27 replies to this topic

[Cooperman]

If heated manifolds are so necessary, how on earth did the original Cooper & Cooper 'S' manage without them?
I've built Minis of all types for over 50 years, have never used a heated manifold and have never had any problem.
My view is that it was done by the hopeless Rover engineers to try to get a bit more smoothness from cold to please the target market of older ladies who found the choke difficult to live with.

[Dan]

The heated manifold wont do anything for carb icing, it happens in the venturi....

 

  Indeed, it's to prevent fuel condensation.

 

  The Cooper & S had twin carbs, which means a short and straight manifold.  Most single carb cars had an iron manifold that was heated by being the same casting as the exhaust manifold.  The twin point has a similar arrangement to the twin carb cars, with the added bonus of the fuel being fired through it.  All single carb cars with an alloy manifold and the SPi (which is essentially a digital carb in that the fuel is mixed before the charge leaves the throttle body) had the manifold heated as standard.  It's nothing to do with smoothness or the choke, it's to stop fuel condensing in the manifold and forming droplets which collect and pour into the cylinders.  In other makes, with more torturous mainfolds, alloy manifolds for carbs or central injection are more or less universally heated.  Even aftermarket and performance ones.  Most of the time they pickup the water jacket at the manifold gasket.

Edited by Dan, 15 June 2013 - 06:22 PM.

[Captain Mainwaring]

The heated manifold wont do anything for carb icing, it happens in the venturi....

 

Ye it does, but it also takes place in the inlet manifold. Carbs may be prevented from icing by using an inlet position that is preheated.

Inlet manifolds aren't just heated to help vaporization, they are heated to stop icing.

That's why TBI systems may be fitted with heated manifolds.

 

Manifolds may be heated to increase vaporization, but mainly to prevent icing....longer the inlet tract, more chance of coldspots and manifold icing as well as carb icing.

 

I suppose I could do the sums on the heat of vaporization for petrol at mini consumption values.

[Captain Mainwaring]

If heated manifolds are so necessary, how on earth did the original Cooper & Cooper 'S' manage without them?
I've built Minis of all types for over 50 years, have never used a heated manifold and have never had any problem.
My view is that it was done by the hopeless Rover engineers to try to get a bit more smoothness from cold to please the target market of older ladies who found the choke difficult to live with.

 

 

It's a bit more complicated than that, and manifold heating isn't done without a reason...

The old cast manifolds used to have an exhaust hotspot as I'm sure you know.

Ask yourself why the performance boys added them.......

Perhaps they had a few cases of manifolds coming back because of icing....... 

Also remind me of the carb setup on cooper and S variants - did they have a big single of two smaller twins?

Interesting post on here talking about carbs if you're interested.

 

Some people may never experience carb and manifold icing, some cars may be an absolute pig for it, but let me tell you coming in for short finals on a trailing throttle when you've forgot to switch on manifold and carb de-icing can give you a new perspective on life....

[jaydee]

What icing Cpt moaning??

Dan explained pretty well above, the heated manifold was introduced simply because the better vaporization gives a better combustion resulting in 'cleaner' emissions and a slightly better mpg.

[jaydee]

Heating the inlet will turn down both CO and HC

The standard air box is enough to prevent carb icing

[Ethel]

Have we all got the same definition of icing? To me it means frozen water vapour in the carb that affects its mechanical function - like the piston sticking. Can you get petrol cold enough to turn into a solid in your induction system, or could you deposit enough ice in a manifold to affect airflow?

[Tamworthbay]

Have we all got the same definition of icing? To me it means frozen water vapour in the carb that affects its mechanical function - like the piston sticking. Can you get petrol cold enough to turn into a solid in your induction system, or could you deposit enough ice in a manifold to affect airflow?

The 'freezing' point of petrol is anywhere from -55C to -110C dependant on formula.It gels at first anyway, It doesn't freeze as such until much colder. My understanding is the same as yours so it is very unlikely that heating the manifold in that way could have significant effect whatsoever.

