I am chaning out my exhaust and noticed the "old" heat riser did not have a flapper valve inside. Exactly what does the heat riser do? The '76 does not have the A.I.R. system on it and wandering if I need the heat riser.

Any help is appreciated.

 

The heat riser is used to direct hot exhaust gases under the carburetor by paritally restricting the right exhaust pipe, thru a passage in the intake manifold. A coil on the heat-riser (later versions use a vacuum activated valve) allows the valve to open up when the engine warms up. It is good to have in cold climates...

 

Leave the flapper out! And, make darn sure it hasn't fallen into the exhaust pipe. That happened on my '77 and it burned up the motor beyond reasonable repair--quick.

It is closed to channel exhaust air into the intake manifold to help the motor heat up faster. It opens at 180F coolant temperature. Your '76 probably has a TVS (temperature vacuum switch) and vacuum actuator like my '77. I'm not sure.

 

You can get the piece without the valve from Parargon. Just a spacer.

In addition to what was stated,(it does take a lot longer for a manifold choke to pull off), the heat riser does a very good job of rotting out the right side muffler with the condensation it creates on start up. (right exhaust blows steam a lot longer than the left during the cold season)

Replaced 2 right mufflers to one left. Than I treated the cause instead of the effect.

 

Here in NC the emissions Laws, (as I vaguely understand them) say you have to have the original emission related equipment on the car to pass. They don't have to be working, but you gotta have 'em....stuff like the A.I.R. exhaust manifolds, tubing , oxygen sensor, other related sensors, fog pump, cats, and the exhaust system has to be like it originally was ...this is for my 1981, but seems like my "68 also had the smog pump and A I R system.
Some say that after the ride is over 25 years old, the safety inspection is all that s required. I've talked with 3 different inspections stations, and they all say the same thing: you gotta have the emission stuff on it that you had originally...that APPEARS to be working.
I've been looking w/o success for a place that will PASS me w/o looking under the hood or car....I've heard these exist but can't find.
On that heat riser, ...if it's not visible...I'd leave the flapper out for reasons already posted. good luck , jim

 

Just take it to an oil change place; those kids don't know what a heat riser valve is anyhow.

You want a good place in NC for inspection? I know just the one--they just scrape off the old sticker and put the new one on. I've been there 4 years in a row now.

 

So lets pretend I'm a State Emissions Official... and I contact you offline... and then I put that dude out of business and in Jail.
My Duh. I don't think he would appreciate the "press". LOL

A few years back... someone posted about a guy (NJ) who would (illegally) mess with the cat "test" pipes.... and the shop got in a heap of trouble.

NC changed it's testing laws this year.
I contacted them directly because I was getting conflicting stories at the testing stations. As I understand it, cars 35 years old or older (1970 & back as of now) are exempt from ALL inspection requirements. Other changes involving non-OBD-2 were also made. I'll try to find my bookmark.


On the heat riser, it opens based upon a temp sensor, whether it is vacuum controlled or wound-spring controlled. It's consistent, but not always responsive to any set temp.

As posted multiple times above, it's purpose is to heat up the carb/intake to reduce the time the engine is running on the choke... most effective in colder climates to improve driveability. The system was in place long before there were any emissions laws. My 1959 Ford had one.

If it's sensor/vacuum controlled, it -usually- defaults to "open". So by plugging the vacuum line to it (or disconnecting the line) it would be open all the time, with no heat going to the carb.

If it's thermostatic spring controlled, it defaults to "closed" when the engine is cold. If you disable the spring, and the valve remains closed on a hot engine, you will damage your engine. On this type riser, there are multiple designs... some will float to an open position (and rattle) when the spring is removed, some will not.

In the warmer climates, you can get away with not using a heat riser.

FYI... when the intake passage is not clogged with carbon (as it usually is after 30-40K miles) the hot exhaust will burn off high temp engine enamel you have applied near the crossover passages. It's a good test to see if it's even working.

Edit:
http://www.ncdot.org/dmv/driver_serv...nspection.html

1976 appears to still be subject to a sniffer test.

I could certainly be wrong, but believe they can nail you on the absence of the heat riser, but the probability of most of them even knowing what it is is questionalble, as posted above.

They did know that my 1980 Pinto was missing the thermactor control on the air cleaner. They nailed me on it, as obscure as it was.

Could not find the 35 year exempt stuff. Hard to find that in writing.