DeTomaso Mailing List: April 98, Message #95

From:	Fred Terry <GT5S@erols.com>
Subject:	Carburetor v EFI
Date:	Wed, 1 Apr 1998 21:36:37 +0000


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To anyone interested,
        I have been an advocate of fuel injection since the sixties when
I had a Rochester used by Chevrolet and Pontiac (yes Pontiac offered
injection in '58 as well as Chrysler). These were of the mechanical type
and on the Corvette produced higher torque and hp  than the equivalent
in carbureted engines. When comparing EFI to a carb, a good port
injection using a fully programmable ECM should be considered. Throttle
body types such as Holley just don't offer the versatility in program
control.
    In the gasoline engine, hp is derived from the energy content in the
fuel when mixed in the proper ratio with air. Either a carb or injector
can be used to "try" to meter the fuel in the proper ratio. Very simply,
the difference is that a carb meters fuel using a low pressure area in
the carb venturi and the modern fuel injector uses a computer. The
computer meters fuel electronically based the conditions of its program.
The parameters of the program  can be tailored with a fuel "map" to
deliver fuel at any ratio under any load condition at any engine rpm. A
carburetor lacks this capability and this is why a radical engine can be
tuned to be more driveable with injection.
    Most after market injection systems are added to manifolds intended
for carburetors so how can the same manifold be good for a carb but bad
for injection. By eliminating the carb you also eliminate the
restriction of the carb venturi and thus the same manifold will flow
more air when using equal throttle butterfly sizes.
    The only moving parts of a EFI are the pintals in the injectors, the
fuel pressure regulator, the fuel pump and throttle butterflies.
Excepting the butterflies, none of these items compare to the many parts
of a carb with its sensitive choke linkage, fuel passages and sloshing
fuel bowls. As far as fuel atomization goes, modern engines would not
pass emissions with poorly atomized fuel.
    Some systems offer a distributor less ignition with a programmable
advance curve. This puts the spark in direct sync with the crank without
the slop from the timing chain and distributor.

Fred Terry

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<HTML>
To anyone interested,
<BR>        I have been an advocate
of fuel injection since the sixties when I had a Rochester used by Chevrolet
and Pontiac (yes Pontiac offered injection in '58 as well as Chrysler).
These were of the mechanical type and on the Corvette produced higher torque
and hp  than the equivalent in carbureted engines. When comparing
EFI to a carb, a good port injection using a fully programmable ECM should
be considered. Throttle body types such as Holley just don't offer the
versatility in program control.
<BR>    In the gasoline engine, hp is derived from the energy
content in the fuel when mixed in the proper ratio with air. Either a carb
or injector can be used to "<I>try" to meter the fuel in the proper
ratio. Very simply, the difference is that a carb meters fuel using a low
pressure area in the carb venturi and the modern fuel injector uses a computer.
The computer meters fuel electronically based the conditions of its program.
The parameters of the program  can be tailored with a fuel "map" to
deliver fuel at any ratio under any load condition at any engine rpm. A
carburetor lacks this capability and this is why a radical engine can be
tuned to be more driveable with injection.
<BR>    Most after market injection systems are added to
manifolds intended for carburetors so how can the same manifold be good
for a carb but bad for injection. By eliminating the carb you also eliminate
the restriction of the carb venturi and thus the same manifold will flow
more air when using equal throttle butterfly sizes.
<BR>    The only moving parts of a EFI are the pintals in
the injectors, the fuel pressure regulator, the fuel pump and throttle
butterflies. Excepting the butterflies, none of these items compare to
the many parts of a carb with its sensitive choke linkage, fuel passages
and sloshing fuel bowls. As far as fuel atomization goes, modern engines
would not pass emissions with poorly atomized fuel.
<BR>    Some systems offer a distributor less ignition with
a programmable advance curve. This puts the spark in direct sync with the
crank without the slop from the timing chain and distributor. 

<P>Fred Terry

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