402 Question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**'70_402** · 10-29-2004, 05:33 PM

Was The 402 Bored Out From The Factory? If Not Then How Does It Get The Extra 6 C.i.'s From The 396?

72 CustomCamper · 10-29-2004, 08:48 PM

The 402 is a factory .030 over bored 396...

Chuck

Bowtiefreak · 10-29-2004, 09:26 PM

Yea, the reason for this was due to some bad cores they had. They bored them .030 over to clean up the bores and still use the blocks.

cableguy0 · 10-29-2004, 10:40 PM

no theres a lot of myths about why the bored the most logical and most realistic is because of the 400 small block gm didnt want a small block that was bigger than a big block it doesnt look good so they bored em out. theres other stories about a flood from a fire sprinkler all kinds of neat stuff

3 on the tree · 10-29-2004, 11:21 PM

I read somewhere that Chevy did it to pick some of the lost HP from new emission controls-but they still called it a 396 in the Chevelles, but my 72 Burb had 400 emblems on it.

Fred T · 10-29-2004, 11:38 PM

Quote:

Originally Posted by 3 on the tree

I read somewhere that Chevy did it to pick some of the lost HP from new emission controls-but they still called it a 396 in the Chevelles, but my 72 Burb had 400 emblems on it.

Reason they used the 400 emblems was to appease the insurance companies. They were also under-rating many of the musclecar engines at that time.

Longhorn Man · 10-30-2004, 12:40 AM

And they called it a 396 in the performance cars becouse the 396 had already earned respect.
I agree with cableguy, I think it was inner corperate politics. If you were to look into it, (IIRC) the 400 small block is also a 402...which if this is true, it would just back up the numbers game they may have been playing on the big block verses small block.

1-PU70 · 10-30-2004, 01:19 PM

FYI They didnt start to make a 400SB till 75 I think

68w/sbc406 · 10-30-2004, 01:24 PM

my sb400 came out of a 73 caprice. i know when they are bored .030 over the actual c.i.d. is 407 but i have never heard anyone call it that so 406 it is

LONGHAIR · 10-30-2004, 03:22 PM

Small Blocks
265..........3.750 bore X 3.000 stroke...265.0
283..........3.875 bore X 3.000 stroke...283.0
302..........4.000 bore X 3.000 stroke...301.7
305..........3.740 bore X 3.480 stroke...305.8
307..........3.875 bore X 3.250 stroke...306.6
327..........4.000 bore X 3.250 stroke...326.7
350..........4.000 bore X 3.480 stroke...349.8
400..........4.125 bore X 3.750 stroke...400.9

Big Blocks
396..........4.095 bore X 3.760 stroke...396.1
402..........4.125 bore X 3.760 stroke...401.9........the big block is bigger .010
427..........4.250 bore X 3.760 stroke...426.7
454..........4.250 bore X 4.000 stroke...454.1

I know that there are others.......mostly insignificant though.

I am currently looking into building a "backward of GM's way" 427 by using a 454 crank 4.000 and a 402 block 4.215 ...427.6. Thus being a stroker 427 rather than a big bore 427. I have yet to mock the crank up to see if I have rod clearence though. The 402 block is different near the bottom of the bores, so I'm not 100% that this will work.
BTW, has anyone done this? does it in fact work?

Longhorn Man · 10-31-2004, 12:02 AM

The 400 small block was made from 70 untill either 79 or 80.

GMC Jim · 10-31-2004, 08:27 PM

Looking thru a GM Tune Up manual;specs are listed for the 400 engine for the following years.-- Chev auto- thru 1976; Chev/GMC trucks- thru 1977; Olds- thru 1975 and Pontiac thru 1978.

Baradium · 10-31-2004, 09:21 PM

Quote:

Originally Posted by GMC Jim

Looking thru a GM Tune Up manual;specs are listed for the 400 engine for the following years.-- Chev auto- thru 1976; Chev/GMC trucks- thru 1977; Olds- thru 1975 and Pontiac thru 1978.

Through a year doesn't help... because we need to know what year it started in!

And I guarantee that it wasn't around in 1940.

pound41 · 10-31-2004, 10:52 PM

Had A stock originial 1970 Monte carlo with a small block.. 1970 was the first year

Longhorn Man · 10-31-2004, 11:04 PM

Hmmm, acording to the red book, the chevy trucks could be had with a 400 untill '80.

10-29-2004, 05:33 PM	#1
'70_402 Senior Member Join Date: Dec 2003 Location: Pampa, Texas Posts: 1,553	402 Question Was The 402 Bored Out From The Factory? If Not Then How Does It Get The Extra 6 C.i.'s From The 396? __________________ https://www.ebay.com/itm/29620574751...mis&media=COPY

10-29-2004, 08:48 PM	#2
72 CustomCamper huh ??? Join Date: Nov 2002 Location: Fredericksburg,Va. Posts: 3,368	The 402 is a factory .030 over bored 396... Chuck __________________ 90 Blazer Silverado 350w/ 700R4 and 32" Kelly's "I am a bomb technician. If you see me running try to keep up!"

