Hi Trevor Boicey!!
On Mon, 23 Jun 1997, Trevor Boicey wrote:
> I think he must have been testing a specific fuel injection
> system and getting those results. It's very possible that
Of course he was, but that doesn't change the results. He was somewhat
surprised, and double checked his set up. Same results...
> some carburetor combination will be better than some fuel
QED.
> injection combination, but it's highly unlikely that ANY
> carb setting is better than ALL fuel injection possibilities.
Trevor, were I Bob Allen, this is where I'd eviscerate you. You have
just made a pronouncement without knowing all the facts. There is more
to an engine's performance abilities than what type of fuel delivery
system it has. Theory is wonderful, but it is a only a guide to
enlightenment.
After consulting with other "A" series tuners, Vizard found that the
head design wasn't able to pass enough air, so that the size of the fuel
droplets was critical. The carb supplied relatively large droplets that
allowed a proportionatly larger amount of air through the inlet ports
than the fine spray from the injectors that prevented as much air to
pass through the port. The carb also improved volumetric efficiency
through charge cooling within the cylinder. Given a cross-flow overhead
cam head, the results would be different, but we don't have cross-flow
heads. The push rods intrude into our intake ports and we have those
goofy siameesed ports as well.
> Ironically, if you wanted to, you could program your fuel
> injection to duplicate SUs and get at least the same performance
> as SUs, faults and all.
Apparently, unless you change the injector design, you can't.
> Fuel injection generally gives more performance because it's
> adjustments and tunings can be done without compromise, generally
Nope, it gives more performance because the internal combustion engine
is an AIR PUMP, and f/i, being less restrictive in the intake passages,
allows the engine to breath better. The more air you take in, the more
fuel you can burn.
> unlike carburetors where most design traits are tradeoffs between
> performance and mileage, performance and emissions, or performance
> and driveability.
Trevor, from what little I know about fuel injection systems, this
statement doesn't make any sense. For instance, one of the hot
performance modifications to the Mustang 5 litre f/i is to replace the
throttle body/opening (I don't know the name of it) with a larger one,
so that it will flow more air than the stock one. You are faced with
the same compromises with f/i design as you are with carburation.
TTUL8r, Kirk Cowen (who spends most of his time at part throttle
these days...)
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