For the Hemi Guru's

This is the number on the side of my hemi block.
I am trying to determine how old it is and who manufactured it.

Thanks
Ed

It should have a date on it cast in. That is a later Mopar performance block or pre world.

Mopar "Mega " block maybe
Not OEM

Here is the info on the block.

I agree with this, but to clarify Mopar Performance block, and NOT a later (newer) World block.
It's a good replacement block for a restoration as it looks more like an original.

When these were introduced by Chrysler it was in all the Mopar magazines. The story went, that as Chrysler stopped production of bigblocks in 1978 all the bigblock stuff was scrapped. So when they decided to make a new Hemi block they had to start from scratch. This was the result. The "M" after the casting number was to keep them from being passed off as original blocks.

I am guessing that these were the blocks that MP also used for the new crate Hemis in the Cummins era, but I've no proof.

I do know that there was much rejoicing in the MOPAR world when this announcement came out. Plus the availability of Siamese blocks opened up a whole new range of displacements available.

R.

Yes it is a Siamese Mega block. 4.50 on the bore.
Next time I am at my shop I will look for a cast date, just not sure how to read it.
Glad it is a pre World block

Thanks
Ed

Yes, it is a Mopar Mega block. Started life as a 4.500" pre World block. I have the same block.

iirc the mopar logo and mopar spelled out designated HP mega block.
were the non-siamese blocks cast with the M and mopar?
I'm under the impression the siamese blocks came rough bored at 4.19"

The non siamese blocks had the M cast into them but not the word Mopar.

great, thank you!

Read my two attachments: tells all.