BBC weak points

[DanE1]

9.8" deck too short.
Lifter valley has no oil drain back Gallery. Oil has to drain through the center of the lifter valley and onto the cam and the rotating assembly.
The cam and crank center lines are too close.
Lifter dia too small.
Push rods too long.
Crankcase too narrow.
Head bolt holes go into water jacket.
Head bolt holes go to deck, not block
Head bolts at 7/16" are too small in dia.
Deck to thin.
Combustion chambers too big.
Pistons too heavy to make compression.

Off the top of my head at the moment. And yes, we know that they still make power, but could make more with more reliability.

[swampbuggy]

How is the deck not part of the engine block Mark H.

[DanE1]

Never said the deck was not connected to the block
I said that the head bolts to the too thin deck with too small in dia bolts that go into the water jackets.
I know of other engines where larger dia bolts do not go into the water jacket and they anchor into the block, not the deck. And don't distort the bore anywhere near as much with much stronger clamping force.

[Walter R. Malik]

I was under the impression from reading about it, that this newest engine was to be a truck engine and designed as an improvement to their latest 8.0 liter engine, with that in mind; not designed to be a racing engine but, we all know it would get that type usage if viable.

[FC-Pilot]

Port layout
Combustion chamber
Valve angles

Plenty more if I sat and thought about it.

This was a fresh idea that if done by the oem could have been an improvement.
viewtopic.php?f=1&t=46635&p=788829#p788829

Paul

[Sparksalot]

Weak points: it evolved from a late 1950's era Chevy engine and it has carried some of that old architectural baggage along with it for about 55 years. It was first available to the public in 1965 (had a 396 Malibu SS 4-speed new) not too long after the Mystery Engine debuted. It was the typical cast iron engine lump which roared.

It's an old design which has been extremely successful beyond all expectations of people challenging it in all sorts of racing competition. CanAm racers overcame its good port/bad port to the extent possible fifty years ago. Yes, it's a flawed design as all are. It's the most supported by the aftermarket big engine.

I'm always happy to be moved by one.

[mag2555]

I am more then sure that Chevy engineers are more than capable of getting what they need out of the motor, and with the state that GM seems to be in I am sure the upper management will not let them spend one red cent thinking about getting more performance and longevity out of the motor, once again other then what there needs are!

[bobmc]

hard to please someone who objects to short deck and and long pushrod, if you raise the cam, people will object to the pushrod angles and the timing chain length. I don't know what the oil pump drive problem is?

[Newold1]

9.8" deck too short.
Lifter valley has no oil drain back Gallery. Oil has to drain through the center of the lifter valley and onto the cam and the rotating assembly.
The cam and crank center lines are too close.
Lifter dia too small.
Push rods too long.
Crankcase too narrow.
Head bolt holes go into water jacket.
Head bolt holes go to deck, not block
Head bolts at 7/16" are too small in dia.
Deck to thin.
Combustion chambers too big.
Pistons too heavy to make compression.

Off the top of my head at the moment. And yes, we know that they still make power, but could make more with more reliability.

Dan has done a nice job of hitting some of the major points. For an engine design that is over 50 years old Chevy did a good job back then that hit the mark early on and with all these years of factory and aftermarket tweaking and variations that has kept this design strong and competitive.

I hope if GM does this that they spend enough effort and money to allow a bit of a "clean sheet of paper" design that will be the best new generation of the GM pushrod-OHV larger cubic inch engine.

I think from a simplicity standpoint, just take the basic LS-LSX design and increase the bore centers to a 4.90" and use a tall deck 10.50" deck height large bore 4.375" or so and a 4.250" stoke, long forged rod and lightweight struted piston. The block can be a nice strong deep wide sump CGI material and a nice set of aluminum long symmetrical ports and an 11-12 degree valve angles and small combustion chamber design with simple LS type rocker arm and short pushrod design. Keep the weight down and make sure this big boy makes it's torque in the 1500 rpms range at 400+lb/ft. and at 3500 rpms it make about 600lb/ft. This is what GEN 8 big block needs to be in my opinion.

This is an engine that can put Ford's new 7.3L "On the Bus" and help eliminate the needs for expensive diesels and maybe help keep the cost of medium duty pickups and trucks out of the stratosphere and more affordable.

[Walter R. Malik]

hard to please someone who objects to short deck and and long pushrod, if you raise the cam, people will object to the pushrod angles and the timing chain length. I don't know what the oil pump drive problem is?

AND, their most recent 8.0 liter engine did have symmetrical intake ports.

[Newold1]

Walter, you got me on that one. GM has a recent 8.0L big block engine with symmetrical ports??
Oh I am catching on now you mean that 8.1L 496 iron boat anchor beast that was basically a lightly modified 454 Vortec.
That engine was short lived, barely met modified emissions, to heavy, drank oil and gas like a drunken sailor. If that's the best GM engineers can do , fire the idiots and hire some new ones! They developed and released the LS engines at the same time 1999 and look at the difference in all aspects of the two engines! No decent comparison!

