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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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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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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.
 

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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 :devil:
 

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Discussion Starter #5
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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Do me a favor when you get the chance. Are the heads square port or oval?
 

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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. . . :D ).
 

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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).
 

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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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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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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.
 

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Discussion Starter #13
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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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.
 

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From what I've been able to gather Googling that casting #, those were the only BBC heads made that year. They went on 402's and 454's, in trucks, Chevelles, Impalas, Vettes, etc. Horsepower was 270 net in the Vette (about 300-325 gross flywheel - not bad for a low-compression, neo-smog wonder).

Most every site I looked at has the same sparse info as Mortec - however, I did manage to find one with the intake runner volume, as that really defines how well heads flow - 252cc. My 702 castings have 260cc intake runners (before porting), for example - one of the biggest oval ports they ever made.

Main issue is to keep compression up. Meaning if you rebuild it, be sure to use domed pistons for open chamber heads. You can easily get that 400 HP you were dreaming about, something like a Comp XE274 cam, Edelbrock RPM intake, 750 Holley carb, and headers - easy.

So, in spite of my earlier gloom & doom, I think you've got yourself something to work with. Congratulations!

(Depending upon who you want to believe, my ET/MPH calculate out somewhere between 400 RWHP and 500 GFWHP.)
 

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Discussion Starter #17
Thanks for the info.... should be easy enough to throw in a cam, intake, carb and headers.

One thing I forgot, the guy I bought it from started rambling on about the engine. First he said that the crank journals are all standard sized. So I immediatly asked if the engine had been apart before and he said he wasn't sure. A couple minutes later he said that the heads have oversized intake valves. I continued asking questions about the engine history and he didn't know any more at that point. This scared me a little....

With oversized intake valves...... what does this gain me?

Weather the engine has been rebuilt I don't know... it looks like the heads are a different color than the block... from the valve comment I am guessing the heads have at least been rebuilt (hopefully for unleaded gas) It was passed down to about a 45 year old guy from his father so who knows what went on.

I am sticking this into a hot rod that I am building from scratch... I may just drop it in with the basic mods listed above and have some fun for awhile.
 

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I'd take everything with a grain of salt. As far as I know, the factory only used two different sizes of valves: 2.06/1.72" (typical for oval port heads), and 2.19/1.88" (always for rectangular port heads). To put in 2.19/1.72" valve combo would be pretty weird - to use any other size intake valve would be even weirder.

Oh, about unleaded gas: It would be a very good idea to pull the heads and have a machine shop look at them. If it hasn't been done already, the exhaust valves should have hardened seats installed, and new hardened exhaust valves. Although there is a little bit of controversy on this, hardened exhaust valves are the best set-up when using unleaded gasoline (sounds like you already know about this). While you're doing that would be the best time to upgrade to 2.19/1.88" valves, but if this is just going to be a mild street engine, it really isn't necessary. And can even hurt a mild engine at low RPMs.

I believe the 402 crank is steel - I know the 396 is. That means it's a little more resistant to wear, so standard size journals wouldn't be too surprising.
 

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I have a buddy that has a 71 chevelle (4100pounds) and it had a stock 454 bbc Jasper motor a nice cam and victor jr intake and a well tuned 750 dbp he had that thing in the high to mid 12s with Edlelbrock rpm heads and a 100 shot mid to low 11s and now its a 500+ cid with a LOT of head work and a trans brake(th400) and lets just say it ran a 10 something once and they kicked him off the track for not having a cage .Its like I always say the only thing better than a then a sbc is a bbc. And on a side note what kind of car are you putting it in?
 

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Discussion Starter #20
I try not to use the term rat rod..... I say hot rod. I am building it from scratch with 2x4 tubing which will have a kickup in the front and rear, suicide front end, coilover rear. I have a 1935 international truck cab that I am going to chop and channel & build my own truck bed. With 350-400 net hp... it will be all I can handle as I am guessing the car shouldn't weigh more than 2500 lbs. when I am done.
 
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