I think Frank's comments rounded this topic out nicely.

It stands to reason that this riser has a purpose and it may or may not give a desired effect depending on useage.

Knowing more about what how and why helps everyone deceide on their own.

You go Dennis!, but I don't think anyone was gonna stop you anyways.

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1980 Aspen 225 super six

As a footnote, I think it should be added that one thing driving Frank's and my opinions on this subject could have a great deal to do with the respective climates in which we live. There would not be much point in defeating manifold heat in a climate where it is generally mild or cold for a lot of the year (Ontario). Here, where it is screaming hot much of the year and temperate most of the rest, warm-up time is such an insignificant factor most of the time that manifold heat can become quite superflous. I would be like me arguing against block heaters.....

D/W

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If it ain't broke, fix it!

For what it is worth, the plugs in my car have a nice even tan all across. And for the record, I removed the valve fully knowing the consequences.

Yes Dennis, I was speaking about people in general. I think often people modify things on an impulse and often because they don't fully understand how those things work. My point is that we should try to understand the processes as much as possible before we start making changes.

An important part of engineering is measurement. If we make a modification we would hope that there is a benefit. If take the manifold heat idea as an example, we could hope for better fuel economy and better acceleration as benefits. We could measure before and after with gas mileage and quarter mile times. If there is no improvement, then we have gained nothing with the modification. If there is an improvement, we have succeeded. If we don't know, then we have just been guessing.

You are also right about the respective climates we live in. However, the basis for my experiences is with summer driving and it can get quite hot here in the summer (often 30°C or 86°F). This would probably be cool weather for Georgia though. Anyway, I found that after adding heat to my intake manifold, my car completely lost its off-idle bog.

Kesteb, thanks for the update. I really did want to know.

Frank

...except for the week I was up there in July 2002 - mid to upper 90's the whole time I was there. The heat and misery follows me!

D/W

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If it ain't broke, fix it!

this is all great stuff, i am gearing up for a weekend of super sixxing (and a host of other work) on my 69 dart mix match. i seriously considered removing the heat riser valvadoo ( im in L.A.) I am also considering adding ram air or at least fresh air intake and thinking that the valvamathing might be an essential part. I read somewhere the mopars of the time were known for accepting ram air mods easily. does anyone know where to get the bushings for it so i can make a tight seal?

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anything worth doing is worth re-doing, again and again and again...........

I'd like to point out that the goal of "ram-air" and defeating the heat riser valve are the same - getting as much cool dense air (w/fuel) packed into the engine as possible...

D/W

...now for a rebuttal from "engineering"...

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If it ain't broke, fix it!

There are no bushings for the vavle. The shaft rides on the cast iron. At one time your local dodge dealer had a lubricate for the valve.

The reason they add heat to the carburator is to prevent "carb icing". The very process of atomizing the air/fuel mixture can lower the manifold inlet tempurature by 30*. This 30* is below the surrounding ambient tempurature. So when you hit a 50* day, your inlet temp is below freezing and the water within the air will happily freeze up. If you every experience this, open your hood and look at the base of the carb. There will be a nice frost ring around it. This ring can get so bad it blocks the jets and may even prevent the throttle flaps from closeing all the way.

On a V type of engine you can have intake manifolds with an "air gap" and never have a problem with "carb icing". This is becuase the carb is sitting down inside a heat source, ie. the engine. On an inline engine the carb is setting out away from the engine. An inline engine needs a heat source to prevent "carb icing".

The idea of removing the diverter valve and adding ram air, may work in sunny california. But I would recommend that you not remove the valve.

Uh, I think the bushing thing was a joke!

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If it ain't broke, fix it!

actually, someone said there was bushings, but looking at the valve i figured they were inside and made of something suceptable to 1000+ degrees or who knows it really defys common sense now that i think about it. and i actually was thinking keeping the heat riser valve would help keep a ram air setup from bieng a too extreme change to the system especially at idle. My knowledge of the goal of ram air is to induct cooler air at high rpms. i thought the valve might have been causing an exhaust leak at one point, it was soon after that i was pointed to by some experienced members that some brainiac had put a holley 1945 on a manifold for a 1920 on my car with no choke. Hence the super six conversion. so in the end i too will be keeping the "lil flapper" i think the real reason most people think of cutting it out because it looks so hoaky on an otherwise handsome motor. I know the first time i opened the hood of a dart i said "WHAT?"

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anything worth doing is worth re-doing, again and again and again...........

I remove the heat riser as matter of course, despite my attempts to keep them serviced all they have ever done is freeze in the closed position and no amount of cussing-torching or banging frees them.

My GT is unusual in that it doesn't care if it has a choke or not as well and no i'm not running rich or have magical carb settings and yes I have done a few snow runs with no adverse cold weather related issues. One turn of the key and after a brief moment i'm ready to go with no hesitation or other ill effects.

