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Re: [GMCnet] Injection versus Carbs [message #74253 is a reply to message #74227]

Thu, 18 February 2010 08:38

mlincoln

Messages: 107
Registered: August 2006
Location: Salt Lake City

Karma:

Senior Member

I understand and agree, Matt. First that auto carbs are certainly more complex. Second, that carburetors are volume pumps and not mass pumps. Regarding your second point, I earlier noted that very same problem: the volume pumping of air stays the about the same in the carburetor, even when the atmospheric pressure drops significantly. When this happens, usually with increasing altitude, the *mass* pumping of air decreases significantly while the volume pumping of fuel remains about the same. (Perhaps temperature and thermal expansion/contraction can affect fuel mass pumping by a few percent). In this case, the molar matching of fuel molecules to air molecules is significantly, and non-optimally, altered and affects the mixture to the detriment of performance. The mixture richens with increasing altitude, or if optimally leaned at altitude and subsequently not adjusted, becomes too lean as altitude decreases.

Naturally, any engine is less powerful when less oxygen can be burned, but the non-optimal matching of air to fuel further degrades performance and raises emissions as altitude increases. In airplanes, we correct the second factor with our bone-simple mixture controls. We just have to suffer with the first factor unless we are turbocharged, which probably decreases reliability and certainly increases aircraft power plant cost significantly. Of course, fuel injection with air mass meters (e.g., a hot wire in the airstream) can correct those deficiencies, but it sounds to me that the juice may not be worth the squeeze with our engines. Interestingly, many of the newest self-launching sailplanes (like this one: http://www.alisport.com/eu/eng/index.html ) now have EFI. My wife is in dental school now...just a few rich kids with bad teeth down the road a few years, and maybe I can afford one :-)

So, I agree with you entirely. But here's the core question: can the volume pumping characteristics of auto carburetors be predictably altered in a beneficial way in the GMC MH application, using either 1) different jets/metering rods (by someone who knows what they're doing, specifically not me), or 2) this adjustable part throttle screw that Kosier mentioned, in order to adjust the volumetric mixing properties of the carburetor so as to achieve a better mass air/fuel balance at high (or even intermediate, e.g., Appalachian) altitudes? Or is it like the aircraft turbocharger, expensive and perhaps too much bother--what do you think?

Specifically, I'm thinking of trying to acquire a second Quadrajet (actually, I have one) and have it rebuilt with slightly leaner mixture, perhaps optimized for 5000 feet MSL. Then I'd have two carbs and could change at will; it looks like a simple job for a tyro mechanic with little skill (which would describe me). In your opinion, is there anything to Kosier's adjusting screw in the latter model Quadrajets?

Mike

On Feb 18, 2010, at 8:49 AM, Matt Colie wrote:

>
>
> Mike and Ken (and other pilots onboard),
>
> There is a danger in relating aircraft carburetors to their distant automotive cousins.
>
> Aircraft carburetors are relatively simple when compared to the automotive version for similar rating.
>
> It you had all the courses in engineering school, you were taught that carburetors were mass-flow devices and as such should match a mass of air with a mass of fuel (thus says the mathematics).
>
> Unfortunately, this is not the case. There are profound volumetric effects. Matching fuel volume with air volume does not work well when the volume of air has less mass. This can cause some profound issues even east of the Mississippi. (Like when the portable equipment you counted on will not run at 4KMSL.)
>
> It matters more to automotive than aircraft because:
> Aircraft traditionally have pilot adjustable mixture and carburetor heat.
> Aircraft are a stable load situation so time to manually adjust the mixture is available.
> Automotive applications require that operation be predicable with operators regardless of experience and education.
> Automotive engine operational envelope is extremely large and way outside normal good practices turn-down limits.
>
> There are many reasons why the automotive industry has cheerfully abandon the artform of calibrating our old carburetors. Emissions was just a real good excuse to make the investment.
>
> Matt
> --
> Matt & Mary Colie
> '73 Glacier 23 Chaumiere (say show-me-air)
> SE Michigan
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[Message index]

