I purchased a 400 sbc complete and disassembled. All the machining has been done, etc, etc..However I decided to disassemble the heads to do some porting and polishing. That is when I noticed that even though both heads ARE for a 400 (the steam holes are there) the casting numbers are different. One head is a 333882 and the other is a 3998997. I looked them up online and they both have 76cc chambers, and are for a 400 block. But my question is this. Will the two different heads somehow affect the performance? I have never used mismatched heads before and I am not sure if it's advisable. Any comments would be appreciated.
I really hate to burst anyone's bubble, but I feel it is important for you to be aware of one thing. The 882 head is a 75-later head-----------------NOT GOOD.
I don't know how much you may be familiar with SB heads, BUUUUUUUUUUUT, 74 was the LAST year for "good" production SB heads. Beginning in 75, Chevy started cutting corners on the SB heads, and by 77 they were basically junk. The castings became thinner, they got 2 exhaust crossover passages and some of the water jackets had been eliminated. All of this contributes to head cracking. If that 882 head is not cracked now, there is a VERY GOOD possibility that it will after you spend your time and hard earned money having it rebuilt. Depending on the casting date of your 882 head (75 or 76), it could be a marginal head. But, if it has a Aug 77 or later casting date, I would discourage anyone from using it.
The 997 head will likely have a 71 to 74 casting date, and should be a very acceoptable head to use. The 997 heads were among the last of the heavier, thicker, stronger castings.
Also, it is not readily recognizable, the 882 and 997 heads do have a different shape to the intake runners. Now, just how much this may affect performance on a street engine, I can't say. Probably not too much, but it would certainly have an effect on a healthy performance engine.