What makes the 396 a BB and the 400 SB?
Wouldn't they have almost the same performance capability?

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JARRET GRATHWOL
TEAM CHEVELLE MEMBER #573

1970 Chevelle SS 396- Documented Number Matching Original.
"Tuxedo Black" with white stripes and Ivory interiour with Factory Guage Package
Built NNM 396 inside- 427 Heads, 780 Holley, Roller-Tip Rockers, Edlebrock Performer RPM, Weiland Water Pump, Hooker Heders, DynoMax 3" exhuast.
Original M-21, Functional Cowl Induction, Original Sheet Metal
Number Matching 396/350 being built-up.
You can see my Chevelle SS here:
http://www.geocities.com/stangsvt99/Jarret_s__70_Chevelle_SS.html

Totally different engines. The small block 400 is from the 265/283/327/350 engine family. Externally it is the same size as the above mentioned engines with more internal displacement than the 396. The 396 is the same engine family as the 402/427/454. Wide valve covers make them easy to spot.

The 400 small block is a fun torquey motor.

There's always SOMEONE who doubts me when I say there is a 400 big block, so I put-together this page:

http://home.netcom.com/~radiojoe/Malibu.html

Joe

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"Yes, I'm still workin' on those Chevelle radio pages!"

Coppertop, I read through your page, and seeing as you say the 396 actually displaces 402ci and the 400 displaced 402ci it seems like a little more than a coincidence and would lead me to believe that they are the same engines but just referred to by different names. I'm not trying to start an argumen or say your wrong because I really have no knowledge on this topic.

If they are different engines what makes them different?

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Chris Dagenais
Saskatchewan
'71 Malibu with a home built 454!
My Chevelle (http://www.ycworld.dynip.com/home/car.html)

Chris,

No offense taken http://www.chevelles.com/forum/smile.gif,

Actually I've got to update that page. Initially in my research I came across "..based on the MARK IV Big Block..." but after talking to some people and thinking it over I'm now led to believe that YES the "400" 402 uses the same block as the "396" 402. I can't comment on any heads difference at this time, but the cam used in the "400" was basically the old '69 396 325hp cam. Left-overs perhaps?!

Basically the same thing.

Joe

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"Yes, I'm still workin' on those Chevelle radio pages!"

I've heard that there was some sort of mistake with the 1970 396 that caused GM to over bore all 1970 and most 1971 396's .030 which equals 402. Some were called 396's and some were called 400's even though all were 402's. I dont know, I dont know, I just heard.

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Ray (NJ)
72 BB Chevelle
A.C.E.S #3750

<BLOCKQUOTE>quote:</font><HR>Totally different engines. The small block 400 is from the 265/283/327/350 engine family. Externally it is the same size as the above mentioned engines with more internal displacement than the 396.<HR></BLOCKQUOTE>
So, the SB 400 is internally LARGER than the BB 396/402??
What makes a BB a BB and what makes a SB an SB? Internal size or external size?
Or is the 400SB and the 396/402BB the same block just bored differently?
<BLOCKQUOTE>quote:</font><HR>The 400 small block is a fun torquey motor<HR></BLOCKQUOTE>
Does the STOCK 396/402 have more torque than 400SB- thought the BB had more torque?

[This message has been edited by Jarret Grathwol (edited 06-14-2000).]

[This message has been edited by Jarret Grathwol (edited 06-14-2000).]

It's the external dimensions that make it a SB or a BB. They share almost the same internal dimensions. 400 is basically the largest SB and 396/402 is the smallest BB. The SB 400 was never HP from the factory and pretty much dogs, but built right it is an excellent engine. If you do the calculation, the SB 400 is actually a 401. I won't comment about which one produces more torque, since this is pretty much a BB site. Oops, I guess I just did.

Coppertop,
Don't 396/402's have a 3.76 stroke?

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www.geocities.com/lonnie67_1966 (http://www.geocities.com/lonnie67_1966)

Some people would also argue that the canted valve design of the Chevrolet big block family is a superior performance application. The heads were born to compete on the superspeedway's of Nascar.

Some people would also argue that the canted valve design of the Chevrolet big block family is a superior performance application. The heads were born to compete on the superspeedway's of Nascar.