		[GMCnet] Injection versus Carbs By: Richard Lister on Mon, 08 February 2010 10:01
		Re: [GMCnet] Injection versus Carbs By: Mr ERFisher on Mon, 08 February 2010 10:10
		Re: [GMCnet] Injection versus Carbs By: GeorgeRud on Mon, 08 February 2010 10:17
		Re: [GMCnet] Injection versus Carbs By: Ron on Mon, 08 February 2010 11:08
		Re: [GMCnet] Injection versus Carbs By: Matt Colie on Mon, 08 February 2010 11:14
		Re: [GMCnet] Injection versus Carbs By: Steven Ferguson on Mon, 08 February 2010 12:25
		Re: [GMCnet] Injection versus Carbs By: k2gkk on Mon, 08 February 2010 12:35
		Re: [GMCnet] Injection versus Carbs By: Mr ERFisher on Mon, 08 February 2010 12:46
		Re: [GMCnet] Injection versus Carbs By: Steven Ferguson on Mon, 08 February 2010 18:31
		Re: [GMCnet] Injection versus Carbs By: Larry on Mon, 08 February 2010 22:00
		Re: [GMCnet] Injection versus Carbs By: Steven Ferguson on Tue, 09 February 2010 07:19
		Re: [GMCnet] Injection versus Carbs By: bill schurman on Mon, 08 February 2010 13:11
		Re: [GMCnet] Injection versus Carbs By: Ron on Mon, 08 February 2010 14:31
		Re: [GMCnet] Injection versus Carbs By: Ken Burton on Tue, 09 February 2010 02:11
		Re: [GMCnet] Injection versus Carbs By: Jim Bounds on Tue, 09 February 2010 06:40
		Re: [GMCnet] Injection versus Carbs By: tgeiger on Tue, 09 February 2010 09:51
		Re: [GMCnet] Injection versus Carbs By: Jim Bounds on Wed, 10 February 2010 07:57
		Re: [GMCnet] Injection versus Carbs By: Jim Galbavy on Mon, 08 February 2010 15:30
		Re: [GMCnet] Injection versus Carbs By: USAussie on Mon, 08 February 2010 16:23
		Re: [GMCnet] Injection versus Carbs By: Larry C on Thu, 18 February 2010 09:06
		Re: [GMCnet] Injection versus Carbs By: Jim Bounds on Thu, 18 February 2010 11:17
		Re: [GMCnet] Injection versus Carbs By: Gary Worobec on Thu, 18 February 2010 11:33
		Re: [GMCnet] Injection versus Carbs By: Chr$ on Mon, 08 February 2010 16:48
		Re: [GMCnet] Injection versus Carbs By: Chr$ on Mon, 08 February 2010 16:49
		Re: [GMCnet] Injection versus Carbs By: k2gkk on Mon, 08 February 2010 18:12
		Re: [GMCnet] Injection versus Carbs By: Rick Williams on Mon, 08 February 2010 18:45
		Re: [GMCnet] Injection versus Carbs By: David L Greenberg on Mon, 08 February 2010 19:55
		Re: [GMCnet] Injection versus Carbs By: George Beckman on Mon, 08 February 2010 20:14
		Re: [GMCnet] Injection versus Carbs By: Matt Colie on Tue, 09 February 2010 13:25
		Re: [GMCnet] Injection versus Carbs By: Richard Lister on Tue, 09 February 2010 14:36
		Re: [GMCnet] Injection versus Carbs By: George Beckman on Tue, 09 February 2010 20:50
		Re: [GMCnet] Injection versus Carbs By: GeorgeRud on Tue, 09 February 2010 15:04
		Re: [GMCnet] Injection versus Carbs By: Jim Galbavy on Tue, 09 February 2010 15:54
		Re: [GMCnet] Injection versus Carbs By: Jim Galbavy on Tue, 09 February 2010 17:03
		Re: [GMCnet] Injection versus Carbs By: Jim Bounds on Wed, 10 February 2010 05:41
		Re: [GMCnet] Injection versus Carbs By: klassic kampers on Tue, 09 February 2010 17:34
		Re: [GMCnet] Injection versus Carbs By: Bob de Kruyff on Tue, 09 February 2010 18:35
		Re: [GMCnet] Injection versus Carbs By: Sandra Price on Wed, 10 February 2010 11:18
		Re: [GMCnet] Injection versus Carbs By: tgeiger on Wed, 10 February 2010 14:37
		Re: [GMCnet] Injection versus Carbs By: ljdavick on Wed, 10 February 2010 14:45
		Re: [GMCnet] Injection versus Carbs By: Jim Bounds on Sat, 13 February 2010 08:20
		Re: [GMCnet] Injection versus Carbs By: Bill Freeman on Sat, 13 February 2010 09:01
