Big-block engines

[Shannow]

I agree with 440Magnum, it's bore spacing typically.

e.g. Lima was (simplistically) a Cleveland, with the photopier set to 1.1:1 (or something like that)

As to the monster mouse small blocks, remember, that's cutting the absolute edge of modern technology, not 1950s and 60s architecture...the 400 SBC was a radical departure to tradition, having siamesed bores etc.

 

[dailydriver]

Originally Posted By: A_Harman
Originally Posted By: JHZR2
Was next to an old chevy C/50 (I think from the early-mid 1970s) today, and it had a 366 badge on it. Got into reading up on the 366, as it is an engine I hadnt heard of.

But my one question is this - what designates a big block v8 from a small block? For example, GM made a 348 big block v8 that apparently sold, even in cars, alongside the small block 350. What's the difference?

Could I make a 6, 7 or 8L V8 that is not a big block? For example, the old 366 was a big block. Is the 6.0L vortec truck engine a big block? What about the upsize V8 engines used in the vette Z06?

Similarly, GM made some giant V6 engines for medium duty trucks back in the 60s. Are they considered big block, small block, or because they are V6, do they get neither designation?

Thanks!


Chevy's small block had a bore spacing of 4.400" and a deck height of 8.900". The big block Chevy is a 10% upscaling of the small-block, with 4.840" bore spacing and 9.8" deck height. The tall-deck big block had a deck height of 10.2", and was built in 366, 427, and 496 (Vortec 8100) displacements.

The 348 big block was the first of Chevy's big block that sold in 348, 409, and 427 (very few) displacements. These are known as the "W-motors" because the shape of the valve covers resembles a W. This engine was built from '58-'63, and was then redesigned with canted-valve heads to become the big-block Chevy.

You could make a 6 or 7-liter small-block, but my opinion is that traditional small-blocks are stretched too far at 400 cubic inches (6.6 L). The Vortec 6000 is the modern small-block (LS-series, as some call it), and has the same bore spacing of 4.400" as the traditional, but has a taller deck of 9.240". This engine is built up to the 7-liter (4.125" x 4.000") displacement that is the LS7 engine of the C6 Z06 Corvette.



^^^THIS!! (At least as far as GM/Chevy are concerned.)

There have been some LSx series 'small blocks' built north of 454 c.i. of displacement, but I for one would not trust anything stretched that far (and cylinder walls that thin, sleeved or not), especially in an alloy block, and am a big fan of at least 'square' if not 'oversquare' engine configurations.

Dart on the other hand even has an alloy 'small block' capable of safely/reliably going to (and above even) 500 c.i., but that is an aftermarket manufacturer, not a GM product.

(This is what's used in the Katech/Pratt & Miller C6RS Corvette.)

 

[SwampSurvivor]

Originally Posted By: hemitom
If i remember correctly the 366 was used to power school buses at one time.


When I was a kid the company my school contracted to ...Ryder I think ... had a fleet of 366 school busses. They had the whninest automatic transmissions ...

 

[Spazdog]

Originally Posted By: Miller88
Originally Posted By: hemitom
If i remember correctly the 366 was used to power school buses at one time.


When I was a kid the company my school contracted to ...Ryder I think ... had a fleet of 366 school busses. They had the whninest automatic transmissions ...


That would have been our IH 345 powered bus

Chatham County Schools Bus #266.

Bus Driver sounded like he was standing on the pedal all the time and it had a distinct and loud whine. Even over the driver's 8-track player playing through a speaker mounted on the forward bulkhead and all the girls (and some of the boys) singing along to the Jackson 5's ABC or the Trammps' Disco Inferno

 

[JHZR2]

Originally Posted By: Miller88
Originally Posted By: hemitom
If i remember correctly the 366 was used to power school buses at one time.


When I was a kid the company my school contracted to ...Ryder I think ... had a fleet of 366 school busses. They had the whninest automatic transmissions ...


In school, we had a walking district, but the town had busses for getting around to events. We had an old chevy and an old Ford. Both had whiny transmissions (both were MY 1987 or 88 as I recall). I thought that was the signature of an Allison AT.