There is NO QUESTION that performance wise, the BB 396-402 is superior to the SB400. Yes, that canted valve angle contributes to the added performance, but the real reason is because of the port design of a BB.
I've said this before--------------A BB CAN BREATHE! PERIOD! I am a SB400 lover, but I also like BBs and there is no comparison. You put a lot of money into building a SB400 to get it to perform like a BB, but then you put just the same amount into a BB402 and it just blows away the SB400. I have a 70conv with a stout SB400 and my son has a 71 with a BB402 and it just blows the doors off the 70 with the B400.
Always remember that the BIGGEST ports and valves of any SB (OEM or aftermarket) head are still smaller than the SMALLEST BB head. A SB head just WILL NOT flow like a BB head.

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Tom Parsons

In all actuality, the 366 is the smallest B/B, but for car purposes, the 396 is it!

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1972 Malibu (1 st. car) Project waiting to happen
Team Chevelle # 427
A.C.E.S. # 1282

When Chevrolet introduced the markIV it was an improvement, the first all-new design since the 55 small block. The porcupine heads were an excellent design (horsepower=move air thru motor), followed by later open chamber "D port" designs. The big difference between small block/ big block is torque. Chevelle is a big heavy car, get a big block if you want to have any fun. Having said that, lonnie67 remark about sb400's as "dogs" depends on the year, I had a 75 Monte 400/4bbl/TH400 with a 12 bolt that would eat Camaros and some 396s

Don't anyone turn up your nose at a SB400. When properly built with the RIGHT heads, it is an excellent power plant------for a small block. I never have and I never will say that a SB400 is better than a BB396-402, because it is not. The SB400 does weigh less, it is not too expensive to build and if a person has a car that was a factory SB to start with, the SB400 sure helps keep things simple. I admit, it does cost money to build a really stout SB400. But for a good, strong street motor that you can live with in a SB pkg, you just can't beat 'um. I have a 70 conv with full pwr, air, 4sp and 3.07 12bolt posi. I built the 400 for it to be moderately strong, be liveable on the street and be compatable with a stock cooling system. It does all that and WITHOUT banging the clutch it will easily burn the 235/60R15 tires and turn 6Krpm easy. The great thing about using the SB400 is that the car was originally a 307 and EVERYTHING just bolted right up to the 400 and there is more room to work on it. Although I did have to go with the bigger bell housing because of the bigger 400 flywheel. Too simple. With enough money and the right parts/machine work, you can almost duplicate an L78 396 performance.
By no means am I an expert on SB400s, but I have built probably 25 over the years, I personally have 4 of them (one is a 420 in a boat) and I just DO NOT see any problems.

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Tom Parsons

In some of the GM Factory lit. they refer to the SB motors as "turbo fire" and the BB motors as "turbo jet". It seems like Chevy couldn't decide what to call the 402. At one time they had a SB 400 turbo fire engine and a BB 400 turbo jet engine but then the BB went back to the 396 eventhough it was a 402 cu. in. motor. Some people say it was because the 396 was well known and popular and the marketing people wanted to retain it.

[This message has been edited by joe58 (edited 06-15-2000).]

Jarrett,
To answer your first question, the size makes the difference.

The SB400 would have the same performance capability if you could bolt the BB heads on the SB400. But you can't. The BB is plain and simply bigger than the SB and can "pump" more air. That means more power.

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-Mark

1967 Chevelle SS396/375
1964 Chevelle 283/195
1971 Vega 350/400

Actually registered 10/98

Ya i have the 402 in my 66 what a performer it is never go back to sb.

The big blocks in 1970 have the following stroke specs:

"400" 402: (330 hp)

3.75

"396" 402: (both 350 AND 375hp)

3.766

454 (both 360 and 450hp):

4.0


YES YES YES YES, BB's are the best performers hands down. I would never shrug off a small block 400 or any other one, but nothing touches the T-O-R-Q-U-E OF A BIG BLOCK!!!

Why just look at the stroke measurements. The farther down the piston travels from the top of its movement is where the torque comes from. The small blocks are just that, small, less travel for each piston on its connecting rod, less torque.

Horsepower comes from compression, so yessss you can have a 400 sb put out some serious power, but your still limited on that torque which you need to make a 4000 lb Chevelle launch off the line.

_______________ http://www.chevelles.com/forum/smile.gif____________________

Why did CHEVY have the "402" in 1970 but continue referring to it as the 396....

