FWIW, I got this first-hand from Francis Preve, the Chevrolet engine historian. Cheverolet needed a big block engine for the bigger, heavier cars and trucks to come. In 1957, GM had three studies under way:

1. Mark I study was to take the already designed and production ready 348" out to 427" and beyond. This block turned out to be too weak for the 500" they figured to need twenty years down the road.
2. The Mark III study was to buy the Packard V8 tooling for pennies. It could easily go to 500", but the marketing folks didn't want to be associated with a loser and the engineering department wanted the chance to try some new cylinder head ideas. They knew they could do better than a first-iteration Kettering knockoff.
3. The Mark IV study developed the cylinder heads which ultimately became the 396", 402", 427", 454", 502" and 572" big block Chevrolet, still in production today.

So bottom line, Chevrolet assigned an engineering number to a formal study of buying and using the Packard V8, but it went no further than the bean counters asking for it because it would have been less expensive. Marketing and engineering were the deciders and they said, "Let's invent it here." More than you want to know below:

thnx, jack vines


Mark I: The first big block Chevy, also called the W-engine perhaps because of the layout of the valves and therefore the shape of the valve covers--although another possibility is that GM chose the "W" prototype for production rather than the competing "X" or "Y" prototypes, and therefore it's a convenient coincidence that the valve layout is in the shape of a "W". It should be noted that this engine became known outside Chevrolet as the Mark I only after the Mark II was being designed years after the "W" was introduced. Whatever the origin of the name, this engine family was installed in vehicles beginning in 1958, as a 348". In 1961, it went to 409" and in 1963 a few well-connected racers could buy a 427". The 427" version was racing-only and had special parts which were not directly interchangeable with the 348"/409". While production of the 427" was limited, both the 348" and 409" were offered in passenger cars and light and medium-duty trucks. The truck blocks were somewhat different from the passenger car blocks, having slightly different water jackets and of course, lower compression achieved by changes in the piston in addition to more machining of the top of the cylinder. A novel feature of this engine is that the top of the cylinders are not machined at a 90-degree angle to the bore centerline. The top of the cylinder block is machined at a 16 degree angle, and the cylinder head has almost no "combustion chamber" cast into it. The combustion chamber is the top wedge-shaped section of the cylinder. Ford also introduced a similar design in '58 - the Mercury/Edsel/Lincoln "MEL" 383"/410"/430"/462". The "W" engine ended in 1965.5 when the 409" Mk I was superseded by the 396" Mk IV engine.

Mark II: This is more of a prototype than a production engine. It is the 1963-only "Mystery Engine" several of which ran the Daytona 500 race, and in fact won the 100-mile qualifier setting a new record. It is largely the result of engineering work by Dick Keinath. Produced mainly as a 427" but with a few 396" and 409" cubic inch versions, all in VERY limited numbers. The bore and stroke of the 427" MK II is based on the W-engine and is not the same as the 427" MK IV on which the heads are still in use. Even though it was intended as a NASCAR-capable engine, it had 2-bolt main caps. This engine was never installed in a production-line vehicle by Chevrolet It only went to racers in time to run at Daytona in 1963. The Mark II was a breakthrough cylinder head design using intake and exhaust valves that are tilted in two planes--a canted-valve cylinder head, nicknamed the "semi-hemi" or "porcupine". The engine was the subject of an extensive article in the May 1963 Hot Rod Magazine. Because of NASCAR politics, Chevrolet was forced to sell two 427" Mark II engines to Ford after the '63 Daytona race to prove it was a production engine, and therefore eligible to race in NASCAR events. Thus, the Mark II is the grandfather of the Mark IV and later big block Chevys, it's also the grandfather of the canted-valve Ford engines: Boss 302", 351" Cleveland and the 429"/460" big block Ford.

Mark III: An in-house study on the feasibility of buying the Packard V-8 engine tooling. The Packard engine was truly huge, having 5" bore centers; bigger than any engine GM would build for the next twenty years. The former president of Packard wound up at Ford after Packard folded, perhaps because of that, Ford was also interested in this engine. Ford wanted to make a V-12 variant from it just as Packard had once envisioned. One way or another, neither GM nor Ford actually went forward with the purchase.

