X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from ispmxmta06-srv.windstream.net ([166.102.165.167] verified) by logan.com (CommuniGate Pro SMTP 5.1.10) with ESMTP id 2194416 for flyrotary@lancaironline.net; Mon, 23 Jul 2007 11:48:09 -0400 Received-SPF: pass receiver=logan.com; client-ip=166.102.165.167; envelope-from=montyr2157@alltel.net Received: from ispmxaamta08-gx.windstream.net ([71.29.244.202]) by ispmxmta06-srv.windstream.net with ESMTP id <20070723154730.IHVE4133.ispmxmta06-srv.windstream.net@ispmxaamta08-gx.windstream.net> for ; Mon, 23 Jul 2007 10:47:30 -0500 Received: from Thorstwin ([71.29.244.202]) by ispmxaamta08-gx.windstream.net with SMTP id <20070723154729.OQGY16279.ispmxaamta08-gx.windstream.net@Thorstwin> for ; Mon, 23 Jul 2007 10:47:29 -0500 Message-ID: <005701c7cd40$c6cd8ff0$6501a8c0@Thorstwin> From: "M Roberts" To: "Rotary motors in aircraft" Subject: Carb vs. EFI Date: Mon, 23 Jul 2007 10:47:29 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0054_01C7CD16.DDCF1860" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3138 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.3138 This is a multi-part message in MIME format. ------=_NextPart_000_0054_01C7CD16.DDCF1860 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable 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.=20 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.=20 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.=20 When things can kill me I like the risks to be easily understood. just my $.02 Monty =20 ------=_NextPart_000_0054_01C7CD16.DDCF1860 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Ernest = wrote:
 
Point of interest and it = should be=20 kept in mind for any comparison is how "well-tuned" the components are. = The=20 article writers appear to be professionals, and yet even they had to = swapped=20 several components on both type of systems to get maximum performance. = Lynn=20 could probably make a carb outperform most other's EFI on a particular = race day.=20 Give me another 6 months of study with this EFI, and I might be able to = give him=20 a run for his money, though*.

Another point is that I keep = reading "Carbs=20 are simpler. You just have to bolt it on and go." Well, yeah. That's = true, IF=20 you want to leave a lot of performance on the ground. Once you start = talking=20 about getting all the performance out of the engine, especially if you = want to=20 accomplish that over a large range of environmental conditions, then the = carb=20 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=20 bolt on another 'simple' carb. If there is an improvement, they'll tell = everyone=20 the old carb sucks and the new one is the cat's meow, and at no point = will they=20 consider they haven't a clue. I'm not trying to say EFI is simple, just = that a=20 carb is more forgiving of cluelessness.
 
Ernest,
 
I have worked with carbs and EFI both. = I have used=20 throttle body and also tuned multi-point injection.
 
For the most part the carb and dual point distributor were the = bad old=20 days. You had to tune for the specific track and the specific = atmospheric=20 conditions at that time. EFI was a God send. Dry manifolds, great = torque=20 curves, less peaky operation....and no more blown %*&#(@) power = valves. No=20 springs, jets, and diaphragms to fool with.
 
I would not even think of running anything other than EFI in a = car. That=20 is a no brainer. Carbs are simple in concept, but to make them = work for the=20 varying conditions in an automotive setting they become complicated = nightmares=20 that are prone to failure. 
 
That said an airplane is not a car. It is operated at = a=20 relatively narrow band of power settings 65-100%. You (the = pilot) have=20 direct control of the mixture. The carb doesn't have to adjust for = changing=20 conditons, you do. The only time this is a problem is takeoff and = landing. So=20 you run a rich mixture during these regimes. So you burn an extra couple = of=20 pints of fuel per flight. That is your big savings with EFI in a plane; = a couple=20 pints of fuel per cross country. The rest of the time you lean for = cruise and=20 forget it. This is no big deal and anybody who can fly a Cessna 150 can = do this.=20 You don't really need an accelerator pump. I have yet to fly a Cessna = that=20 didn't stumble if I slam the throttle from idle to full. It didn't seem = to cause=20 me any problems.
 
If you carve off all the crap needed to make a carb work in a = car they=20 become very simple devices.
 
As far as power goes, Theoretically all things equal, a = fuel=20 injection system will make slightly more power due to the drop in = manifold=20 pressure caused by the venturi in the carb. In practice, unless you are = flying a=20 CS prop, you will not be flying at WOT. So there will be=20 no significant difference in power.
 
Tracy makes a great system and I am not = trying to=20 knock it. Ed, Tracy and others have been running it for a long time. If = you want=20 EFI I would suggest you use Tracy's. Otherwise stick to a carb. The = failure=20 modes for a carb are few and easy to fix. There are far fewer = catastrophic=20 failure modes for a carb than an EFI system. I certainly would not fly = an=20 untried non redundant EFI system.
 
It is not that I am uncomfortable with = software, or=20 wiring. I have built and wired machine tools, and worked on rocket = engine=20 test stands with lots of data acquisition and control equipment. = All=20 requiring lots of wires and software. I just know all the things that = can go=20 wrong, and therefore I am afraid of untested, non redundant=20 electronics. If you don't know the MTBF of every component and the = system=20 as a whole, and you rely on a single controller that runs your engine, = you are=20 playing Russian Roulette. Any little component, solder joint, you name = it can=20 bring you down (think kill you). Think about that long and hard. Are you = really=20 gaining anything worth that risk? Perceived efficiency? Perceived = benefits?=20 Tracy's system is very reasonably priced for what you get. I certainly = would not=20 use some other single controller system just to save a few hundred = dollars.=20
 
When things can kill me I like the = risks to be=20 easily understood.
 
just my $.02
 
Monty
 
  

 
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