Well, I heard somewhere(and totally agree) that due to stricter governmental mandates on emissions for clean air, Chevy had to intentional punch the blocks larger because anything 400 cubic inches and over at that time in a BB put those engines in a different emissions bracket.

Kinda like intentionally making less money to put yourself in another tax bracket http://www.chevelles.com/forum/wink.gif

By having the larger engine, it was okay to have more emissions pouring out the tail pipes, thereby making those BB's exempt from stricter guidelines.

Now the rest is easy. MARKETING! Why on earth would you want to scare off consumers by saying "here's the brand new 402"????

The 396 was an instant legend. People would have feared that GM axed this engine, and no one had experience with this unknown "402",

SO, to prevent loss of sales and mass hysteria/confusion ALL decals, emblems, literature said 396 to continue the grand Chevrolet tradition in big blocks.

Hope that helps!
http://www.chevelles.com/forum/smile.gif

Joe

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"Yes, I'm still workin' on those Chevelle radio pages!"

[This message has been edited by Coppertop (edited 06-15-2000).]

the 396 was a 402 from 70 to 72 except from early 396 cars (from what Ive read)..supposedly GM didnt want to lose the recognition of the "ss396", so did not change emblems on the car even though the engine was a 402. In 70, parts books listed it as a 396. In 71, as a 400 4bbl (400 2bbl being the smallblock), and finally got it right in 72 listing it as a 402. Just a .030 over 396 the whole time. As far as the small block vs big comarison, I did it myself years ago. Street raced with a smallblock 400 nova that was mildly built for daily driving but still ran great. Great off the line torque up to 5500 with the mild cam. Next I did a 402 BB with a similar streetable setup, and it actually lost some lowend but pulled harder to 6000. The 402 seemed more of a revver and could of used more gear (only running 3:08). I then put the 400 smallblock in a 70 chevelle and it was a lot slower than the nova, just from the weight of the car. So from my experiences the 400 smallblock works great in lighter cars, where the chevelle really needs a big block for that "hit the pedal in any gear anytime and hang on" feeling.

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70 chevelle ss396 conv
66 chevelle ss396 hdp/conv
55 chevy prostreet
69/71 camaros
91 formula
85 monte SS
TC member #493

When referring to cars fitted with the sb400
GM did only mark the Impalas with the 350/400,4bbl sticker ,no one knew until one checked,which engine was fitted,guess they weren´t advertising there was also a 400 sb produced.
HR

Lets hear some track times from you 396/402 guys. My Camaro weighs 3400lbs w/me 11.63 @117+ w/iron bowties, before with stock heads from a 68 327 and .520 lift cam it went 12.36 @ 108+. Both are pump gas, SB400. My 70 chevelle weighs 3525 w/me, 2.73 gears stock converter, hit a 13.33 @107 with my daily driven SB 388. Engine is now in another Camaro, my new daily driver, no ET yet.

I'm just visiting from the Camaros.net site and thinking about owning a Chevelle one of these days. I noticed this topic and had posted something similar myself without nearly the responses I see here so I thought I'd toss it out over here and get some new input.

Here's the gist of my other post:

Let's say I'm building 2 motors - 1 is a 400 small block and the other is a 396 big block. Let's also assume I go for the Edlebrock Performer RPM setup for both. The displacement in both motors is essentially the same:

400 SB Bore & Stroke = 4.125 X 3.75
396 BB Bore & Stroke = 4.096 X 3.76
(kinda blows the stroke difference arguement!)

The RPM cams, intake, and carbs are the same or very close in spec. But, the heads are very different:

SB
Intake Runner Vol. 170cc
Exhaust Runner Vol. 60cc
Int Valve 2.02
Ex Valve 1.60

BB
Intake Runner Vol. 290cc
Exhaust Runner Vol. 110cc
Int Valve 2.19
Ex Valve 1.88

The RPM steup is just an example - the comparison and questions generally apply to other products as well.

Why the extreme difference in flow capacity of the heads? Is it because they have more real estate in the BB heads and take advantage of it? What would happen if you put a BB sized head on the 400 SB? Why does the BB remain "driveable" and "responsive" with (relatively speaking) huge ports and valves but everyone maintains that taking the same approach with the SB is a bad idea? The bore and stroke numbers certainly do not support any different approaches with the heads.

One answer that seems valid is that much of the increased volume in the BB heads actually comes from longer ports. The valves are then made slightly larger to keep the flow with the increased length. Any thoughts?

