I've heard that you can drill the steam holes yourself, using a 400 head gasket as a guide, and a drill press of course. The steam holes are sort of between the cylinders, one on either side (you can check your block to see where they are) and are VERY important to have. Otherwise, I think the heads are pretty much identical.
this can be done as previously stated by drilling the steam holes yourself, but it is imperative that it is done with extreme care. remember that engines are precision. a few thousanths off and start over. take into consideration the boost in compression your'e looking at also. depending on the build i would use forged pistons. you might need a high-torque starter to crank it also.
[ May 06, 2002: Message edited by: middspecauto ]</p>
Guys he's talking about an olds 403.I would
not try to do this(don't think it's possible).
a 350 olds yes,a 350 chev no.(actually 350 olds
heads flow better and will give you a slight
If you are talking about putting 350 chevy heads on a 400 chevy you have to drill the steam holes, but there is more to it to that. You cant just drill the steam holes straight in. The steam holes on the exhaust side should be drilled staight into the head after using a 400 head gasket to mark the holes and a punch to start it in the correct spot. The hard part are the steam holes on the intake side of the head. The have to be drilled at a 45 degree angle toward the exhaust side of the head. If you are looking at putting heads on a 403 olds engine then you need to use olds heads. The 350 olds head will work, but on some of them, one of the two dowel holes in the head are smaller than the dowels in the block, so you will have to drill them out larger. You could also look into using edelbrocks performer heads, but that is pretty expensive, and you would have to buy a performer RPM intake manifolt to make it work. Good luck in whatever direction you are going.
I forgot to mention a few other things on my last reply. If you are using 350 olds heads you will have to enlarge the head bolt holes to fit half inch bolts since they had seven sixteenth bolts in them. You will also need to drill steam holes in the 350 heads just like with chevy 350 to 400 style build. I do not know for sure if they need to be angled at all though. You might check out a sight I just came across. It is 442.com/oldsfaq/ofeng.htm and it has a lot of good advice for building a rocket of a 403. I wish I had seen it before working mine over.