I am thinking of removing the heat riser from my exhaust manifold.

has anyone done this?

if so, how does it come out and does it improve the flow?

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'67 Dart 225 Super Six

If you aren't going to need it for cold morning starts, then I'd just take a torch and cut the rod and blade out of it, then fill the holes with a couple of bolts and nuts with hi-temp sealant....

Had this setup in my rear dutra dual until I needed the flap and heat box for the hyperpak setup in winter time.

-D.Idiot

Lots of people have removed their heat riser valves. I am not sure what they were trying to gain but they didn't achieve better flow. If you have a V8, removing the valve would marginally reduce the flow restriction but the valve on an in-line engine is a flow diverter not a flow blocker.

See for yourself. Look in the exhaust manifold from the bottom where the exhaust pipe connects. With the valve closed (hot position), the valve blocks off flow to the intake manifold so the resulting flow path is smoother. Only when the engine is cold will you see the valve directing hot exhaust gases up to the intake manifold.

You can get by without this valve in warmer climates but why would you make your exhaust manifold flow more turbulently all the time? Besides, engines work better with intake manifold heat.

Frank

I removed the heat riser valve. My car is a bitch to drive when it starts to get cold and damp. I need to warm up the engine until the temp gauge starts to move and then turn off the engine to let the intake heat soak. After this the car operates normally. If you have the exhaust tube hooked up to the air cleaner this may be a mote point. I am using a '65 air cleaner and this is not an option. You do need some heat to keep the carb from icing up.

Some heat is transfered into the intake from the exhaust just from the physical connection of the two. The valve does interfere with the exhaust flow. This can be tested by running water thru the manifold with a garden hose. Close the valve and the water backs up in the maifold, remove or open the valve and there is no restriction and the water flows quite nicely thru the manifold.

thanks for the posts. I think I'm going to keep my heat riser after all

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'67 Dart 225 Super Six

kesteb,

I'm having trouble picturing what is happening with the water from the garden hose. It sound like you tried this experiment with the exhaust manifold off the engine and ran water through one of the exhaust ports.

When you say the valve was closed, were you looking in through the top of the manifold where the intake would have been bolted? If so, was the flapper blocking the flow through the collector or was it covering the opening you were looking through?

If it was blocking the flow, the flapper was in the cold position to divert exhaust gas up to the intake for heating. This would explain why water backing up in the manifold because it was doing exactly what it was designed to do. As the engine warms up, the flapper should rotate to cover the opening and make a smooth exit for the exhaust gases. I was calling this the closed position because the flapper closed off flow to the intake manifold.

Whenever pressure drops are calculated in piping systems, the lowest restriction is found in a straight smooth section of pipe. Any change in flow area or direction causes a restriction (or pressure loss). When you remove the flapper, you create a permanent sudden increase and sudden decrease in the flow area of the exhaust manifold collector. Not a large restriction but measurable.

Frank

I agree.

I wire the valve open on my stocker for warm weather use. I would think removing it would create a flow disturbance, making things worse, and you'd have the underside of the intake exposed directly to hot exhaust gasses at all times which is exactly the opposite of the goal in eliminating it from the picture in the first place.

D/W

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If it ain't broke, fix it!

If the thermostatic spring automatically closes the valve when the engine heats up, why do you wire it open?

Frank

...to divert heat away from the get-go. Also, if you check the operation of this valve (reference the service manual as well), you will notice that with a good thermostat and properly adjusted, the valve is actually not in the full "closed" (or "open", depending on how you are looking at things) position at all times after warm up. At idle and at low RPM, the valve is still "open" enough to divert a small amout of heat up to the intake.

D/W

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If it ain't broke, fix it!

My experience is that when you remove the valve you do not overheat the bottom of the intake manifold. Quite the opposite instead. After an extended run, the bottom of the carb and the mount area are cool to the touch.

how come the poly bushings on my heat riser are whisper quiet!? ron

Intake manifold heat for street-driven engines is good and necessary for good fuel distribution. Air flowing through the intake and especially vaporizing fuel will cool the intake manifold. On the highway, this would happen even more.

To get the utmost performance from a race car, the intake manifold is as cold as possible but these cars usually don't run well year-round on the street. Street-driven engines work much better when heat is supplied to the intake manifold. If heat is causing problems with percolation in the carburetor, insulation between the manifold and the carb is a better choice than eliminating heat from the intake.

I would be curious to know if there is a connection between having rich & lean running cylinders and non-functioning manifold heat control systems.

Frank

...plenty of heat gets to the intake in warm weather just by being situated over the exhaust, not to mention the fact that it is bolted to it. The cooler the intake air, the better in hot weather, once warm-up has been achieved.

D/W, PhD

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If it ain't broke, fix it!

Engines need more intake manifold heat than you think. Let me give you some references for your reading pleasure:

Holley Carburetors & Manifolds by Urich & Fisher, page 14
"Exhaust-heated hot spots are typically small areas under the area which is fed by the carburetor. The ends of the manifold are not usually heated. The size is kept as small as possible, consistent with the needs for flexible operating and smooth running. By keeping the spot fairly small, the manifold automatically cools off as RPM is increased. The large amount of fuel being vaporized at high speed extracts extracts heat from the manifold -- often making it so cold that water condenses on its exterior surfaces. Although most passenger-car manifolds heat the mixture with an exhaust-heated spot, some manifolds are water-heated by engine coolant. Cars equipped with emission controls often heat the incoming air by passing the air over the exhaust manifold on its way to the air-cleaner system.

Excepting racing intake systems, intake manifolds are compromise devices. Their shape, cross-sectional areas, and heating arrangements accomplish the necessary compromises between good mixture distribution, and volumetric efficiency over the range of speeds speeds at which the engine will be used. If only maximum or near-maximum RPM is being used, high mixture velocity through the manifold will help to ensure good distribution and will help to vaporize the fuel -- or at least hold the smaller particles in suspension in the mixture. At slower speeds, the use of manifold heat becomes essential to ensure that the fuel is vaporized. If heat is not used, the engine will become rough running at slower speeds and distribution problems will be worsened."

Carter Carburetors by Emanuel, page 64
"The dichotomy of carburetor operation is that fuel should be cool when in the liquid state but heat is necessary for satisfactory vaporization. ... But for street driven applications, the blocked heat riser can be of more harm than benefit. ..."

Rochester Carburetors by Roe, page 26
"Intake Manifolds -- Fuel distribution is affected by exhaust-heated hot spots in the manifold just under the carburetor. ... If heat isn't used, the engine will run rough and distribution problems will increase"

I still say factory engineers design engine components with sound engineering principles and research. Designs are always a compromise of a number of competing requirements. Before you re-engineer their designs, you should put a lot of thought into it before hand.

If you have a properly working stock exhaust manifold, there is no need to modify the valve. If you have a Clifford intake, hook up the water jacket.

Frank

Thanks for sharing. I'm sure many will find the information very informative. Those books are all in my library and have been thoroghly perused. I am quite happy with all of my setups, both /6 and V8, carbureted and injected some of which employ stock manifold heat, and others which do not. Those that I drive regularly as transportation in winter months all have some form of carb/intake heat functional, at least during those few cold months we have here in GA.
Surely you are not implying that I do not put a lot of thought into what I do - you don't even know me, so I am assuming hopefully you are speaking to people in general. If I or anyone else deem it beneficial to their own goals to "re-engineer" or modify an existing design, then more power to us - that is the essence of hot-rodding. Your point is well taken, however, sometimes it IS best to stick with the factory plan. If I deem it beneficial to my ends to eliminate or modify my heat riser valve, I damn well will!


D/W

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If it ain't broke, fix it!