Official Difference btween the 396 and 402 BB Because you asked.

[70cst]

Another point...the CST option was ended in 1970 and replaced by the Cheyenne package ... but it is not unusual to see a 71 C10 with the Cheyenne option but the SPID will list it as a CST optioned truck. This just goes to show that the engine wasn't the only area of confusion. The only other option that has really confused C10 owners is the elusive Corvette option.

[Walts_restoration]

dont forget the road hog option.
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[Monte Carlo Man]

Originally Posted by 67/72junkie

starting in 1970 all 396 where changed to 030 from factory to make 402.030 396 piston is same as standard bore 402.This was done due to the fact that small block 400 was introduced in 1970 and gm did not want a sb with more cubic inches than bb.I have friend who collects chevelles. he has 1969 and 1970 SS396. Both have SS396 badges both are 325 hp 1970 is 402 but has same casting # on the block and both have 290 casting closed chamber heads monte carlo man 400 sb introduced in 1970 was hi torque motor and not considered hp at the time 515 casting 4 bolt block with 265 hp. With lt1 186 casting heads and cam it will make more hp and outperform lt1 but not from the factory. lt1 was 360hp in camaro and 370 in corvette

Exactly

It had nothing to do with a flood or anything else because engine blocks are cast every day and the heads are matched to the blocks. I had a friend that worked as a machinist in that era up at the Towanda plant.

Chevrolet and Ford had a heated race going between them where each was trying to produce a larger engine. Chevrolet came out with the 283 and Ford came out with the 289, Chevrolet came out with the 302 and Ford came out with the 302, Chevrolet came out with the 350 and Ford came out with the 351 and 360, Chevrolet came out with the 396 and Ford came out with the 427, Chevrolet came out with the 454 and Ford came out with the 460.

The reason for producing the 396 - which was sold as a 402, was to keep the confusion at bay as to which engine you had. Which as soon as you opened the hood, you knew if it was a small block or a big block - you just didn't know what size it was.

It had nothing to do with core shift or left over blocks because each truck and automobile made had a production date cast into the block and the numbers between the engine and the chassis # matched.

From the 1970 Motor Auto Repair Manual
Page 2-115
Serial Number Location - plate on left front door pillar or top of left side instrument panel
Engine Number location -
4 - 6 cylinder : pad at front right hand side of cylinder block at rear of distributor.
V-8 Engines: Pad at front right hand side of cylinder block.

Trucks were not included in the Auto Repair Manual - you had to buy a Truck Repair Manual and daddy was cheap and there was not much in the truck manual that was not in the car manual - because it had a whole section for the K/5 Blazer included in the book.

But - you could get a 1969 / 70 Camaro, Nova, Chevelle or Monte Carlo with a 396 / 402, but not a full sized passenger car, Full Sized car's had a 454

Page 2-122
* Marketed as 396 cu. in. but actually 402 Cu. In.

You got to remember that Chevrolet was getting back into racing in 1970 on the Nascar circuit and the big block Chevrolet engine was the one that the Pioneers of racing such as Jr Johnson were using.

It was not until the advent of the newer version SBC and the rule change to limit CU In size and the catch up of technology and production standards that the small block Chevrolet was introduced to modern racing.

People used them, they just wouldn't run good enough to keep up with the big blocks. Probably the same reason why Speedy Thompson won only one race in 1955 for Chevrolet with a 265 - because the Pontiac's and Oldsmobile's and Dodge had bigger engines.

[67/72junkie]

the 302 chevy came out in 67 for 1 reason only. scca road racing had a 305 cubic inch limit.They put a small journal 283 crank in a small journal 327 block and came up with 302 cubic inches with off the shelf parts and left just enough to clearance the block once and then the block would have to be replaced.made 602 67 z28s to meet the standard required sold to the public and be legal to the rules.in 68 they change to 4 bolt main 350 block with large journals.302 was only for 3 years 67/69 camaro z28 only.under rated at 290hp from the factory.would make over 400hp with 2nd design solid lift cam and headers installed that gm would ship in the trunk if ordered.all this info and reason 396 to 402 info I listed in earlier post is from early eighties gm hi performace book my step dad gave me.has part #s for all gm special order hipo parts engine specs ,how to bue print and build race engines , even chassis specs and parts # to build road race cars.He was the head wrench at the local GM dealership when he married my mom.

