[DeTomaso] Theoretical question of the day
jgkrenton at comcast.net
jgkrenton at comcast.net
Mon Feb 27 12:40:15 EST 2017
Charles:
RE: "If this is so, why would Holley make a jet change set and why wouldn't one size fit all?"
Many extensive books have been written on this subject. The jet size is dependent on lots of things, air density, (temperature and altitude/pressure) humidity, float level/fuel pressure, specific gravity of the fuel (Pure gasoline vs 10% alcohol, vs pure alcohol, car gas vs airplane gas etc etc.) cam profile, timing, compression ratio and lots more.
All of these add up to subtle changes in the ideal s toichiometric air to fuel ratio for the best performance for that particular engine and chassis. Is it a race car where maximum power is needed only at full throttle, but runs at full throttle all the time, or is it a economy car where minimum fuel burn and good idle is the goal?
It's a very complex issue and zillions of dollars have been spent on solving the issue. The common Holley has taken a rather simplistic approach to the problem which makes it relatively easy to tune, the Weber on the other hand had a much more sophisticated methodology to manage the air/fuel ratio and is thought by many to be the ultimate in "analog" non-electronic carburetor systems. Webers can be difficult to tune due to the number of variable items in the carb. But once you get them right they are wonderful.
Taking off the air cleaner may in some cases improve the air flow and increase the over all flow through the carburetor, but the venturi in the carb is the final determination as to how much air the carburetor can pass. The jets will provide appropriate fuel up to the limits of the venturi.
As many modern air cleaners are well designed "velocity stacks" in disguise, sometimes removing the air cleaner increases the turbulence at the entrance to the carburetor actually decreasing the maximum amount of air that can pass through the carb.
Modern EFI systems actively manage this air to fuel ratio depending on many factors and provide the best ratio for any condition and fuel.
Good luck, it's an interesting area to study and a good understanding of it will help you have a much more enjoyable hobby with the Pantera.
Jeff/2467
----- Original Message -----
From: "Charles McCall" <charlesmccall at gmail.com>
To: shawkins777 at comcast.net
Cc: "Detomaso Email List" <detomaso at detomasolist.com>
Sent: Monday, February 27, 2017 8:51:52 AM
Subject: Re: [DeTomaso] Theoretical question of the day
Thanks all - consensus seems to be that more air will suck more fuel and
will make more power. If this is so, why would Holley make a jet change set
and why wouldn't one size fit all?
El El lun, 27 feb 2017 a las 17:26, <shawkins777 at comcast.net> escribió:
> Charles,
> I'd expect that the increased air flow would pull more fuel from the
> jets at the venturi.
> Steve
> __________________________________________________________________
>
> From: "to Charles McCall" <charlesmccall at gmail.com>
> To: "Detomaso Email List" <detomaso at detomasolist.com>
> Sent: Monday, February 27, 2017 9:05:18 AM
> Subject: [DeTomaso] Theoretical question of the day
> Will a carburated engine make more power by simply installing a freer
> flowing air filter with no changes to the carb? Or removing the filter
> for
> that matter?
> A fuel injection computer will adjust the mixture to be able to take
> advantage of more oxygen, but fuel flow in the carb is limited by jet
> size.
> I'd expect a small increase in power to be possible but the fuel flow
> will
> soon be limited by jet orifice diameter, and it won't make much more
> power
> despite the extra air.
> A significant change in airflow would require rejetting the carb to
> take
> advantage of the improvement, right? Or wrong?
> Thanks all!
> _______________________________________________
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>
>
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-------------- next part --------------
Charles:
RE: "If this is so, why would Holley make a jet change set and why
wouldn't one size fit all?"
Many extensive books have been written on this subject. The jet size
is dependent on lots of things, air density, (temperature and
altitude/pressure) humidity, float level/fuel pressure, specific
gravity of the fuel (Pure gasoline vs 10% alcohol, vs pure alcohol, car
gas vs airplane gas etc etc.) cam profile, timing, compression ratio
and lots more.
All of these add up to subtle changes in the ideal stoichiometric air
to fuel ratio for the best performance for that particular engine and
chassis. Is it a race car where maximum power is needed only at full
throttle, but runs at full throttle all the time, or is it a economy
car where minimum fuel burn and good idle is the goal?
It's a very complex issue and zillions of dollars have been spent on
solving the issue. The common Holley has taken a rather simplistic
approach to the problem which makes it relatively easy to tune, the
Weber on the other hand had a much more sophisticated methodology to
manage the air/fuel ratio and is thought by many to be the ultimate in
"analog" non-electronic carburetor systems. Webers can be difficult to
tune due to the number of variable items in the carb. But once you get
them right they are wonderful.
Taking off the air cleaner may in some cases improve the air flow and
increase the over all flow through the carburetor, but the venturi in
the carb is the final determination as to how much air the carburetor
can pass. The jets will provide appropriate fuel up to the limits of
the venturi.
As many modern air cleaners are well designed "velocity stacks" in
disguise, sometimes removing the air cleaner increases the turbulence
at the entrance to the carburetor actually decreasing the maximum
amount of air that can pass through the carb.
Modern EFI systems actively manage this air to fuel ratio depending on
many factors and provide the best ratio for any condition and fuel.
Good luck, it's an interesting area to study and a good understanding
of it will help you have a much more enjoyable hobby with the Pantera.
Jeff/2467
__________________________________________________________________
From: "Charles McCall" <charlesmccall at gmail.com>
To: shawkins777 at comcast.net
Cc: "Detomaso Email List" <detomaso at detomasolist.com>
Sent: Monday, February 27, 2017 8:51:52 AM
Subject: Re: [DeTomaso] Theoretical question of the day
Thanks all - consensus seems to be that more air will suck more fuel
and
will make more power. If this is so, why would Holley make a jet change
set
and why wouldn't one size fit all?
El El lun, 27 feb 2017 a las 17:26, <shawkins777 at comcast.net>
escribiA^3:
> Charles,
> I'd expect that the increased air flow would pull more fuel from
the
> jets at the venturi.
> Steve
>
__________________________________________________________________
>
> From: "to Charles McCall" <charlesmccall at gmail.com>
> To: "Detomaso Email List" <detomaso at detomasolist.com>
> Sent: Monday, February 27, 2017 9:05:18 AM
> Subject: [DeTomaso] Theoretical question of the day
> Will a carburated engine make more power by simply installing a
freer
> flowing air filter with no changes to the carb? Or removing the
filter
> for
> that matter?
> A fuel injection computer will adjust the mixture to be able to
take
> advantage of more oxygen, but fuel flow in the carb is limited by
jet
> size.
> I'd expect a small increase in power to be possible but the fuel
flow
> will
> soon be limited by jet orifice diameter, and it won't make much
more
> power
> despite the extra air.
> A significant change in airflow would require rejetting the carb
to
> take
> advantage of the improvement, right? Or wrong?
> Thanks all!
> _______________________________________________
> 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.
> _______________________________________________
>
>
> Detomaso Email List is not managed by POCA
> Posted emails must not exceed 1.5 Megabytes
> DeTomaso mailing list
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> 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.
_______________________________________________
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