454?

[Taylorman]

Is the gen IV the most common bbc. im starting to look for parts to build a bbc and need to know which one is best to build. im assuming its the gen IV. Also, is rectangle or oval port heads better?

[Shallow Minded]

just from my own experience, Gen V's seem fairly tough to find. I think the Gen IV's are a little more common. Might be easier to track down parts, etc.

[powerplay230]

Mark IV was a generation of BBC's that were replaced by the Gen V in 1991 I think, then came the Gen V+, then Gen VI... some parts are interchangeable some are not. Some differences are posted on here- http://www.chevyhiperformance.com/te...567/index.html, also you can find some information on Mortec's site among others. The Mark/Gen IV stuff is probably most plentiful as they had a longer manufacturing run.
:hammerhea
Rick

[Dave C]

Stay with the IV. More performance parts are available for them. big, big, example is "heads"
Most aftermarket blocks like Merlins and Big M's are based upon the Mark IV, which you can increase the CID.
Although, if you want to build a 502 then get a VI. 502's are good motors. "Most" parts are compatible with the IV except the oil pan and timing cover and lifters. Cam is the same but they have a fancy groove in them that is not really necessary.
don't get a V, heads are not compatible. They say they are ...... but..... they are not.
which heads are better?... thats really depends on your application. you can start a whole new thread on this topic alone.

[GofastRacer]

Keep in mind if you're using a mechanical fuel pump, you 'll have to go with an early block!.