1971 Big Block Exhaust Manifolds???????
 

Seeking an education please. EDIT: EDUCATED. The variable is for A.I.R., not air conditioning.

I was looking into fitting the heat shield for the stove pipe for the 402. Out of curiosity, I took note of the exhaust manifolds, which are (LH 3994045) and (RH 353030). First off, the truck is stock A/C. I just never put it back on with a engine rebuild long ago, but I plan on re-assembling. So here's where the fun begins. Take a peak at this here Wiki link, right out of the Light Truck Parts Catalog (below).

First, I don't believe they put a 396 in a 1971 Chevy (402 replaced the 396). Second, they don't show a 402 (aka 400) for the 1971, but they do for a 1972............They also don't differentiate between exhaust manifolds (A/C and not) within the grid for 1971.

If that wasn't confusing enough, if I go by the 1971 396, then my LH exhaust manifold is correct (assuming A/C doesn't matter), but the RH manifold is incorrect. If I go by the 1972 400, then the LH exhaust manifold is incorrect for A/C, but the RH is correct for A/C.

WTH? With all this mess in mind, safe to say the A/C cannot be mounted properly with one of these exhaust manifolds?

For the record, the heads on this 402 came off of a 396. I'm way to green to know if that matters for this application, though I suspect it doesn't. The LH exhaust manifold had to be replaced with the engine rebuild.

HELP!

http://www.t.gmpartswiki.com/getbigpage?pageid=21508

Re: 1971 Big Block Exhaust Manifolds???????
 

Off topic. I really want to start dismantling. I'd rather not until I drop off the bed with the body man, pending his phone call.

Re: 1971 Big Block Exhaust Manifolds???????
 

I have headers and a 402 (1972 C10) with AC and everything is fine. No brackets mount to the exhaust manifolds and I am sure headers take more room than stockmanifolds. Secondly, 396 if 67-68, 400 69-70 and 402 71-72, even thought they are the same block. I just had the same problem with a top rad hose. The parts place had no listing for a 402 and the 400 hose didn't fit, but the 396 hose did-go figure

Re: 1971 Big Block Exhaust Manifolds???????
 

cause the 396 is a big block and the 400 is a small block...the 402 is a .030 over 396...

Re: 1971 Big Block Exhaust Manifolds???????
 

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My '71 has "396 V-8 Engine" on the SPID and 8-400 badges on the front fenders so the "400" designation was used for the big blocks too.

Lockdoc

Re: 1971 Big Block Exhaust Manifolds???????
 

These numbers are for service replacement parts.
The applications are intended to depopulate parts inventories as much as possible by using one part number for as many applications as possible.

Parts manuals are easy to use if you read them carefully.

But don't expect a number in there to match a part you pulled from your truck.

Overall its real simple, the replacement manifolds at the time of printing (5/79) were:
3994045 LH
333846 RH

with A.I.R. this is the air pump for emission reduction
343787 LH
353030 RH

There is nothing there on that parts manual page to show application specific parts for a 396-402 C10-30 Air Conditioned vehicle. If there were it would probably be notated w/AC, C.A.C., or C60.

Re: 1971 Big Block Exhaust Manifolds???????
 

I have a 70. 402/TH400 w/air. stock if I can help with pics or anything ?

Re: 1971 Big Block Exhaust Manifolds???????
 

True. And I didn't know for certain the 396 came in a 71. Must have been "left-overs". I don't believe any 71-72 Chevy came with a small block 400. When it comes to 400s, the information can be kind of sketchy. Sometimes you don't know what the block they're talking about. They should have called the 402 a 402, all the time.

Re: 1971 Big Block Exhaust Manifolds???????
 

Re: 1971 Big Block Exhaust Manifolds???????
 

Someday I may take you up on that. Thank you.

Re: 1971 Big Block Exhaust Manifolds???????
 

the 400 is a big block as well and identical to the 402, just badged 400-don't know why

Re: 1971 Big Block Exhaust Manifolds???????
 

Fender sticker reads 402.
I believe the owner's manual reads 402.
SPID reads 400.
Emblems read 400.
Small and Big block 400 are both referenced as 6.6 liter (rounded).

The info. is all over the map.

Speak of SPID, anyone recommend a clear cover for these? Mine started a peal at the corner. I think it may be able to peal the old one off w/o damaging the SPID (maybe). Otherwise I suppose I could cut the edges, apply a second cover on top.

Re: 1971 Big Block Exhaust Manifolds???????
 

Dude you are really driving all the way around the block to vist the house next door.
The A.I.R. aka Air Injection Reactor aka air pump was basically an external, belt driven, accessory pump plumbed through a valve and hoses to manifold mounted air pipes. The big difference on the manifolds were the holes to thread the air pipe into at each exhaust port. Often you will find these holes simply plugged.

Again as I stated above A/C is not a factor with this P/N manifold used in this application.

As far as the whole 396/400/402 things goes its mostly marketing. The year breakouts above are correct. The SPID may list a 402 actual as a 396 or 400 so it is always a good idea to verify the engine suffix code if there is any question.

Re: 1971 Big Block Exhaust Manifolds???????
 

Ha...........I thought A.I.R. was A/C..........I see the difference. The RH (A.I.R.) has a ridge that runs along the side, and a small screw plugged in. The LH is smooth. Don't tell anyone my manifolds don't match. I used to know that and forgot all about it. I don't believe this truck had A.I.R.

Re: 1971 Big Block Exhaust Manifolds???????
 

Please don't confuse it. Yes there was a 400 small block in Impalas but never in trucks.

You and I both know the 402 was advertised as a 400. The emblems say 400. The SPID says 400. It's a 400. Internal displacement often doesn't exactly match marketing designations.

Besides, if you do the math, it's not actually 0.030 over. I'll leave that as an exercise for the reader.

Re: 1971 Big Block Exhaust Manifolds???????
 

Drive around the block, to get to the house next door. Hah! Gotta remember that. I run into that all the time.

Re: 1971 Big Block Exhaust Manifolds???????
 

Owner's manual reads 400 engine, 402 displacement. As davepl eluded to, GM may have consistently referred to the "engine" as a 400, while 402 is displacement.

https://lh5.googleusercontent.com/-n...19-no/SPID.png

https://lh5.googleusercontent.com/-p.../Emmisions.png

https://lh5.googleusercontent.com/-h...per%2BWork.png

Re: 1971 Big Block Exhaust Manifolds???????
 

I tend to do that until dialed in. Still some blonde left. Tim knows how to hit the reset button.