Old 454 Crate Motor Specs Question

[Supercharged111]

So the motor and trans in my Monte 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.

 

[Doug Chahoy]

The 454 was a CRATE engine from Chevy in the 80s along with the ZZ small block.

 

[64nailhead]

Since it's older, and assuming you don't have any paperwork on it, I'd say pull the heads to see what's what.

If runs well without any oil consumption, then most likely the short block is in good condition. I'll assume, again, that it makes bottom end torque that'll drag a house and gives up the ghost by 4500-5000 rpm's. If these things are true, then you're a cam and set of heads away from a very easy 400h-450hp and 550-600 ft/lb motor.

Regarding what's in the bottom end for parts, I'd assume the worst stock parts available, but all of them will live forever at 500hp/600ft lbs. If you're looking for more than that, then a full tear down is in order and another financial lesson into BB equates into B$ as compared to a SBC.


If you couldn't tell, I recommend a cam and head swap that will lead to 'no tire left behind' after a week or two of wild burnouts that'll let you know your neighbors' opinions of BBC's.

 

[69hurstolds]

Part numbers say it's a lo-po engine Gen 6. Oval peanut port heads. I'd bet closer to 8:1 compression ratio. Even the HO engines with better heads and stuff were likely to be 9:1. But as you say, 100cc heads would pop that ratio up about 1, so if that's where you want to go...

If the motorhome was a 1990s and got a new crate motor, it likely is a 1990s crate engine. Which, being a Gen 6 454, may or may not have the mechanical fuel pump provision, but should have a non-drilled boss for a clutch cross-bar pivot. Not all had it though. 4 bolt mains. 6 bolt timing cover. If the guts are original, should have a hyd. roller cam. Camshaft should be .483/.483 lift and 209 duration (.050). 115 lobe separation. It's more of a torque monster, but the small ports doesn't allow for good top end numbers. But for a street engine, it's fine. I'm not sure if earlier IV heads would bolt on the block. They made cooling port changes in those engines along the way. I can't recall all the details on that. You will have to upgrade to HO heads or something if you wanted rectangular ports.

The intake could be original to the motor home. Most likely they ordered a short block and bolted the heads/intake on from the old stuff. Or at least the intake is likely to be original to the motorhome. Who knows? Should have an EGR provision in the front next to the water outlet.

But- I could be wrong.

They sold all sorts of junk and combos across the counter back then. Engines were flying over the parts counter shelf. I had a good relationship with my local dealership's parts guys, I picked up the phone and ordered a complete 502 crate engine without having to pay for it first. This was around 1995 or so. And it came in a crate, wrapped in plastic baggie. Nothing else. No instructions, warning stuff, nothing. To GM, it was just another part. This was right before they started offering kitchen sink crate engines that came fully loaded.

 

[fleming442]

Spray
It

 

[Pc3]

Spray
It

yea... with a 200 shot

 

[64nailhead]

Spray
It

You first

 

[Supercharged111]

I'm 100% on board with bigger cam and heads. It has a Comp 256 something or other in there now, a flat tappet cam 212/218 .480/.485 110/106. I'm thinking an intake lobe around 230 and as much lift as I can cram in there should do. These heads are destined for the scrapper. The bottom end gives me the indication that it's the low mileage healthy piece we thought it was. It does have the fuel pump boss as that's what feeds the carb which truly was the smoking gun in validating it wasn't the POS GenV block. I guess I'll keep looking at the differences in rotating assemblies between GenV and VI. I don't feel like lifting a head until I have a superior replacement so my answer there may wait if I can't unearth that info on the interwebs. This motor has a couple blockoff plates on the intake and zero evidence otherwise of an emissions presence. The cam that was tossed in favor of the current one was a flat tappet which muddied the waters a bit for me.

 

[64nailhead]

I have to say, because it hasn't been said yet, BBC's eat FT cams for breakfast, lunch and dinner. And we all know what that means if you hope to keep the motor together for long.

I know the conversion to a roller cam is $6-700 deal, but it's worth triple that in the long run just for longevity alone. Then throw in the more area under the curve concept and it's worth 2x the previous triple.

I think that equals...umm 2 x 3 ...=6?

👌

 

[Supercharged111]

They also eat rollers, but my intent is roller as the block is all set up for it.