Don Terrill’s Speed-Talk

I posted this on another thread and several suggested it needed it's own heading to help with searches. Here it is:

FWIW, I got this first-hand from Francis Preve, the Chevrolet engine historian. By the time it was in production, it was obvious the 348"-409"-427" W-series head/block interface was a technological dead-end and Chevrolet Engineering studied several options for their next big block. Cheverolet needed a better big block engine for the bigger, heavier cars and trucks to come. From late 1957-63, GM had four study teams working:

Mark I study was to take the already in-production 348" out to 427" and beyond. They knew the heads were not the way to go and the bottom end proved to be too weak for the 500" they figured to need twenty years down the road.

The Mark II option was the new Mystery Motor porcupine head design introduced as a proof of concept on the modified 427" W-short block at Daytona in 1963.

The Mark III study was to buy the Packard V8 tooling for pennies. It could easily go to 500", but Marketing didn't want to be associated with a loser and Engineering knew they could do better than a first-iteration Kettering knockoff and wanted the chance to try some new cylinder head ideas. That, plus the Packard V8 has 5.00" bore centers and was "not invented here" killed it.

The Mark IV study continued the Mark II proposal, further developed the cylinder heads and bottom end which ultimately became the 396", 402", 427", 454", 502" and 572" big block Chevrolet, introduced in mid-1965 and still in production today. As previously mentioned, the Mark IV was both evolutionary and designed in-house; it combined the best of several ideas, but also kept the same 4.84" bore centers and 9.800" deck height as the W-engine.

Best Big Block Engine to ever come out, Chevy got it done right.

Certainly the cheapest serious horsepower a budget guy can make. I'm doing a 348 right now for a period correct Model A hot rod. It's pretty interesting, in a perverse sort of way, to handle the parts and sort of immagine the evolution in thinking of the engineers while they were trying to get from the W to the MK-4. The pistons are monsters and the rods were a little spindley but had the BBC big end size. Trying to put the piston assemblies in the block, especially in an overbore, can make you wonder what those engineers were eating for breakfast!

My understanding was Joe Mondello designed the head .

Speedbump wrote:Certainly the cheapest serious horsepower a budget guy can make. I'm doing a 348 right now for a period correct Model A hot rod. It's pretty interesting, in a perverse sort of way, to handle the parts and sort of immagine the evolution in thinking of the engineers while they were trying to get from the W to the MK-4. The pistons are monsters and the rods were a little spindley but had the BBC big end size. Trying to put the piston assemblies in the block, especially in an overbore, can make you wonder what those engineers were eating for breakfast!

I love this aspect of engine building.

PackardV8 wrote:I posted this on another thread and several suggested it needed it's own heading to help with searches. Here it is:

FWIW, I got this first-hand from Francis Preve, the Chevrolet engine historian. By the time it was in production, it was obvious the 348"-409"-427" W-series head/block interface was a technological dead-end and Chevrolet Engineering studied several options for their next big block. Cheverolet needed a better big block engine for the bigger, heavier cars and trucks to come. From late 1957-63, GM had four study teams working:

Mark I study was to take the already in-production 348" out to 427" and beyond. They knew the heads were not the way to go and the bottom end proved to be too weak for the 500" they figured to need twenty years down the road.

The Mark II option was the new Mystery Motor porcupine head design introduced as a proof of concept on the modified 427" W-short block at Daytona in 1963.

The Mark III study was to buy the Packard V8 tooling for pennies. It could easily go to 500", but Marketing didn't want to be associated with a loser and Engineering knew they could do better than a first-iteration Kettering knockoff and wanted the chance to try some new cylinder head ideas. That, plus the Packard V8 has 5.00" bore centers and was "not invented here" killed it.

The Mark IV study continued the Mark II proposal, further developed the cylinder heads and bottom end which ultimately became the 396", 402", 427", 454", 502" and 572" big block Chevrolet, introduced in mid-1965 and still in production today. As previously mentioned, the Mark IV was both evolutionary and designed in-house; it combined the best of several ideas, but also kept the same 4.84" bore centers and 9.800" deck height as the W-engine.

