History of the Chevrolet/GM BBC big block Chevy

General engine tech -- Drag Racing to Circle Track

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

Post by Horndog »

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

Post by 140Air »

lorax wrote:
140Air wrote:
The most reproduced, copied design in automotive history.
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.
Canting was IMPOSSIBLE!

The "polyspherical" chamber that resulted from taking two divergent valve angles off the same rocker shaft is poor. This valve arrangement is in the same category as any rocker shaft head including the two rocker shaft hemi. In one axis the valve angles are dictated by the shafts. But in the poly, the valves DIVERGE. This appears to have been a dead end unless their is a copycat in development somewhere. Do you know of any?
Having the valve locations and angles FREE is what GM innovated. The ball stud mechanism that inspired imaginative designs from the W engine stagger-valved head, the splayed valve Corvair and the multi-angle canted valve Mark engines was the most economical way to achieve the freedom to vary the valve alignments and angles. This GM development has been widely copied. Ford's versions are excellent.
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Re: History of the Chevrolet/GM BBC big block Chevy

Post by lorax »

140Air wrote:
The "polyspherical" chamber that resulted from taking two divergent valve angles off the same rocker shaft is poor. This valve arrangement is in the same category as any rocker shaft head including the two rocker shaft hemi. In one axis the valve angles are dictated by the shafts. But in the poly, the valves DIVERGE. This appears to have been a dead end unless their is a copycat in development somewhere. Do you know of any?
Having the valve locations and angles FREE is what GM innovated. The ball stud mechanism that inspired imaginative designs from the W engine stagger-valved head, the splayed valve Corvair and the multi-angle canted valve Mark engines was the most economical way to achieve the freedom to vary the valve alignments and angles. This GM development has been widely copied. Ford's versions are excellent.
And then we all spend a small fortune getting rid of the skid ball heat generator, the flippy floppy guided pushrod, and flexing studs, to put them all back on shafts. :?

I'd say the Boss 429 handles the individual rocker better.
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Re: History of the Chevrolet/GM BBC big block Chevy

Post by 140Air »

lorax wrote:
140Air wrote:
The "polyspherical" chamber that resulted from taking two divergent valve angles off the same rocker shaft is poor. This valve arrangement is in the same category as any rocker shaft head including the two rocker shaft hemi. In one axis the valve angles are dictated by the shafts. But in the poly, the valves DIVERGE. This appears to have been a dead end unless their is a copycat in development somewhere. Do you know of any?
Having the valve locations and angles FREE is what GM innovated. The ball stud mechanism that inspired imaginative designs from the W engine stagger-valved head, the splayed valve Corvair and the multi-angle canted valve Mark engines was the most economical way to achieve the freedom to vary the valve alignments and angles. This GM development has been widely copied. Ford's versions are excellent.
And then we all spend a small fortune getting rid of the skid ball heat generator, the flippy floppy guided pushrod, and flexing studs, to put them all back on shafts. :?

I'd say the Boss 429 handles the individual rocker better.
The ball stud is a GM invention. To quote myself "Having the valve locations and angles FREE is what GM innovated" and "Ford's versions are excellent".
The assertion by another poster was that the BBC inspired copies. I agree with your mention of the Boss 429 (one of my favorites). It's a perfect example.
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Re: History of the Chevrolet/GM BBC big block Chevy

Post by novadude »

If nothing else, this made me search for a photo of the Chrysler poly engine valvetrain, snce I had never really looked at that engine.

Doesn't look like that design would be very stable at RPM, compared to a Chevy where you are not constrained by a single rocker shaft. Crazy pushrod angles there if this drawing is correct.

http://wildaboutcarsonline.com/cgi-bin/ ... 0393898760
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Re: History of the Chevrolet/GM BBC big block Chevy

Post by lorax »

novadude wrote:If nothing else, this made me search for a photo of the Chrysler poly engine valvetrain, snce I had never really looked at that engine.

Doesn't look like that design would be very stable at RPM, compared to a Chevy where you are not constrained by a single rocker shaft. Crazy pushrod angles there if this drawing is correct.

http://wildaboutcarsonline.com/cgi-bin/ ... 0393898760
You think there is something stable about stud rockers?
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Re: History of the Chevrolet/GM BBC big block Chevy

Post by stokerboats »

In early production form the bbc 396 suffered a rash of valve spring breakage problems. It was common for those who had this engine to carry a roadside repair kit with them when out cruising. There were also some oiling issue's/con rod bearing issue's as well, I'm assuming due to the early oiling system. I think this was mentioned earlier in another post. Oddly enough, when the oval port headed engine was equipped with the cam and valvespring combo from the shp version it became a very good contender. Not all versions of the 396 could be bored to 4.250 thus they were limited depending on the block you had, considering the 4.094 bore. When racers figured out that you could bolt on rectangle intake to the oval heads and get great results that became the norm to many. In 1966 when the 427 went into the production car it raised the bar just a little more and that engine was a pretty good contender around the racing circuits. In 1967 Chevrolet produced the 1st version of the L-88 which was closed chamber and had some compression (12.5) with a stout camshaft and the bar was raised even higher. Then the second version came along with open chamber heads and accompanying pistons which allowed a bit better breathing fllowed by the ZL-1 and then the 454 inch versions. Oddly the bbc family up to and including the 454 production versions typically used the same shp camshaft and same 6.135 rod length. I was fortunate to have purchased the early L-88 shortblock ($322.) and a pair of warrantied heads for $15 bucks each (a broken valve guide each head) repaired them, added the Corvette high rise tri power (67 version) and there wasn't a damned thing in so cal that could touch it. No Hemi, no Ford, no nothin. That was an excellent engine for its time and in those days the stud rockers weren't an issue because the cams in hindsight were just not that radical. A Chevelle equipped with that powertrain even today with all the modern technology would easily hold its own against current offerings from various mfg's.
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Re: History of the Chevrolet/GM BBC big block Chevy

