[Healeys] 100M cold air boxes and flow

[Chris Dimmock]

Hi Alan,
No, you cant pressurise a cold air box.
Never set up your cold air box so it rams air in at higher than  
atmospheric pressure straight into your carbs
If you do, the end result will be too much air, not enough fuel, a  
lean mixture and a destroyed/ melted piston or 4. Probably at high rpm.
A cold air box is just that. A cold air box  - the ability for cold  
air to be sucked into a carb on a hot engine. A cold air box generally  
is not sealed. It is open at one end (or somewhere) so it can't  
pressurize and force air into the carbs at higher than atmosperic  
pressure.
Think about an old supercharger for a minute. The carb - often an SU  
on the sort of superchargers found on BMC cars - is on the outside, it  
mixes the fuel and air which is then compressed and fed to the engine.
I.e it is a fuel air mix which is compressed, not compressed air alone.
I've seen the results from some homemade "cold air sealed ram boxes" -  
and trust me, unless your dad owns a piston company, you don't want to  
go there.
So the end issue is the 'flow' into the cold air box is pretty  
irrelevent, it's just a way to get cooler than underbonnet air in  
front of the carbs.
Whether the volumetric area of a 100m cold air box is enough - no idea.
But pressurize or seal a cold air box on SUs at your own peril....

Best
Chris

Sent from my iPhone

On 19/01/2012, at 5:55 PM, Alan Seigrist <healey.nut at gmail.com> wrote:

> Adam -
>
> Any flow.....
>
>
> It's about the air pressure, not the air temperature.  Basically it's
> a cheap supercharger when you are driving fast.
>
> Alan
>
> On 1/14/12, Adam Nolde <adamnolde at yahoo.com> wrote:
>> All,
>>
>> ...The box depth in front of each carb opening is only 1.75".  I  
>> can see potential
>> for not only vacuum creation and inefficient atmospheric  
>> replacement, but
>> add
>> to that the inefficient dynamics of the flat and non radiused  
>> orifices.
>> I've also discovered a fair amount of scavenging occurs between carb
>> orifices
>> in-spite of the wide and presumably ample open ended box.