History of the Chevrolet/GM BBC big block Chevy

[RAS]

A lot of the BBC design was just a carry over from the 348-409 because they wanted to use the current tooling. Thus, we didn't see block updates or improvements that one might have expected from an all new design. I think a center main thrust bearing would have been the optimal change from what we did get. The heads suffered because there was no flow bench work at the time other than what was in the carb div at AC Rochester. With a good flow bench the short comings of the heads could have been improved had time and a budget been allocated. For a drawing design, this pump made some impressive power. Casting back in 63 was also just emerging to the newer technology. Still pretty rough. The original bath tub chamber heads were very limiting did not last long. Compare the latest SR20 heads to the originals and see what could have been.

[SchmidtMotorWorks]

OK Jack!!

When are we gonna recreate the 5.00"bore modern Packard block???

Or should we say ta hell with time's gone past and use the 500" Cad by turning it into a syamised (Sp?) bore block and put BBC heads on it and be done with it......

pdq67

PS., my spelling sucks..

The 500 Cadilac block I have seen had a 4 bolt head pattern with the bolts too close to the center of the bore. I think it would need more bolts toward the inside and outside or at least reposition the bolts to seal any serious power reliably.

[Dan Timberlake]

Remember, the BBC had no approval, budget or design to follow when conceived. The Corporate racing ban was in effect. This engine was built by several hand picked people that worked on a stealth program. The engine only saw factory support with CanAm type racing. NOT Nascar or Drag racing. The combustion chamber was horrible due to exhaust valve layout, and the head bolt pattern was changed from the original Daytona design, still a curse to this day, and it has a rear main thrust bearing. BBC like to kill the #2 main and rod bearings. The MK5 502 is a perfect example. Everyone I know of spun bearings. The MK6 is much better. I think the MK5 was done on the old MK4 tooling. Regardless, this pump makes insane power. For 50 years! The most reproduced, copied design in automotive history.

Hi RAS,

I've heard the BBC thrust bearing location "causing" rod bearing failures a few times before, but never with an explanation I understood.

What is your take on it?

thanks

Dan T

[pdq67]

Jack,

I said a MODERN 500" Cad block so we can still add two top and bottom head-bolts in the middle between the 4 that are around each cylinder that are stock just like they did to the next Gen LS-- engines block to hold the HP...

I would love to see such a siamesded(Sp?) cylinder block cast out of Ductile Iron so that say 3,000 HP or more would be possible like the top fuel engines.

pdq67

[RAS]

Dan, I just sold my last new 502 block to a Marina that is rebuilding a customers blown engine. The entire rear main is breaking out of the block. Cracks everywhere. Now we all know boaters have 2 speeds, no wake and full speed. Tough customers. The BBC having a rear bearing with thrust puts a lot of stress in one location. The crank harmonics usually take out the no2 main. Note the Chrysler and Ford Big Blocks have center thrust bearings and do not have this issue,ever. Every Mk5 502 I know of that was built in the early to mid 90s killed this bearing, mine included. I think these blocks were run on the MK4 tooling production line. The later Mk6 blocks were better but keep in mind that these were not intended to race at 8000 rpm either. The BBC was designed to run at 6000 rpm all day long in 1963. The engine had a very heavy reciprocating mass and valve train. Go 50 rpm to much and it flew apart. The best explanation on BBC thrust bearing issues comes from Jon Kaase. You might find it on the WWW. I still consider the BBC the pump all others will be measured by for a long time to come.

[wyrmrider]

I've lost big block Chrysler "3 main thrusts
Chrysler cam out with a wider thrust for a reason
I drill through to the oil feed and chamfer the parting line to the rear

[rfoll]

All of this discussion about valvetrain geometry makes me think of the Jeep "Tornado" engine with an overhead cam. The intake and exhaust valves operated off the same lobe. You have to love a company that names their engines "Go Devil", "Super Hurricane", and "Lightning". The "Go Devil" had a 3.125" bore with a 4.375" stroke. That would make it a stroker motor.

[RAS]

I've sat in on quarterly review meetings and there is no way I would have enjoyed telling the finance guys we have a new BB engine that we want to put into production and Oh, by the way, we took it to Daytona won the 125 and then Ford took the engine back to Dearborn ! I've seen people cry at these meetings. My appreciation goes to all on the team that got it done, even the factory guys that got the machine work done. Were talking balls here guys. Slide rules and pencils. What an amazing achievement. The feds were trying to break GM apart at the time. I bet the lawyers wanted blood. Anybody's.

