A guy that I know was cleaning out his garage last week.
He had a pair of iron BBC heads that he picked up a number of years ago at a swap meet and never did anything with. He asked me if I wanted them so I went a head and took them. They seem to be pretty clean so I was doing some poking around just to see what they were or what they might of come off. First off the heads have 2
different casting numbers (bummer). One casting number is 3964291 and the other is 3919840. I looked both of these up and as far as I can tell they both come back on heads that were possibly used on 396, 402, 427 & 454 motors during the time frame of 1967 to 1972.
Here is the information I found on them on one web-site:

Casting Year Motor Intake Exh Chamber CC
3919840 1967-69 396 2.19 1.72 Closed 106.8
3964291 1969-70 396/402 2.19 1.88 Closed 109

3919840 1967-70 427 2.19 1.88 Closed 106.8
3964291 1969-71 427 2.19 1.88 Closed 109

3919840 does not show up as a valid casting for any 454's.
3964291 1969-72 454 2.19 1.88 Closed 108

So here is my question. Lets say the heads I have come back on the castings that came off a 427 motor listed in the middle above and have the identical sized valves in each head. What do you think having one head that has 106.8 cc chamber vs another head that has a 109 cc chamber would do on a motor? Do you think you Would even be able to tell? Could it cause you problems down? Just curious to see what you guys think. Do not know if I will do anything with them just curious more than anything.

 

I personally wouldn't think it would be a good idea to run different castings on the same motor in stock form. One reason being the different cc of the cumbustion chambers would cause pressures and tempretures from one head to the other to be different causing all sorts of possible fun tuning issues, such as running different heat range plugs in one head then the other. The other issue is flow numbers, albeit they are both closed chambered heads with the same size valves they will flow different. Now if you took both heads to a quality machine shop with a flow bench and could get the cc's and flow rates of both heads equal then I wouldn't see any problems with running the two heads on the same engine. But after spending the cash to do that you could of bought a matching set of heads to begin with for the same amount, but if you got them for free then it might be worth it.


Pat Kunz

 

Take 'em to your shop and have them cc'd. You may be able to mill the biggest to match the smaller ones and as long as the intake runners are the same (should be), you'd be good to go. You really need the chambers to match if you expect the engine to run well and last.