Inliners International Forums General Discussion Engines Swapping a 250 for a 292 exhaust manifold

I own a 1977 292 G20 Sportvan with a major exhaust leak. Somewhere on this forum or another I was read that you cam switch manifolds on the 250/292.

So when a 1974 Nova with a 250 intake/exhaust and carb for a very resonable price I bought it.

Is is okay do downgrade manifolds?

If so I am having a hard time finding the right exhuast flange.
The 2 bolt style. It looks like your friend at 12 bolt has something that might work

http://www.12bolt.com/store/p154/Exh_Hardware_Kit.html

I found a site that may have what I need but the specs are not really meshing 2"13 or 2"25

http://www.mandrelbends.com/flanges-gaskets/exhaust-flanges.html?p=10

In the mean time the 292 exhaust manfold is totally shot as there is now some cracks as weel as I broke an ear off the face that leads to the tail pipe by over torqueing?

All that being said i am looking to replace the exhaust, but at the moment just broke to get her moving again.

I am on a serious budget, I had no plans to do any work to van van except change the oil,whaen i bought it 5 years ago but alas I can't let her go. Any advice you inliners coukd give would be greatly appreciated.

Mr. MUSTARD

Have you verified that it doesn't have an integral head?

1974 was the last non-integrated year for the 250, and it did have a 2" exhaust manifold with a 2-bolt flange. After that, the 292 exhaust and two versions of the 250 integrated had a 2.25" with 3-bolt flange that are both angled downward to gun under the oil pan to the passenger side (as opposed to the angled exhaust that runs under the driver's side). The exception is the HD 292 which has the 2.5" manifold, and the 1979 Camaro, Nova, and Caprice 250 that got a non-integrated head along with the SD 292 exhaust manifold.

The 3 bolt 292 exh manifold is available new. Here is one on ebay.
https://www.ebay.com/itm/250-4-1-292-4-8-GMC-Chevrolet-New-Exhaust-Manifold/283068812437?hash=item41e8374c95%3Ag%3AayUAAOSwP79bVdfy&_sacat=0&_nkw=292+exhaust+mainfold&_from=R40&rt=nc&_trksid=m570.l1313

I would also suggest going to your local exhaust shop. They will have the flanges in stock if you really want to do the 2 bolt flange.

One other difference between the integrated exhaust and the 292 non-integrated is that my 2nd version '77-'78 integrated exhaust manifold appears to have the EFE valve built into the manifold itself. Whereas I believe the non-integrated 292 in SD and HD version has a separate bolt on part for the exhaust flange much like the small block Chevy passenger side manifold.

I haven't taken my top end off to really look at it yet, but that's how it appears from underneath the engine. I'm also not sure if there is an exhaust manifold difference between the '75-'76 version of the integrated head, and the '77-'78 version?

If you can't afford the price of a replacement 292 exhaust manifold, and the '74 manifold is within your budget, then you can interchange the two. If you don't need the second intake manifold, I'm actually looking to pick up a factory manifold for the next stage of my project when I swap my integrated top end for a non-integrated top end. So I could buy it from you and help defray the cost some too.

Keep in mind will be changing the '77 2.25" outlet 292 manifold for the '74 2" outlet 250, so you will have some exhaust restriction. The new replacement 292 manifolds are 2.5", so it is actually an improvement if you put a 2.5" exhaust on it.

Your factory '77 header pipe will be at the wrong angle tho. The '74 and earlier manifolds angle backward so the 2" header pipe ran back under the linkage and down the driver's side of the car. In the '75 to '79 passenger cars, the 2.25" header pipe runs downward and then bends 90* under the oil pan to go out the passenger side to the catalytic converter. I have been looking for a diagram of the van exhaust in '74 and '77 and haven't found one yet. What is the path of your exhaust pipe when it leaves the manifold? Driver or passenger side?

They are both exactly the same except the 77 2.25 inch hole has 3 bolt and the 74 2.25 inch hole has 2 bolt and a shield for the stove and two/metal choke wire wrapped up liike a coil on it to control the stove. With an opening for pipe to go to the air cleaner.

77's wire is not there anymore and may be why we need a new manifold.

They are on the drivers side angled at about 5 o'clock when looking at it from the drivers side. The exhaust pipe meets it and a foot or two make 130 degrees tunr and then straighten out, all on driver side.

Will the exhaust hardware from 12-bolt not work?

**Edit***
Well like I said I am not a mechanic but this muffler and brake shop in my neighborhood sold me a coluple flanges that may do the trick but they are 2 inchs but they fir the manifold but look a little small for the donut.

Thanks to everyone I hope to get working on it tomorrow after a quick trip to return this spilt flange that didn't fit the bolt holes.

Choke wires? Didn't know they had any? Yeah, my '78 Camaro 250 has an electric choke, so no wires either. I guess those coiled wires are the old system that function more like V8 manifold heat choke.

Ok, so the truck and van exhaust pipes follow a different path from the cars. That should make retrofitting the older one easier for you.

Are you putting the 2 bolt flange on the original 2.25" pipe, or cutting off the collector to put another 2" one on the old pipe? Never tried to mate up a 2" manifold with a 2.25" pipe, not sure if the donut will have issues?