SBC exhaust manifolds don't fit

[deucecoupe]

Thank you in advance for any insights you can provide.

I'm swapping out a 250 engine in my '84 C10 for a small block V8. The new engine is a rebuilt 327 with double hump heads.

I purchased a set of used exhaust manifolds from a guy up near Seattle. The casting numbers indicated they were from a '76 to '80 SBC.

Two questions:

1. when I went to install them, the bolt pattern didn't match up to my heads. On the exhaust manifolds, it is 17-1/4" distance from the two outer mounting bolts. My heads are 17-1/2" for the same measurement. Are these from a 305 or a different engine?

2. the guy who sold them to me said they were from the same truck. But the surface areas where the y-pipe matches up are totally different. The RH is flat (for the heat riser valve) and the LH one is domed. With the little beveled donuts, I don't see how the left side would even work. Are these two manifolds from two different models or engines? Or is this how they came.

I obviously won't be able to use them, but I want to know for my own knowledge.

Pics attached.

Thanks much

 

[AyWoSch Motors]

Thank you in advance for any insights you can provide.

I'm swapping out a 250 engine in my '84 C10 for a small block V8. The new engine is a rebuilt 327 with double hump heads.

I purchased a set of used exhaust manifolds from a guy up near Seattle. The casting numbers indicated they were from a '76 to '80 SBC.

Two questions:

1. when I went to install them, the bolt pattern didn't match up to my heads. On the exhaust manifolds, it is 17-1/4" distance from the two outer mounting bolts. My heads are 17-1/2" for the same measurement. Are these from a 305 or a different engine?

2. the guy who sold them to me said they were from the same truck. But the surface areas where the y-pipe matches up are totally different. The RH is flat (for the heat riser valve) and the LH one is domed. With the little beveled donuts, I don't see how the left side would even work. Are these two manifolds from two different models or engines? Or is this how they came.

I obviously won't be able to use them, but I want to know for my own knowledge.

Pics attached.

Thanks much

I had double hump heads on my 350, and I had the hardest time getting manifolds to fit. I went threw like 4 sets, finally settled on some vortec ones and had to get them super hot and stretch them with a pry bar to get them to bolt up. Dont have a clue why.

As far as the shape of the manifolds, that's a standard shape difference from left to right. Ones shaped like that to clear the starter and the other is to clear the oil filter. That's a standard shape.

 

[fast 99]

That's normal, you need set of exhaust manifold spreaders. Even then the outer holes in the manifolds may need to be enlarged. Believe it or not it helps if they are heated up a bit in an oven.

edit: do not use gaskets, just high temp silicone.

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[AuroraGirl]

Thank you in advance for any insights you can provide.

I'm swapping out a 250 engine in my '84 C10 for a small block V8. The new engine is a rebuilt 327 with double hump heads.

I purchased a set of used exhaust manifolds from a guy up near Seattle. The casting numbers indicated they were from a '76 to '80 SBC.

Two questions:

1. when I went to install them, the bolt pattern didn't match up to my heads. On the exhaust manifolds, it is 17-1/4" distance from the two outer mounting bolts. My heads are 17-1/2" for the same measurement. Are these from a 305 or a different engine?

2. the guy who sold them to me said they were from the same truck. But the surface areas where the y-pipe matches up are totally different. The RH is flat (for the heat riser valve) and the LH one is domed. With the little beveled donuts, I don't see how the left side would even work. Are these two manifolds from two different models or engines? Or is this how they came.

I obviously won't be able to use them, but I want to know for my own knowledge.

Pics attached.

Thanks much

You must be registered for see images attach

You must be registered for see images attach

 

[JeffK10America]

Spreader works great . I have seen some of those dimensions in car and truck engines vary . But the spreader makes it happen easily .

 

[Turbo4whl]

Do the double hump heads have the threaded bolt holes for the engine accessories? Early 327 heads do not have the threaded holes.

 

[AyWoSch Motors]

That's normal, you need set of exhaust manifold spreaders. Even then the outer holes in the manifolds may need to be enlarged. Believe it or not it helps if they are heated up a bit in an oven.

edit: do not use gaskets, just high temp silicone.

You must be registered for see images attach

What I did with mine, was bolt them on with the center 2 bolts, and ran the engine for a little while get them hot. 2 went in afterwards, 2 just took a little prying with a lug wrench to get the other 2.

 

[AuroraGirl]

Do the double hump heads have the threaded bolt holes for the engine accessories? Early 327 heads do not have the threaded holes.

im guessing once any cars were optioned with power steering and/or ac in the late 60s early 70s you would see small blocks come with accessory holes. Just a guess, but I believe they came either way. From what ive read.

 

[Turbo4whl]

im guessing once any cars were optioned with power steering and/or ac in the late 60s early 70s you would see small blocks come with accessory holes. Just a guess, but I believe they came either way. From what ive read.

Yes, the early engines still had all the accessories but they were mounted to the sides of the engine, not in front. They bolted to the short watet pump and exhaust manifold bolts.

 

[Turbo4whl]

@AuroraGirl

Check this picture of the 327, (L-79?) No bolt holes.

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[deucecoupe]

Thanks everyone for your quick response.

I've worked on 327s before but always ran headers. So I didn't know the spreaders were a thing for mis-aligned manifolds! But clearly a useful tool. A 1/4" seems like a lot of gap to overcome, but the manifolds must have enough expansion ability. I like the idea of heating them a bit.

On comments about bolt holes in the double hump heads - I ran into that issue when trying to figure out how to mount the alternator brackets. I went to Alan Grove and he sells a bracket and fittings to line up with the factory lower mount (the one closer to the radiator). Problem solved.

My original second question was not worded clearly. It wasn't about the shape of the manifolds themselves but rather the mating surface where the manifolds bolt to the y-pipe or first section of exhaust pipe. I'll post some LH and RH pics so it will be clear what I'm trying to understand.

Thanks again, at least I know the manifolds will work once I get the spreaders.

 

[deucecoupe]

Addendum - pic of the Alan Grove bracket for alternator mounting when there is no bolt hole in the head. Stock bracket on the right, Alan Grove bracket on the left.

 

[SquareRoot]

Nothing like fighting with 50 year old parts just to get lousy performance. You can buy new, much improved manifolds from Hooker for like $200....no prybar or "spreader" required.

 

[Catbox]

Addendum - pic of the Alan Grove bracket for alternator mounting when there is no bolt hole in the head. Stock bracket on the right, Alan Grove bracket on the left.

That is a nifty bracket for sure.

Plus, if you ever want help, let me know as we are very close over in Tigard.

 

[MikeB]

Exhaust manifold spreader? Is that also known as exhaust manifold cracker?

Man, that's a first for me after 50+ years of working on Chevy small blocks. I still learn something new almost every day.