History of the Chevrolet/GM BBC big block Chevy

General engine tech -- Drag Racing to Circle Track

Moderator: Team

pdq67
Guru
Guru
Posts: 9841
Joined: Thu Mar 04, 2010 8:05 pm
Location:

Re: History of the Chevrolet/GM BBC big block Chevy

Post by pdq67 »

I think that I just may have the old mag. that looked at all the old engines back then and it came to the opinion that the 375/427hp/396 was right at a 410hp engine.... And, imho, the difference between 375 and 425hp was that they used the Big Car exhaust manifolds on the Big Cars and the Vette's vs the smaller AFX car exhaust manifolds in them.

I want to say that the most truthful engine back then was the W-31 or so Olds, I forget which one it was, but the article claimed that it's advertised numbers were almost spot-on with the tests over time..

pdq67

Ps., oh, and btw, the old 409 truck exhaust manifolds were 2.5" jobbers that I figure flowed quite well for back then. and they fit in my '67SS/RS Camaro on my 350 engine mounts fine...
lorax
Guru
Guru
Posts: 1778
Joined: Fri Aug 24, 2012 1:00 am
Location:

Re: History of the Chevrolet/GM BBC big block Chevy

Post by lorax »

raynorshine wrote: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 :oops:
You have to remember the 990 open chamber came 5 years later. The open chamber was considered to be a backwards step, no different than the Ford 335 open chamber or the Mopar LA open head. The large open chamber was a emissions change. In the case of of the BBC, it just happened to make more power as well.
140Air
Guru
Guru
Posts: 1542
Joined: Sun Mar 17, 2013 11:55 pm
Location:

Re: History of the Chevrolet/GM BBC big block Chevy

Post by 140Air »

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.
I think this is generally correct in that the flow characteristics with the paired port, 180 degree manifold gives the best mixture distribution. Most GM engines and several others used this pattern. This hurt performance when Weber carbs were used and the manifolds for them had to have drastic bends to reach the carbs.
lorax
Guru
Guru
Posts: 1778
Joined: Fri Aug 24, 2012 1:00 am
Location:

Re: History of the Chevrolet/GM BBC big block Chevy

Post by lorax »

140Air wrote:
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.
Keeping in mind that Nascar and truck/passenger car production were the primary dirvers of the design of the MKIV. If the MKIV was such a superior engine to the FE maybe you can explain why it didn't win a single champioship while the FE and the MKIV ran together. Ford won 2 and Mopar won 2 between 1965 and 1969 and Ford didn't race in 1966. In 1969 Ford switched to the 385 series engine. No championship for GM in those years. It took until 1973, 3 years after the introduction of the open chamber for Chevy to win a Nascar championship with their flagship engine.
How many Nascar champiohships did the MKIV win in it entire history.
The MKIV didn't when a champioship for 3 years after the open chamber head arrived. Curious, how many Nascar Championships did the MKIV win in its entire life on the Nascar circuit?
I can tell you this, they blew up more MKIVs than won races.
SchmidtMotorWorks
Vendor
Posts: 11003
Joined: Mon Apr 11, 2005 2:30 am
Location: CA

Re: History of the Chevrolet/GM BBC big block Chevy

Post by SchmidtMotorWorks »

140Air wrote:
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.
I think this is generally correct in that the flow characteristics with the paired port, 180 degree manifold gives the best mixture distribution. Most GM engines and several others used this pattern. This hurt performance when Weber carbs were used and the manifolds for them had to have drastic bends to reach the carbs.
The BBC paired port sure isn't an example of balanced porting, the ports are different and they are very offset from the cyliner centers, even though the left bank is further forward than the right, the ports on the left bank are further back. Just look at a BBC single plane manifold from the top, kind of a mess.
Helping to Deliver the Promise of Flying Cars
rocks409
Member
Member
Posts: 80
Joined: Sat Oct 10, 2009 3:31 pm
Location: Texas

Re: History of the Chevrolet/GM BBC big block Chevy

Post by rocks409 »

w-engine deck heigth = 9.600 , not 9.800..........
RAS
Pro
Pro
Posts: 304
Joined: Mon Jun 04, 2012 9:46 am
Location: Edmund Ok.

Re: History of the Chevrolet/GM BBC big block Chevy

Post by RAS »

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.
PackardV8
Guru
Guru
Posts: 7619
Joined: Sun Jul 30, 2006 2:03 pm
Location: Spokane, WA

Re: History of the Chevrolet/GM BBC big block Chevy

Post by PackardV8 »

rocks409 wrote:w-engine deck heigth = 9.600 , not 9.800..........
With the angled deck, that depends upon where it's measured, innit? ;>)

Actually, both sharing the 9.800" deck came from a quick-reference of our friend Panic's data table. Since a W-specialist says it's 9.600", good enough for me; maybe Panic can correct the error in the near future.

jack vines
Jack Vines
Studebaker-Packard V8 Limited
Obsolete Engineering
SchmidtMotorWorks
Vendor
Posts: 11003
Joined: Mon Apr 11, 2005 2:30 am
Location: CA

Re: History of the Chevrolet/GM BBC big block Chevy

Post by SchmidtMotorWorks »

