396 to 400

[flip66]

Can you interchange parts (heads, intake, cam,) between a 1969 396 with a 71-72 402. In other words are the blocks the same, I have 396 that is blown, not sure how bad yet but want to be ready when I get it apart.

[1972RedNeck]

I think a 402 is just a .030 over 396.

[leddzepp]

Originally Posted by 1972RedNeck

I think a 402 is just a .030 over 396.

This is correct

[70GMCBB]

I have a 70 GMC that the block ID indicates it's a 402. It sold advertised as a 396 in the day. I originally thought it was just bored over 0.030 also but my machine shop guy said they had casting for a 402 also. Personally don't know if they did. All parts except pistons of course will interchange.

[MARKDTN]

Originally Posted by 1972RedNeck

I think a 402 is just a .030 over 396.

x3

[stsalvage]

the story on the 402 GM had a lot of 396 blocks that would not clean up to 396 and there where a lot of them 25K of them dam critters.Back in the day Most company's where not into waist.And sence the block could be used again like a 350 going from stock to 3.55 it just made sence.Now here is a Peace of evidence the 1970--72 Monte Carlo only had 2 options of engine's the 350 and the SS 454 But i've found a few that had the 402 in them.I did research on this GM had a lot of these blocks and they where trying to throw them into as many trucks car's and motor homes as they could before the 454 was a real option..The 402 was a mistake But instead of Gm just junking them they made a profit.Most of are trucks have the 400 logo on the side of are trucks that logo was stolen from the Blazer 400 small block GM did make a limited run of the 400 big blocks.But never put them in any production car's I've never seen one But i hear most of them where used in Race Car's.

Its funny you read all you can about the MONTE Carlo and it started in 1970 when the 402 came about.One guy did say this about the Monte Carlo.It had very low numbers of productions in its first 3 years.From out of them 3 years only 6XXX Monte's had the SS option the option was the 454 Now that was a LS 6 motor Now some of them had the dealer add on alum heads making it a LS 7 motor with alum intake a Holley carb and I've seen 3 of them.

But the real truth in it When i bought 2 Monte Carlos they both had big blocks in them and i thought i hit pay dirt But with the SS Monte Carlo had bucket seats and shifter on the floor the 2 i bought had bench seat and column shifter.Pulled the motor out they had the casting numbers for the 396 and casting numbers of another block but none of my books listed it until 1977 most of them refer to the 396 casting

[68Gold/white]

Originally Posted by stsalvage

the story on the 402 GM had a lot of 396 blocks that would not clean up to 396 and there where a lot of them 25K of them dam critters.Back in the day Most company's where not into waist.And sence the block could be used again like a 350 going from stock to 3.55 it just made sence.Now here is a Peace of evidence the 1970--72 Monte Carlo only had 2 options of engine's the 350 and the SS 454 But i've found a few that had the 402 in them.I did research on this GM had a lot of these blocks and they where trying to throw them into as many trucks car's and motor homes as they could before the 454 was a real option..The 402 was a mistake But instead of Gm just junking them they made a profit.Most of are trucks have the 400 logo on the side of are trucks that logo was stolen from the Blazer 400 small block GM did make a limited run of the 400 big blocks.But never put them in any production car's I've never seen one But i hear most of them where used in Race Car's.

Its funny you read all you can about the MONTE Carlo and it started in 1970 when the 402 came about.One guy did say this about the Monte Carlo.It had very low numbers of productions in its first 3 years.From out of them 3 years only 6XXX Monte's had the SS option the option was the 454 Now that was a LS 6 motor Now some of them had the dealer add on alum heads making it a LS 7 motor with alum intake a Holley carb and I've seen 3 of them.

But the real truth in it When i bought 2 Monte Carlos they both had big blocks in them and i thought i hit pay dirt But with the SS Monte Carlo had bucket seats and shifter on the floor the 2 i bought had bench seat and column shifter.Pulled the motor out they had the casting numbers for the 396 and casting numbers of another block but none of my books listed it until 1977 most of them refer to the 396 casting

Sounds resonable to me.
I heard a story, that the 396 was punched .030 over to a 402 to help pass an emission test.....who knows...I'm not an expert...

[Longhorn Man]

there's a few stories, none can be 100% verified. inner office politics (not wanting a small block to be bigger than a big block) smog regs, a bunch of blocks not being cast properly... those are the 3 main ones I've heard... in the order that I believe. (I basicly don't believe GM had 25000 blocks before they 'noticed' a mistake) I also question this blazer 400 small block?
A 402 and a 396 are the same except the pistons, rings, and I think there was a couple other odds and ends. Most (if not all) the blocks share a casting number.

