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Ernest wrote:
Point of interest and it should be
kept in mind for any comparison is how "well-tuned" the components are. The
article writers appear to be professionals, and yet even they had to swapped
several components on both type of systems to get maximum performance. Lynn
could probably make a carb outperform most other's EFI on a particular race day.
Give me another 6 months of study with this EFI, and I might be able to give him
a run for his money, though*.
Another point is that I keep reading "Carbs
are simpler. You just have to bolt it on and go." Well, yeah. That's true, IF
you want to leave a lot of performance on the ground. Once you start talking
about getting all the performance out of the engine, especially if you want to
accomplish that over a large range of environmental conditions, then the carb
starts getting VERY complicated. Most people are oblivious that all that
complication even exists and will opt to just take what they get, power-wise, or
bolt on another 'simple' carb. If there is an improvement, they'll tell everyone
the old carb sucks and the new one is the cat's meow, and at no point will they
consider they haven't a clue. I'm not trying to say EFI is simple, just that a
carb is more forgiving of cluelessness.
Ernest,
I have worked with carbs and EFI both. I have used
throttle body and also tuned multi-point injection.
For the most part the carb and dual point distributor were the bad old
days. You had to tune for the specific track and the specific atmospheric
conditions at that time. EFI was a God send. Dry manifolds, great torque
curves, less peaky operation....and no more blown %*&#(@) power valves. No
springs, jets, and diaphragms to fool with.
I would not even think of running anything other than EFI in a car. That
is a no brainer. Carbs are simple in concept, but to make them work for the
varying conditions in an automotive setting they become complicated nightmares
that are prone to failure.
That said an airplane is not a car. It is operated at a
relatively narrow band of power settings 65-100%. You (the pilot) have
direct control of the mixture. The carb doesn't have to adjust for changing
conditons, you do. The only time this is a problem is takeoff and landing. So
you run a rich mixture during these regimes. So you burn an extra couple of
pints of fuel per flight. That is your big savings with EFI in a plane; a couple
pints of fuel per cross country. The rest of the time you lean for cruise and
forget it. This is no big deal and anybody who can fly a Cessna 150 can do this.
You don't really need an accelerator pump. I have yet to fly a Cessna that
didn't stumble if I slam the throttle from idle to full. It didn't seem to cause
me any problems.
If you carve off all the crap needed to make a carb work in a car they
become very simple devices.
As far as power goes, Theoretically all things equal, a fuel
injection system will make slightly more power due to the drop in manifold
pressure caused by the venturi in the carb. In practice, unless you are flying a
CS prop, you will not be flying at WOT. So there will be
no significant difference in power.
Tracy makes a great system and I am not trying to
knock it. Ed, Tracy and others have been running it for a long time. If you want
EFI I would suggest you use Tracy's. Otherwise stick to a carb. The failure
modes for a carb are few and easy to fix. There are far fewer catastrophic
failure modes for a carb than an EFI system. I certainly would not fly an
untried non redundant EFI system.
It is not that I am uncomfortable with software, or
wiring. I have built and wired machine tools, and worked on rocket engine
test stands with lots of data acquisition and control equipment. All
requiring lots of wires and software. I just know all the things that can go
wrong, and therefore I am afraid of untested, non redundant
electronics. If you don't know the MTBF of every component and the system
as a whole, and you rely on a single controller that runs your engine, you are
playing Russian Roulette. Any little component, solder joint, you name it can
bring you down (think kill you). Think about that long and hard. Are you really
gaining anything worth that risk? Perceived efficiency? Perceived benefits?
Tracy's system is very reasonably priced for what you get. I certainly would not
use some other single controller system just to save a few hundred dollars.
When things can kill me I like the risks to be
easily understood.
just my $.02
Monty
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