intake manifold heat riser

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kittypancake

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Am I missing something? Other than cold weather warm up, what benefit is there to heating up the intake manifold? I've always heard it's best to keep your air/fuel as cool as possible, but slant sixers seem to have mixed opinions on this. Any thoughts?
 
If you have an Eddie carb do yourself a favor and block the crossover.
 
kittypancake said:
I'm afraid I don't know what an Eddie carb is...
Click to expand...

Sorry about that.
I actually don't like abreviations for that exact reason.

Edelbrock carbs are easily heat soaked due to thier float bowls being integrated into the carb body.
This causes warm start issue's (acts like it's flooded) upon restarts.
 
Quickly heating intake manifold from a cold start aids in cold weather drivability, fuel distribution, and fuel economy. That flapper rotates once the manifolds are heated, and shunts added heat away from intake. Unlike a V8 intake nestled between two banks, the slant six intake is hanging out in the air, constantly being cooled by air flow over it.

Driving in humid weather when ambient temperature is below 40 f degrees with an unheated manifold often results in carburetor icing, real crappy drivability, and single digit fuel mileage. Also when fuel drops out of suspension in a cold intake manifold raw gas will wash down cylinder walls causing accelerated ring wear.

Rebuild the heat riser if it is not working, let it do its job, and enjoy better drivability, faster warm-ups, better fuel mileage, and longer engine life.
 
wjajr said:
Quickly heating intake manifold from a cold start aids in cold weather drivability, fuel distribution, and fuel economy. That flapper rotates once the manifolds are heated, and shunts added heat away from intake. Unlike a V8 intake nestled between two banks, the slant six intake is hanging out in the air, constantly being cooled by air flow over it.

Driving in humid weather when ambient temperature is below 40 f degrees with an unheated manifold often results in carburetor icing, real crappy drivability, and single digit fuel mileage. Also when fuel drops out of suspension in a cold intake manifold raw gas will wash down cylinder walls causing accelerated ring wear.

Rebuild the heat riser if it is not working, let it do its job, and enjoy better drivability, faster warm-ups, better fuel mileage, and longer engine life.
Click to expand...

So,,,,all the engines that didn't have heat risers of some sort died an early death from washing down the cylinders?
And what about cold air intake systems?

Just askin, as if we were sitting around talking about it.
 
I actually don't know of any factory engines that did NOT have a heat riser or heated intake.

The cooling on a 6 manifold with no exhaust heat, as when headers are added, does NOT come mostly from airflow around the outside, but rather via what is known as the "refrigeration effect" which is the evaporation/ pressure change as the fuel atomises in the manifold.

Anyone who has every seen stuff like Corvair / aftermarket intakes on dune buggies has seen ICE forming on the intake even on a hot day. This is why aircraft engines used to be a big problem, and in fact has actually caused crashes and deaths.

Having said all this, my own 67 (when using Edelbrock carb) has no carb heat and no heat riser. But I don't drive it in very cold/ wet weather. The other thing is, if you use an aluminum manifold (V8) the aluminum conducts heat way faster than cast iron. This means that the manifold heats up much quicker from a cold start, and once the engine is warm, hot oil is hitting the bottom of the manifold. Many people incorrectly think that aluminum manifolds run cooler, but this is not the case. The high conductivity of aluminum carries heat FROM the heads (the heat SOURCE) TO the manifold, which is trying to cool things because of the carb.
 
I drove VW bugs for many years to save my mopars in the salt belt. Under certain conditions when it was cold and damp, the carb would internally ice to the point of stopping the the car. The small exhaust tubes bonded to the intake did not provide enough heat transfer. It was less of a problem in town, at low speed where the engine heated the engine compartment. It was a problem cruising at highway speeds.
 
The reason for heating the manifold in a street car is to improve initial cold weather drivability. The heat helps to maintain the fuel vapor mix until it can get into the combustion chamber.

We blocked the heat riser on our racers to provide a denser fuel/air mixture to the carb. We didn't run in real cold weather and it didn't matter when the car bucked, sputtered, and backfired when we first pulled it off the truck. Once the motor got some heat in it, the car ran fine.

Since it is my car, and I live without real winter, I completely removed the EGR and the heat riser in my 73 /6. I went further by installing an exhaust manifold that does not have a heat riser. It starts and runs fine, but if I open the throttle too quickly, it bucks and pops when the motor is cold. At normal operating temperature, it runs fine. On a 400 mile round trip I make often, fuel mileage has improved by 2 mpg. Around town, mileage dropped by about 1 mpg. I attribute this to lack of heat in the engine on the shorter trips.

