[DeTomaso] Theoretical question of the day

[j g]

Ok:
Sort of! A well tuned carb will make as much or more Hp than a fuel injection system depending on the design and the particular engine dynamics.a carburetor is designed to flow fuel based on the mass flow of the air through the venturi's , if the mass flow of air exceeds the main jet mass flow of fuel dictated by the jet size carb etc: then the system will begin to lean out. In general one can take a carburetor and place a good carburetor like a weber , set the main jet , the idle jet and  a basic emulsion tube  number  on the bench and with average air corrector jets the carb will run correctly on most engines that the main and booster venturi's have been sized for . If the cam is pretty wild or there are resonances in the intake or exhaust system then these will require either richer jetting , different emulsion tubes ( determines when the main  fuel circuits transfer ) and different air correctors . On certain carbs ( like DCOE and some holley) the accelerator pump nozzles are used for full throttle enrichment above what the main jets can or will flow. These are usually in either a booster venture  or right out in front of the main venture. Thus WOT performance can be hindered or helped by the pump nozzle and jet size.  starting to flow because of low pressure moving up the carb (away from the throttle plate) at wot. So, if the carb has been set up for normal wet flow and a specific fuel air ratio on a bench flow set up at a specific flow it will do that regardless of the  air filter or any other restrictor , what happens is that the flow and pressure ratio through the carburetor changes as a function of the restrictions and can dramatically effect both reversion and wot performance at a specific rpm and spark timing.Kind of a little  information on very wild straight and short individual runner systems carburetor or EFI , I have seen that due to reversion pulses at part throttle a longer intake horn above the carb. throttle body or a conical common air filter box actually improves hp and throttle transient response because the air flow reversion pulse is damped by the trapped air mass inside the filter box , so with a filter is better than without in this case. 
jg

      From: Fred Foreman <fred4man at att.net>
 To: "detomaso at detomasolist.com" <detomaso at detomasolist.com> 
 Sent: Monday, February 27, 2017 12:00 PM
 Subject: [DeTomaso] Theoretical question of the day
   
    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

_______________________________________________


Detomaso Email List is not managed by POCA
Posted emails must not exceed 1.5 Megabytes
DeTomaso mailing list
DeTomaso at server.detomasolist.com
http://server.detomasolist.com/mailman/listinfo/detomaso

To manage your subscription (change email address, unsubscribe, etc.) use the links above.

Members who post to this list grant license to the list to forward any message posted here to all past, current, or future members of the list. They also grant the list owner permission to maintain an archive or approve the archiving of list messages.

   
-------------- next part --------------
   Ok:
   Sort of! A well tuned carb will make as much or more Hp than a fuel
   injection system depending on the design and the particular engine
   dynamics.
   a carburetor is designed to flow fuel based on the mass flow of the air
   through the venturi's , if the mass flow of air exceeds the main jet
   mass flow of fuel dictated by the jet size carb etc: then the system
   will begin to lean out. In general one can take a carburetor and place
   a good carburetor like a weber , set the main jet , the idle jet and  a
   basic emulsion tube  number  on the bench and with average air
   corrector jets the carb will run correctly on most engines that the
   main and booster venturi's have been sized for . If the cam is pretty
   wild or there are resonances in the intake or exhaust system then these
   will require either richer jetting , different emulsion tubes (
   determines when the main  fuel circuits transfer ) and different air
   correctors . On certain carbs ( like DCOE and some holley) the
   accelerator pump nozzles are used for full throttle enrichment above
   what the main jets can or will flow. These are usually in either a
   booster venture  or right out in front of the main venture. Thus WOT
   performance can be hindered or helped by the pump nozzle and jet size.
   starting to flow because of low pressure moving up the carb (away from
   the throttle plate) at wot.
   So, if the carb has been set up for normal wet flow and a specific fuel
   air ratio on a bench flow set up at a specific flow it will do that
   regardless of the  air filter or any other restrictor , what happens is
   that the flow and pressure ratio through the carburetor changes as a
   function of the restrictions and can dramatically effect both reversion
   and wot performance at a specific rpm and spark timing.
   Kind of a little  information on very wild straight and short
   individual runner systems carburetor or EFI , I have seen that due to
   reversion pulses at part throttle a longer intake horn above the carb.
   throttle body or a conical common air filter box actually improves hp
   and throttle transient response because the air flow reversion pulse is
   damped by the trapped air mass inside the filter box , so with a filter
   is better than without in this case.
   jg
     __________________________________________________________________

   From: Fred Foreman <fred4man at att.net>
   To: "detomaso at detomasolist.com" <detomaso at detomasolist.com>
   Sent: Monday, February 27, 2017 12:00 PM
   Subject: [DeTomaso] Theoretical question of the day
       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
   _______________________________________________
   Detomaso Email List is not managed by POCA
   Posted emails must not exceed 1.5 Megabytes
   DeTomaso mailing list
   [1]DeTomaso at server.detomasolist.com
   [2]http://server.detomasolist.com/mailman/listinfo/detomaso
   To manage your subscription (change email address, unsubscribe, etc.)
   use the links above.
   Members who post to this list grant license to the list to forward any
   message posted here to all past, current, or future members of the
   list. They also grant the list owner permission to maintain an archive
   or approve the archiving of list messages.

References

   1. file://localhost/tmp/tmpFDuVNL.html
   2. file://localhost/tmp/tmpFDuVNL.html