[leddzepp]

Originally Posted by lovnthe70

I personally think there was a conspiracy between two guys sitting in an office having a little whiskey in their coffee one morning when one of them said to the other " you know what would be funny John" "whats that Bob?" "lets turn this 396 into a 402 and then badge it as a 400……. then when the internet comes out we can sit back and laugh at all the enthusiasts who try to figure it out!!!!! ” “sounds good Bob…. Lets get to work”

With all the different reasons and GM workers with different explanations, this one makes the most sense to me now

[Monte Carlo Man]

Just for the sake of telling you, my Uncle was one of those SCCA Racers that you are talking about. Telling me how the 302 was designed and built would be like telling Colonel Sanders how to make chicken.

When I was a kid, there was a 68 Z/28 in my friends parents front yard that he bought to keep the pine tree sap from hitting the ground.
There was also a 1963 Split Window Coupe Corvette and several other cars in his parents yard that he never drove.

My Uncles last race car was a 70 1/2 Z 28 - Brown with White stripes.
373 posi with a M 22 transmission.
We kept rock salt in a crate from Chevrolet that they sent a set of replacement heads in. They were known to crack.

Also, my uncle was associated with Yenko Chevrolet when he lived in Pittsburgh in the late 60's. He was also very good friends with Don and a woman named Donna Mae Mims who worked for Don Yenko that was a new car salesperson and drag raced under the name - The Pink Lady. You might recognize her from the movie Cannonball Run.

Big block stuff is ok for wreckers and crew cab pick up trucks and heavy hauling, but for real performance you got to stick to the small block stuff.

Here is a really good one for you though.

The 70 1/2 Z 28 came with a 350 that was conservatively rated at 350 HP, it was actually more like 500. The 400 Small Block Chevrolet was rated at 375 HP.... They had 4 bolt mains also and were discontinued in late 72...
With the 400 - you didn't have to worry about the heads cracking - you knew that they were going to crack around the steam holes. The bigger problem was when the crank fell in the pan because the whole bottom end (block) would crack around the webbing for the main caps and the engine would self destruct. I had one that the rod came out through the oil pan and it still ran and when I took one bolt out of the oil pan, the oil filter fell off - engine block and all.

The big block engines were known for throwing the #7 rod or loosing the bearings or the wrist pins in the #7 piston or puking the rings out the exhaust. I had several sets of heads that had .

[Monte Carlo Man]

There also was correspondence out in the garage from that era from Vince Piggins and also from Joe Pike..

Joe Pike was the head of sales and promotions. He was the person responsible for getting those high performance parts out the back door and into the hands of the racing community. Stock car racing - Junior Johnson
Drag Racing - Donna Mae Mims and road racing Don Yenko and Mark Donahue.

http://www.67z28.com/history.htm

Yenko Chevrolet - 575 West Pike St., Canonsburg, PA
Nickey Chevrolet - 4501 Irving Park Road, Chicago, IL.
Dana - Long Beach Blvd. South Gate, CA.
Berger - 2525 28th Street SE, Grand Rapids, MI.
Baldwin Motion - 598 Sunrise Highway Baldwin, Long Island, NY
Fred Gibb - LaHarpe, IL
Those were some of the dealers authorized to sell those cars...

http://www.hotrodscustomstuff.com/camaro-history.html

http://www.firstgencamaro.com/hiperf.html

[70cst]

As I look at these posts it's interesting how many of us have heard as to why the change from 396 to a 402BB took place. These are all interesting reads. Who knows...maybe someday we will get actual GM Documentation to what really happened. Good read all..

