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-----Original Message-----
From: Ernest Christley <echristley@nc.rr.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Sun, 22 Jul 2007 11:31 am
Subject: [FlyRotary] Re: carbs vs efi
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.
Well put Ernest,
A engine is a dynamic system with a ton of variables. Working with what you are familiar with is a good idea. I built race engines as a young man of 20, and even then the mantra was, "everything effects everything!" Consider it the internal combustion engine law of unintended consequences. A small change can sometimes effect several other systems, in ways both good or bad.
Bill Jepson
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