Post by novadude »

When racers figured out that you could bolt on rectangle intake to the oval heads and get great results that became the norm to many.
I'd still like to know *why* that works? Just looking at it, you'd think it would be a performance disaster.
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Re: History of the Chevrolet/GM BBC big block Chevy

Post by BrazilianZ28Camaro »

novadude wrote:
When racers figured out that you could bolt on rectangle intake to the oval heads and get great results that became the norm to many.
I'd still like to know *why* that works? Just looking at it, you'd think it would be a performance disaster.
Probably , the bigger intake port area act like a small plenum , a good thing to a starved, big CI engine.

The edges of the port mismatch may shear condensed fuel droplets back into the air stream, next to the valve, improving combustion.

The large difference in port profile would dampen the reverse intake pulse right in the gasket area, reducing the potential flow reversion into the port through all the rpm band.

Just thoughts, no data to prove this, unfortunatelly.
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Re: History of the Chevrolet/GM BBC big block Chevy

Post by pdq67 »

OK!,

I am a fan of the MOPAR 318 engine poli valve layout but I want it to be a modern design and if possible using stud rocker balls...

Like the still-born ball-stud Hemi...

Has anybody ever really looked at the old Willys F-head engine that has the intake valve in the head and the exhaust valve in the block that still has kind of a wedge chamber???

Might consider designing a flat to the piston intake valve with way stood up ports and then put the combustion chamber above the flathead exhaust valve, (centrally located sparkplug), and again with an exhaust port down since it is an exhaust valve flathead design that would be reversed pointed down for max exhaust flow.

Make the combustion chamber tall and skinny, sparkplug on top or to the side like the early BBC closed chamber heads and not worry about emissions.....

RACE STUFF ONLY HERE!!

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

Post by PackardV8 »

Having been there in 1965-1/2 when the 425hp 396" solid lifter Corvette debuted, it was an unmitigated disaster. The valve spring technology of the day wasn't up to handling the long, heavy intake valves at higher RPMs. Every single one of those sold by Tom Gloor Chevrolet in Midfield, AL came back once or twice with a blown engine caused by a dropped valve.

FWIW, it was the same ten years earlier with the 3-speed overdrive equipped 1956 Studebaker Golden Hawk with the 352" Packard V8. Over the years, every one of those I've torn down showed evidence of a dropped valve. In this case, the valve spring retainers were too soft for the long, heavy valves. They'd pull the keeper right through the retainer, drop the valve, break a piston, sometimes the rod would hole the cylinder.

Bottom line - each step up in performance usually catches the engineers a bit behind. Despite long evidence. they can't believe some new car owner would rev the engine to destruction. Warranties tend to make owners a bit adventurous and more than a bit racy. Tom Gloor sold one of those Corvettes to a 20-year-old friend of mine. I knew him and wondered what were they thinking? He had two engines replaced under warranty.
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Re: History of the Chevrolet/GM BBC big block Chevy

Post by pdq67 »

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

Post by ZIGGY »

Many years ago there was a letter to the tech column in HR magazine from a kid asking for help with his problem. It seems the family Chevy kept having valvetrain failures. After multiple warranty repairs, the dealer had refused any further help. The kid wanted to know what was wrong. The answer still cracks me up: "First, hide this magazine from your parents. Then either shift to a higher gear or back off the gas..."
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Re: History of the Chevrolet/GM BBC big block Chevy

Post by BrazilianZ28Camaro »

PackardV8 wrote: Tom Gloor sold one of those Corvettes to a 20-year-old friend of mine. I knew him and wondered what were they thinking? He had two engines replaced under warranty.

On the other side of the coin, we could thank your friend by "obligate" the GM / engineers design better parts when the blow up engines started to comeback to inspection :?:
'71 Z28 street strip car
Pump gas All motor SBC 427
3308 lbs-29x10.5 Hoosiers
NEW BEST ET
1.38 60' / 4.05 330' / 6.32@111.25mph

https://www.youtube.com/watch?v=99p13UK ... ture=share
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Re: History of the Chevrolet/GM BBC big block Chevy

Post by stokerboats »

A word on the old warranty. I was driving my chevelle in 1967 after I installed the L-88 in the car, it was an M-20 muncie 4 speed and I had a diapragm clutch in the car. I had the clutch adjusted a bit past optimal and at somwhere above 7K rpm shifted from 1st to 2nd gear and things went south. The clutch stuck to the floor and over revved the engine thereby kissing the pistons with all 16 valves. I towed the car to a chevy dealer (Guardian Chevrolet in Brea Ca) and believe it or not Chevrolet agreed to replace all the damaged parts at their expense but I was on the hook for the labor. I think it was because it was one of the first L-88's sold to the public but just maybe because I was a GM employee at the time it helped. They guy who performed the work was a drag racer who had a 409 in his race car. He could not believe the power that 427 made. True story.
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