Pontiac 400 - Casting Number 500557
 

I guess there's some truth to what others are saying about the Pontiac 400 blocks with casting number "500557". Have a look at the picture (Left side, midway up), this is what I found after removing the crank tonight. Everything looked great until I turned the block over and heard a thump and something fell on the ground. Good night folks.

I had one crack there and found the dowel pin in the oil pan. I got lucky when I pulled it to change the pan gasket since it ran great.

I have a half dozen pics saved of other 557 blocks that look exactly the same as that.

Now I got another.

Yet still some will argue this deal... :-ohwell:

Sorry 'bout the block,that has to be a bit of a downer.

But better to find out about it now rather than when you were out there thrashing hard on it.

Bret P.

what was your setup? heads, intake, cam, compression, stroke

I was educated a long time ago to not use any of the later blocks... im fortunate to have a pretty good stash of '68-'72 400s and 4 running 1970-1972 455s... Dad told me when i was a kid that the early stuff was the best. THanks Dad! Sorry bout your block!

Ouch that hurts. Sorry for you block lost.

Hey Guys,

The motor came in a 1968 GTO Convertible I bought late last year and this is what I now know about it (The seller didn't know much about it).

1975 Pontiac 400 Bored.030
Speed Pro Flat Top Forged Pistons
Stock Rods & Crank
Comp Cams Extreme Energy 284 Series Cam
JBP Prepared Edelbrock Heads
Torker 2 Intake
Holley 750 DP
Hooker Super Comp RP Headers

IMHO, The motor was a little too radical for a convertible and I planned on swapping it @ some point in time so I wasn't too upset. I guess everything happens for a reason, I was fortunate to have bought a very nice 455 from a PY member who was very helpful. Thanks Stags, I can't wait to get the motor in my car.

I was going to make a planter out of the block however I'm not sure what my wife's reaction would be if it were sitting in the front yard in "Fresh" Pontiac Blue Paint. Have a great Memorial Day Weekend and don't forget to fly the flag.

Paul

Glad I listened and got rid of mine.

I read to keep the power below 375hp with these blocks. looks like you were over that. DD shows around 450hp at 6,000 rpm

I have a 75 557 block on my stand now. It's my old bracket motor and I am freshening it up for my new 65 LeMans bracket car. I'm playing it safe and am using a puny Elgin cam with iron heads. I'm cleaning up the bowls and gasket matching and that's it. It should be okay but I very well know I am rolling the dice...

Pontiac Planter..
 

Do it! Here's my planter.. It's not a 400, unfortunately it's a 428 with a broken bottom end... But wife likes it.
Garage Sale Garden.. Since I bought it from a Garage Sale where I also got a whole bunch of other great Pontiac parts one day..

I just showed that to my wife and she said "don't even THINK about it!" :wife:

so this begs the question..are there any differences in 455 blocks from 70 to 76? discounting the ram air blocks and four bolt mains in some....

Dropped the block of @ the scrap yard yesterday. A lean 159 lbs which got me a whooping $19...

Interesting..Pretty sure the "standard", non-557 blocks weigh in the 180-185lb range. Not sure the exact reason, but pontiac wanted to make these 557 blocks lighter for better gas mileage or emissions (lol) or some other reason. Pretty much screwed the pooch with that design.

Same deal on the 75/76 455 blocks....

NEW 500813 casting ID.

Best to stay with 485428 for ANY serious HP builds.

I don't really think so. Certainly a 76 455 doesn't have the same weakness issue as that 76 557 block. Maybe older castings had more nickle?? - not sure that applies to the 455 blocks.

The 76 455 blocks were not drilled for four-bolt mains. Some folks think that may make them stronger as less of the meat has been removed around the crank for the four bolt caps. A studded two-bolt cap is plenty strong - especially if the block has not been drilled for four bolt caps.

If you "do" want to strengthen one of those 455 blocks, then you should only use splayed four bolt caps as a non-splayed four bolt cap motor may actually be weaker than a studded two bolt main motor for the reason above.

TooMany - I didn't think the undercut cap rails were present on the 455 blocks for those years...you got any pics? It is pretty dramatic w/ the 400 blocks as far as the missing meat in that area.

No.....just assuming that they cheaped out on the casting & it would have greater potential for similar type problems to develop......

The casting # wasn't changed for NO reason.

Anybody done a weight comparison?