Weird exhaust (emmissions?) thing on right-side manifold

MaineShark · 01-22-03, 08:32 PM

On my right-side exhaust manifold, there is some sort of vacuum actuator, controlling what looks to be a valve, down below. I believe it gets its vacuum from a temperature-controlled switch.

I'm guessing it's some sort of emissions thing, but I'm not certain what it does. I tried looking in my Haynes manual, but I couldn't find anything that seemed to refer to it.

Anyone know what it is?

Joe

01-22-03, 09:45 PM

I also have a 1979. that is a temp valve designed to route warm exhaust gas to the other side during cold mornings. Since I live in Vegas I yanked the actuater and hose. Its hot here. The default for the valve is open held by a spring. My concern was if it was really opening to allow unobstructed exhaust.

01-23-03, 12:00 AM

The heat riser valve, I believe thats what its called

rpounds · 01-23-03, 12:37 AM

Frank is right, it's the actuator for the heat riser. The proper name for the cannister is 'EFE'. The EFE is hooked to a thermal vacuum switch that provides vacuum to hold the heat riser closed until the engine reaches operating temperature. As was mentioned earlier, this routes exhaust gasses from one side of the engine up through the intake manifold in order to quickly heat the carburetor (actually the choke) so that the engine will go from a cold start rich condition to a normal lean condition more quickly. It also supposedly helps cold start driveability.

As a PS . . . I can't remember what EFE stands for. Maybe someone can chip in here with the answer.

Ron

wwilkins · 01-23-03, 04:01 AM

It's called Early Fuel Evaporation.

It's usually the first casualty in engine upgrades. If you decide to pull it off like most people in non emissions comtrolled areas do then I would like the mounting bolts and spacers.

MaineShark · 01-24-03, 04:37 PM

So, how is this supposed to work? It looks like it is just a valve in the middle of the pipe. Unless there is something I can't see, it looks like all it does is increase the backpressure on one side of the engine.

It definitely is getting chucked. I'm already running no cats; I don't think anyone is going to worry about a silly little valve

wwilkins, can you explain which parts you mean? The exhaust-mounted piece, or the actuator end? Also, while I don't think I have any use for it, wouldn't it be cheaper to buy it locally, instead of paying shipping? Still, once I make sure that my new exhaust will fit without it (assuming you are talking about the lower end), if you still want it, let me know.

Joe

rpounds · 01-24-03, 05:11 PM

The heat riser is nothing more than a butterfly valve which closes off the path of the exhaust gasses in the right hand head pipe. This is what forces the exhaust from the right hand cylinder bank to find a different path of escape, which happens to be through the intake manifold and out the left hand side. When vacuum is applied to the EFE actuator, it opens the butterfly valve. When the engine reaches operating temperature and the thermostatically controlled vacuum switch in the thermostat housing switches states, vacuum is applied to the EFE and it opens up. So, at normal operating temperature, there is no restriction caused by the EFE. The restriction is only present (if working properly) when the engine is cold.

I agree with an earlier post. If you are going to scrap the EFE, sell it on E-bay or something like that if you don't mind. I searched high and low to find a complete setup for my '75. I finally found one and was very grateful.

wwilkins · 01-24-03, 05:18 PM

Thats a lot better explanation than I was working on. Thanks for the education.

I am visiting a corvette restoration center near London tomorrow and if they don't have the mounting hardware I would like yours. I want the bolts and spacers at the bottom of the actuator bracket where it mounts to the exhaust manifold. Right now I have bolts that are too long and many washers on them. Yes I get burned everytime I reach into that crowded area.

Living in England makes it kind of difficult to restore an old vette. When you can find parts you never get the original hardware.

Bill

MaineShark · 01-24-03, 06:04 PM

Okay, that makes some sense. Well, it doesn't make sense, like most emissions stuff, but that does explain how it is supposed to work.

I can't imagine needing the bracketry for anything, so I'll let you know when I take it all off.

Now I'm wondering if I can use the valve body as a place for an O2 sensor. If I take the butterfly out, and tap the hole, I may be able to install the O2 sensor right there, and save having to weld on my SS exhaust. I'll have to measure it and compare to the O2 sensor diameter...

Thanks for the help,
Joe

JohnZ · 01-24-03, 07:22 PM

If you remove yours, you'll need to replace it with a spacer or your exhaust pipe won't fit any more; the C1/C2 cars with fuel injection used that spacer (they didn't use a heat riser, as there was no crossover passage on F.I. units) so they could use the same exhaust system as carbureted cars. All the resto houses have the spacer (which you could modify to accept an 02 sensor instead of carving up your vacuum-operated heat riser valve, which is readily salable).

MaineShark · 01-25-03, 12:07 PM

Hmmm.... Eckler's says those spacers are 2 1/2", not 2" like my manifold. Anyway, they are $25, which is more than I think I could get for a used heat riser valve (they are only $40, new).

But I'll check around locally for anyone who might have them cheaper, and the right size.

Joe