Both town busses were ga$$ers, likely because they were cheaper to acquire and werent used a huge amount. No idea if they had 454/460 engines or something else.

 

[2004tdigls]

366

The 366 Big block V-8 (6.0 L) gasoline engine was used only in Chevrolet Medium duty trucks and in school buses. It had a bore of 3.935" and a stroke of 3.760". This engine was made from the 1960s until the mid-1990s. The 366 used 3 compression rings on the pistons as it was designed from the very beginning as a truck engine. The 366 was only produced as a tall deck engine with a 0.400" taller deck than the 396, 402, & 454 short deck big blocks.

 

[punisher]

One of my high school buds had a dad with 5 C60 tractors he used to haul dirt/road materials with. Everyone had a 427. When they would hit 500/600K miles he would get a new complete GM replacement engine, by complete, from the carb down, everything new. I would swap the engines out, and keep the old ones as payment.

Those tall decks were the ticket. New tall deck intake, MSD dist, and long rods,you were in business. Best deal was the steel 427 cranks. People ate those up.

 

[RH+G]

GM never had an official way of saying it was a big block or small block. Chevy had big and small blocks but pontiac didnt and they went up to 455. It was just a name designation

 

[Garak]

Originally Posted By: hemitom
If i remember correctly the 366 was used to power school buses at one time.


I had one in a gravel truck many moons ago, too.

 

[A_Harman]

Originally Posted By: RH+G
GM never had an official way of saying it was a big block or small block. Chevy had big and small blocks but pontiac didnt and they went up to 455. It was just a name designation


Yes, the Pontiac V8 has the distinction of being built in more displacements than any other V8 of Detroit's golden age: 287, 317, 326, 336, 347, 350, 370, 389, 400, 421, 428, and 455. That's 12 displacements, and the Chevy small block was only built in 9. The Pontiac block was sized between the small block and big block Chevy, but became too stretched by the time they got it to 455, ending up undersquare at 4.150 x 4.210. I think the Pontiac engine was at its best at 400 cubes.

 

[440Magnum]

Originally Posted By: TFB1
Originally Posted By: 440Magnum

When you get right down to it, its arbitrary. In GENERAL, though, I'd say that for the most part anything where the block is long enough to support a cylinder bore of over 4" is a big-block, anything with a bore under 4" is a smallblock. But you can immediately find exceptions like the Mopar 340 (bore 4.04") which is still a smallblock because its based on the LA block that started out at 273 CID.


I'd agree with you IF you'd said 4" stroke but defiantly not 4" bore... Even the miniscule Ford 5.0 small block with 8.2" deck height will support a 4.04 bore but you'll play [censored] getting more than a 3.4" crank inside one of those, that with a .030 overbore produces a 347 ...


That's why this is all debatable ;-) I agree to an extent, but I still think that if you had to name ONE characteristic, its bore spacing that's most critical to whether the block is "big" or not because that affects both length and width as well as cooling system capacity and adequate coolant flow around the cylinders. A manufacturer can come up with a raised deck casting or notched bores that support a huge stroke (look at the Z06 7-liter/427cid LS7 smallblock engine- the stroke is so long that they let the cylinder liners protrude into the sump, and then notch them for the counterweights to clear!) And of course they can "siamese" bores to get those few big-bore smallblocks like the Chevy 400- but the price is paid in longevity most of the time. But if you don't have the length and width, you can't have a *durable* adequately-cooled engine with lots of cooling capacity, which is also a characteristic of big-blocks. A~200 horsepower industrial big-block can run *at* 200 horsepower all day long for days at a time, but a 400-horsepower automobile smallblock usually can't put out half its rated power continuously, although the newer ones are getting there.

All you really have to do is look at an International 345 or 392 block to see how a real, serious big-block engine casting differs from a smallblock. Its physical size and mass of metal so the whirly parts and coolant have extra room. And the cylinders of a 345 are spaced so far apart that you could practically shove your hand through the space between them inside the water jacket.

