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.....
>
> If you look at pictures of some 100S/4 racers in the day, many of the
> cars have run the paper air tube past the grill or even through the
> shroud into the oncoming air stream to maximize positive pressure in
> the CAB.
>
> 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,
>>
>> Has anyone conducted or read the results of anyone else's research
>> regarding the fluid dynamics of the 100M cold air box?
>>
>> I'm no engineer, but a
>> keen mind looking at the 1956 cold air box design can quickly work
>> out the
>> fact that it may have some ill effects on air delivery at higher
>> RPM's. I'm
>> specifically concerned about the size and depth of the box causing
>> delivery
>> issues for both, but more likely the rear carb.
>>
>>
>> I've done some very crude
>> calculations and crude bench testing just as a base to understand
>> the flow
>> involved and the possible scale. I've learned my engine can suck
>> as much as
>> 263CFM at 100% VE, but obviously it should be less, so I use this
>> as a max.
>> That puts the velocity at each carb above 85mph static, but much
>> faster
>> during
>> intake stroke. The velocity at the air box inlet is above 65mph
>> static.
>> 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.
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