Old 454 Crate Motor Specs

So the motor and trans (454/TH400) in my dad's Monte Carlo came from a 1990ish motorhome built on a Workhorse chassis. At some point in its life, the motor was replaced with a GM crate engine. The casting numbers tell the tale. It appears to have started life as a MarkIV engine before the crate came along.

Block: 12550313 GenVI
Heads: 12562932 GenV
Intake: 14087487 MarkIV

While the block is a GenVI, I'm not sure about the internals. As a long lock, it seems it was sold as a GenV replacement assembly so I wonder if it isn't stuffed with GenV guts and not GenVI? I thought the later motors had better cranks, maybe different pistons. I'm not sure. The good news is that I have all the head options wide open with the GenVI block, though I find it odd that GenV heads live on it and that's OK. But from what I've googled this is how they sold them. Does anyone on here know about these engines? I don't think they're available anymore. I'm mostly curious about the compression ratio. I suspect it's something lame like 8.0:1. Heads with 100cc chambers would bump it a full point vs the 118cc on there now.

Is there any difference between Gen V and Gen VI internals aside from the roller-cam? Be interesting to pop the valve cover and see if the lifters have dogbones connecting them, or if the crate engines used a flat-tappet cam.

I'd expect cranks 'n' rods to be the same, probably pistons, too.

For that matter, same oil pump, same oil pan. The Gen VI may have had a different timing cover with provisions for a crank sensor. Which in the small-blocks, meant adding a reluctor and shortening the damper hub to compensate. But as a crate engine replacement for a prior design, no telling what parts they used.

The Gen VI heads were said to be an improvement over the round-port Gen V heads; but given that they had "swirl-port" intakes like the horrible TBI small-block heads, the gains were probably more due to the ~100 cc chambers increasing compression and making for a faster burn than any increase in airflow.

Those four engine designs were all "F" blocks
Mark Four
Gen Five
Gen Fix (because GM finally showed some brains, and Fix-ed almost all of the screwups in the Gen Five.)

Supercharged111 said:

So the motor and trans (454/TH400) in my dad's Monte Carlo came from a 1990ish motorhome built on a Workhorse chassis.

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I don't think Workhorse goes back to 90..... I think it was still GM P-Chassis, but that probably doesn't make a difference for you presently.

At some point in its life, the motor was replaced with a GM crate engine. The casting numbers tell the tale. It appears to have started life as a MarkIV engine before the crate came along.

Block: 12550313 GenVI
Heads: 12562932 GenV
Intake: 14087487 MarkIV

While the block is a GenVI, I'm not sure about the internals. As a long lock, it seems it was sold as a GenV replacement assembly so I wonder if it isn't stuffed with GenV guts and not GenVI?

Click to expand...

Hmm, I've read that some of the Gen V blocks were actually Gen VI castings, but I'm not sure how to differentiate the two. I expect that the GenVI castings used for GenV engines would have been machined differently. I would also expect that the internals would be more GenV like, but I'm really just agreeing with your already stated questions.

I thought the later motors had better cranks, maybe different pistons. I'm not sure. The good news is that I have all the head options wide open with the GenVI block, though I find it odd that GenV heads live on it and that's OK. But from what I've googled this is how they sold them. Does anyone on here know about these engines? I don't think they're available anymore. I'm mostly curious about the compression ratio. I suspect it's something lame like 8.0:1. Heads with 100cc chambers would bump it a full point vs the 118cc on there now.

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I'd verify that block is machined the same as a real GenVI, since there is some weirdness with swapping heads between the different generations. I don't recall the details, but in some combinations you need specific/special gaskets.

Gen V was a cost-cutting turd. The "engineers" screwed-up the coolant passages in the block decks (along with other mistakes.) Mark IV heads may or may not leak coolant on a Gen V block. There are "conversion" gaskets made, which usually solve this problem.

Gen VI blocks reduced the size of the coolant passages, so that they were compatible with Mark IV, or Gen V heads.


I put Gen VI (Vortec) heads on a Mark IV block. The coolant passages were just BARELY sealed; but this is with an old-fashioned Mr. Gasket steel-shim head gasket. A different gasket may have worked better.

Schurkey said:

Gen VI blocks reduced the size of the coolant passages, so that they were compatible with Mark IV, or Gen V heads.

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I thought the cooling system was completely changed on the Gen VI..... or am I thinking of the oiling system?

There's some oil system differences from Mark IV to Gen V, and the Gen VI is the same as the V. The Mark IV had the main oil gallery on the oil-filter side of the block, near the oil pan rail. That gallery was moved up by the camshaft in the newer engines.

Photo 1. Mark IV oil gallery plugs (removed; front plug replaced with brass) with brush being inserted into gallery.
http://hbassociates.us/454SideOilerPlugsSM.jpg



SOME Mark IV have parallel cooling, most have series cooling. ALL Gen V-VI-VII have parallel cooling.

A series-cooled Mk IV can be converted to parallel cooling by drilling a few holes in the block deck surfaces, and using a parallel-flow head gasket. Parallel cooling is SLIGHTLY better at keeping engine temperatures consistent throughout the block and heads.

The heads are the same for either style of cooling. Only the block and head gaskets are different.

This particular motor came with a flat tappet cam. As for the Workhorse comment, it's semantics as I was really just trying to point out how heavy a chassis this setup started life in as they seem to rock the older motors longer. If the rest of the spinny bits are the same across GenV/VI then that's good news as I see them holding quite a bit of power in GenVI form. Seeing how there's a mechanical fuel pump bolted to the block there's no way it could be a GenV. I'm still weirded out as to how GenV heads on a GenVI block are OK as vise versa is not so much from what I understand.

Don't need hi dollar forged stuff for naturally aspirated build. I built a couple big blocks with cast crank, 2 bolt mains, small rods (bolts actually) and hyper-whatever pistons. 1st one was about 575 horse, 2nd was bout 400 something. Both ran great, even with a ****-tuned carb. Not up on the newer big block stuff, mine were always 70s/80s stuff.

One thing I forgot to mention with the GenVI heads is that they tolerate a lot more lift so you open yourself up for some gains there as well. I have the tools to knock out the ski jumps and could do some blending too. I'm thinking a cam in this range and a different intake would be the way to go.

https://www.summitracing.com/parts/cca-cl01-600-8/make/chevrolet

Supercharged111 said:

Seeing how there's a mechanical fuel pump bolted to the block there's no way it could be a GenV.

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How so? Production Gen VI engines don't get mechanical pumps either.