0.325"

Makes me wonder if the Indy heads actually used a smaller (0.299") offset then the others.
I don't worry about 0.016" differences, as manufacturing tolerance for the location can easily be that much.
But the 0.070" difference the other poster pointed out is notable.

all things staying the same as they are now with the cover bolt hole location, what oversize hole would be needed to interchange the covers ?
or am i missing something on the prints ?
please understand i have never had any of these covers in my hand to personally inspect.
as always, T.I.A. !

That is exactly the problem. Mopar Performance (or more correctly DC since it was a long time ago) could've solved this mess 40 years ago by releasing key dimensions. After they shut down big block production they had no reason to keep the dimensions secret. Had they just published key dimensions the aftermarket would have been able to produce parts that fit correctly.

I dont think its diameter of the holes.. I think its the angle of them
EDIT
I guess my first thought was wrong.. not the angle but the diameter of each

I assume you measured the locations? If so, how did you measure - just curious? I got my B1 numbers from Scott Koffel. Your numbers vary just a little bit - I am not surprised they worked. I made the holes in my B1 spacer/adapter 0.0290" just to be on the safe side. They fit very well.

Jim - the 0.070" difference is very real. I am o-ringing a set of valve covers for a member here and he has the Indy EZ heads. The covers are unbranded cast aluminum valve covers. You can see the layout of the valve cover holes in this attachment. I tried these valve covers on my TF270 heads and NO WAY were they gonna fit. They didn't fit exactly per the numbers. I am making spacers for the TF270 heads and my trial spacer fit perfectly using the numbers TF gave me.

He also measured the EZ head bolt hole locations with calipers and you can see that it confirms the numbers Indy gave me.

When I have a chance I will measure a set of 906 heads.

i "thought" [same as ASSume ] that the aftermarket heads and valvecovers were machined to have the bolt holes at 90 degrees to the sealing surface, except the 440 stealth head, which mimicked the stock bolt hole angle.
learning new stuff is fun for me.
that is, if i can just remember when needed !
with that said, what is the "most common" hole angle, or are they ALL different ?

I drilled the holes bigger in my Indy covers. Made things much easier.

When I designed my billet valve covers I used a drawing from Cometic. The Cometic blueprint is almost identical to the Trick Flow numbers that you show on your document. I wouldn't trust numbers from Indy or B1. Trick Flow and Cometic stuff usually fits spot on.

From the numbers, it appears the unbranded cast covers (0.305") have the smaller Indy offset for the corner bolts (0.299").
Unlikely to fit on TF heads unless the holes are very oversize for a 1/4" bolt.

FWIW, The B1 original heads in my possession have an offset about 0.326". But that is using calipers and a straight edge from the other two holes, so it could be 0.005-0.010" error, IMO.

I guess we still need a "tie-breaker" to verify if Koffel's B1 heads use 0.325" or 0.350" offset for those corner bolt holes.

My rough measurement supports 0.325", but my method could have some error.
With the calipers and dowel pins threaded in the holes, with a lock nut to square it to the threads, I came up with these other dimensions:
9.596" (9.600" print)
4.046" (4.050" print)

If I didn't just square up the vice on my Bridgeport milling machine, I would use the DRO for a better set of numbers. But it needs to be out of the way to put the head on the milling table. And I am behind on several projects that need my time.

Maybe I’m missing something here. Indy, B-1, were able to develop and build a head without print specs from Chrysler.

But they couldn’t copy the bolt hole location for the valve covers? Or they had prints to do the head but no specs provided for the valve cover attachments?

My money is on the fact that the heads requiring unique valve cover attaching locations were purposely done so they could sell their own valve covers.

When it doesn’t make sense - follow the money.

Call Russ and ask him why the bolt holes are in the wrong spot. After he yells at you for 20 minutes and tells you how dumb you are and how dumb your mother is you'll forget what the question is and hang up.

I will have to check those B1 dimensions against what I measured to make billet valve covers. The ones I've made seem to fit well. I think from memory I measured off an original cast B1 valve cover.

As a few of you have said, it would be so much easier if they just released the blueprints for all of their engines. Even if there was a small fee.

I have the offset as being 0.3125" for the B1's

I will have to check to see how they look on the head.

I machined my B1 adapters to the number Scott Koffel gave me. I think I wanted to locate these tightly (I get too anal sometimes) and made the 4 inner holes .260" and the outer ones .270". The adapters fit well. So I guess the numbers I received are correct. I attached a drawing of my M/T cast aluminum valve cover to B1MC adapter - note: I know I shouldn't be referencing from the center but its my drawing made for me and I like it that way....... LOL!

The numbers from Indy for the EZ heads came right off the CNC machine - they read them off to me. So unless they changed over time, they should be accurate. I made a sample spacer and sent it to the owner of the heads - will know soon how well they fit.