Exhaust spacer

[Canuck]

My pass side 454 exhaust manifold has a spacer on it. I assume it is to take the place of the original heat riser assembly. I’m not sure which direction it should be on the manifold. One side is more flat and the other has a bit of a rounded edge surface. I assume the flat side should face the manifold but that wasn’t the way it was when I took it off. Which way should this go?

On another note, this piece looks restrictive with a hole smaller than my pipes. Maybe I should just get a more open spacer altogether?
 

Flat side

other side

[Grant MacPherson]

Flat side up, but I would change it or open it up to manifold size.

[Whons]

If you want to send it to me I can machine it to a larger I.D.

[cny first gen 71]

Isn't that a 71? Heat riser was 70 was the last year they used them on chevys. You may be able to just leave it our if the manifold has the recess for the gasket. Check to make sure no one has swapped the manifold at some point in time.

[Canuck]

1 hour ago, cny first gen 71 said:

Isn't that a 71? Heat riser was 70 was the last year they used them on chevys. You may be able to just leave it our if the manifold has the recess for the gasket. Check to make sure no one has swapped the manifold at some point in time.

Yes, 1971. I wasn’t aware the heat riser was eliminated after 1970. Maybe this spacer was in place of that? The manifold does have a beveled recess for the gasket but the exhaust was made to fit with that spacer in place. I don’t believe the exhaust pipe will reach the manifold. I’ll check the part number of the manifolds to see if they are for 1971.

[Dtret]

Both my 70 & 71 SS’s have the spacer. Not sure about my 72 W code. 

[stangeba]

My 71 350 4bbl had one of these restrictors, until I added dual exhaust, now it only has a donut.

This brought the front right (passenger side) pipe up a bit but no problems. 

I must have thrown it out because I can't find, it and didn't take a picture of it. 🥲

 

[cny first gen 71]

Maybe they used up the last of the 70 manifolds on some 71s I do remember from back in the day working in a muffler shop that it was eliminated in the 71 model year which we liked because it was easier to change crossover pipes without the heat riser. I do know that my 71 sb didn't have one when I switched from single to dual exhaust. I even still remember the ap crossover number because we changed so so many of them. I don't remember any big block single exhaust I'm pretty sure they were all dual exhaust. 

[willie]

I know when i restored my 72 Custom BB, the heat riser was there. Not sure if it should be, but that's how i put it back! It was frozen open so i had to replace it.

[Canuck]

The part numbers on my exhaust manifolds came back as 1970. The car was built in September 1970 so could be they still installed some 1970 manifolds at that time. This spacer/restrictor appears to be a factory type part but who knows for sure.

[Vaughn]

If I remember correctly Aaron, those exhaust manifolds are the correct date coded originals for the car. 

[Vaughn]

You cant open up the interior of this spacer very much as it is meant to hold the exhaust donut to connect to the exhaust pipe. 

[Scott S.]

I would imagine that this piece was carried on after '70 in cold climate and emission controlled markets. 

That could be why they don't appear in all cars. ???

[70white402]

My 70 Monte had original heat riser in it.  When I put the chambered exhaust on from Gardner I had to put in spacer. The pipe would not fit.

[Canuck]

According to the 1971 assembly manual this spacer is correct for the LS3 and LS5. The LS6 got the heat riser valve though.

LS3 assembly

 

Page stating the LS5 has the same assembly as the LS3

 

LS6 assembly

 

[Vaughn]

Good information Aaron. I have two 1971 with the 402 and they have the spacer, not the spring loaded heat riser.