My 2¢ worth is if you live in a temperate climate, go for blocking the heat riser. If you live in the frozen wastelands of the north, fuggetaboutit. Note: In my area, a 25 yr-old car is exempt from emissions testing. You may need working EGR to pass emissions requirements.
 
67Dart273 said:
I actually don't know of any factory engines that did NOT have a heat riser or heated intake.

The cooling on a 6 manifold with no exhaust heat, as when headers are added, does NOT come mostly from airflow around the outside, but rather via what is known as the "refrigeration effect" which is the evaporation/ pressure change as the fuel atomises in the manifold.

Anyone who has every seen stuff like Corvair / aftermarket intakes on dune buggies has seen ICE forming on the intake even on a hot day. This is why aircraft engines used to be a big problem, and in fact has actually caused crashes and deaths.

Having said all this, my own 67 (when using Edelbrock carb) has no carb heat and no heat riser. But I don't drive it in very cold/ wet weather. The other thing is, if you use an aluminum manifold (V8) the aluminum conducts heat way faster than cast iron. This means that the manifold heats up much quicker from a cold start, and once the engine is warm, hot oil is hitting the bottom of the manifold. Many people incorrectly think that aluminum manifolds run cooler, but this is not the case. The high conductivity of aluminum carries heat FROM the heads (the heat SOURCE) TO the manifold, which is trying to cool things because of the carb.
Click to expand...

so...the fuel/air mixture may be COOLER entering the combustion chamber when running through a cast iron manifold versus an aluminum manifold? I can't wrap my head around this...I'm thought the aluminum would heat up faster, but also run cooler overall secondary being able to disapate heat faster. I don't understand how aluminum could be HOTTER than iron. Being as both manifolds draw heat from the riser and head, wouldn't the maximum temp be the same for both?
 
I believe this is only true of heating/ cooling cycles. If you are "tootin" down the road at a fairly steady pace, both manifolds would probably be about the same. But many guys mistakenly think "aluminum runs cooler" because it's associated with stuff like heat sinks which RADIATE heat. In this case, as on a V8, an aluminum manifold has most of it's area heated. IE the heat conducting into it from the heads, the (after warming) hot oil underneath, and the exhaust crossover.

The cooling effect I mentioned comes from the low pressure and evaporation of fuel, which can be considerable.
 
67Dart273 said:
I believe this is only true of heating/ cooling cycles. If you are "tootin" down the road at a fairly steady pace, both manifolds would probably be about the same. But many guys mistakenly think "aluminum runs cooler" because it's associated with stuff like heat sinks which RADIATE heat. In this case, as on a V8, an aluminum manifold has most of it's area heated. IE the heat conducting into it from the heads, the (after warming) hot oil underneath, and the exhaust crossover.

The cooling effect I mentioned comes from the low pressure and evaporation of fuel, which can be considerable.
Click to expand...

and I'm assuming the 'hot oil' pertains to V8's only? I just want to make sure I'm not overlooking something...
 
What has been said and more:
On a street driven car..
Warming manifold quickly makes car more drivable quickly.
Makes fuel efficiency better during initial 15 - 30 minutes.
Prevents raw fuel washing oil from cylinders so prevents accelerated engine failure.
ALSO, prevents raw fuel from polluting your oil and ruining it, so prevents accelerating engine failure.
Reduces need for massive accelerator booster mods needed or need to compensate for increased manifold wetting delay and effect.
 
Copied from this thread:

http://www.forabodiesonly.com/mopar/showthread.php?t=119527&highlight=intake+heat

Slantsixdan explained it and added a great vintage video which shows manifold wetting and fuel falling out of suspension:

"True and correct. A lot of guys think the manifold heat is nothing but a cold-weather assist. That's wrong. Fact is, it is greatly beneficial no matter what the weather or climate. This 1935 Jam Handy cartoon would be a real trip to watch even if it didn't contain a sequence (which it does, at 5:37) specifically and correctly answering the question about the manifold heat.

[ame="http://www.youtube.com/watch?v=S_bFo2mg9Ss"]Down the Gasoline Trail (1935) - YouTube[/ame]

Below a certain temperature, gasoline is a liquid. Liquid fuel does not burn. Only vapor burns. The latent heat of vaporization of gasoline works to cool down the intake manifold even as engine heat works to warm it up. The debate is whether it's necessary to apply heat to the intake manifold. There are opinions "yes" and "no", and there are varying levels of understanding of how the system works and why it's there, and the right answer also depends on the engine configuration and vehicle purpose. I don't mind saying I have a very complete and accurate understanding of how and why the system is there, and my opinion is that on a street-driven vehicle in any climate with a non-race engine, an intake heat system should be in place and working correctly for best driveability, performance, and fuel economy. On a street-driven vehicle, intake manifold heat only makes things better, not worse."
 
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