[Land-speed] Fuel Mixture Change?

drmayf drmayf at mayfco.com
Fri Jun 5 09:50:11 MDT 2009


Skip, here is why, I think.  YMMV, lol. The rootes is a positive 
displacement device. It pulls the air from whatever ambient conditions 
are. But the mass of the air is always the same per revolution. When 
that air gets under the blower it is hot, but it is still the same mass 
of air. That did not change. It goes through the intercooler and gets 
chilled somewhat. But the mass of air does not change.  Just the temp 
changed. The mass that goes into the engine is the same mass that the 
blower pulled in. Since the mass is the same, the fuel requirements are 
still the same. You just now have a much cooler combustion chamber and 
are not killing pistons etc from detonation or heat. If you were still 
running the turbo, which is a constant pressure device rather than a 
constant volume, then yes, the fuel requirements would need changing 
becuase the mass of air changes. Thats what makes a turbo the far better 
choice for power adders (but efi required to make changes, lol). Cool 
the turbo air and it puts more mass in.

mayf....



Skip Higginbotham wrote:

> List,
>
> I am adding an intercooler to my freshened, blown/injected BBC gas 
> engine (15 lbs and 8:1 compression).
>
> It seems to me that I should richen the mixture since the induction 
> temp is expected to go down about 300 degrees. BUT....the intercooler 
> and the blower companies say no that the mixture should be left alone 
> for the first pass.
>
> How can the engine make more horsepower with cooler induction air but 
> no added fuel?????
>
> First pass will be to the 1 and then shut off.........even with the 
> wide band O2 sensor. Because I'm "old school" and parts are expensive.
>
> Skip
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