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!
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.
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.
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
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.
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.