You better check again...

You said:

"400 SB Bore & Stroke = 4.125 X 3.75
396 BB Bore & Stroke = 4.096 X 3.76
(kinda blows the stroke difference arguement!)"

The numbers for the 400 SB are wrong.

The numbers you gave were for the "400" Malibu big block (actually a 402), not for the small block 400.

Joe

The bore /stroke on a 400 S/B, which is refered to as a 400 2bbl. for ' 70 is :
Bore: 4.1253
Stroke:3.7502
The B/B is either a 4.094 bore for a 396, or a 4.125 bore for a 402, with a stroke of 3.76. The same stroke was used for a 366-396-402-427.It is refered to as a 400 4bbl. engine in the parts books, or a 396-402.

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1972 Malibu (1 st. car) Project waiting to happen
Team Chevelle # 427
A.C.E.S. # 1282

No, he's right. 4.125 X 3.75. SB400's actually displace 401. So, .030 over is 407 not 406 and .040 is 409 not 408.

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www.geocities.com/lonnie67_1966 (http://www.geocities.com/lonnie67_1966)

Sorry!

I stand corrected, but I always thought torque comes from stroke (well it comes from other engine characteristics too) the greater the distance in the piston's travel is where the tire lurchin' torque comes from.

Oh well.

thanks for the info.

Joe

Here's where I got my numbers:
http://members.primary.net/~cys.dean/chevspec.htm

Am I missing something?

The point here is not to debate minute differences in the numbers. The point is to try to understand some of the differences between the engines and heads and use that info to our benefit, i.e.; go faster! http://www.chevelles.com/forum/biggrin.gif.

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Scott

[This message has been edited by RockyMtnRacer (edited 07-11-2000).]

I love my stroked 400sb, I love big displacement. Thats where the BB has alot of advantage. No substitute for cubic inches.
476hp @6000rpm 457lbft @4500rpm. Not too shabby for a mouse! http://www.chevelles.com/forum/biggrin.gif

Well, you can look at it like this: Take a 2" water line, and a 4 " water line, and fill 2 equal 55 gal. containers with water. Hook the lines into the containers, and empty the water. The 4" water line will be able to disperse the water faster , since there is more internal displacement in the pipe. That is the trick with the B/B, the stock heads flow alot better than a stock set of S/B ones. Engines are air pumps essentially, so the one that moves the air more freely, and at a larger quantity, and rate is better. That's the reasoning behind a B/B's larger ports, and more volume moving through the heads.

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1972 Malibu (1 st. car) Project waiting to happen
Team Chevelle # 427
A.C.E.S. # 1282

So if you bumped the 400 SB to the below (or similar) numbers...

Intake Runner Vol. 290cc
Exhaust Runner Vol. 110cc
Int Valve 2.19
Ex Valve 1.88

What would be the result? A lighter version of the "396"?

Doug -

Look at the water line analogy a little different way - if it's a 2" water line - and you have a 6" length and a 12" length - which one moves water faster? Neither, of course, although the 12" line has more "total volume". That's where the suggestion about increased port volume due to length came from. However, even without measuring I'd bet the BB heads have larger cross sectional ports and the valves are certainly larger.

A large part of my intention here is to understand why you can run larger valves and ports on the BB version of a 400 while all "experts and tech guys" generally agree that you can't do the same with the SB version. WHY?

Why are 215 to 230cc heads too big for a SB 400 but 260 to 290cc heads are fine for a BB 400?

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Scott

Well I don't personally have any experience with a 400 SB. But the difference between a SB and BB is pretty dramatic.

If you were to have engines on stands the 400SB would look nothing like a 396/402. In fact without digging a little deeper the 327/350/383/400 will look pretty much identical same for the 396/402/427/454.

The 400SB also has siamesed bores and has a slight tendency to develop hot spots compared to a 396/402.

There is one thing maybe someone can explain to me, I thought long runners meant more torque, but less RPM potential. I know my 350 TPI Corvette has long runners and produces huge amounts of torque but falls flat on its face (in stock form) at 3500-4000 RPM. But if you replace the runners plennum with an LT1 design (short-fat runners) the engine loses low-end torque and revs to 6k. This of course is with a hi-po cam.

