| [GMCnet] Jim Bounds interesting recent posts [message #325912] |
Fri, 10 November 2017 09:58  |
glwgmc
Messages: 1014
Registered: June 2004
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I have followed with interest his comments about why carbs no longer work (todays gas won’t vaporize correctly for use in a carb) and now why our engines are blowing up mote frequently (they run too hot under some condition).
Take a look at the presentation I did on Fitech (http://www.bdub.net/FiTech_is_the_Real_Deal.pdf). Near the end are two important slides that I think help explain what he is saying. The slide with the two charts is very telling. Those charts are based on an engine running pure gasoline with a stoichiometric air/fuel ratio of 14.7:1. One chart shows peak power at an air fuel ratio of around 12.5:1 (quite rich) while peak economy is around 16:1 (way too lean for our engines to survive for very long). Those charts are based on UNADULTERATED gasoline. The curves for gasoline laced with alcohol would look much differently.
The slide on the next page shows stoichiometric A/F ratios for various chemical compounds. For octane it is 15:1, for ethanol it is 9:1. We not only have been adding ethanol, we have also added a number of other distillates and removed others. So, just as he has been saying, everything we learned about engines when we were all much younger is out the window given whatever it is we now pump into our fuel tanks. Just for giggles, see what happens to those curves if the only change was adding 10% alcohol. The stoichiometric would shift from 14.7 to 14.1. Now guess what happens if you go to lean, either because you reprogram your fuel injection to do that, or because your carb gets dirty inside and does it on its own without you even knowing it, or because you monkey around with the jets, air correctors, power valve springs, etc. in the hope of better mileage. On flat land you might get away with that if you drive at 50 to 60 mph where the air drag is low, but climb any kind of hill or load the engine up with head wind or by speeding up and you will quickly be running way too lean for the conditions and way to hot for any kind of engine longevity. Just what he has been saying.
I am not a petroleum engineer so don’t know for sure how those curves change shape for whatever is in our fuel today, but my guess is however those curves change the result is we should now be striving to burn MORE FUEL day in and day out if we want to keep these old engines healthy. I’m going to guess there is a direct correlation between fuel consumption and engine life. Likely 8mpg is around the BEST one should shoot for these days.
How many times have we heard people say that their coaches ran much better and got much better fuel economy driving in Canada on premium fuel with no alcohol. The only way that could happen is if that coach was set up way too lean for driving on gasoline laced with alcohol. My thoughts anyway.
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
glwork@mac.com
http://jerrywork.com
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Jerry & Sharon Work
78 Royale
Kerby, OR
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