Mk II vs Mk III detail differences?

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numboltz
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Mk II vs Mk III detail differences?

Post by numboltz » Thu Jan 18, 2018 12:00 am

http://www.hotrod.com/articles/mickey-t ... -stingray/

Always interested in reading about the first canted valve engines, and have often seen that
Chevy made many changes' all apparently in the cheaper direction, between 1963 and 1965.
Anyone know, in detail, what the changes were?

GLHS60
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Re: Mk II vs Mk III detail differences?

Post by GLHS60 » Thu Jan 18, 2018 2:36 am

MK II vs MK IV:

There was no MK III.

There's a great article in a 1963 Hot Rod magazine where they do a tear down on a Mystery Engine.

An interesting thing, as Chevy had 2 427's at the time, H-D 427 was suggested as it's name!!

I don't think anything was really downgraded, pushrod guides were cast rather than stamped.

Mystery Engines were all 2 bolt main and the lifter bores were in line.

I have the magazine somewhere, I'll try and find the date.

May, 1963.

Thanks
Randy

Link to story!!

Post your input.

https://macsmotorcitygarage.com/inside- ... ry-engine/
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Ratu
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Re: Mk II vs Mk III detail differences?

Post by Ratu » Thu Jan 18, 2018 3:16 am

Mk III was a place holder, a lable reserved for a potential engine. Packard had a V-8 line and when that company failed there was a proposal for GM to purchase the production line and designs etc from the Packard liquidator. GM were seeking a new V-8 big block at the time and Packard's V-8 was set on 5" centres which meant plenty of room to grow in future. Further, it appears there was a V-12 variant of the V-8 which could be manufactured on many of the same tools. In the end the Mk III project never progressed much further than investigations and analysis work (possibly some testing). It was not taken much further and instead it was decided to modify the MII, developing it into the Mk IV.

Smokey Yunick commented favourably on the Mk II design and expressed his admiration for its lead designer on several occasions. He mentioned to me that the Mk IV was "productionised" in an unsympathetic manner and that some of the good aspects of the original design were discarded. He was dismissive of the early versions of the Mk IV. It does appear he had a point, as it took a while to sort out the Mk IV BBC and make it work reliably for high performance application. I recall him saying that during the transition the valve centres were altered some and that the port shapes were changed. There were other amendments but I can't recall all of them. I regret not asking a few more questions and writing it all down, but he sure was a prickly personality, sometimes impatient and fast to annoy. He could close a conversation down quite quickly and make a person feel unwelcome real fast!

It would be interesting to revisit the two engines, put them side by side and go through the details and analyse the differences.

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Re: Mk II vs Mk III detail differences?

Post by GLHS60 » Thu Jan 18, 2018 3:32 am

One of my links seem to have disappeared, I'll try again

It is the article with pictures.

Thanks
Randy

http://wildaboutcarsonline.com/members/ ... ne_1-9.pdf
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Re: Mk II vs Mk III detail differences?

Post by Newold1 » Thu Jan 18, 2018 7:52 am

Thanks for the magazine article and its pics. I long ago tossed mine but I remember those pictures very well. I always loved two early developments in those Mark IV's. One was the interesting little bump in the upper left corner of the exhaust port and the oval shape of the exhaust port. Somehow those two developments got lost in the original production Mark IV's and only appeared as improvements in later years through testing and performance version aluminum heads. The other early great part in the pictures for me were those great cast iron header manifolds. The Corvettes received a later variant exhaust manifold but it was not as good as these early racing offerings.

I always understood that the two iterations of the Mark versions were really not both Mark engines. One was the modified 409 (427) W engine named the Z11 and the HD-427 Mark III engine described in that article that appeared at the 63 Daytona race. There have been some releases of info and pics on some prototype developments but I have always heard that none of those made in into GM Racing programs or production. IE: the overhead cam 427, etc.

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Re: Mk II vs Mk III detail differences?

Post by ProPower engines » Thu Jan 18, 2018 1:46 pm

having never seen the original block and valve train lay out that was some fancy push rod guide plate engineering.
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Re: Mk II vs Mk III detail differences?

Post by numboltz » Fri Jan 19, 2018 11:52 pm

Interesting that in spite of multiple statements in the articles of the day stating it was entirely a racing
engine, the cylinder heads have heat crossovers in their castings and it appears that the intakes
have those provisions, too.

Other trivia I have seen includes the fact that they used the same basic rod forging as the 409, with
the pin hole moved a small amount. I would assume that the block went down the same line as the
409s did, even though the decks were at a different angle. With the cranks being interchangeable,
the rods similar and the bore spacing the same I wonder just how much detail difference there was
in the basic block castings? Be fascinating to compare the two blocks.

Finally, I have read that Chevy was forced to sell 2 engines to Ford to prove the engines were
available in the market place and thus NASCAR legal. Apparently late in the season Junior
Johnson was plumb out of engines and by some form of shenanigans was able to acquire one
of the two from Holman & Moody. I suspect the other one is the grandfather of the 385 series not
too mention the Cleveland family.

There must be at least one patent for the canted valve idea, but so far I haven't found it.

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