[DeTomaso] Theoretical question of the day

Fred Foreman fred4man at att.net
Mon Feb 27 13:00:35 EST 2017


 Whew,
Charlie, you really make a person think!  My first impression was to agree with Steve about more air equals more fuel.  
But, that probably is true, up to a point, such as wide open throttle (which is also the time at which we are concerned about the restriction of the air filter).   So, at this point I think we are talking about only the main jets.  The other jets are used at idle, part throttle, and under dynamic conditions such as acceleration and not in the discussion. 
When I think about it, the jet is a fuel restrictor and the air filter along with the throttle plates are air restrictors.  So, at WOT the throttle are wide open, and out of the equation, and the air filter is, all other variables remaining constant, controlling the air flow.  The main jets are used to restrict the fuel flow to match the air flow.    So, if the air flow is changed through the carb by changing the air induction system or filter, the main jets should be changed to match the fuel follow to the new air flow.
That statement raises memories of old car magazines and books, talking about carbs, and saying that changes to induction and exhaust systems will require one to rejet the carb (and retune your SU carb, I used to be into British cars).  I never really thought about why they said that back then!
Fred Foreman
-------------- next part --------------
    Whew,
   Charlie, you really make a person think!  My first impression was to
   agree with Steve about more air equals more fuel.
   But, that probably is true, up to a point, such as wide open throttle
   (which is also the time at which we are concerned about the restriction
   of the air filter).   So, at this point I think we are talking about
   only the main jets.  The other jets are used at idle, part
   throttle, and under dynamic conditions such as acceleration and not in
   the discussion.
   When I think about it, the jet is a fuel restrictor and the air filter
   along with the throttle plates are air restrictors.  So, at WOT the
   throttle are wide open, and out of the equation, and the air filter is,
   all other variables remaining constant, controlling the air flow.  The
   main jets are used to restrict the fuel flow to match the air flow.
   So, if the air flow is changed through the carb by changing the air
   induction system or filter, the main jets should be changed to match
   the fuel follow to the new air flow.
   That statement raises memories of old car magazines and books, talking
   about carbs, and saying that changes to induction and exhaust systems
   will require one to rejet the carb (and retune your SU carb, I used to
   be into British cars).  I never really thought about why they said that
   back then!
   Fred Foreman


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