 

[440Magnum]

Originally Posted By: A_Harman
The Pontiac block was sized between the small block and big block Chevy, but became too stretched by the time they got it to 455, ending up undersquare at 4.150 x 4.210. I think the Pontiac engine was at its best at 400 cubes.


That's basically what SteveSRT8 said in another thread, and I think I agree (although I know less about Pantycracks than I do about most other GM engines) Buick's engine is the one that's interesting to me- they put a huge displacement in a very small amount of metal with their big block. I've read that a fully-dressed Buick 455 weighs about the same as a fully dressed stock Chevy 350 smallblock. But it could still support a huge bore (4.3" stock in a 455) where the Chevy smallblock couldn't- the Buick was the *only* one of the three GM 455cid engines (Buick, Pontiac, and Olds all had 455s) that was undersquare with a bore bigger than stroke. And it made the power, too- the Stage II 455 held the factory stock 1/4 mile record for a couple of decades IIRC. The downside was that they had to have some block reinforcement (main bearing cap girdle, etc.) at the higher powers where things like the Olds and Mopar big-blocks did not. Buick is usually overlooked when it comes to 60s and 70s muscle cars, but the 455 Stage II GSx was a *beast*. Probably one of the best overall muscle cars ever.

And speaking of stretching an intermediate-sized block WAY past its initial displacement- don't forget the AMC 401, either. I think it was at its best at 390 cid.

 

[Hokiefyd]

Originally Posted By: 440Magnum
the Buick was the *only* one of the three GM 455cid engines (Buick, Pontiac, and Olds all had 455s) that was undersquare with a bore bigger than stroke.


A bore larger than stroke -- that's oversquare, right?

The Olds 455 was undersquare, at 4.126" bore and 4.250" stroke.

 

[TFB1]

Originally Posted By: Hokiefyd
Originally Posted By: 440Magnum
the Buick was the *only* one of the three GM 455cid engines (Buick, Pontiac, and Olds all had 455s) that was undersquare with a bore bigger than stroke.


A bore larger than stroke -- that's oversquare, right?

The Olds 455 was undersquare, at 4.126" bore and 4.250" stroke.


Correct...

Probably the best identifier of a factory big block is that it can support at least a 4.1" bore & 4" stroke(not that it necessary had either).. Even this definition isn't going to cover all the engines produced... Small blocks from 4" bore and 3.5" stroke while intermediate engines are between the two... There are just too many variables say it's either big or small...

Those 455 GS Buicks are the ones that often embarrassed the LS6(450Hp) 454 Chevy guys... Was especially mortifying cause the Buick was rated at 360Hp...

 

[Hokiefyd]

Originally Posted By: 440Magnum
And speaking of stretching an intermediate-sized block WAY past its initial displacement- don't forget the AMC 401, either. I think it was at its best at 390 cid.


The distinction for the engine series with the widest displacement range, at least on the same stroke and using only bore changes for the difference, may be the Olds small block. They were as small as 260 cui. and as large as 403 cui. The 260 had a 3.5" bore, all the way up to the 4.35" bore of the 403. In fact, the 403 was noted as being more prone to overheating because it used siamesed cooling passages in the block because of the relatively thin cylinder walls between cylinders.

Here are a few pictures of the 403 I built for my '87 Buick Regal.

Look at those close bores. That's with a .030" over hone as well. Large components are all factory Oldsmobile, including the correct 4A heads (though with slightly larger valves) and aluminum EGR intake from a 307 (same port size as 403).

 

[440Magnum]

Originally Posted By: Hokiefyd
Originally Posted By: 440Magnum
the Buick was the *only* one of the three GM 455cid engines (Buick, Pontiac, and Olds all had 455s) that was undersquare with a bore bigger than stroke.


A bore larger than stroke -- that's oversquare, right?

The Olds 455 was undersquare, at 4.126" bore and 4.250" stroke.


Yep. I fumble-typed. The Buick (and all Mopar big-blocks) are oversquare, the Olds and Ponchos are undersquare. So are a lot of modern engines because small bores burn cleaner, leaving stroke as the more viable way of increasing displacement.

