The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - 1971 heat riser for big block- components and operation?

**71CHEVYSHORTBED402** · 04-18-2015, 07:47 PM

So now I know how it operates, as motivated by SSTim. Anyway, for anyone curious, this is how it functions.

1. Snorkel passage should be open when the engine is off and it's under 85 degrees.

2. Snorkel passage closes somehow (must be the vacuum motor) when the engine is started and it's under 85 degrees.

3. Snorkel passage reopens at/over 85 degrees.

Parts: The "Vacuum Motor" (sensor/vacuum) moves the Damper Door in the air cleaner, and the Damper Door moves the Snorkel Passage. Very cool

........I'm going to buy it. Still not sure how the shield mounts, though I believe it's with two bolts used to mount the manifold. Not certain how to restore these pieces yet.

A new question comes to me brain. If they don't operate and all else works, then you need a new sensor unit. I don't imagine those are easy to locate, but I'm just guessing at this point.

04-18-2015, 07:47 PM	#6
71CHEVYSHORTBED402 Senior Member Join Date: Feb 2009 Location: Northern Nevada Posts: 7,160	Re: 1971 heat riser for big block- components and operation? So now I know how it operates, as motivated by SSTim. Anyway, for anyone curious, this is how it functions. 1. Snorkel passage should be open when the engine is off and it's under 85 degrees. 2. Snorkel passage closes somehow (must be the vacuum motor) when the engine is started and it's under 85 degrees. 3. Snorkel passage reopens at/over 85 degrees. Parts: The "Vacuum Motor" (sensor/vacuum) moves the Damper Door in the air cleaner, and the Damper Door moves the Snorkel Passage. Very cool ........I'm going to buy it. Still not sure how the shield mounts, though I believe it's with two bolts used to mount the manifold. Not certain how to restore these pieces yet. A new question comes to me brain. If they don't operate and all else works, then you need a new sensor unit. I don't imagine those are easy to locate, but I'm just guessing at this point. __________________ Tony 71 Custom Deluxe, SWB, 2WD, 402, A/C. I developed an assm. guide "kit" for restoring the truck from ground up. With assys, the guide accts for 1000s details, OEM identifications & part numbers, written in short order. 700+ images of assm., illust., charts, and points of interest. Much of the info. applies to all 67-72 GM trucks, and to a lessor degree all 67-72 GM vehicles. My build thread, and more on the guide https://67-72chevytrucks.com/vboard/...d.php?t=730025 Last edited by 71CHEVYSHORTBED402; 04-18-2015 at 07:57 PM.