10-29-2004, 09:26 PM	#3
Bowtiefreak Registered User Join Date: Jul 2003 Location: LeRoy, Mich. Posts: 854	Yea, the reason for this was due to some bad cores they had. They bored them .030 over to clean up the bores and still use the blocks. __________________ 1968 Chevy C10 Short Fleetside/Wood floor ECE 4-6 Drop / 406 Small Block 1971 Chevelle 427 Big Block

10-29-2004, 10:40 PM	#4
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,948	no theres a lot of myths about why the bored the most logical and most realistic is because of the 400 small block gm didnt want a small block that was bigger than a big block it doesnt look good so they bored em out. theres other stories about a flood from a fire sprinkler all kinds of neat stuff __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

10-30-2004, 01:19 PM	#8
1-PU70 Registered User Join Date: Apr 2000 Location: Bradenton, FL Posts: 1,036	FYI They didnt start to make a 400SB till 75 I think __________________ 1970 CST/10 402,700R4,3:73 posi,AC,PS,PB,TLT,PW,Buckets with heaters

10-29-2004, 11:21 PM	#5
3 on the tree Registered User Join Date: Oct 2004 Posts: 392	I read somewhere that Chevy did it to pick some of the lost HP from new emission controls-but they still called it a 396 in the Chevelles, but my 72 Burb had 400 emblems on it.

10-30-2004, 12:40 AM	#7
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	And they called it a 396 in the performance cars becouse the 396 had already earned respect. I agree with cableguy, I think it was inner corperate politics. If you were to look into it, (IIRC) the 400 small block is also a 402...which if this is true, it would just back up the numbers game they may have been playing on the big block verses small block.

10-30-2004, 01:24 PM	#9
68w/sbc406 Got Light Emitting Diode? Join Date: Apr 2004 Location: Newberg, OR Posts: 2,485	my sb400 came out of a 73 caprice. i know when they are bored .030 over the actual c.i.d. is 407 but i have never heard anyone call it that so 406 it is __________________ 1968 1/2 ton 2wd lwb 6 lug disc and bags up front. Next c notch and rear bags '02 Chevy Silverado LT ext cab short bed 2WD 5/7 drop on 22's(the family car) 1993 Cherokee work ride/weekend wheeler

10-30-2004, 03:22 PM	#10
LONGHAIR just can't cover up my redneck Join Date: May 2004 Location: Columbus OH Posts: 11,414	Small Blocks 265..........3.750 bore X 3.000 stroke...265.0 283..........3.875 bore X 3.000 stroke...283.0 302..........4.000 bore X 3.000 stroke...301.7 305..........3.740 bore X 3.480 stroke...305.8 307..........3.875 bore X 3.250 stroke...306.6 327..........4.000 bore X 3.250 stroke...326.7 350..........4.000 bore X 3.480 stroke...349.8 400..........4.125 bore X 3.750 stroke...400.9 Big Blocks 396..........4.095 bore X 3.760 stroke...396.1 402..........4.125 bore X 3.760 stroke...401.9........the big block is bigger .010 427..........4.250 bore X 3.760 stroke...426.7 454..........4.250 bore X 4.000 stroke...454.1 I know that there are others.......mostly insignificant though. I am currently looking into building a "backward of GM's way" 427 by using a 454 crank 4.000 and a 402 block 4.215 ...427.6. Thus being a stroker 427 rather than a big bore 427. I have yet to mock the crank up to see if I have rod clearence though. The 402 block is different near the bottom of the bores, so I'm not 100% that this will work. BTW, has anyone done this? does it in fact work?

10-31-2004, 12:02 AM	#11
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	The 400 small block was made from 70 untill either 79 or 80.

10-31-2004, 08:27 PM	#12
GMC Jim Senior Member Join Date: Dec 2002 Location: Portland, Oregon Posts: 901	Looking thru a GM Tune Up manual;specs are listed for the 400 engine for the following years.-- Chev auto- thru 1976; Chev/GMC trucks- thru 1977; Olds- thru 1975 and Pontiac thru 1978. __________________ '71 GMC;fleetside;PB/PS/AC/CC/402 Eng./Custom Paint/110,000act miles/3 fuel tanks(52gal).

10-31-2004, 10:52 PM	#14
pound41 Registered User Join Date: Dec 2002 Location: Northern Virginia Posts: 1,268	Had A stock originial 1970 Monte carlo with a small block.. 1970 was the first year

10-31-2004, 11:04 PM	#15
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Hmmm, acording to the red book, the chevy trucks could be had with a 400 untill '80.



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