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Official Difference btween the 396 and 402 BB Because you asked.
The official difference between the 396 and 402 BB according to the Feb, 1970 Chevrolet Dealers Memo
The top power option for all Chevrolets Series 1030 trucks (except the Blazer) is a big 400 V8 with 310 horsepower. It has the same power output as the 396 V8 it replaces, but it has a number of significant differences, such as: 1. Gasketless, tapered-seat spark plugs and conforming heads. 2. Throwaway-type oil filters. 3. Two-step automatic choke for better engine warm up characteristics. The increase in displacement was accomplished by enlarging the cylinder bore rather than lengthening the stroke. This, plus the use of a low profile inlet manifolds, keeps overall height low for more room under the hood. And remember, with this engine, you get a lot more horses under the hood than competition can offer. Here’s the way the top engine of each major make compares: Biggest V8 & Max. Gross H.P. CHEV. 400/310 FORD 390/255 DODGE 383/258 IHC 392/236 Now you know the rest of the real story...:metal: |
Re: Official Difference btween the 396 and 402 BB Because you asked.
Actually it was marketed by year and model and not just by the numbers.
If you read in the Motor Repair Manual for 1970 - it will say 396, marketed as a 402. Not 400 - because the 400 technically was a small block Chevrolet which came out in 1970 which was listed with 4 bolt mains and had 25 more horsepower then the LT1 350 Most truck engines smaller then 1 ton had High Performance Passenger Car cast into the blocks and heads. My buddy had one in a 1974 Chevy wrecker they bought when he was a kid. It came with 454 rocker covers and when we went to rebuild the engine, the pistons would not fit in the bore. When you get into Square Port vs. Oval port, you will have a heated discussion as to which was better. The last set of Oval Port heads I had, I had traded for a set of double hump SBC heads and then sold for $500.00 I probably sold them too cheap, because they were already built up, but I needed the money more then I needed another set of heads on the shelf! |
Re: Official Difference btween the 396 and 402 BB Because you asked.
70cst,
Thanks for posting that bit of interesting information! Jim |
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ttt for those who missed this. :metal:
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Re: Official Difference btween the 396 and 402 BB Because you asked.
Does it say why they went to a 402 instead of a 396? Not a lot of people know this...;)
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Re: Official Difference btween the 396 and 402 BB Because you asked.
As told to me by someone who worked for GM (you won't find it in any book or brochure): The 396 blocks had a casting imperfection in the cylinders, so rather than scrap all of them, GM "fixed" the problem by punching them .030 over making it a 402.
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good to know info...hope the 396 I just bought is punched out enough...guy told me it sounded really healthy...keep your fingers crossed...:lol:
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Re: Official Difference btween the 396 and 402 BB Because you asked.
I've heard the one about a casting defect and even a fire in an engine plant. The one that makes the most sense to me is that in 1970, Chevy introduced the 400 small block. It would not make much sense for Chevrolet to have a 396 "big" block and a 400 "small" block!
Joshua |
Re: Official Difference btween the 396 and 402 BB Because you asked.
Yeah except that a 72 402 had 185 horse due to lower compression
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Re: Official Difference btween the 396 and 402 BB Because you asked.
So when I go to NAPA, and they are looking up parts,,, it is either a 396 or a 402, but the side of the truck says 400!! And the SPI says L47 396 cu.in. V-8 engine
http://67-72chevytrucks.com/vboard/s...d.php?t=389526 So I go with 396,,,, |
Re: Official Difference btween the 396 and 402 BB Because you asked.
The old IHC 392 might only show as 236hp, but I bet it has the lowest torque curve of all the engines there.
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Re: Official Difference btween the 396 and 402 BB Because you asked.
Well... I'm glad that is cleared up. ;) john
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Good info guys...:metal:
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I have heard the flood thing before too, but I'm not so sure that I buy either of the "damaged" block theories.
If the bores were rusty, the rest of the block would have been too, lifter bores, main saddles, etc... If the bores were "crooked" they would have gone back to the supplier.... They couldn't possibly have been "sitting on" that many blocks. If that really had been the case, they would have either used them and just said nothing, sent them back to be "recycled", held them as warranty replacements, etc. They would not have spent the time/money to re-bore them and create new pistons to make it happen. Plus, they would have gone back the "standard" 396 configuration when the "supply" of these "bad blocks" was exhausted. I think the 400 in small block form was the issue. The smallest "big block" needed to be bigger. The 400 came out in the same year, coincidence? Now why they used the 400 name badge for trucks? and 402 in cars? Who knows? |
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My 70 Chevelle 402 BB had "400" on the side as well. I assumed either it was close enough, or it was for the TH400 backing the 402. |
Re: Official Difference btween the 396 and 402 BB Because you asked.
So is the motor in the truck a 396 or 402?
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LONGHAIR....you make some valid points. |
Re: Official Difference btween the 396 and 402 BB Because you asked.
1970 c10
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Re: Official Difference btween the 396 and 402 BB Because you asked.
Of course, 1970 was the "gray" year. I think it would be a 402. 68 and 69 are 396, and 71 72 are 402. You could get the casting numbers and front pad numbers and we could try to identify it for sure.
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Oh it's not my truck, but I am curious because I have seen a few with the 400 emblem and didn't know which engine they had.
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Re: Official Difference btween the 396 and 402 BB Because you asked.
What about with the above discussion where the spec order sheet for the 1970 reads "L47 396 CU. IN. V-8 ENG". Could that still be a 402 eventhough it reads 396.
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Re: Official Difference btween the 396 and 402 BB Because you asked.
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
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Good info. From a marketing perspection that does sound logical and makes sense. Thanks:metal: |
Re: Official Difference btween the 396 and 402 BB Because you asked.
I've heard that they kept badging the 402's as 396's because the 396 was so popular and people don't like change as much as 6 c.i.
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WOW...I am watching "Whats My Car Worth" ... and they said that up until 1969 GM put out an edict which said no intermediate car could be bigger than a 400. Then in 1970 this edict as lifted. Interesting. :hmm:
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The "imperfections" in the blocks story sounds weird, I thought the water jackets were different.
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i have a 71 cheyenne super the SPID says l47 400 ci v8 and its a bigblock 402 so i am totally confused
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