[pdq67]

I don't know anything about the center placed thrust bearing but if that is the case, then why not move it in a modern block like Jack and I are talking about.

For myself, I'd love to be able to afford to make a light-weight 534 MEL Super Duty block out of Ductile Iron but that ain't goonna happen in my life time.

pdq67

[peejay]

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.

Audi 4.2 V8s, at least the timing belt driven ones, have an asymmetrical head bolt pattern by default. That is, the pattern is still square, but it's not centered.

The 4.2 was the ONLY engine VW made that differed from the 88mm bore center that they used on fours/fives/sixes/V6s/V10s/early V8s. (Even today, VW's engine lineup is determined by compromises they made in the 70s to make a short-length engine to fit in the nose of the Dasher) To get more than .5l/cylinder they expanded the bore center a bit, so the block and crank are different, but the heads are still 88mm bore center. The valve offset is quite visible on the corner cylinders but the engines work just fine. (I bring this up whenever the subject of LS1 heads on Ford blocks comes up. Yes, the bore center is a skotch different. No, it's not enough to matter much in the real world.)

I forget if the head bolt pattern is centered over the block or the heads. Probably the heads, so they could just use two 1.8 20v heads per block, would be my guess.

[140Air]

The heads suffered because there was no flow bench work at the time other than what was in the carb div at AC Rochester. With a good flow bench the short comings of the heads could have been improved had time and a budget been allocated.

Ras, why do you say this? Although aftermarket head porters generally, or universally, did not do flow benching, the port contours of OEM heads appeared to be the result of flow benching. This is more apparent when you look at the cross sections of early SBCs. A prominent feature of the powerpack and the camel hump heads was a venturi neck that Mondello and others would promptly grind away. There also was the finding that SBC heads flowed more with the valve in than with it out, an uncommon result that had to be the result of flow contouring, not free-hand design. People like Harry Weslake had been flow benching for years before 1963.
The chambers were bad in that they were too-deep bathtubs, but that was a near universal design style apparently based on the theory of wedge chamber combustion.

[wyrmrider]

wedge chambers with the plug at the bottom of the wedge not the top
not a good idea

[RAS]

Let me clarify. Were talking about GM in 1963 concerning a production engine. Not, what racers do or did, today or back then with it. The engine met all criteria. The first racer mod this engine got was to the combustion chamber by Joe Mondello for his fuel fiat. He basically opened it up. Fuel motors tend to show you weaknesses real quick. As to the question about the thrust bearing. The crank tends to whip. That being the case, would you want to support it from the furthest end (chevy) or in the middle? Note the LS engine has a center main thrust bearing. Just hold a 35" 5 lb. bar a arms length, once holding it in the center and then holding it an one end. Ad some wobble to it and the answer comes up quickly. It's not a killer at 6000 rpm but at 8000, not best practice! Back then fuel racers tuned by reading bearings, not looking at recorded data on a computer screen. Today, no fuel motor runs the same compression in every hole.
The BBC engine was completed rather quickly. By any standard, amazing. Back then, guys that made it home from the war and got an education on the GI bill were very serious and had incredible disciplines. My best teachers. They were self starters that required very little supervision had no computers (data) but knew how to use a slide rule. The new for 1963 Chevy II was designed and built to full production status in 6 months. From drawing to showroom. A simple car, but still done like we were still on war footing. Many of GMs machine tools were bought by the US Government during the war and still had war production tags on them in the 90s. Many of GM factory's were built just for war production. Lots of history here. You can see that when these people retired during the 80s, what happened to the company. In 1982 GM had 100 billion in cash and could have bought controlling interest of Honda and Toyota. Instead, mindless accountant, Roger Smith drove it over a cliff. I'm off point. Sorry.

[rocks409]

" the new for 1963 Chevy II " ( 1962) picky, picky, picky )

[pdq67]

rfoll ,

And I am fascinated by the old mail jeep engine that had a SOHC in it with a cam that had one lobe per cylinder that operated both valves..

6-banger, 6-lobes here...

pdq67