BBC vs SBC do you notice a big difference?

[71400lb]

Just wondering if I'd notice a huge difference or hardly any if I had the 396 (402) big block Chevy in my truck instead of the 400 Small block Chevy I have now?

My SBC is a 400 bored .30 over with a 4 bbl Quadrajet carb, and a Competition Towing cam...the motor is actually out of a 1972 Chevy Nova(and I believe it has the stock heads, whatever they were on 72 400"s in Nova's).
Rest of the line-up includes a T400 3 spd and the H052 rear with 3.73 gears open differential.

Thanks,
Rick
1971 Chevy Cheyenne
C/20 Long Bed

[CHEVYE]

i don`t know about your combo but i went from a 350 sbc to a 454 bbc. the bb kills a 350. it seems slower since it doesn`t rev as fast i guess but it puts you back in the seat. the engines you have sound pretty similar in stroke and size, there may not be too much of a diff with weight factor and all.

[1972C10]

the 400 sb isnt going to have as much Torque as the 400 BB due to the big block having more reciprocating mass.

[crazy longhorn]

the big diff in power on the 406 sb vs the 402 bb will be in the heads.....kind of tit for tat IMO , if you are running aftermarket heads on the sb if you get into a 460+ inch BB , the compairison is a joke.....that bb will flat @ss kill that mouse motor! crazyL

[CHEVYE]

big blocks rule!!!

[miket]

When cubes are close---the terms BBC and SBC are irrelevant (some may disagree). What becomes relevant are the bore and stroke of each, their heads and intake systems and weight. All of these factors make a big difference in the two motors. From what I have read, it is a little more challenging to find high flowing heads for big inch small block motors (less material to work with)---however that isn't something to worry about for your existing combo.

My guess is---if you had the same components in each motor (relatively speaking) I would only guess that the BB motor might make more power due to the heads and intake. I believe it would also make power (HP and torque ) in different rpm ranges----this you will most likely notice more than anything else. You may feel the BB pull harder in the rpm ranges that you usually drive your truck and maybe less in the higher rpm ranges....just depends on the variables above.

All this goes out the window when you compare a SBC 406 and a BBC of larger displacement---there is no replacement for displacement---unless it's virtual displacement like a turbo, blower or NOS.

[68C15]

the main reason that a BB has more torque is due strictly to the fact that it has more stroke. stroke is where the combustion happens. if you were to put an MSD 6A on the 406 SB then you would have close to the torque of the BB but have less cost.
BTW, horsepower is a mathematical derivative of torque. build for torque & HP will follow. about 4 years ago I built a 355 that put out 435ftlbs @ 3800rpm using this theory.

[shuttermutt]

...and big blocks go to 11!

[stllookn]

Very interesting question. Here are the stock numbers for these engines:

'70 sb 400 4.125 x 3.75 265 hp @ 4400 400 ft-lb @ 2400 9.0:1
Firebird Ram Air IV
'69 sb 400 4.1212 x 3.75 370 hp @ 5500 445 ft-lb @ 3900 10.75:1

'67 bb 396 4.094 x 3.76 325 hp @ 4800 410 ft-lb @ 3200 10.25:1
'69 bb 396 4.094 x 3.76 375 hp @ 5600 415 ft-lb @ 3600 11.0:1
'70 bb 402 4.126 x 3.76 350 hp @ 5200 415 ft-lb @ 3400 10.25:1

'70 bb 454 4.251 x 4.00 360 hp @ 4400 500 ft-lb @ 3200 10.25:1

These engines have basically the same potential...virtually no difference in bore and stroke except the rpm at which maximum torque is developed. The numbers for the Chevrolet sb 400 are with a 2 barrel since I don't have the truck 4 barrel configuration but listed the killer sb 400 (put into the Firebird) to show the potential with that engine.

The summary...if you are considering big block...go BIG BLOCK 454+ to offset the weight difference! You really have to look at the entire torque curve to see how flat it is...that is what will accelerate a big heavy truck.

[67shortie]

Originally Posted by 1972C10

the 400 sb isnt going to have as much Torque as the 400 BB due to the big block having more reciprocating mass.

Not totally true, the 396 BB has a 3.76 stroke crank and the 400 SB is at 3.75 and 4.145 bore.

Where the difference is is in the stock heads, BB oval ports let the thing breath. The design lets the valves breath with the bore size that it has. The downfall to the small block getting into that bore size is the limitations of the head design. It shrouds the valves and hinders flow.

I believe Car Craft did a apples to apples (sort of) comarison against the SB 400 and 402 BB with similar builds into a 70 Camaro and the 402 won out everytime (1/4 mile) This was a few years ago, sorry no links.

Me, I like the 400 small block, but in lighter cars. A 402 BB will be at home in your truck's engine bay.

stllookin, thanks for posting those #'s that is what I was after :p

[Bobalouie]

Just for fun, I DD'd a 427 BB and a 427 SB, and the power potential was the same. They both made within 10 HP and within 20 lbs-ft of torque of each other. They had vastly different head flow rates, and cam specifications, and the SB made its power about 1000 RPMs higher than the BB. The SB 400 runs a 4.125" bore x 3.75" stroke, and the BB 402 runs a 4.125" bore x 3.76" stroke. Tit for tat on reciprocating masses, etc. It all comes down to the head/intake flow and the differences in what you have to do with the cams to get all the power out.