BTW - My other car is an 85 Corvette

Robert
72 Chevelle Wagon
396 bored .030, TH-400, 10-bolt (I know, the 12-bolt posi is in the works).

whadda you guys doin' here?! you guys a bunch of engineers here or what?!! http://www.chevelles.com/forum/smile.gif

All I can say is this: a 400 SB is a beautiful thing.Lot of potential in that there mighty mouse.
But,if I had a 400 SB and a 396/402 side by side,I'd go with the BB without a doubt!! http://www.chevelles.com/forum/biggrin.gif

No offense to you SB guys,(had an 85 Monte SS once with a 400SB)just my twisted .02!! http://www.chevelles.com/forum/biggrin.gif

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1970 Chevelle SS396/L78/M21/4.10
1972 Olds 442 convertible(455,W25,M40)
1982 Oldsmobile Cutlass 350 Olds,TH350(daily driver)
1969 CHEVELLE SS396/TH400/FOR SALE!!
"Be aware of the possible ramifications of the potential outcome"

It's not possible to put BB heads on a SB 400 is it??? I thought I've heard of people doing this before. If it can be done how would you do it?

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Soon to be completed 406 sbc..."Love to spank them ricers!"

Of course theres no comparison. They are two totaly diffrent blocks, and designs.

The question now has become...

If you were to build a 400SB with intake, and exhaust specifications matching the 396 numbers, which motor would have the advantage?

Can't run them on a small block. And to paraphrase an old Harley saying: IF I HAVE TO EXPLAIN IT, YOU WOULDN'T UNDERSTAND!

BIG BLOCK

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1972 Malibu (1 st. car) Project waiting to happen
Team Chevelle # 427
A.C.E.S. # 1282

[This message has been edited by Doug Garland (edited 07-12-2000).]

I guess that I am one of the people here who do have side by side experience with a BB and SB 400. I have always said, the same as most people, if you have a choice (that is economical and practical) go with the BB. It WILL out perform the SB. We (my wife) have a 70 conv with a well built .030 over SB400 (406) and my son's car is a 71 2dr with a well built .030 over 402 BB (408 or 9, whichever you prefer). The BB kicks the SB everytime, hands down. Now don't misunderstand, that SB400 is strong and runs real good, but just not AS GOOD AS the BB in my son's car. I built BOTH drive trains in the 2 cars, so I built them my way.
Not only do BB heads flow better than SB heads, but the BB engines also have longer rods, 5.7 vs 6.135, which is also another contributing factor in favor of stronger top end for a BB. And another thing, the lobes on a BB cam have a much larger base circle than a SB, which allows more flexability with ramp speeds. So, no matter what, the BB (of the same displacement) wins.
Most everyone here knows I built a 420SB (.030 bore and .100 stroked) for my boat. Even with those few more inches in the SB, I'm sure that if I jerked the engine out of my son's car and put it in the boat it would run a little faster on top end (the only thing is, is that he ain't goin' for that!).

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Tom Parsons

Doug, I knew it was probably a real stupid question, I was just curious. I'm still just a damn whippersnapper at 17. http://www.chevelles.com/forum/smile.gif

Coppertop, I caught a little flak from a co-worker of mine who swore that the only 400 was the SB 400. As I tried to tell him, you are right about the BB 400. Chevrolet and GMC also offered a 400 big block in their trucks in either the 70 or 71 model year. Saw one with my own eyes back in 1974 and that's the only big block vehicle I've ever seen with the 400 badges. But 400 BBs do exist. I don't think many 400 BB trucks were built either, and they were only offered one or two years. The one I saw was owned by a classmate's father.

[This message has been edited by Randy Mosier (edited 07-12-2000).]

And they also offered the bb400 in the 70 impala the 400 badge is down at the front of the drivers door on the chrome strip that runs from back of the front wheel well to the front rear wheel well.On the raditor info tag its displaies "402 cubic in"I saw this car only three days ago.So this engine is in more than just Chevelles.
Rick

Guys , i think what Jason is trying to say is that.... if it was pyshically possible to have a set of small block chevy heads that flowed as well as the big block chevy heads which enginge would run harder. My guess jason would be the small block - same engine characteristics - only much lighter.

That's the spirit 68chevelle! My point exactly.

I know of course that the BB has much more potential, but if the SB heads could flow the same as the BB, then what?

PS. I don't pretend to know allot about engines, but am learning. http://www.chevelles.com/forum/smile.gif