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

Skinny Kid · 01-12-2015, 11:08 AM

I'm a little confused as to what the correct size engine is in my truck. It's the original big block and the fenders say 400, but the SPID says 396? I've also heard 402. Which is correct? Thanks

**landy** · 01-12-2015, 03:08 PM

What year and model is your truck?

**68350** · 01-12-2015, 03:11 PM

In 1970 they went to the 402. So if its a 68-69 its a 396 or 70-72 is a 402. Sometimes the guys making spids just typed whatever the RPO code was for. If it has 400 badges I'm assuming its a 70-72

MARKDTN · 01-12-2015, 03:18 PM

You need to Google to find the history of this, it's too complicated for a quick answer.

Basically the BB Chevy as we know it was introduced as a 396. Used in a truck application, they rounded off to 400. Also the 402 was a 396 with an .030 overbore. That is what was used in 70-72. There are a lot of rumors as to why:
-bunch of pistons made wrong and could not be rejected
-bunch of bad blocks that required an overbore to use
-couldn't have a 400SB that was bigger than a BB
-etc.

Redline novdog · 01-12-2015, 09:18 PM

My 2cents worth. I was under the impression '70 and later 400cid was of small block configuration509/511 blocks 2bolt and 4 bolt,hence most are in dirt stock cars. the 396 was 396 (unless you do the math bore x stroke=402).The 396 was for insurance/road racing certification.Then GM went to the 454. cars and c40,50,60 got the 427(truck tall block 366/427,cars 427/454). Please someone that actually has facts step in.

**68350** · 01-12-2015, 09:38 PM

The 402 replaced the 396 in all gm vehicles in 1970. Some reason cause gm to bore all of the 396 out. Even a Ss396 in 71-72 chevelles, etc have a 402, but the SS396 stuck because of its reputation as a potent package. There have been other threads on this board discussing this.

**68350** · 01-12-2015, 09:39 PM

And for some unknown reason, on the pickups they used a fender badge that said 8-400 when it was in fact a 402. Why? I do not know.

Skinny Kid · 01-14-2015, 11:41 AM

It's a 71 C20. The fenders say 400 and so does the build sheet, but the SPID says 396. The option code on both the build sheet and SPID are the same, L47 I think, but I don't have it in front of me at the moment.

01-12-2015, 11:08 AM	#1
Skinny Kid Registered User Join Date: Jan 2015 Location: Costa Mesa, CA Posts: 40	Engine Size Question I'm a little confused as to what the correct size engine is in my truck. It's the original big block and the fenders say 400, but the SPID says 396? I've also heard 402. Which is correct? Thanks

01-12-2015, 03:08 PM	#2
landy Senior Member Join Date: Jun 2000 Location: alb, nm Posts: 413	Re: Engine Size Question What year and model is your truck?

01-12-2015, 03:11 PM	#3
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Re: Engine Size Question In 1970 they went to the 402. So if its a 68-69 its a 396 or 70-72 is a 402. Sometimes the guys making spids just typed whatever the RPO code was for. If it has 400 badges I'm assuming its a 70-72 __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

01-12-2015, 03:18 PM	#4
MARKDTN Registered User Join Date: Jan 2011 Location: Chattanooga, TN Posts: 2,197	Re: Engine Size Question You need to Google to find the history of this, it's too complicated for a quick answer. Basically the BB Chevy as we know it was introduced as a 396. Used in a truck application, they rounded off to 400. Also the 402 was a 396 with an .030 overbore. That is what was used in 70-72. There are a lot of rumors as to why: -bunch of pistons made wrong and could not be rejected -bunch of bad blocks that required an overbore to use -couldn't have a 400SB that was bigger than a BB -etc. __________________ '83 K20-TPI '73 C10 '79 C10-ex-diesel(SOLD) '07 Tahoe(Son driving) '14 Suburban-DD '71 C10-current project

01-12-2015, 09:18 PM	#5
Redline novdog Registered User Join Date: Jan 2012 Location: Washington,Il Posts: 632	Re: Engine Size Question My 2cents worth. I was under the impression '70 and later 400cid was of small block configuration509/511 blocks 2bolt and 4 bolt,hence most are in dirt stock cars. the 396 was 396 (unless you do the math bore x stroke=402).The 396 was for insurance/road racing certification.Then GM went to the 454. cars and c40,50,60 got the 427(truck tall block 366/427,cars 427/454). Please someone that actually has facts step in. __________________ It builds on my intelligence when I make a mistake, Boy am I building on it! '67 C-10,'70 Nova SS

01-12-2015, 09:38 PM	#6
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Re: Engine Size Question The 402 replaced the 396 in all gm vehicles in 1970. Some reason cause gm to bore all of the 396 out. Even a Ss396 in 71-72 chevelles, etc have a 402, but the SS396 stuck because of its reputation as a potent package. There have been other threads on this board discussing this. __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

01-12-2015, 09:39 PM	#7
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Re: Engine Size Question And for some unknown reason, on the pickups they used a fender badge that said 8-400 when it was in fact a 402. Why? I do not know. __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

01-14-2015, 11:41 AM	#8
Skinny Kid Registered User Join Date: Jan 2015 Location: Costa Mesa, CA Posts: 40	Re: Engine Size Question It's a 71 C20. The fenders say 400 and so does the build sheet, but the SPID says 396. The option code on both the build sheet and SPID are the same, L47 I think, but I don't have it in front of me at the moment. __________________ 1971 Chevy Custom Camper/20, Hugger Orange with White Top 31,000 original miles (when purchased), 402, TH400, PS, PB, AC As of May 2017 it now has a turbo LS in it! (Still looks stock though) Last edited by Skinny Kid; 01-14-2015 at 11:46 AM.



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