[silver79ta]

well does anyone have any spare big blocks laying around not in use. i could use one of them sure would like to ditch the 350 . thanks

['72customdeluxe]

Originally Posted by Monte Carlo Man

The 70 1/2 Z 28 came with a 350 that was conservatively rated at 350 HP, it was actually more like 500. The 400 Small Block Chevrolet was rated at 375 HP.... They had 4 bolt mains also and were discontinued in late 72...
With the 400 - you didn't have to worry about the heads cracking - you knew that they were going to crack around the steam holes. The bigger problem was when the crank fell in the pan because the whole bottom end (block) would crack around the webbing for the main caps and the engine would self destruct. I had one that the rod came out through the oil pan and it still ran and when I took one bolt out of the oil pan, the oil filter fell off - engine block and all.

errm, i'd say 350 gross was about right http://www.superchevy.com/technical/...lley_carb.html
Sure it has compression and plenty of cam, but the heads flow maybe 210 cfm and it's only 350 cubes. Not a recipe for a monster. Through full exhaust, accesories, and stock manifolds it *might* have made 300 at the crank

[67/72junkie]

show me pics ,mag article,gm lit of any chevy car with 375hp 400sb from the factory and make a beliver out of me.All 400 sb are low comp from the factory.I have blue 1971 GM motors manual and specs for all engines with codes to decode witch paticular model it came in.I have 5 70/72 515 casting 4 bolt main 400s and 4 more later 2 bolt main 400s which are the stronger blocks.I can show you specs for any 1970 gm engine you what right down to the gm specified clearances.Lt1 370 hp 010 casting high nickle 4 bolt main block 11 1/2 comp,forged steel crank,pink rods 186 casting 64cc heads 3/8s screw in studs 2.02 & 1.6valves solid lift cam,aluminum dual plane intake,780 holley.1970 400 sb 515 casting block heads 598 casting ,441 in water port on underside of head 3/8s press in studs 1.94 & 1.6 valves light dishtop 4 eyebrow pistons 9 1/2 comp cast crank small hyd cam most came with 2 barrel carb.This is not from a book but in my head.I have built at least 50 sb 350s and 400s in the last 20 years.I have 13 sets 64cc heads from stock to super stock modified at least 1 set every casting made from 1963/1971 461,461x,462,291,292,040,041,186 show me specs for 375 hp 400 sb factory.Teach me something I don't know about a small block chevy.

[67/72junkie]

only the copos where factory gm built with 427 .all the others where factory SS396 with dealer installed gm crate 427.Out the back door is not factory availible from the assembly line to the public and they had no crate perfomance small block bigger than Lt1 350.Hence Yenko Decuce if you wanted sb super car.

[Walts_restoration]

Originally Posted by 67/72junkie

show me pics ,mag article,gm lit of any chevy car with 375hp 400sb from the factory and make a beliver out of me.All 400 sb are low comp from the factory.I have blue 1971 GM motors manual and specs for all engines with codes to decode witch paticular model it came in.I have 5 70/72 515 casting 4 bolt main 400s and 4 more later 2 bolt main 400s which are the stronger blocks.I can show you specs for any 1970 gm engine you what right down to the gm specified clearances.Lt1 370 hp 010 casting high nickle 4 bolt main block 11 1/2 comp,forged steel crank,pink rods 186 casting 64cc heads 3/8s screw in studs 2.02 & 1.6valves solid lift cam,aluminum dual plane intake,780 holley.1970 400 sb 515 casting block heads 598 casting ,441 in water port on underside of head 3/8s press in studs 1.94 & 1.6 valves light dishtop 4 eyebrow pistons 9 1/2 comp cast crank small hyd cam most came with 2 barrel carb.This is not from a book but in my head.I have built at least 50 sb 350s and 400s in the last 20 years.I have 13 sets 64cc heads from stock to super stock modified at least 1 set every casting made from 1963/1971 461,461x,462,291,292,040,041,186 show me specs for 375 hp 400 sb factory.Teach me something I don't know about a small block chevy.

Ever seen a 64 327 300 horse chevelle? They did make many
Had factory 2.5inch exhaust manifold, all by them selves, exhaust all by them selves.. we have the block and trans out of the car, dad saw the car come in new on the car hauler, and pulled the block from a hedge row out of a circle track car about 15 years back.



Also, didnt 400s, at least some, have the nodular iron crank? isnt that why people had the 400 cranks turned down for a 350 over an aftermarket forged?