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Troops on the battlefield have a far better view of the battle then the generals who lead them

okay i just washed the grime off my hands from stripping the hardware off my super six parts. that whole valve system really seems engineered for about ten years of use, it is hoaky. i am split on pulling it out since there is no going back. i tested it with a torch and it seems to work okay. it does'nt seem to do alot in warming the intake manifold there or not, exhaust is hot and under pressure in that area unless there is raging leaks from the gaskets between the manifolds, into the head and into the exhaust pipe. all of which the slant seems to be prone to, especially the one between the manifolds. I also noticed that area rusts up quick so you guys in colder areas probably are riddled with exhaust leaks. that whole carb ice thing seems a little fishy, i lived in boston for some time with a ford (never again) pickup with an inline 300 (only ford engine worth having). and never had "carb ice". and i have never heard of this problem with volvo's which are a cold weather favorite (not mine). and how many of you have even looked that close to these things THERE ARE BUSHINGS, they are brass, steel on steel would be rusted together faster than you can say fopar? and as for working in sunny california, two hours and i am in big bear, which is close to freezing at night, an hour in one direction and its 0% humidity an hour in the other it so foggy its hard to see. this all makes tuning very tricky, nevermind gas prices and environmental concerns. mopar is like any other company, there is some real quality and some b.s. i mean c'mon special lube just for this piece

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anything worth doing is worth re-doing, again and again and again...........

The shaft and valve blade and probably the bushings are some kind of stainless steel.

Umm.... you put a torch on the thermal spring? You probably ruined it doing that. The spring does not get torch hot hanging on the end of the shaft.

Reading and re-reading the above posts, it seems that some of you don't understand what the heat riser valve does on the slant 6 engines. In the "cold engine" position it diverts exhaust flow up to the "hot spot" in the intake manifold. In the "hot engine" position it swings to allow the exhaust gasses to flow out the exhaust pipe without diverting them through the "hot spot" in the intake manifold, actually diverting the hot exhaust gas to bypass the hot spot in the intake manifold. If you remove the valve you will no longer have the valve plate in there to divert the exhaust gas away from the intake hot spot when the engine is hot and driving down the highway. I really think it is silly to remove the valve. If anything, just wire it to the "open" position (counter clockwise if you are standing in front of the car and looking toward the back of the car).

Shall I draw a picture?

On my Dart, I have a Dutra Dual front exhaust section, and a modified stock rear exhaust manifold section. On the rear section, the heat riser was ground down flush with the main branch of the manifold and closed off with a welded-on steel plate I also knocked out the heat riser and shaft and welded up the holes. This was done originally to clear the water jacket on a Clifford water-heated manifold. Now, however, I do not even run that manifold heat even in winter in Pennsylvania.

The aluminum intake seems to get enough heat just from its proximity to the exhaust. Also, I have never had cold weather driveability issues since changing my carburetor to a Weber 32/36 DGEV.

I'm saying all of this because I think there are a lot of factors that go into whether somebody needs the heat riser valve or not. I'd say if you have a stock iron intake manifold and Holley 1bbl carburetor you most likely need it. If you have exotic tripple carbs, fuel injection, etc., etc. you probably do not. If you have headers, you certainly don't need it.

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'68 Dodge Dart 4dr Sedan

Well Dennis, I think people sometimes read information and only pick out the parts that justify their point of view. Getting cold air into an engine should not be an end in itself. The true goal should really be to increase the horsepower of your engine or get better gas mileage or both. Unless you really need to pack your engine with as much cold air as possible, like if you are going for a land speed record or you are running a high revving engine on the drag strip, heat in the intake manifold will help your street-driven engine run better.

Some of you might think a heated intake might be contradictory with a cool fresh air supply. It isn't. Cooler air supplied to the carb is better for power because it is denser. Once the cool air picks up fuel from the carb, some of it will vaporize and some of it will remain as tiny particles of liquid fuel. When the air stream makes a sharp turn from going straight down from the carb to horizontal in the plenum, some of the liquid fuel won't make the turn and will collect on the floor of the plenum. The liquid fuel will then work its way along the bottom of the intake manifold to the cylinders to end up in the crankcase. A hot spot on the plenum floor evaporates the liquid fuel so that the vaporized fuel can get to the cylinders for combustion. Cleaner oil and longer engine life would also be a benefit from manifold heat.

The valve might seem hokey but it does the job when it works. If it stops working, you could try to loosen it up and I think a valve that is always moving stands a better chance of remaining free. If it is really sticky, I think it would be better to have it stuck in the fully hot (I'm calling this closed) position like Craig says than for it to be removed completely. The exhaust manifold is smoother and less restrictive to flow with the valve in place and closed rather with the valve removed.

I have used a BBS 1bbl carb with headers and, once the engine was warm, the car ran great. When I installed the AFB afterwards, I always seemed to have an off-idle bog than only seemed to go away when I dramatically richened the power mixture and disappeared completely when I installed my intake manifold heater. Obviously, the airflow through a small carb with a high pressure drop helps keep the atomized fuel suspended in the airflow. I don't know what the flow rating is of the Weber 32/36 DGEV but I suspect it would be closer to the BBS than to the AFB. The Weber probably even atomizes the fuel better than either of the Carters. Patrick, even though you car runs fine without manifold heat, I think it still would work at least as well if you were to hook it up.

That's my rebuttal. Dennis, back to you!