Nicked from Wikipedia:

Carburetor, or carb icing, is an icing condition which can affect any carburetor under certain atmospheric conditions. Carburetor icing occurs when there is humid air, and the temperature drop in the venturi causes the water vapor to freeze. The ice will form on the surfaces of the carburetor throat, further restricting it. This may increase the Venturi effect initially, but eventually restricts airflow, perhaps even causing a complete blockage of the carburetor. Icing may also cause jamming of the mechanical parts of the carburetor, such as the throttle, typically a butterfly valve.

[sonikk4]

I suffered bad carb icing on my RS2000 with two different carbs. A 38DGAS and a 32/36 DGAV. Both carbs were in excellent condition and the common denominator on both was the K&N air filter. Oh the car came with a heated manifold as standard.

 

As there was no warm air being taken into the carb the venturi effect caused ice crystals to form blocking the jets. Symptoms were loss in power and serious fuel consumption. Cure here was to fit twin 45 DCOE webers although the proper cure would be to have refitted the original filter housing or to attach a warm air intake to the K&N. The heated manifold made no difference whatsoever in this instance. 

[Captain Mainwaring]

What icing Cpt moaning??

Dan explained pretty well above, the heated manifold was introduced simply because the better vaporization gives a better combustion resulting in 'cleaner' emissions and a slightly better mpg.

 

 

What do you mean "what icing?" - since we're into silly comments, well the fondant icing on my cinnamon swirls, isn't that what we were all talking about? If you don't understand, then use google.

Everyone is entitled to comment, not just you and people with 10000 plus posts.

 

It's quite clear that some people weren't sure what actually iced and where. 

There is an ignore button I'm sure if you don't like what I write.

 

More to the point - we've ascertained that a heated manifold can aid smooth running, can you explain to me what the downsides would be for use on a performance system? if indeed there are any, and if there are, why did lot's of the major manufactures of after market inlet manifolds fit them with water heating galleries? Feel free to answer if you can do it politely.

Edited by Captain Mainwaring, 17 June 2013 - 03:08 AM.

[Dan]

  There are none.  People have this idea that the inlet charge will pickup significant heat from being in a warm tube for an almost immeasurable fraction of a second, when it's just been refrigerated by the venturi.  But what happens in the manifold is not icing.  Some people have traditionally called it icing because it feels very similar to carb icing from the driver's perspective but that's not what is happening.  It is fuel condensing out.  This leans the mix a little and then drips into the chambers and as we all know, liquid fuel doesn't burn.  Does dissolve oil nicely though.  It's just a matter of terminology.  Some people call this effect icing and that has been a traditional way of looking at it, but if we are being completely accurate that is not what happens.

[jaydee]

Sorry guys this is just getting ridicolous.

Will only talk with people with millions post and know sematics from now 

[Captain Mainwaring]

  There are none.  People have this idea that the inlet charge will pickup significant heat from being in a warm tube for an almost immeasurable fraction of a second, when it's just been refrigerated by the venturi.  But what happens in the manifold is not icing.  Some people have traditionally called it icing because it feels very similar to carb icing from the driver's perspective but that's not what is happening.  It is fuel condensing out.  This leans the mix a little and then drips into the chambers and as we all know, liquid fuel doesn't burn.  Does dissolve oil nicely though.  It's just a matter of terminology.  Some people call this effect icing and that has been a traditional way of looking at it, but if we are being completely accurate that is not what happens.

 

I'm sure you already know, but the inlet charge is twice cooled - once through the venturi, and the second time by the latent heat of vaporization of the fuel.

Air velocities are sufficient that there wouldn't be much dripping of anything.

I'll disagree with you a bit about fuel condensation - I'm not saying it doesn't happen, but without a doubt inlet manifolds can ice, and the longer they are, the more chance there is that the cold inlet charge, together with the latent heat of vaporization will cool down the manifold walls enough that they will ice. VW Bug engines are well know for it as are many older aircraft engines with flat 4/6 cyl config and central carburation.

Edited by Captain Mainwaring, 17 June 2013 - 10:34 AM.