| Re: [GMCnet] 16.5 to 1 lean burn cruise isn't a problem with the Howell/GM system. [message #324246 is a reply to message #324206] |
Fri, 22 September 2017 21:08   |
mrgmc3
Messages: 210
Registered: September 2013
Location: W Washington
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Keith V wrote on Fri, 22 September 2017 12:41The other variable is the E10 gas we run now.
What does that do to EGT and AFR?
Do you have an afr gauge installed? I've never seen a carb run that lean Intentionally even at cruise.
Justin Brady
Keith,
E10 will run 4% leaner than E0 (no ethanol), and so I kind of split the difference in jetting since you can't count on one fuel or the other. There is no direct affect on EGT due to E10 other than the slight enleanment. Spark advance has a much greater impact on EGT than small changes in A/F. This is why I urge everyone to make sure both their vacuum and centrifugal advance are fully functional. Retarded timing increases EGT a lot, in addition to lowering power and economy.
Justin,
My quadrajet runs about 15:5 at 60 mph level road cruise but drops to 13.5 for slight grades or speed 70 and above (and 11.5 at WOT). There is a lot of tunability with a quadrajet. Most people change main jets but the power piston spring controls when enrichment occurs from cruise and light throttle, so changing to stiffer spring will push the primary rods out of the jets from a higher vacuum starting point (i.e. smaller increase in load to gain some enrichment - i.e. Lean out the cruise point but make sure it rapidly enriches with load).
An AFR gauge or monitor and the patience to make numerous small changes can provide good results. Start with a tool box full of spare jets, power piston springs, a notebook for all changes and a good quadrajet book (like Doug Roe's) and you can make a lot of improvement.
I would not recommend this for a novice as there are many variables that can end badly, but if you read up and understand the basics of engine performance and the limits of where an engine should run for A/F and spark you can make significant gains.
Chris Geils - Twin Cities / W Wa
1978 26' Kingsley w/ very few mods; PD9040, aux trans cooler, one repaint in stock colors, R134a, Al rad, Alcoas, 54k mi
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