I have been running without one and do not see any issues other than a bit slower warm up. I live in western PA where we get cold weather but I don't drive my car much in cold temperatures.

 

it doesn’t hurt in having one

 

The heat riser valve closes the exhaust to force it thru the intake manifold to help warm the carburetor in cold weather and improve fuel atomization when the engine is cold. The noticeable effects of not having one will be a little longer time warming up in cold weather and a bit longer choke opening. Both could affect drive-ability.
That said, the ethanol fuel offsets some of the fuel atomization as it evaporates quicker at a lower temperature. The choke opening may be a problem with an electric choke as it doesn't sense engine temperature, but a divorced choke operation does and thus should not be a problem.
The warm up time could be a problem, but I doubt you will notice. Might take a little longer before the car idles down and runs at NOT (normal operating temperature).
The largest problem with the heat riser is it can freeze closed due to rust and then the extra heat is forced under the carburetor all of the time. This can cause fuel percolation.
My cars are in a heated garage and thus rarely sell less than 50 degrees. I wired the heat riser open on both and don't really drive them when the weather is less than 50 degrees.
With today's ethanol, I would eliminate it or wire it open unless you are driving in freezing weather where the car is allowed to see temperatures near freezing. Just a long way around to $.02 worth of info.

 

Unless you drive in winter I see no point and the added heat under the carburetor in summer is not optimum. Keep your carburetor and fuel as cool as possible for best performance.

I block the crossover too.

Don

 

I have an aluminum intake, so heat riser has been rmoved. It was that way, way when I bought it and I am leaving it as configured. Don't need it down here in south east Georgia. I am not going to drive it when it is 25 degrees down here. More heat going out the exhaust, the better for for my purposes.

 

It will likely rust closed on a car that isn’t used much. Or you can gut it to make it look stock If you really want that.

 

If you have the original intake and carb setup, I recommend you replace the heat riser. That is the way the car was designed. I have had my replacement installed for 15 years with no problems. But like you, I only drive my car in the summer.

 

Thanks for all the opinions. Not sure what I will do yet with the riser. Would the opinions be similar for the exhaust manifold cover and stove pipe to the air cleaner housing? That is, use or not use depending upon ambient temperatures for driving?

 

It really boils down to how original you want it to look and if you want it to perform well in cold temperatures without a warm up.

Everything that r-66 daid and i would like to add . When they were new and worked properly they had thier us somewhat limited but usefull . The problem is if you did not keep them lubricated with the gm or Chrysler heat riser graphite lubricant they rusted up. Now if it rusted open no problem but most times they rusted shut. My solution was remove ith and cut the butterfly and shaft right out then tap and thread where the spring handle was with a 3/8ths 16 tap and then use a short bolt to plug it up now you have a free flowing spacer . I have never had a problem with that here north of Boston. i hals drive my car till it snows. then its garaged til spring and three rain storms to wash the road salt away . takes a bit to warm up but its manageable . Alex

 

It really boils down to how original you want it to look and if you want it to perform well in cold temperatures without a warm up.

 

Although not a Chevy engine, Pontiac issued a Tech bulletin (68-I-56 Exhaust Manifold Heat Riser Valve Eliminated – 1968 V-8 Engines) eliminating their heat riser in V8s after 4/68. I know the one on my '68 Firebird (January build) rattled so bad that I had it wired permanently open over 50 years ago. Eventually, the exposed thermostat finally fell off and the counter weight has held it open since. With an air intake heat riser system, there was no need for the exhaust one anyway. I had the tube for the intake riser come loose one time and the car ran terrible on cold days.

 

If you don’t have it no good reason to add it based on the way we drive our classic cars

 

If you are buying stock exhaust pipes on the passenger side, they will not fit up without the heat riser or an adaper. The heat riser has a flat surface to the original manifold and a beveled opening on the bottom for the donut gasket on the pipe. Also, your new pipe will be about an inch too short if you don't use it.
Removing the flapper valve inside the heat riser works well. I have also tack welded the pivot rod to the body of the valve with a small tack while in the open position of course.
Also, as stated above, if you are using an aftermarket intake, most don't have the heat passage under the carburetor and thus you won't get the hot air circulation anyway.
Keep in mind this is my memory, which may not be totally correct, but look at your fitup and verify.

 

Thanks all. The one I have doesn't have the valve in it and has the holes welded shut so essentially it is just a spacer. Good point about connecting to the exhaust pipe flange. I have the original cast iron intake manifold.

 

The judges may not care . 🧐😆

 

If you have the original intake manifold, it has the passages for the exhaust gasses to warm the carburetor. It could still warm the carburetor enough in the summer time to cause some problems with ethanol fuel, especially when you shut if off as the fuel may percolate out of the bowls into the intake causing hard restart (flooding) and an empty carb. If you are removing the intake, you might consider installing the sheet metal block off inserts that block the exhaust gases from the intake. I do this on my cars as I rarely drive them in cold weather. Just a thought.

 

Not an answer but I remember my Dad saying he would check to see if his was working, and he bet a lot of the cars (in Wisconsin in the 70's) had non working heat risers, and was because they didn't know better.

 

If you building a number matching car, go for it. If not and you not taking a classic car out in the winter and the snow and the salt in the cold, you don't need. But it's totally your call. Good luck with the project.

 

1985 Chevy dually 427 BB. That's just one example. Winter or summer had no issues with no choke. Depends on how much you know how to start and run a car.

 

OP is asking about heat riser not the choke.

 

I didn't want to burn the paint on the intake manifold, so I blocked off the ports at the head with thin sheet metal. Then - I cut the inner flap out of the heat riser so as not to impede the exhaust flow. Yeah - it may be a pain to start - but once it runs, keep the engine at about 1200rpm for a minute or so for the engine to warm up some and it should be good to go from there. I saw a segment of a show from Peter Klutt (forgot the name of the show) he said once you get gas to the carb......press the accelerator to the floor two times - wait for about 20-30 secs and it should start right up. Ever since I headed his words - no problem.