Mark IV: The engine that most people think of as the "big block Chevy". Released partway into the 1965 model year as a 396", superseding the older 409". It is a development of the Mark II cylinder heads, using similar but not identical canted valve (semi-hemi/porcupine) layout. It was later expanded to 402", often still labeled as a 396", or even a 400", 427", 454", and a few special engines were produced in the late '60's for offshore boat racing as a 482". There was a 366" and a 427" truck version that each had a .400" taller deck height to accommodate .400" taller pistons using four rings instead of the more usual three rings. These tall-deck engines were used only in medium-duty trucks (NOT in pickup trucks--think in terms of big farm trucks, garbage trucks, dump trucks, school buses, etc.) The tall-deck blocks all had 4-bolt main caps, forged crankshafts, and the strongest of the 3/8" bolt connecting rods. All-out performance engines used 7/16" bolt connecting rods, along with other changes. This engine family was discontinued in 1990, with the redesign, known as the Gen 5 appearing in 1991.

(From Fran Preve and other internet sources, edited by JV)

The CCs in the table seem just a bit different than I got for head volume. Did you remember to subtract the block deck volume and head gasket volume in your calculations? For the actual head combustion chamber, I calculate:

'56 352" - 75 cc
'55 352" - 86 cc
'55 320" - 78 cc

thnx, jack vines

Thanks, JD. Firefox was indeed the problem.

Hi, Kev,

For whatever reason, the VintageSpeed.com site, which worked last week won't open for me this week. Anyone else having a problem?

thnx, jack vines

AFAIK, all '56 heads were the same and are the smallest. That's where the 9.5 and 10.0 compression comes from.

thnx, jack vines.

Two things here don't add up for me:

1. I've never seen a Packard V8 with .012" valve guide wear. May be common, I've just never seen it.
2. That sort of valve guide wear noise wouldn't come on suddenly. It starts soft and gets progressively louder over a long time.

Wonder if it could be rather a sticking valve which is hanging open and then closing with a clang? Could even be sticking open enough to be hitting the piston. I've seen pistons with valve marks on them, but attributed that to over-revving and lifter pump up.

thnx, jack vines

It is usually the three middle mains which are the worst first, but I've seen all five into the copper. I'd say 80% of Packard V8s have had main bearing replacement and the crank turned .010", but less than 50% have had rod bearings. I have found one with .003" oversize piston pins in STD bore pistons. I have yet to tear down an engine which has been bored oversize. Every Golden Hawk engine had evidence of a dropped valve. One had a sleeved cylinder, one had the entire top of a piston gone, one has nicks in the bottom of a cylinder bore, evidence of either a broken piston or thrown rod. The OEM Packard intake valves are just too heavy for the springs. Add the problem caused by the first-generation retainers being too soft and it didn't take many races to drop a valve.

thnx jack vines

FWIW, remember, this engine has perfect oil pressure, as described in the initial post. How then does it have an oil pump problem allowing the lifters to clatter enough to require a flat bed ride home? Lifters click and clack. They don't make the "sharp metallic rap" like a big ball pein hammer hitting iron. Spun rod bearings are not common on Packard V8s. Could be a rod, but the main bearings usually fail way before the rods.

Don't guess. Do the diagnostics. Pull the rocker covers. Pull one plug wire at a time. Let us know what you find.

thnx, jack vines

Yes, if the 320" heads are 8cc smaller than the 352" heads, that would be why they can have the same 8.5 compression ratio.

Yes, putting the 352" heads on the 320" Hash engines would drop the C.R. to 7.8, because if they are 8cc larger, thus the lower ratio.

It checks mathematically. What is the question?

thnx, jack vines

Hi, Kev,

Is it desirable to move the crankshaft info to a different thread? Seems if we might make future searches easier if we left this one thread for head numbers, started another for crankshafts and I plan to begin another for connecting rods.

thnx, jack vines