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73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: cwest on July 23, 2014, 09:24:39 PM
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I recently put two new exhaust manifolds on my 86' K20. The studs that came with the kit seem to be too long. I have a feeling I am suppose to have the stock hear risers in place to make up the gap. The heat riser didn't seem to be functioning as the control arm was not attached to the exhaust flow valve. So two fold question.. The truck warms up fine even in cold weather, so I'm thinking about going without. Is that a smart move for the truck? If so, what size/type studs should I go with to shorten the gap and allow me to tighten everything down?
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If you don't need to worry about smog inspections and the engine warms and runs fine in cold weather, you can dispense with the vacuum operated EFE valve and use shorter studs to attach the headpipe to the manifold... assuming the headpipe will close the gap and reach the manifold.
Edit:
You'll need to look at the way the headpipe seals against the EFE valve and the way the EFE valve seals against the manifold. IIRC, the headpipe uses a doughnut, the EFE valve uses a flat gasket. If the manifold doesn't have a beveled seat for the doughnut, you may have to get creative....
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Not to hijack the thread but I want to disable or remove the flapper in the exhaust pipe
Mines missing the vacuum actuated linkage. And the flap appears to be moveable by hand
I can wire it open. But don't know which way to position it
It has the clock spring still on it
Is the spring supposed to hold it open ?
Or closed?
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Not to hijack the thread but I want to disable or remove the flapper in the exhaust pipe
Mines missing the vacuum actuated linkage. And the flap appears to be moveable by hand
I can wire it open. But don't know which way to position it
It has the clock spring still on it
Is the spring supposed to hold it open ?
Or closed?
If you have (had) vacuum operated EFE, the vacuum actuator "pulls to close" the flapper. The older bi-metal spring-and-weight heat riser valves (pre-EFE) were closed by default until thoroughly heated by the exhaust flow.
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Not to hijack the thread but I want to disable or remove the flapper in the exhaust pipe
Mines missing the vacuum actuated linkage. And the flap appears to be moveable by hand
I can wire it open. But don't know which way to position it
It has the clock spring still on it
Is the spring supposed to hold it open ?
Or closed?
If you have (had) vacuum operated EFE, the vacuum actuator "pulls to close" the flapper. The older bi-metal spring-and-weight heat riser valves (pre-EFE) were closed by default until thoroughly heated by the exhaust flow.
mine has the spring and weight
I thought they all were vacuum and mine was missing parts
I want to wire it open. But i can't tell which is open. I can't feel any difference putting my hand over the exhaust and having someone move the flapper
My dual exhaust does not have a crossover so I figured you could tell when was closed and when was opened
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If you don't need to worry about smog inspections and the engine warms and runs fine in cold weather, you can dispense with the vacuum operated EFE valve and use shorter studs to attach the headpipe to the manifold... assuming the headpipe will close the gap and reach the manifold.
Edit:
You'll need to look at the way the headpipe seals against the EFE valve and the way the EFE valve seals against the manifold. IIRC, the headpipe uses a doughnut, the EFE valve uses a flat gasket. If the manifold doesn't have a beveled seat for the doughnut, you may have to get creative....
I ended up using the riser after all because like you said the pipe wasn't going to close the gap easily without it, and the actuator arm had just been bent out and away from the control arm so it was an easy enough fix to put it back in place. I just used two donut gaskets, one on either side of the riser. Got'er started yesterday and after a TON of smoke came rolling off of the new exhaust manifolds everything appeared to be in tact.
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I ended up using the riser after all because like you said the pipe wasn't going to close the gap easily without it, and the actuator arm had just been bent out and away from the control arm so it was an easy enough fix to put it back in place. I just used two donut gaskets, one on either side of the riser. Got'er started yesterday and after a TON of smoke came rolling off of the new exhaust manifolds everything appeared to be in tact.
Glad to hear you got it sorted and working.
mine has the spring and weight
I thought they all were vacuum and mine was missing parts
I want to wire it open. But i can't tell which is open. I can't feel any difference putting my hand over the exhaust and having someone move the flapper
My dual exhaust does not have a crossover so I figured you could tell when was closed and when was opened
The flapper may be missing.
Look at the position the weight is in when the heat riser valve is cold - that's closed. Once the engine is fully warmed up, you'll notice the weight has rotated - that's open. Actually, I'm surprised the heat riser isn't seized. It must have been serviced regularly.
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It doesn't change position with temperature changes
If does move easily though.
Could be the flapper is gone
Only one way to find out .....
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You need to keep the heat riser. The reason theres a gap is not just because theres supposed to be a heat riser, but because the right manifold is cast a certain length and the pipe that mounts up is a certain length. If you try to force the 2 together, you are going to damage something.
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I plan ion keeping the empty hollowed out shell
The flapper is gonna go if it's still in there when i take it apart
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I would recommend replacing the piece as a whole. The purpose of it is to allow more heat to your choke so it warms up faster and uses less fuel. Not that old chevs get great gas mileage. Its gonna be about 10 to 13 mpgs no matter what. The point still though is the richer you burn, the less power you have, the more fuel you burn, and the more deposits you build up quicker in your cylinders, pistons, piston rings, valves, it will eventually even start causing enough problems with your rings to where you have oil consumption.