		Re: [GMCnet] Injection versus Carbs By: emerystora on Sat, 13 February 2010 09:47
		Re: [GMCnet] Injection versus Carbs By: Bill Freeman on Sat, 13 February 2010 15:47
		Re: [GMCnet] Injection versus Carbs By: Ron on Sat, 13 February 2010 16:14
		Re: [GMCnet] Injection versus Carbs By: Surbo on Sat, 13 February 2010 17:45
		Re: [GMCnet] Injection versus Carbs By: Ron on Sat, 13 February 2010 17:57
		Re: [GMCnet] Injection versus Carbs By: Bill Freeman on Mon, 15 February 2010 13:33
		Re: [GMCnet] Injection versus Carbs By: emerystora on Mon, 15 February 2010 13:42
		Re: [GMCnet] Injection versus Carbs By: Larry on Mon, 15 February 2010 14:40
		Re: [GMCnet] Injection versus Carbs By: mlincoln on Mon, 15 February 2010 15:31
		Re: [GMCnet] Injection versus Carbs By: Bill Freeman on Tue, 16 February 2010 07:49
		Re: [GMCnet] Injection versus Carbs By: Matt Colie on Wed, 17 February 2010 17:34
		Re: [GMCnet] Injection versus Carbs By: GMCWiperMan on Wed, 17 February 2010 17:57
		Re: [GMCnet] Injection versus Carbs By: mlincoln on Wed, 17 February 2010 19:31
		Re: [GMCnet] Injection versus Carbs By: Ken Burton on Wed, 17 February 2010 20:23
		Re: [GMCnet] Injection versus Carbs By: Kosier on Wed, 17 February 2010 21:46
		Re: [GMCnet] Injection versus Carbs By: mlincoln on Wed, 17 February 2010 22:01
		Re: [GMCnet] Injection versus Carbs By: Kosier on Wed, 17 February 2010 22:34
		Re: [GMCnet] Injection versus Carbs By: klassic kampers on Thu, 18 February 2010 14:22
		Re: [GMCnet] Injection versus Carbs By: Jim Bounds on Thu, 18 February 2010 09:09
		Re: [GMCnet] Injection versus Carbs By: Matt Colie on Thu, 18 February 2010 07:49
		Re: [GMCnet] Injection versus Carbs By: mlincoln on Thu, 18 February 2010 08:38
		Re: [GMCnet] Injection versus Carbs By: Kosier on Wed, 17 February 2010 20:57
		Re: [GMCnet] Injection versus Carbs By: Surbo on Mon, 15 February 2010 14:09
		Re: [GMCnet] Injection versus Carbs By: Jim Galbavy on Mon, 15 February 2010 14:38
		Re: [GMCnet] Injection versus Carbs By: Bill Freeman on Tue, 16 February 2010 07:38
		Re: [GMCnet] Injection versus Carbs By: Carleton Douglas[1] on Wed, 10 February 2010 14:53
		Re: [GMCnet] Injection versus Carbs By: jimk on Wed, 10 February 2010 22:18
		Re: [GMCnet] Injection versus Carbs By: Richard Lister on Tue, 16 February 2010 10:55
		Re: [GMCnet] Injection versus Carbs By: bryant374 on Tue, 16 February 2010 12:21
		Re: [GMCnet] Injection versus Carbs By: Bill Massey on Tue, 16 February 2010 13:24
		Re: [GMCnet] Injection versus Carbs By: psakw on Sat, 13 February 2010 21:58
		Re: [GMCnet] Injection versus Carbs By: emerystora on Sat, 13 February 2010 22:07
		Re: [GMCnet] Injection versus Carbs By: rallymaster on Thu, 18 February 2010 11:45
		Re: [GMCnet] Injection versus Carbs By: g.winger on Thu, 18 February 2010 14:11
		Re: [GMCnet] Injection versus Carbs By: Larry on Thu, 18 February 2010 15:08
		Re: [GMCnet] Injection versus Carbs By: wally on Thu, 18 February 2010 15:33
		Re: [GMCnet] Injection versus Carbs By: Larry on Fri, 19 February 2010 13:44
		Re: [GMCnet] Injection versus Carbs By: wally on Fri, 19 February 2010 14:44
		Re: [GMCnet] Injection versus Carbs By: Larry on Fri, 19 February 2010 19:05
		Re: [GMCnet] Injection versus Carbs By: GMCWiperMan on Fri, 19 February 2010 19:23
		Re: [GMCnet] Injection versus Carbs By: Keith V on Sat, 20 February 2010 10:12
		Re: [GMCnet] Injection versus Carbs By: GMC_LES on Sat, 20 February 2010 16:45
		Re: [GMCnet] Injection versus Carbs By: WD0AFQ on Sat, 20 February 2010 17:35

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