[Alan Roehrich]

Walter, you got me on that one. GM has a recent 8.0L big block engine with symmetrical ports??
Oh I am catching on now you mean that 8.1L 496 iron boat anchor beast that was basically a lightly modified 454 Vortec.
That engine was short lived, barely met modified emissions, to heavy, drank oil and gas like a drunken sailor. If that's the best GM engineers can do , fire the idiots and hire some new ones! They developed and released the LS engines at the same time 1999 and look at the difference in all aspects of the two engines! No decent comparison!

I'm amused at what a piece of junk my truck apparently is. It gets 11 MPG with a decent load, it uses far less than 1 quart of oil in 3500 miles, it pulls the maximum load it is rated for with relative ease. It does all of that with little or no maintenance or repairs, consistently, reliably, and affordably. My buddy's 3/4 ton is apparently junk, too.

[Alan Roehrich]

As to the original post, what is wrong with the big block as a TRUCK engine for TRUCKS with a GVWR of 10,000 pounds or more, needing instant torque at as low an RPM as feasible, and maximum power at no more than 5500 RPM?

Actually, not much.

The crank case on even the old Mark IV is wide enough to contain a 4.5" stroke with steel connecting rods. The newer version does not have the oil gallery at the pan rail, which allows for a 4.750" stroke with steel connecting rods. The truck in question will not need more than 4.375" stroke, as displacement with the requisite bore size is around 4.250".

The lifters are big enough, as it will certainly be a hydraulic roller cam engine.

The cam is more than high enough.

At 5500 RPM, pushrod length is irrelevant, especially given the cam is not likely to be bigger than 210 @ 0.050" and 0.500" lift. Even a 3/8" diameter pshrod is stiff enough.

The missing head bolt means... nothing. The engine won't exceed 10.5:1 static compression, and will not be supercharged.

The deck height is likely to be 10.200", where the tall deck has been since the late sixties, and where it was on the 8.1L, plenty tall. More than adequate for a long stroke and a long connecting rod.

The deck is thick enough. Again, 10.5:1 at best, no supercharger.

The later big block engine blocks have blind head bolt holes.

The 7/16" -14 head bolts, again, will easily hold 10.5:1 compression.

At 100-110cc, with approximately 480-500 cubic inches, 10.5:1 compression doesn't require much dome. And besides, with a peak HP RPM of maybe 4800 RPM, how light do you need the piston to be?

Stop thinking that you're going to get some sort of magic big block truck engine that will be the basis for a world altering race engine.

Speaking as the exact customer GM would be looking to appeal to, none of the "improvements" people keep asking for mean ANYTHING to me for my TRUCK engine. IF, and it's a big if, GM decides to do this, they're trying to sell a big cubic inch pushrod gasoline engine to people who do not want a diesel, they want an inexpensive, simple, reliable gasoline engine. They're NOT trying to sell a race engine to people with WORK TRUCKS.

What can they fix on their last big displacement gasoline truck engine?

The intake is not great, honestly it's pretty poor, it has too much restriction, and the distribution sucks. The plenum has a lot of bias in it, and the inlet is restricted behind the throttle body that is far too small. Of course, the air intake system from the filter box to the engine is poor, it is restrictive,and the MAF is small enough that removing the screens reduces the restriction and improves power on a dead stock engine.

The PCV system draws directly from the lifter valley with little or no baffling, so it sucks oil into the intake system, and THAT creates a lot of the oil consumption.

The pistons are not a great design. The ring seal isn't great, the compression is low, and some of them have piston slap and increased oil consumption.

The heads aren't great. They flow okay, but not really good enough if the engine is to be more efficient. They could be aluminum to reduce weight, but at the cost of thermal efficiency.

There are a LOT of the old 8.1L engines with a modified intake, a bigger throttle body, a very mild camshaft, a good tune, and decent exhaust making an easy 450HP and well over 500 ft/lb, while still getting 14-15 MPG, and even around 12 MPG fully loaded. The emissions aren't out of control, either. GM can easily get there without any "clean sheet of paper" redesign, and the attending expense and high warranty risk.

[prairiehotrodder]

is this thread about the old original BBC engine or the newer ones ?

I don't know much about the newer engines but sure like the older rat motors for most types of racing. From a drag racers standpoint i'd say the biggest downfall is just the weight. Most other weak points can be fixed easy enough but having all that weight on your front end is hard to deal with. Of course with enough money even that can be reduced.
Brian

[Dave Koehler]

I was under the impression from reading about it, that this newest engine was to be a truck engine and designed as an improvement to their latest 8.0 liter engine, with that in mind; not designed to be a racing engine but, we all know it would get that type usage if viable.

chuckle. When did that ever stop us?