[boraxman]

'70 sb 400 4.125 x 3.75 265 hp @ 4400 400 ft-lb @ 2400 9.0:1
Firebird Ram Air IV
'69 sb 400 4.1212 x 3.75 370 hp @ 5500 445 ft-lb @ 3900 10.75:1

I believe these are actually big block Pontiac engines. I had one and it was big.

[skid]

The 400 small block will make more torque than a 396 big block, and the big block will make more horsepower with all things being equal (cam, compression, carb., etc.). The reason for this is in the heads. The s/b has smaller heads which have more velocity which is good for low end torque. The big block ports are much larger, which is better for higher rpm and hp.

I dug into the archives (Chevy High Performance 1999) 7 best engine combo edition where they have similar built s/b 406 vs. 408 rat. Small block best torque was 509 @ 4000 vs. big block 465 @ 5000. Horsepower was s/b 452@5300 vs. b/b 480@6000. Estimated 1/4 mile for the same car was s/b 12.29@114.1 vs. B/B 12.21@116, so the big block would be a fender length ahead. However the small block would be a slightly better driver/tower due to its better low end torque. But the difference would be small.

Really, a big block vs. a small block of the same size and spec's will be very equal. I have a 480 hp/500 torque 406 small block motor in my Vette (with a very mild 222 intake duration @ .050" camshaft), and there are not too many street big blocks that can out run me, least 'round where I live.

[neonlarry]

I looked at a 78 chevy truck with a stock 454. It was very very slow. For a stock engine, I would actually prefer a 350. If I wasnt worried about gas mileage, and I had money for aftermarket heads, thne I would think about a 454. I havent ever driven or ridden in a vehicle with a built big block, but I was not impressed at all with the stock ones I have seen. It all just depends on how much money you have, and what you want to do with it.

[bigjimzlll]

I see no reason for the 396-402 BBC for performance....sure they made good HP back in 69-70...but the valve train is the killer in the small Big blocks..and ofcourse the weight..if you gotto go BBC....468 or larger by all means

[1972C10]

What im saying is the big block would have more torque due to heavier rotating assembly.

[68hotrod]

I have the same combo in my truck now. Sbc 400 30 over with a comp 270h cam and vortec heads and is putting out so were around 400hp. It is backed up by a th350 and a 3000 stall with 373s in the rear. And I have a friend with a 402 out of a 72 C-20 in his nova and we stay side by side. So I would put better heads and a bigger cam in the sbc it will be cheper. But that is just me.

[71400lb]

Well, I can't say that I'm dissatisfied with the performance of my 400 sbc. I don't know if this means anything, but the truck will lay a pretty good streak of rubber on the pavement from a stop(maybe 20-25 feet), with the 3.73 rear gears(open diff).

I also have a 1967 Chrysler 300 with a big block 440/4 bbl, auto with 2.76:1 gears(open diff)...From a stop, the Chrysler will burn rubber for about 60 feet!

In comparing the two, they both weigh near the 4500 lb mark...
The 400 sbc seems to have more "umph" off-the line than the Chrysler, and it's easier to break the tires loose.(probably because of the 3.73 gears, right?)

The Chrysler with the big block is respectable off-the-line, but the sbc would jump out ahead by about a length...but on the highway is where the BB Chrysler comes into its own...at 60-65 mph, the Chrysler would easily pull away from the truck, and probably burry the 120 mph speedometer if kept floored.

But again, I suspect the gearing has alot to do with these differences.


Thanks for all the replies,
Rick

[Joe67]

"There is no substitue for cubic inches"

[skid]

!972C10, The dyno does not back up your claim that a heavier rotating assembly will make more torque. Actually, a heavier rotating assembly is a detriment to accelleration. That's why people try to lighten the rotating pieces as much as possible.
What a heavy flywheel/crank does have going for it is momentum. Makes it harder to stall a manual vehicle when leaving a stop

[browndawg71]

Displacment Is King . I Have A 468 With 781 Oval Ports 248@ 50 Solid Lift Cam , Roller Rockers , 10-1 Compression, Total Investment Of 2500.00 . It Rear Wheel Dynoed At490 Rwhp And 600 Rwt. Displacment Is Why Small Blocks Are Being Built So Big Nowdays

[miket]

Originally Posted by browndawg71

Displacment Is King . I Have A 468 With 781 Oval Ports 248@ 50 Solid Lift Cam , Roller Rockers , 10-1 Compression, Total Investment Of 2500.00 . It Rear Wheel Dynoed At490 Rwhp And 600 Rwt. Displacment Is Why Small Blocks Are Being Built So Big Nowdays

Thats great and I am with you---but the question and debate--which is a good one---had to do with two engines having identical DISPLACEMENT but built on the small block and big block castings. Assuming the stroke and bore are the same, I can only surmise the difference will be in the heads (and possibly intake?) of the two units----assuming you would be testing "as originally equipped" heads on the two motors. The flow rates of each and the intakes of each will have the largest impact on the qty of power they make and where it get's made--- (this assumes the originally equipped cams are close as well).

Does that sound right---all other things being equal?

[Bobalouie]

All things being equal, I agree with you. The above example I quoted with the 427's was with me iterating to find the cam specs that worked with various heads on both engines to find the most power and torque that each one would produce. And like you said, nearly equally sized engines with nearly identical bores and strokes, make similar power and torque, they just do it at very different RPMs. Or at least they appear to on paper.

[LONGHAIR]

I believe these are actually big block Pontiac engines. I had one and it was big.

No such thing as a "big block" Pontiac......or small block for that matter.
They were all the same.
326,350,389,400,421,428,455 are all the same block (externally) they do have different bore sizes obviously.