| Re: [GMCnet] Jim Bounds interesting recent posts [message #325921 is a reply to message #325912] |
Fri, 10 November 2017 11:50   |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
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I did read JimB's blog, and there is a little I disagree with but there is also very little hard information there.
As an auto-lab rat from the early 70's (on and off), I can tell you for a fact that at lot of both Jim's and your premise is correct, but some is not.
Since the early 70's (at Chrysler Proving Grounds) is has been a stated fact that the carburetors we all know are not a vaporizing or gasifying device. In actual fact, the industry has referred to them as "solid fuel" carburetors for years. While the droplet size does matter for emissions (back when a carburetor could even meet those standards), there was a running game (with a large number of really strange plays) between large and small. Small droplets cold burn faster and the larger more slowly. Not too different than gun powder grain size. Which you wanted depended on just what you were trying to accomplish at that moment. The capability to maintain a stoichiometric over a wide band did not arrive until the EGO sensors got reliable. Even then, the "closed loop" carburetors were not that good at much of anything.
Other running issue is: What is gasoline?
Even before "reformulating" this was an open question. When we were getting non-indolene test fuels, we always got a report with the carbon/hydrogen ratio. even if this number was in target, we still could only use indolene (a specific chemical hydrocarbon that can be used as motor fuel) because it was the only thing stable enough to give stable emissions values.
So, the fact that reformulated motorfuel may have a stoich number that is other than 14.68 is just not an issue. From an SI engine's point of view, there is little change over a significantly wide range. Again, this is just one of the problems that new engine controls manage. Just about all of the engines that have a EGO per bank and a modern ECU, are actually doing a cylinder by cylinder mixture control. This has to happen for current standards. It was not desired in the mid-70s cat cars, because they counted on the rich/lean pulses to keep the cat lit and still provide enough O2 for the desired reactions to complete.
Then there is the issue that not all the cylinders see the same mixture (the end cylinders often get lean) with any central fuel feed system. The initial charge pressure (present in the cylinder when the intake valve closes) has a lot to do with what is going to happen when the fire gets started. No, all the cylinders of an engine are never the same and less than a wide open manifold only exacerbates that issue by steering the charge mixture in different directions.
We live east of the Mississippi and rarely encounter altitudes above 6KMSL, but the coach rolled over the Big Horn on the way to Yellowstone and the coach did not complain. We even had to go around a couple of little four-wheels that could not keep speed up at 9200MSL (according to my GPS). They were all too new to be open loop. And, we still did our regular 9.2 for that journey.
So, before you get all fired up to change to a tack-on "fuel injection", decide if it is something you really want to do.
As Dick Paterson has been known to say, most carburetor problems start with the ignition. I am not fond of HEI, but it can be serviceable, you just have to be sure you have the spares along. But, you should carry ignition spares in any case.
Matt - I'll get down off the milk crate now, I have some passcar work to do today still.
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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