27th Dec 2004, 02:29

Coming from Germany and driving US cars since nearly 20 years I never heard of a 400 cu Chevy Big Block. 400 is a small block and e.g. 396 is a big block. As the word says the size of the block matters no the displacement.

27th Feb 2006, 01:49

There is a 396 big block. There is a 402 big block which is a 396 bored 0.030" over. There is a 400 SMALL block. The biggest small block is the 400, while the smallest big block is a 366 (found in school buses etc).

It has nothing to do with displacement. They are two different designs. Apple, and orange.

If you want to tell the diff between a small block Chevy and a big block, pop the hood and look at the exhaust manifolds. If the two middle exhaust ports are "siamesed", it's a smallblock. If all four ports are equidistant, it's a BIG block. Enough said!

15th Mar 2006, 23:42

The guy from the 5th of November is correct.

24th Mar 2006, 16:51

I just couldn't resist to respond to the engine size debate. I own a 1973 Caprice Classic Convertible fully loaded with the factory 454, and it is indeed a big block. Back in high school, I owned a 1973 Impala, no accessories, with a 350, and compared to the 454 the 350 looked lost at sea in that engine compartment.

These cars were built solid by todays cars standards. The bumper thickness gives you the first clue, I don't know how many times I hit my shin leaning over the front end, and that hurt, and the car was stationary. Fortunately the only crumple zone you'll encounter if heaven forbid you're in an accident in one these cars is the other car.

24th May 2006, 02:08

What production engine was 505-cubic-inches?

The largest post-war V-8 I've heard of is the '70-'76 Cadillac 500-cu.-in. engine.

13th Jan 2007, 15:55

Even the Oldsmobile 6.6 Liter 403 V8 is a small block. It shares the block with the 260, 307, and 350. Being Over 400 cubes has nothing to do with the block size. The 403 does hsae the largest bore of any gas postwar V8 in a passenger car, If I'm not mistaken: 4.351 inches.

29th Mar 2007, 07:27

Actually guys, the Corvette uses a 427 which is considered a small black, it is just bored and or stroked more, can't remember, but either way, the 7 liter Z06 Corvette is a small block. Also, Chevy Performance Parts is getting ready to release a 454 small block, an even more performance oriented small block that is stroked and bored out the ass!! The block is being called the LSX and will be available through GMPP. But back on topic, the 400 standard bore and stroke is a small block. The 396 is a big block.

5th Apr 2007, 05:32

The 400ci small block is not a big block. Now. I have put a 454 crank in to a small block 400, but it's a small block 400 anyway you look at it. The 400 can't put out the power a big block can without flying apart.

6th Oct 2007, 10:15

5 April guy that put a 454 crank in a 400 must be a machinist extraordinaire or a magician. Big blk cranks are of another breed!

6th Oct 2007, 16:01


Small block vs. big block has to do with bore spacing, not displacement of the engine (400 vs. 396, etc.). To the best of my knowledge, the "small block" has a bore spacing of 4.4 inches, while the "big block" has a bore spacing of 4.84 inches. Naturally, they are different castings, and the "big block has larger external dimensions. The comment about the different exhaust manifold configurations between the two is also correct. They are both awesome engines, as is the new Chevy LS series. I'll definitely take mine (LS) in cast iron though, not aluminum. They are available in both.

9th Oct 2007, 21:25

I recently purchased a 1973 Caprice Classic with a 400 small block. The 400 may be a small block V8 but I do not agree with anyone who says that a small block V8 cannot produce as much power as a big block, that's all a matter of opinion. Its all a matter of displacement and how much torque the engine can produce. most people will argue that since there is less steel on the small blocks, they will come apart under high pressure, but this is simply not true, only die hard big block lovers will say things like that.

10th Oct 2007, 01:59

About the 400 small block and the 396/402 big block Chevy, in terms of potential torque there would be next to no difference between the two groups of engines, all things being equal. But as I learned from racing many moons ago, the 400 small block has a more limited peak rpm than the 396/402. The 400 small block was only safe up to about 6200 rpms, while the 396/402 was good to 7000 rpm and even greater. This is where the big block would have the advantage in the horsepower race.

The Chevy 400 small block generally had a relatively low power peak at around 3600-4000, thanks to a modest 2-barrel carburetor, while the 402 4bbl's power peaked at around 4400, with high-performance engines going to 5200-5600 rpms (and sometimes higher.) However, had the small-block been equipped and tuned similarly to the 402/396, there would be no reason to expect any less performance.

28th May 2008, 17:10

Hey Chevy lovers, I have a Chevy small block 400 motor, and I still have the front radiator cover. Mine reads 350-400 cubic inch 6.6 4barrel.

26th Dec 2008, 19:55

The term small block and big block refer to the external size of the block and have nothing to do with the internal size i.e. cubic inches. Any gear-head can immediately identify either by a visual look. Nuf said!!!

8th Jan 2010, 21:59

I own a 73 Caprice Classic 4 door with the 454 c.i. big block, A/C, power windows and the 50/50 spilt bench with power drivers side control. I'm in the process of getting it back on the road.

My question is the power seat; it has seized, and I can't get the seat out because the track is seized, and the electric motor won't turn the seat mechanism anymore. So I took out the electric seat motor, it still spins when hooked up to 12 volts, but seems to make not much torque anymore, took that out to try and turn it by hand, but it needs power to make the actual transmission in the seat work, it's really tight in the working space, but it's not as large a space as I thought it would be. Any advice would be sweet.

23rd Sep 2010, 19:29

The biggest small block is the 403 Olds, which is a bored out Olds 350.

1st Oct 2014, 12:38

Big block does not mean that it contains more cui's, but occupies more space under the hood due to the overall engineering and material differences. So, you can have a 350 cui small block as well as a 348 cui "big block".

3rd Oct 2014, 11:57

So our choices are a 454 with 245 HP or a 350 with 175 HP. This is a 1973 model. I have owned 4 Impalas pre 73. This is a large heavy full framed car that's well suited for families. Or cruising. I would focus on finding a good example that runs smoothly. And with cold air.

I was never a fan after 72 due to the government insistence to add anti pollution new bumper laws. It was a low point with gas guzzling underpowered models.

Now you can buy 638 HP in a Cadillac. And even a manual trans in a Cadillac.

70 to 72 I would rather have a well optioned Monte Carlo 454. There was even a 4 speed model.

After 72 I liked a Cadillac convertibles or even a Pontiac CanAm. The rest of the 70s was bleak except for the TransAm.

The Impalas from the start were not great handling cars. Even the 409. The advantage is a full frame for a restorer.

I have owned a variety of GM models over the past 34 years of driving. This car is a good cruiser, rides nice and has room.

If you are on the HP topic, pick a mid size 2 door or a 69 to 72 sub frame model, and just add frame connectors when you drop your 427 in.