[70cst]

Originally Posted by 67/72junkie

show me pics ,mag article,gm lit of any chevy car with 375hp 400sb from the factory and make a beliver out of me.All 400 sb are low comp from the factory.I have blue 1971 GM motors manual and specs for all engines with codes to decode witch paticular model it came in.I have 5 70/72 515 casting 4 bolt main 400s and 4 more later 2 bolt main 400s which are the stronger blocks.I can show you specs for any 1970 gm engine you what right down to the gm specified clearances.Lt1 370 hp 010 casting high nickle 4 bolt main block 11 1/2 comp,forged steel crank,pink rods 186 casting 64cc heads 3/8s screw in studs 2.02 & 1.6valves solid lift cam,aluminum dual plane intake,780 holley.1970 400 sb 515 casting block heads 598 casting ,441 in water port on underside of head 3/8s press in studs 1.94 & 1.6 valves light dishtop 4 eyebrow pistons 9 1/2 comp cast crank small hyd cam most came with 2 barrel carb.This is not from a book but in my head.I have built at least 50 sb 350s and 400s in the last 20 years.I have 13 sets 64cc heads from stock to super stock modified at least 1 set every casting made from 1963/1971 461,461x,462,291,292,040,041,186 show me specs for 375 hp 400 sb factory.Teach me something I don't know about a small block chevy.

Good Info...

Monte Carlo Man ...
I am not sure what your thread has got to do with the 396-402 thread? Lets keep this about the subject at hand and if you want to start a subject about your interest that is great....

[GOPAPA]

[QUOTE=70cst;3845663][COLOR="Blue"]The official difference between the 396 and 402 BB according to the Feb, 1970 Chevrolet Dealers Memo


My thoughts on this is about the same as others . Some very good reading here ,,thx for this posting beings I have a 402 out of a Chevellle ..

The 402 is a big block chevy, Chevrolet bored the 396 .030" larger to make an honest 402 cubic inches.

I read somewhere that the Core Shift during the casting of the blocks lead to an overbore correction. I also read that all Big Blocks were made in Tonawanda NY for fours years straight. All 402 began life as 396's made at Tonawanda.

Emmissions had a big part in why bigger discplacement engines were required to follow slightly less requiremnts than smaller engins. 400cid was a cutoff for the tougher requiremnts.

It was not good for sales for GM to change the badging from 396 to 402 because of the popularity of the 396.
GM wanted to make more power for more sales and found that a 402 gave a little more umph using off the shelf parts but the "402" was not the "396" so they opted to leave the name the same considering they are identical (almost).

With the exception of the 402 having a 030" larger bore, there is very little difference in power . I read that you can only tell the difference by a dyno test.

gp my

[rbagley]

[quote=GOPAPA;3987198]

Originally Posted by 70cst

[COLOR="Blue"] I read that you can only tell the difference by a dyno test.

gp my

Couldn't you also just measure your bore and stroke too?

[67/72junkie]

only differance in 396 and 402 is 030 overbore. Same casting # blocks cranks ,heads,same cam and piston comp in same hp rated engines. 402 would make an estimated 6 hp more than 396 with same parts due to 6 more ci but GM kept the ratings the same.Why call what every one knows as 325 hp 396 a 331 hp 402 lot of trouble and confusion for nothing when everyone knew what SS396 was. You can take late 1969 casting dated 325 hp 396 bore 030 deck the block to remove stamped production code and install in early 1970 402 application and no one would every know the differance if you didn't tell them. most engines have date codes of mid year previous to build.

[junkyardjohn]

WELL... I'M SURE GLAD YOU FELLERS CLEARED THAT UP. JOHN

[67_C-30]

Old post I know, but my problem with buying the theory of GM not wanting a BB with less cu in than the 400 small block doesn't hold water. If that were the case, '70 396 Chevelles and Camaros would not have been badged 396. I have talked to someone who personally worked for GM back then, and though he wasn't working hands-on with the particular engine in question, he says the casting defect was the reason it happened. It wasn't so much for the fact that one batch of engines got casted wrong, it was going to require the tooling having to be redesigned and the downtime involved with that. Kind of a "We can't wait any longer" type of thing. Cars and trucks had to be built, and the only options were 1) Wait until the blocks were corrected, 2) Build the first batch with 402's and then go back 396's (which would have be a terrible idea!), 3) Stay the course with 402's. This is wht I believe haappened.

