1972 402 from a truck... is this worth building? - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums

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post #1 of 23 (permalink) Old 09-30-2007, 09:25 PM Thread Starter
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1972 402 from a truck... is this worth building?

Hello.. I am new to Chevy's and I am looking for a decent engine / transmission for a new project. I ran across a 1972 chevy truck with an original 402 big block with a 400 transmission. My only concern is that these engines were so detuned by this time that I may have to spend some serious $$$ to get the power numbers back up. I think they were rated at around 240hp in the trucks that year. I think the main problem is they brought the compression way down. Am I looking at domed pistons, stroking the engine, shaving the deck or something of that nature? I am most likely going to have to rebuild the engine anyway... just curious what I am going to need to do to it to make it a streetable engine with around 350-400hp. I am guessing if I ditch the 2bbl carb and throw headers on it I may gain something right off the bat. I can get the whole truck for $600
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post #2 of 23 (permalink) Old 09-30-2007, 09:49 PM
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Yes, it is worth the money. My dad had a 402bbc with 9:1 compression and stock casting heads ported and had 600fwhp naturally aspirated. It was built to run a 300 shot but only shot a 150 on it. Had it in a 76 silverado, thing was insane!!!

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post #3 of 23 (permalink) Old 10-01-2007, 05:52 PM
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2 bbl? The big block should have gotten a 4 bbl.

Heads are the big thing. I'm not sure exactly what the truck 402's got, but most likely you'll want to find something else. Post the casting #'s and we can go from there.

The 402 is basically a .031" over 396. I'm pulling about 500 flywheel HP with my .030"-over 396 with a basic rebuild (forged pistons), ported stock heads, a nice cam, and good intake manifold.

'82 Berlinetta, 2000 LS1/4L60E. LS6 intake, shaved 317 heads, free-flowing air intake, long tube headers, 3600 stall, 3.73 posi. Best: 12.57 @ 109 at 5800' elevation; 11.82 @ 114 at HPT.
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post #4 of 23 (permalink) Old 10-07-2007, 12:58 AM
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Quote:
Originally Posted by powerplant View Post
Hello.. I am new to Chevy's and I am looking for a decent engine / transmission for a new project. I ran across a 1972 chevy truck with an original 402 big block with a 400 transmission. My only concern is that these engines were so detuned by this time that I may have to spend some serious $$$ to get the power numbers back up. I think they were rated at around 240hp in the trucks that year. I think the main problem is they brought the compression way down. Am I looking at domed pistons, stroking the engine, shaving the deck or something of that nature? I am most likely going to have to rebuild the engine anyway... just curious what I am going to need to do to it to make it a streetable engine with around 350-400hp. I am guessing if I ditch the 2bbl carb and throw headers on it I may gain something right off the bat. I can get the whole truck for $600
How sure are you it is a 402bbc I think they only put those is cars and it was basicly a beefed up 396 so it should not have a 2bbl carb it is worth it if its not a 348bbc but as far as that goes I think they where long gone in 72 and all ways remember the only thing better then a small block chevy is a BIG BLOCK CHEVY
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post #5 of 23 (permalink) Old 10-07-2007, 07:53 AM Thread Starter
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The previous owner told me it was a 2 barrel carb.... he was wrong.... it was a 4 barrel quadrajet.

I did buy the truck.... I am building a rod and this is going to be my engine.
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post #6 of 23 (permalink) Old 10-07-2007, 01:59 PM
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Do me a favor when you get the chance. Are the heads square port or oval?

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drivers side is a dream....passenger side on the other hand...i lost 2 screwdrivevers and a socket when i chucked them in the woods

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post #7 of 23 (permalink) Old 10-07-2007, 03:39 PM Thread Starter
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Do me a favor when you get the chance. Are the heads square port or oval?

How do you tell?
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post #8 of 23 (permalink) Old 10-07-2007, 11:09 PM
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You can either look up the casting numbers (under the valve covers - then www.mortec.com), or pull the intake manifold and look at the shape of the intake ports.

If this doesn't have oval ports, the heads and intake have been changed somewhere down the road (and remember, I was right about the 4bbl carb. . . ).
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post #9 of 23 (permalink) Old 10-07-2007, 11:14 PM
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Quote:
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How sure are you it is a 402bbc I think they only put those is cars and it was basicly a beefed up 396 so it should not have a 2bbl carb it is worth it if its not a 348bbc but as far as that goes I think they where long gone in 72...
They called them both "400" in the trucks. If small block, it had a 2bbl carb; if big block, it had a 4bbl carb. In Chevelle's, they called the BBC 402 a "396" - go figure.

