Anything and everything Spitfire.

Reading through a thread on carburation, specifically to the temperature of the charge, it seems that the cooler the air, the more dense it is, the more oxygen in a given volume, the better the the combustion.

My question, then. Why arent we all talking about bypassing the heated manifolds on our cars?
I realise that the choke would need to be out for longer, but is that such a big deal compared to having cooler air?
Or have I missed the plot completely?

Ian

I think it is something to do with whether the air is just air or a fuel air mix.

As it is drawn in, it is cold (and dense), then it gets mixed with fuel as it goes through the carbs, and then it gets heated by the manifold.

The effect of heating the fuel air mix is to help keep the fuel properly in suspension so that when the mix enters the cylinder it is a well mixed mixture.

The same thing applies to fuel injected engines - if the injector head is not giving a good spray pattern, the fuel will not mix properly and the burn will be inefficient.

There are folk here who know far more than me and hopefully will chip in. My thoughts are that the amount of oxygen drawn into the inlet manifold can only be proportionate to the volume of air drawn in. Oxygen cannot appear from nowhere. So I'm thinking that, like hot air in a bathroom, the hotter the air drawn in the more moisture it can carry without condensing. Hydrocarbons have a high percentage of water which is released upon combustion. However there has been a discussion about cool boxes that bring cold air to the air intake. Cool air must be denser than hot air. Its drawn into the heated manifold, heats up but cannot expand (?) and into the combustion chamber carrying more vapourised fuel than otherwise. Does that make sense? Anyone??

I'm no expert and can only refer to what I have read. Kas Kastner's book - Triumph Preparation, which I ordered and received from Jason a while back has some explanation on page 92 which I quote below:

Quote - If your manifold has a heating tube (water) do not disconnect if you are using the car for street use. In racing, disconnect the water tubes to the manifold. The heating of the manifold is very important for low speed work and is very noticeable when it is disconnected if the weather is a little cool. This heating helps to keep the vapor of the fuel emitting from the carburettors to stay in a vapor condition. If the heating water is shut off the manifold will actually become cooler than the surrounding parts at part throttle opening. This is because the high speed air going thru the manifold and the low vaporization point of gasoline will draw the heat from the manifold and in some cases the manifold will actually have a frosty coating. In racing this does not happen as the engine is being run at a bigger throttle opening. - Unquote!!

Phew!!

Hope that helps!!

Regards

Thanks to you all, that makes sense - I think!
I just don't like not understanding stuff like this.
Guess Mr Kastner is going on the Christmas list. Although, knowing my family I'll end up with the Dances with Wolves DVD
Ian

Or, now it's been discussed on the forums wait for someone to write an article on it in the next Courier...?

Any predictions as to who will be writing said article ?
My crystal ball says TLD

Can see it now... 'I've been making very successfull vinyl stickers for the last 20 years, none of which anyone has been able to match...'

Not sure it will be.....

There was a very limited quantity imported....

Colin

Section : Carburettors

Inlet manifold 1500 spit

Followups :

Inlet manifold 1500 spit

Inlet manifold 1500 spit

Inlet manifold 1500 spit

Inlet manifold 1500 spit

Inlet manifold 1500 spit

Inlet manifold 1500 spit

Inlet manifold 1500 spit

Inlet manifold 1500 spit