I need some expert advice from all you pontiac enthusiasts. My son-inlaw and daughter have a 1972 Pontiac Lemans with the original drive train. It has a 350 and the heads on it are larger then a small block. The engine looks like a big block. Yesterday they had someone who is pontiac enthusiasts tell them it was a 350 big block, that it was rare but the 350 big block was available in the GTO, Lemans and Tempest in certain years. My kids take this car to car shows and if it is in fact a big block they would like to tell people this.
ANY INFORMATION AT ALL WOULD BE APPRECIATED.

Thanks  

the pontiac block size to my understanding is the same for the 326 350 400 455 the only small bolck is the 305 301 and no one wants those the 350 in 1972 is one of the common blocks but it is a verry good motor  

Codeman1, Sorry to burst the bubble, but a 350 in a 72 Lemans is not rare. The 350 was available from 68 - 77 and was the base V8 in those years for Tempest and Lemans until the 305 became available. With the exception of the 74 GTO, no other GTO ever came with a 350.
The Pontiac 350 is neither a big block nor a small block, it is a Pontiac V8. Other manufacturers had both small and big block motors, most notably Chevy, but Olds and Buick both had small or at least smaller block versions of their motors. Pontiac used one basic size block for everything, with the exception of the later 265 and 301 low deck motors that everyone wants to forget.
The 305 is a Chevrolet small block from the same family as the 283, 327, 350 and 400. They share no parts or design with a true Pontiac V8 other than the Q-jet carb.
Tell your daughter and her hubby to have the engine codes and numbers checked ( a Year One catalog has all the info on how to check them), if all the numbers are correct for the car, they can proudly display the car as having the "original numbers matching Pontiac 350". That way they aren't contributing to the confusion that they have experienced from people who don't have all the info.
They can also contact Pontiac Historical Services on the web for full info on how their car was equipped from the factory.
To tell the truth, I get the same line from anyone who sees my 79 Formula (with the 75 350 installed) "Oh, a big-block 350!", sometimes it's just easier to go along with it and not try to explain it.  

It's amazing how people know so little about Pontiac engine architecture, especially when they own a Pontiac. It’s a good thing there are sources of information like these Pontiac forums- when I was a kid you had to pour through thick auto repair manuals, spend days at the boneyard, and deal with cranky old guys just to get the information you needed.

I think the best way to refer to Pontiac V-8's is by their main journal diameter- the 265, 301, 326, 350, 389, and 400 motors have 3.00" journals, and the 421, 428, and 455 motors have 3.25" journals.
With the exception of the 265 and 301, Pontiac V-8s appear to have the same size externally.

Geno  

Thanks so much for your help everyone. My daughter and hubby will be disappointed about it not being rare, like they were told, but it still is a beautiful car. You guys saved them from looking stupid by telling people it was a big block.
Thanks again  

Hahahahaha... I had the same thing happen to me but at a engine rebuild shop.  I went in there and I told the guy I needed a Pontiac 350 rebuilt and the guys eyes lit right up. He told me my 350 motor was rare and sought after and he would kindly rebuild it for the price of $1,350... I passed as I found a place that would rebuild it for $1000 but yeah I get that a lot and I just tell them its the basic motor lol. It's not a bad motor at all, it's just not rare.  

I had a guy argue for 10 min that my 400 was a sbc.  

Is the 350 block the same as a 305? Can you install headers on a 350 installed in a Firebird?  

The 305 is a Chevy small block V8, there is also a 350 Chevy SB, which is identical to the 305 externally. Our beloved Pontiac V8 (including the 350 discussed above) is an entirely different design that shares nothing with the Chevy, except carburetors and distributor caps- depending on the years. The 350 Pontiac looks identical to the 389/400/421/428/455, the dead give away when comparing Pontiac to Chevy is the stock intake manifold with  a seperate lifter valley cover, the Chevy uses a manifold that covers everything. The chevy 350 design has a larger bore than stroke and Pontiac 350 has a longer stroke than bore for more torque. At one time buick and olds also had their own 350 designs as well.
Steve  

Oh yes, you can get headers with both 350's in a Firebird, but check to be sure what engine you are ordering for.
Steve  

What we have to realize is that when we refer to GM engines that were made earlier than the 80's we have to say if it's an Olds, Poncho, Chevy or Buick. All four divisions shared damn near all common engine sizes 350, 400, 403, 455, 326, 327, 330, or they made an engine similar in size to the other division, 428, 400 big block buick, 428 Poncho, 430 Olds etc. The same cannot be said today because GM has gone to one engine for their particular purpose.....I miss the old days, four different engines, each with their own characteristic. Pontiac, the only engine from the factory with a stock air-gap intake manifold!