The 402 block was a different casting than the 396. It had a .031" larger bore (as I already stated), but the cylinder walls were actually thinner than the early 396's (some of which were also used for the 4.250" bore 427 - same stroke for 396/402/427). The heads on the 402's also tended to flow less than 325 horse 396 heads, and the trucks typically got the worst (from a performance standpoint) of any.

The 348/409's were gone by the early 60's. There were a few 409's in early '65 while they ramped up 396 production, but the 348 was gone before that ('60, if memory serves).

Last edited by five7kid; 10-07-2007 at 11:17 PM.
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post #10 of 23 (permalink) Old 10-08-2007, 07:06 AM
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The oval port were the low performance heads that the 396 pickups got. The square port heads are the high performance bb car heads. It will also tell you if you have a stroked 396 to 402 or a true factory 402.

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Quote:
Originally Posted by 94FormulaBird View Post
drivers side is a dream....passenger side on the other hand...i lost 2 screwdrivevers and a socket when i chucked them in the woods

u can do it



I am permanently banned from all petting zoo's for getting to friendly
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post #11 of 23 (permalink) Old 10-08-2007, 02:21 PM
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Uh, there is no such thing as a "stroked 396". The 396, 402, and 427 all had 3.76" stroke. The difference was the bore - 4.094", 4.125", and 4.250", respectively. My 396 is .030"-over, making its actual displacement 401.79 cubic inches - just one lousy thousandth of an inch less per bore than a 402 (which is actually 401.99 cubic inches).

The 454 is a 4.00" stroke by 4.250" bore (also externally balanced).

Oval port heads were the norm. Only the extreme performance cars got the rectangular ports, and they weren't very street-friendly. They disappeared from production in the early 70's. There were some good oval port heads, some "closed" (small) chamber, some "open" (large) chamber. There were also different valve sizes: "standard" were 2.06"I/1.72"E (makes SBC's drool); "large" were 2.19"I/1.88"E.

As I said earlier, most likely the heads on a '72 pickup 402 will not be much for performance. But, they may be open chamber oval ports, with some potential if ported and large valves installed. Need the casting #'s.
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post #12 of 23 (permalink) Old 10-08-2007, 04:01 PM
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Sorry kid. Bored is want I meant to say. And as for the the question about the heads it was just a thought that someone may have changed them out some time in the past, and he got lucky.

03 Z06, LTs, A&A P1SC running 6psi, 550/471
Quote:
Originally Posted by 94FormulaBird View Post
drivers side is a dream....passenger side on the other hand...i lost 2 screwdrivevers and a socket when i chucked them in the woods

u can do it



I am permanently banned from all petting zoo's for getting to friendly
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post #13 of 23 (permalink) Old 10-09-2007, 12:43 PM Thread Starter
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All the body pannels on this truck are junk... I just figured instead of laying over a fender while working on the engine I may as well remove the whole body and get rid of it first. I was able to fine the block casting number to learn that it is a true 402 block listed as "truck". The listing said it may be either 2 or 4 bolt main so I still don't know quite what I have yet. I will report back with the head type once I get that far.

I may stick with basic mods first.... headers, intake, carb, and a cam.

I did notice one thing... the oem oil pressure gauge pegs out when I start the engine. The oem gauge does not have numbers on it plus it is old so I don't know if it is screwed up or not. I am going to throw my own gauge on it just to double check. If it is too high.... would it be the pressure relief valve sticking?
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post #14 of 23 (permalink) Old 10-09-2007, 08:34 PM
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The truck engine will need a lot of modifying. They were buit for torque not power, the heads are not built for a performance car perspective. I have a Built 402 in my 71 SS Elcamino but it came out of a 70 Chevelle. It allready had 10.5:1 copression and the hi performance heads (I completely rebuilt it with aftermarket parts, new cam, intake, carb, and rebuilt the heads with roller rockers, 3 angle valve job, harden seats, and new valves).
It would be a great motor to get however you will have to go completely through it (New pistons, cam etc...) and add different heads to get any serious horsepower.

00 SS Camaro,6mt,NBM,SLP lid and Bellows,Ceramic LT's,ORY,Borla adjustable,STB,SFC's,LCA's,PHB,TA, 35 splined 9" w/ 430's and Locker, Strange D.S., Pro 5.0 W/short stick, PRC Stg 1.5 Heads, TSP 230/232 604/604 Cam, Fast 90, PTM 90 TB, Spec Stg 4, MT ET Streets for the track
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post #15 of 23 (permalink) Old 10-09-2007, 08:56 PM Thread Starter
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Got the numbers off the head

3999241 was the number

this means 72......oval...OPEN...402, 454, 113cc chamber


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