Original 1957-74 heat riser spacer for FI?

[Richard T.]

Re: Original 1957-74 heat riser spacer for FI?

Ian,
The exhaust crossover that was mentioned before is not the exhaust pipe but the crossover in the intake manifold (or base plate). The carburated engines have an exhaust crossover that runs from cylinder head to cylinder head and is directly underneath the carburator. When the engine is cold (heat riser valve closed) exhaust gasses flow through this passage and heat the air/fuel charge coming from the carburator for better cold operation. Once the engine warms the heat riser valve opens and exhaust gasses can flow out the right hand manifold.
Fuel injected engines do not have this crossover in the manifold (or base plate) as it's not needed therefore the heat riser valve isn't needed so the fuel injected cars got the spacer instead. Rich

[Stuart F.]

Re: Original 1957-74 heat riser spacer for FI?

Ian;

I believe what the JG is referring to is actually a balance pipe between the exhaust header pipes. It has nothing in principle to do with the heat riser cross-over system. Not knowing too much about C-1's, I wasn't aware that the tupe/pipe was used on Vettes, but it was common on passenger cars. I believe it was intended to, as I said, Balance the system for sound and, on those applications that did have the heat riser system, balance the volume of exhaust gases between the dual exhaust systems perhaps to make the right side last as long as the left side. It was common in those days for the right side pipes to rust out sooner than the left because the right side never got enough hot exhaust to get rid of the condensation, specially in the colder ambient conditions of the north. Dual exhaust systems were a new item back in the mid-fifties.

As I recall, the pipe was of a smaller diameter than the header pipes, was clamped to the pipes at each side, but had like a slip connection (not clamped) between them under the oil pan to allow for thermal expansion. The reason I say it may have been something to do with sound, we used to remove them and cap them off to get a better sound, specially with glass pack mufflers. It would "rap" down more than with the tube. Similarly, when we blocked off the heat riser cross overs in the summer, the exhaust system was louder, although we did it more in the vein of looking for more power.

Stu fox

[Ian G.]

Re: Original 1957-74 heat riser spacer for FI?

Thanks for the explanation! I'll have a look at that when I take the intake manifold off and replace it with the one the fuel unit is sitting in (aluminum).

[Ian G.]

Re: Original 1957-74 heat riser spacer for FI?

One last question: I notice in the assembly manual that it doesn't look like a donut is used for the spacer/valve. However, there does look like there is some kind of gasket on the bottom, between the flange and the lip of the pipe... Does anyone know what that gasket is, or is that a donut as well?

[Joe L.]

Re: Original 1957-74 heat riser spacer for FI?

One last question: I notice in the assembly manual that it doesn't look like a donut is used for the spacer/valve. However, there does look like there is some kind of gasket on the bottom, between the flange and the lip of the pipe... Does anyone know what that gasket is, or is that a donut as well?

Ian-----

With EITHER the heat riser valve OR the spacer, there are two gaskets involved. Between the manifold flange and the spacer or valve is a triangular, flat gasket. Between the exhaust pipe and the spacer or heat riser valve there is the "donut" packing.

Examples of both are shown below. These are both 2-1/2" exhaust pieces but the 2" pieces used for your application have the same configuration.

[Stuart F.]

Re: Original 1957-74 heat riser spacer for FI?

Joe;

It was mentioned in another thread about loose nuts on the exhaust pipe to the manifold that one should use the metallic packing as they would not compress so much under tension and allow the nuts to loosen (in fact you may have been the one to mention it). Is the one in the photo the metallic type? It looks, although it is still in a bag, more gray in color. I have a number that are partially blue. Are they the ones that compress? They look like they have a lot of metallic in them, but I'm not sure.

Stu Fox

[Joe L.]

Re: Original 1957-74 heat riser spacer for FI?

Joe;

It was mentioned in another thread about loose nuts on the exhaust pipe to the manifold that one should use the metallic packing as they would not compress so much under tension and allow the nuts to loosen (in fact you may have been the one to mention it). Is the one in the photo the metallic type? It looks, although it is still in a bag, more gray in color. I have a number that are partially blue. Are they the ones that compress? They look like they have a lot of metallic in them, but I'm not sure.

Stu Fox

Stu-----


No, the one I pictured is the standard type which is some sort of high heat resistant material which is "soft". These used to be made largely of asbestos but I'm sure that's no longer used. I don't know what the formulation of the material actually is, though. It is much darker than the "donut" packings of old. I do not use this type (although, I have some which is where the one in the photo came from).

The "sintered iron" type is pictured below. There's no mistaking one of these for the other type. These look and feel just like solid metal.

[Stuart F.]

Re: Original 1957-74 heat riser spacer for FI?

Joe;

Can't say I've ever seen one like the sintered metallic one in the photo. The ones I have are partially blue like they have a composite of material in them. I will probably try one anyway as I'm not too worried about the nuts loosening up. As I mentioned in the other thread, I may just use Pal Nuts on them to be safe. I got a lot of those as we used them a lot in the old days. I recall you quoted a P/No. for those metallic ones though, so I'll go to the other thread and grab it for my list of things to get at the dealer.

Thanks;

Stu Fox

[John H.]

Re: Original 1957-74 heat riser spacer for FI?

One last question: I notice in the assembly manual that it doesn't look like a donut is used for the spacer/valve. However, there does look like there is some kind of gasket on the bottom, between the flange and the lip of the pipe... Does anyone know what that gasket is, or is that a donut as well?

Ian -

Gasketing with an FI spacer is the same as with a heat riser valve - the flat side goes against the exhaust manifold with a triangular gasket, and the bottom side is chamfered to accept the "donut" that goes on the exhaust pipe.

[Ian G.]

Re: Original 1957-74 heat riser spacer for FI?

OK cool. And congrats on being nominated to the hall of fame

[Chuck G.]

Re: Original 1957-74 heat riser spacer for FI?

FWIW, yesterday I was flipping through the East Coast Chevy, Ol'55 catalog. They're in Doylestown, PA.

In their catalog is pictured the 2" spacer for FI engines.

I'm sure it's a repro. Cost was $30.00.

Don't know if more than one company repros them. Might be worth a call.

East Coast Chevy is one of the largest suppliers of 55-57 Chevy parts.

Chuck

[Ian G.]

Original 1957-74 heat riser spacer for FI?

can anyone confirm what the GM part number should be for an original FI 2" heat riser spacer for a 59?

[Joe L.]

Re: Original 1957-74 heat riser spacer for FI?

can anyone confirm what the GM part number should be for an original FI 2" heat riser spacer for a 59?

Ian------


The original part number for the 2" spacer was GM #3750067. It was discontinued more than 25 years ago.

[Stuart F.]

Re: Original 1957-74 heat riser spacer for FI?

Don't know if this the best thread to add this little ditty, but here goes;

We've talked in other threads about the problems of the exhaust pipe to manifold studs and nuts, and the problems keeping them tight, etc. Well, for what it is worth, I noticed in our local auto parts store (while looking for some studs) that they have replacement exhaust stud kits which include SS studs, Brass Nuts and coil springs! My first thought (chuckle) was that they would turn the connection in to a POP OFF VALVE (WOW! Cool!). Seriously, now I know this isn't an item that would pass a litmus test for judging, but what a cool idea and, why didn't I think of that?

Stu Fox

[John D.]

Re: Original 1957-74 heat riser spacer for FI?

Joe, I may have a couple of base plates around here. You are 100% correct Joe. No cross over on FI's. Not from 57 to 65. Only "holes" on the bottom of an FI base plate are for the water passages in the four corners.
John D