Exhaust manifold heat valve

[tirewater]

I have a mechanical valve stuck on the end of my driver side exhaust manifold. It appears to work as an exhaust choke mechanism for cold starts.

Does anyone know if this is considered an emissions thing? I'd like to remove it and have one less vacuum hose line running around.

Is there a spacer made for it if I remove it? Seems I may need to have some custom exhaust work done if I remove it.

Thanks!!
Chris

 

[jckkys]

One of these should work for you;
https://www.npdlink.com/store/?p=ca...h_str=exhaust+manifold+spacer&parent=0&year=0

 

[tirewater]

Thanks, they must be made of gold!

I'll go measure the dimensions of my valve (apparently called heat riser?).

 

[jckkys]

Yes it forces exhaust through the cross over in the intake to heat the floor under the carb on cold starts. Rust often froze the butterfly pivot shaft after a few years creating a maintenance headache. Ford stopped using them after '69-'70. Cal. emissions laws are beyond me. So I can't help much with that.

 

[Rustytruck]

I know for a fact that they were used up until 1974 on California Broncos. Mine has it. Most of them have been removed because back in the day they would get stuck partially closed and over heat the exhaust valves causing premature failure. A really, really smart emission Tech would look for this valve and fail you if it wasn't there. Few tech's these days don't know to look for them. Back in the day the exhaust smarties would cut out the guts of the valve and weld a blob of metal on the shaft. So the shaft and counter weight would turn but there was no flapper valve inside to get hung up. This would pass visual test and save the motor from impending doom. This is illegal to remove on emissions required Broncos.

 

[jckkys]

I'm always thankful to live in a free state.

 

[tirewater]

Thanks guys, I did do more reading. As Rustytruck states, it is a part of the emissions and a tech will fail visual. As far as I can tell, a lot of people confuse the 'heat riser' with the pre heater hose.

The heat riser is the type that's open unless vacuum is applied. It's a simple butterfly valve.

My truck is a CA dso '76, so it was still be used up until then.

The heat riser may have caused some cascading failures. The air injector valve attached to the driver side cylinder head had failed. Allowing exhaust into the air injection bypass valve, causing it to corrode & the nipple to break off when removing it.