This is pretty close to how I understand the history of the BBC. The MKII mystery motor served as the mule they could produce with the existing tooling by modifying the deck to a 90* deck and a crank with larger main bearing and 4 bolt caps. The block and heads do not inter change with the MKIV, but they could prove out all the ideas before commiting to the tooling of a next generation engine. Once they proved the design, the idea of a larger bore center was considered and the Packard line tooling was considered. NOT THE ENGINE, just the line tooling. The bore centers is the chink in the armour of any new generation engine. In the end the bean counters shot down the idea, and GM stayed with the 4.84 BC of the existing MK line tooling.
Ford was no different. When they looked at making a new generation BBF, they stayed with the MEL 4.9 line tooling. Line tooling, at least in those days was a major expense and why many engines from different families share the same BC.
Look at the 292/312 Y block, SBF, 351W, 335 series engines. Same BC as the flathead. The LS SBC has the same BC as the gen 1 SBC.
GM already knew by the time they decided on the MKIV dimensions that they could run a 4.440 bore if needed. I am guessing they figured there was no need of a 5.00 BC

If GM had looked into a crystal ball, they could have made the choice to let Cadillac make the MK engines and build them with a 5.00 BC. But the 472/500 didn't arrive for 3 another years after the MKIV 396.

there was a 65 396 impala in my family and it was a great car ,, loved it ,, 4 speed , my grand father owned it ,, i thought it was cool to say it was one of the first ones

Just imagine if they would have integrated the 5.0 bore centers... What could have been

If they ever invent a time machine. I would like to go back and be in the room when they decided the head bolt layout for the BBC.
That is the only engine I can think of with a pattern that is not symmetrical or uniform from cylinder to cylinder.
If I had to guess, it was a temporay prototype layout that they intended to go back and refine latter, but their never was enough time.

SchmidtMotorWorks wrote:If they ever invent a time machine. I would like to go back and be in the room when they decided the head bolt layout for the BBC.
That is the only engine I can think of with a pattern that is not symmetrical or uniform from cylinder to cylinder.
If I had to guess, it was a temporay prototype layout that they intended to go back and refine latter, but their never was enough time.

While you are in that meeting maybe you could asked them why a head that has a EIEIEIEI layout needed a siamese port layout that resulted in a good and bad port, and also was part of the cause for the goofy bolt pattern

I seem to recall in Smokey's bio, that he had complained they screwed it up when they went from Mark II to Mark IV. Can't recall his specific issue, but it seemed like he preferred the Mark II design?

A bit strange that it was designed with a lot of ci capacity, but they chose to release it as a 396. I can only suppose that is so GM would let them use it in the Chevelle to compete against the GTO. Can't think of any other reason for the tiny bore. One wonders why they wouldn't have put a bigger bore in it and kept the 3.5" crank like the 409 and still hit that 400 ci limit.

lorax wrote: While you are in that meeting maybe you could asked them why a head that has a EIEIEIEI layout needed a siamese port layout that resulted in a good and bad port, and also was part of the cause for the goofy bolt pattern

Probably they figured that a spread port head would require a intake design with runners too different in lenght, and this would cause a greater difference in flow than the siamesed port layout. Every design aspect is a compromise.

BrazilianZ28Camaro wrote:

lorax wrote: While you are in that meeting maybe you could asked them why a head that has a EIEIEIEI layout needed a siamese port layout that resulted in a good and bad port, and also was part of the cause for the goofy bolt pattern

Probably they figured that a spread port head would require a intake design with runners too different in lenght, and this would cause a greater difference in flow than the siamesed port layout. Every design aspect is a compromise.

The Fords, both small and big blocks, the LS Chevys and the Olds/Big Chiefs seem to handle that problem quite well.

novadude wrote: A bit strange that it was designed with a lot of ci capacity, but they chose to release it as a 396. I can only suppose that is so GM would let them use it in the Chevelle to compete against the GTO. Can't think of any other reason for the tiny bore. One wonders why they wouldn't have put a bigger bore in it and kept the 3.5" crank like the 409 and still hit that 400 ci limit.

As I heard the story, at the time there was a NASCAR proposal to reduce the 7L (427) maximum capacity to 6.5L (396). The MkIV was designed for that limit and had enough cylinder wall thickness to be bored out to 427, leaving a normal wall. In fact, Chevy noted that they reduced the weight of the 396 by 31 cu-in of iron when they built it as a 427.
I think Chevy was proud that the single quad 396 made more power than the dual quad Ford 427 and IIRC it's 425hp rating came at 200rpm lower than the Ford 425hp@6000rpm rating. If that had not been the case, I think they would have introduced it as a 427. In 427 form, the BBC's 425hp came at 600rpm lower still (5200rpm). Note that 425hp was the agreed maximum power the manufacturers would report at the time, but sometimes the rated rpm gave you a hint at how much of an under rating it was.

wasn't the MASSIVE combustion chamber volume (118-120cc) of the open chamber design (990 etc) a major step backwards as well? for anyone trying to build, run some compression