GM was afraid to go away from the 396 name in Chevelles, Camaros, and even Novas because those were good selling, well known engines. In 1970, The only cars that got the 400 SB were the Impala/Caprice and the Monte Carlo, so there would no conflicting 396BB vs 400SB in trucks or Chevelles, yet they got a "400" badges. In fact, the Chevelle with 400 badges is a 325HP 402 and the Chevelle SS was 402 badged SS-396, available in 350HP and 375HP versions. The lowest HP big block offered in a '70 Chevelle was badged "400" and the more powerful ones were badged "396". The 400 SB wasn't even in the equation (luckily!)

GM basically just handled the transistion badly, and we have the confusion we have today.

[MusicMan70]

I think it's time to call in a Professional.....

[special-K]

Why single out the 396 to 402? There were 283s,327s,396s,and 427s. Then they all got bumped up: 283 to 307,327 to 350,396 to 402,and 427 to 454. It was always my understanding this was due to federal emissions regulations kicking in (EPA had just come into existence in '69). They dropped compression ratios and increased displacement. Then there was the smog pump added. The other car companies did the same thing. I figured they jumped the displacement up to compensate choking them out for emissions. It was years later when they started actually building emissions efficiency "into" engines instead of building it "onto" them.

[67_C-30]

Originally Posted by special-K

Why single out the 396 to 402? There were 283s,327s,396s,and 427s. Then they all got bumped up: 283 to 307,327 to 350,396 to 402,and 427 to 454. It was always my understanding this was due to federal emissions regulations kicking in (EPA had just come into existence in '69). They dropped compression ratios and increased displacement. Then there was the smog pump added. The other car companies did the same thing. I figured they jumped the displacement up to compensate choking them out for emissions. It was years later when they started actually building emissions efficiency "into" engines instead of building it "onto" them.

GM didn't drop compression in 1970. The 375 HP 396 (that was actually a 402) still had 11 : 1 CR that year. Bumping up the cubes happened all the time, but they never put a 350 in car, printed 327 on the SPID, and put 340 fender emblems on it!
Posted via Mobile Device

[special-K]

The point I was making is about every motor from about every manufacturer got an increase in cubes in this general time frame,not just the 396. So why try to make something special of it? Maybe it wasn't about emissions,more like muscle wars. But 425 became 455,426 became 455 and on,just like Fords and even Volkswagens. A 350 isn't even 350 cubic inches,but that's what they badge it. They just rounded it off,like a 402 badges as a 400. Trucks didn't have 400 SBCs in 70-72,so not confusing at all.

[67_C-30]

Originally Posted by special-K

The point I was making is about every motor from about every manufacturer got an increase in cubes in this general time frame,not just the 396. So why try to make something special of it? Maybe it wasn't about emissions,more like muscle wars. But 425 became 455,426 became 455 and on,just like Fords and even Volkswagens. A 350 isn't even 350 cubic inches,but that's what they badge it. They just rounded it off,like a 402 badges as a 400. Trucks didn't have 400 SBCs in 70-72,so not confusing at all.

I see what you're trying to say, and I agree - increasing cubic inches and rounding off cu in was nothing uncommon. You have to admit though, GM never had another engine that was called one thing in a car and another thing in a truck, while being the same engine. Most car guys know there is no such as a Chevy 400 big block, yet our trucks have a 400 emblem. When you look in an engine manual, you see 402. The only 400 in there is a smal block. I've only had my '70 CST a little over a week and I've had to explain why my SPID says 396, my fender says 400, and the literature confirming that it is the original engine says its a 402. No other GM vehicle ever had this confusion. That's why I consider it out of the ordinary.

[special-K]

It is out of the ordinary and pretty confusing. Been there,done that. I had a '71 402 Cheyenne and had people telling me I had a 396 Custom Sport Truck and somebody changed the badges,once they saw my SPID. To me it's a mystery why they would print SPIDs to say 396 when the 402 was in it's second (and even the first) year. It's not a drinking on the job thing or some other screw up. It's obviously intentional. Each SPID is made individually. I always figured they kept using SS396 after '69 because it had become a model name,just like GTO,and it was really just a minor bump to 402. Not worth changing an icon. In a way,it's still a 396. Just like when I've rebuilt/bored a motor,I still call by it's original displacement. Sometimes I might mention the over bore,if we are talking technically about it.