The most reproduced, copied design in automotive history.
Do you mean by the automotive after market? If so, I would assume the Gen 1 SBC has thay by multiples.
Helping to Deliver the Promise of Flying Cars
lorax
Guru
Guru
Posts: 1778
Joined: Fri Aug 24, 2012 1:00 am
Location:

Re: History of the Chevrolet/GM BBC big block Chevy

Post by lorax »

PackardV8 wrote:
rocks409 wrote:w-engine deck heigth = 9.600 , not 9.800..........
With the angled deck, that depends upon where it's measured, innit? ;>)

Actually, both sharing the 9.800" deck came from a quick-reference of our friend Panic's data table. Since a W-specialist says it's 9.600", good enough for me; maybe Panic can correct the error in the near future.

jack vines
The deck is measured on the valley side AT THE BORE.
Stock deck is 9.6
novadude
Guru
Guru
Posts: 1500
Joined: Thu Oct 11, 2007 3:24 pm
Location: Shippensburg, PA

Re: History of the Chevrolet/GM BBC big block Chevy

Post by novadude »

RAS wrote: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.
I seem to also recall reading that the Mark IV wasn't really designed to be strictly a performance automotive engine. From Day 1, I think heavy truck usage factored into the plans, resulting in design compromises and excess weight. Too bad Dick Keinath passed a few years back - I'll bet he had a lot of stories to tell....

I wonder if the engineers would have still gone down the "canted valve" path if they had a "do-over" opportunity? Seems like that valve layout might have cause more problems than it solved.
140Air
Guru
Guru
Posts: 1542
Joined: Sun Mar 17, 2013 11:55 pm
Location:

Re: History of the Chevrolet/GM BBC big block Chevy

Post by 140Air »

lorax wrote:
140Air wrote:
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.
Keeping in mind that Nascar and truck/passenger car production were the primary dirvers of the design of the MKIV. If the MKIV was such a superior engine to the FE maybe you can explain why it didn't win a single champioship while the FE and the MKIV ran together. Ford won 2 and Mopar won 2 between 1965 and 1969 and Ford didn't race in 1966. In 1969 Ford switched to the 385 series engine. No championship for GM in those years. It took until 1973, 3 years after the introduction of the open chamber for Chevy to win a Nascar championship with their flagship engine.
How many Nascar champiohships did the MKIV win in it entire history.
The MKIV didn't when a champioship for 3 years after the open chamber head arrived. Curious, how many Nascar Championships did the MKIV win in its entire life on the Nascar circuit?
I can tell you this, they blew up more MKIVs than won races.
Lorax, As you well know, the BBC has had loads of success in all forms of racing. You are also, I'm sure, aware of GMs "No Racing" edict that torpedoed the Corvette GS Le Mans assault planned for 1963 and all GM car competitiveness in stock car racing in the immediate following years. This also led to the back-door efforts with Chaparral, Pensky, Yunick, McLaren and others. Chevy managed to show very well in some forms of racing through privateers, but they were mainly absent from stock car racing.
I doubt you would claim that the Ford side oiler could match up to the BBC in all-out NA power. It simply couldn't breath with the Chevy. But racing success is more than just a matter of power potential. Ford's record was superb during the '60s. They stayed competitive against the Chrysler products that had the Hemi, another engine superior to the Ford. My hat is off to them.

BTW, AFAIK the BBC blowups in the early days were due to using pressed piston pins, at least that was the claim.
rally
Expert
Expert
Posts: 927
Joined: Thu Jan 29, 2009 7:08 pm
Location:

Re: History of the Chevrolet/GM BBC big block Chevy

Post by rally »

Yes Chevy never had the backing from GM early as a poster stated. They were at a disadvantage. Anyhow even without Factory backing they won. Duntov had Hemi designed Chevy Big Blocks that never got approved from the Chevy top brass. I have pictures of these massive engines Duntov had, impressive to say the least.
140Air
Guru
Guru
Posts: 1542
Joined: Sun Mar 17, 2013 11:55 pm
Location:

Re: History of the Chevrolet/GM BBC big block Chevy

Post by 140Air »

SchmidtMotorWorks wrote:
The most reproduced, copied design in automotive history.
Do you mean by the automotive after market? If so, I would assume the Gen 1 SBC has thay by multiples.
I think the advent of staggered, splayed and canted valves in automotive engines was a GM development. It was a natural outgrowth of their invention of the ball-stud rocker with the ability to depart from the geometries dictated by rocker shafts. Ford was the first copier of the ball stud rocker and the first copier of canted and staggered valves. The classic SBC was a standard inline valve wedge engine of the style current in 1955. It was simply a particularly good one, the most available and in a good size for many forms of racing.
lorax
Guru
Guru
Posts: 1778
Joined: Fri Aug 24, 2012 1:00 am
Location:

Re: History of the Chevrolet/GM BBC big block Chevy

Post by lorax »

140Air wrote:
SchmidtMotorWorks wrote:
The most reproduced, copied design in automotive history.
Do you mean by the automotive after market? If so, I would assume the Gen 1 SBC has thay by multiples.
I think the advent of staggered, splayed and canted valves in automotive engines was a GM development.
The Mopar poly angle beat them to it. They didn't need to cant the valve because like a hemi, it was already opening away from the cylinder wall and canting was no benefit.
Post Reply