[special-K]

Some 402s are over bored 396s and the rest are their own casting from what I know. So,as said,the pistons & rings are the only thing not compatible from a 396. I won't profess to know how or why GM did anything they did,but it makes sense to me that the 396-402 is no different than the 283-307,327-350,or for that matter,the Ford 289-302,the Chrysler 273-318,etc. Engines grew for more power through the '60s and I figure by the time emission standards were mandated in the late-60s they grew just a tad more to compensate for lowered compression and smog pumps.

[custom1970]

Originally Posted by Longhorn Man

there's a few stories, none can be 100% verified. inner office politics (not wanting a small block to be bigger than a big block) smog regs, a bunch of blocks not being cast properly... those are the 3 main ones I've heard... in the order that I believe. (I basicly don't believe GM had 25000 blocks before they 'noticed' a mistake) I also question this blazer 400 small block?
A 402 and a 396 are the same except the pistons, rings, and I think there was a couple other odds and ends. Most (if not all) the blocks share a casting number.

I remember reading a while back that the reason for the 402 was because of the 1970 Clean Air Act. In the act there was an exception for trucks with engine over 400 cu in. Therefore if GM keep putting 396's in the trucks they would have had to of added all the pollution control systems to make the engines conform to the law. So, it was cheaper to make the 396 a 402 than ad smog equipment.

Would like to know if this is true or just an urban legend or what....

[406 Q-ship]

Originally Posted by stsalvage

the story on the 402 GM had a lot of 396 blocks that would not clean up to 396 and there where a lot of them 25K of them dam critters.Back in the day Most company's where not into waist.And sence the block could be used again like a 350 going from stock to 3.55 it just made sence.Now here is a Peace of evidence the 1970--72 Monte Carlo only had 2 options of engine's the 350 and the SS 454 But i've found a few that had the 402 in them.I did research on this GM had a lot of these blocks and they where trying to throw them into as many trucks car's and motor homes as they could before the 454 was a real option..The 402 was a mistake But instead of Gm just junking them they made a profit.Most of are trucks have the 400 logo on the side of are trucks that logo was stolen from the Blazer 400 small block GM did make a limited run of the 400 big blocks.But never put them in any production car's I've never seen one But i hear most of them where used in Race Car's.

Its funny you read all you can about the MONTE Carlo and it started in 1970 when the 402 came about.One guy did say this about the Monte Carlo.It had very low numbers of productions in its first 3 years.From out of them 3 years only 6XXX Monte's had the SS option the option was the 454 Now that was a LS 6 motor Now some of them had the dealer add on alum heads making it a LS 7 motor with alum intake a Holley carb and I've seen 3 of them.

But the real truth in it When i bought 2 Monte Carlos they both had big blocks in them and i thought i hit pay dirt But with the SS Monte Carlo had bucket seats and shifter on the floor the 2 i bought had bench seat and column shifter.Pulled the motor out they had the casting numbers for the 396 and casting numbers of another block but none of my books listed it until 1977 most of them refer to the 396 casting

Sorry but I call BS on the whole thing. The .030 over bore on the 396 to get it to 402 was an emission deal for California as I understand. If it was the left over bad 396 blocks, then wouldn't people be pulling engines with casting dates of 1965 as an original 402 in a 1970 Chevelle, Camaro, Nova, Impala, and trucks. So it was a planned deal.

On the Monte Carlo you are so far out from reality. I am the owner of a 1971 and have had a love for the Monte since my Grandfather bought a brand new one in Sept 1969. The 402 was an optional engine in the 1970-72 Monte Carlos. There are NO LS-6 Montes, not from GM ever!! (No 4 speed SS454 either in 70 or 71) All the SS454 Monet Carlos in 1970 and 71 have LS-5's in them. The 1972 Monte Carlos is curious in that there is no SS454, but the 454 was available in them as an optional engine (the 402 just carried on as an option). Aluminum heads do not make an LS-6 into an LS-7, two completely different engines. There is some conjector on whether the L89 option was ever delievered on one perticular 1970 LS-6 Chevelle (it seems there was an overlap of the LS-6 and the L89 aluminum heads for a very short window). Did a dealer install an LS-6 or LS-7 in a Monte Carlo SS454, quite possibly, but Chevrolet did not do it.

[leddzepp]

Originally Posted by Longhorn Man

there's a few stories, none can be 100% verified. inner office politics (not wanting a small block to be bigger than a big block) smog regs, a bunch of blocks not being cast properly... those are the 3 main ones I've heard... in the order that I believe. (I basicly don't believe GM had 25000 blocks before they 'noticed' a mistake) I also question this blazer 400 small block?
A 402 and a 396 are the same except the pistons, rings, and I think there was a couple other odds and ends. Most (if not all) the blocks share a casting number.

ive heard all of these stories too. i think people will believe whatever they want, so i say pick whichever one sounds best!
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