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Date: Sun, 22 Jul 2007 18:31:54 +0000
From: Ernest Christley <echristley@nc.rr.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: carbs vs efi
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Russell Duffy wrote:
>  
> EFI is a complex system, but when it's working like it does in your car
> every day, it's a no brainer of a choice.  Since this is a result of
> millions of dollars of R&D work, such a perfect, turn-key system is not
> going to be available to us.  Even if such a system was available, it would
> require everyone to use exactly the same setup, which goes against the grain
> for most of us.  
>   
>


Rusty, all of those arguments can be turned right back around and 
pointed at carbs. 8*)  There has been MUCH more money put in to carb 
development over the years than has been invested in EFI system.  People 
often ask me what the best program to do "XYZ" is.  My canned response 
is that the best program to use is usually the one that you already 
know.  I think it's the same with carbs vs EFI.

See, the problem isn't just delivering fuel to the engine in the right 
amount.  Shucks, that's easy.  It gets complicated when you start trying 
to deliver the right amount of fuel at the right time.  With carbs you 
have to figure out jets size, add an accelerator pump, mess with the 
venturi, and a hundred other things that people have tried over the 
years.  If you change something in the intake, you may have to switch 
out a bunch of stuff in order to retune.  Then you have to fiddle and 
adjust to get it all working properly again.  With EFI, you have to size 
the injector, learn concepts such as acceleration enrichment and  XTau, 
decide between speed-density vs alpha-N for tuning, and then modify a 
program to account for all the variables.  If something changes in the 
intake, you'll have to modify the tuning parameters in the program 
again.  When it's all done, you're going to have to learn a lot before 
you know what you're doing, the learning will only come from fiddling 
with the thing, and you won't know what you're doing until you learn a lot.

For me, I like the EFI.  I won't necessarily smell like gas after 
fiddling, and I can do much of the fiddling from my desk.  A carb is an 
analogue computer, with the drawback that you will never get datalogging 
from it.  But the biggest advantage to EFI for me is the fact that I can 
just hit the AUTOTUNE button to flatten the learning curve.  But, while 
I've rebuilt a few carbs before, I don't really have that Zen 
understanding of how they work.  OTOH, I'm a software engineer.  Program 
a controller is second nature for me.


Your mileage may vary.  Not valid in all states.  No user serviceable 
parts inside.  May cause headaches, heart palpitations, or diarhea. Do 
not take before operating heavy equipment.