 

[440Magnum]

Originally Posted By: Hokiefyd
Originally Posted By: 440Magnum
And speaking of stretching an intermediate-sized block WAY past its initial displacement- don't forget the AMC 401, either. I think it was at its best at 390 cid.


The distinction for the engine series with the widest displacement range, at least on the same stroke and using only bore changes for the difference, may be the Olds small block. They were as small as 260 cui. and as large as 403 cui. The 260 had a 3.5" bore, all the way up to the 4.35" bore of the 403. In fact, the 403 was noted as being more prone to overheating because it used siamesed cooling passages in the block because of the relatively thin cylinder walls between cylinders.

Here are a few pictures of the 403 I built for my '87 Buick Regal.

Look at those close bores. That's with a .030" over hone as well. Large components are all factory Oldsmobile, including the correct 4A heads (though with slightly larger valves) and aluminum EGR intake from a 307 (same port size as 403).


Pretty engine, but that thin head gasket separating the cylinders is kinda scary! Yet the 403 Olds held up better than the 400 Chevy, at least as far as blowing head gaskets between cylinders was concerned. Wasn't the Olds 403 also used in a lot of 6.6L Firebirds instead of the Poncho 400 (which was the more desirable engine). I'm getting to the raggedy edge of my GM knowledge there...

Another advantage of "big" blocks, especially evident in the Chrysler line, is pushrod angle. Chrysler engineers liked to always keep a big separation between the cam and crank, allowing for big rods and/or a long stroke without squeezing the counterweights too close to the cam. In the LA smallblocks they raised the cam to the point that the lifter angle is significantly mismatched from the required pushrod angle, so there's a significant side-loading on the lifters. It rarely caused problems except in high-RPM modified engines, but it still offends my sense of symmetry to see that mismatched angle. The big-blocks keep the lifters directly in-line with the pushrods. Of course the Chevy Rat big-blocks and some other engines including the 426 Hemi did the same thing to the pushrod/lifter angles for different reasons (splayed valves in semi-Hemi or Hemi heads).

 

[SteveSRT8]

Ah, porcupine heads. One of my favorites...

400 Pontiac motors were still being used as late as 1979 in Firebirds, and were still running pretty respectably in the WS-6 package, just very limited production. There was also a wheezy 185 hp version of the 400 ponco that was still a great motor to build up, just not much stock. My 78 Trans Am had the low output version and we were VERY surprised to find double roller timing chain with real steel gears as well as forged pistons in there! A simple cam and head swap was good for 2 seconds in the quarter mile, car ran 12.89 at 110 with 2.56 gears on street tires using only first and second gear in a TH350!

Sorry, but the 403's were regarded pretty poorly. They were stone slow stock and usually quickly [censored] out with any real mods.

 

[Hokiefyd]

Originally Posted By: 440Magnum
Wasn't the Olds 403 also used in a lot of 6.6L Firebirds instead of the Poncho 400 (which was the more desirable engine).


Yes it was.

The Olds 403 was really an engine that shouldn't have been. And even once it was, it was really choked down by emission controls and economy regulations.

The cylinder bores were too large for their own good. As you note, it's easier to control combustion in smaller bores. With the stroke limitation that Oldsmobile was dealing with (3.385"), pushing the bores to the max was the only way they could get their own 400+ cubic inch motor in the small block configuration. You also had to make sure the EGR system was good, or you'd get a good amount of spark knock from those wide cylinders.

This thing had a puny 180 or 185 hp rating stock. Torque was good, at 320 lb*ft, but it peaked at a super-low 1600 rpm. It's clear that it was tuned more like an RV motor; and to be fair, it was usually pulling around big Delta 88s and Regency 98s (which is what mine came from, a '79 Regency 98). The engine REALLY wakes up with some larger valves and a better camshaft. I had a hotter cam in mine and the Regal already had a relatively short (for a standard G-body) 3.08 rear axle ratio. It moved that Buick around pretty good.

 

[mechtech2]

GM Chevy made a 400 small block. No coolant between the cylinders!
Big block / small block are terms from when there were only few USA engines considered for high performance.
It means very little.