Ralley Green Z at MCACN

[maroman]

Does anyone know anything about the '69 Ralley Green Z that is both X-11 and has an engine with a M code? It was featured on Speedville site.

[69Z28-RS]

I talked to the owner (Al Krebs at the time) two different years at the Camaro Nats..  I was a skeptic initially, but after much discussion with him, he made me a believer that the car is real...

[Stingr69]

Whats an "M" code block?

[69Z28-RS]

Hopefully someone that knows more about this will respond, as I don't trust my memory anymore on this sort of stuff, but IIRC from my discussions with Al, the 'M' was used to designate 'Test' or 'prototype' or 'developmental' casting; perhaps they'd made some slight change to the casting, but then decided that the block was usable as it was and proceeded with the engine build...   If I'm remembering this incorrectly, someone please update/correct this...

[maroman]

That is how it was explained in the article. It was a block cast to test a modification but not used in production, had no date code. I am not questioning this car, I have been around long enough to know you never say never. Stuff happens.

[cook_dw]

http://www.camaros.org/drivetrain.shtml#BlockCast

[westonz28]

Kurt will have to weight in on this one. I do remember reading about a original 1969 Z28 that had X11 on the trim tag. I bet Kurt has more information on it. This Camaro may be the "ONE".

[maroman]

It is claimed to be the only one with both X-11 and M code. As no Z-28s were to have X-11 it would be interesting to hear the story, if it was special order or mistake.

[bcmiller]

That’s the car. November of 69 build. X11 was most likely a mistake on the tag - but the car was built as a Z - as intended.

Oh and on the M coded blocks, they used M because L was December - the last month of the year. I have had a few M coded blocks over the years and might still have one. Not sure.

[maroman]

Would they have used M code for all experimental blocks or just four bolt main?

[bcmiller]

Would they have used M code for all experimental blocks or just four bolt main?

"Research by the Saginaw Metal Casting Operations of GM Powertrain Division has found that these "M" codes are not date codes, but actually a foundry code used to indentify parts that were made to evaluate a casting process change."

There is no reason to think that it was only for four bolt main blocks.

[maroman]

I had read that. So, how are blocks marked as whether they are four bolt two bolt, etc.? I realize the blocks were probably not meant to be put into use but it does say they could be, as this one was. I had not heard of these M codes before.

[bcmiller]

Not sure there is a way to tell on a small block, its usually best to remove the oil pan and look.

There are some external clues on big blocks for 2 bolt mains versus 4 bolt mains.

[ZLP955]

There are 'M'-coded heads too. I have a set of 3927186 'M' heads on my CE302. Have compared them to regular production heads and can't see anything obviously different, but so many subtle changes (including internally) could be possible during evaluation. I surmised that they were released into circulation (rather than being scrapped or returned for melting down) because their evaluation pattern was close enough to being finalised for production that it wasn't seen as risky - but purely a guess.

[Kelley W King]

There were more "M" blocks used than you would normally think. I remember years ago they were refered to as "Mexico" engines because they were thought to have been built in Mexico.