| Re: [GMCnet] 16.5 to 1 lean burn cruise isn't a problem with the Howell/GM system. [message #324236 is a reply to message #324201] |
Fri, 22 September 2017 18:00  |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
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mrgmc3 wrote on Fri, 22 September 2017 09:57You can get away with 16:1 A/F at light load up to say a 65 mph level road cruise load. I'd suggest dialing in with the benefit of at least one exhaust thermocouple and someone with real good hearing if you don't have a knock sensor. You'll likely need to go richer with any headwind or grade load.
I concur with Chris. I do run 16.2 and 16.4 and have for years. THe Exhaust temp runs cool at 16.4. Lots of air. Not much fuel. The worry, whether you have a carb or EFI, in my opinion, is not lean cruise but "Does the unit go into Power Enrichment (Power Valve on a carb) soon enough." 12.8:1 or richer. EBL will increase fuel until it is 11.8 on a long pull.
I don't see high exhaust temps in lean cruise. I don't see high exhaust temps in Power Enrichment. At the sweet spot 14.7, light (and I mean slight) pull caused by a bit of upgrade or wind and exhaust temp starts to rise quickly. Like 150* in thirty seconds. (This increase does not show up on the temperature gauge.)
The heat is not a good thing. But for those of you who are familiar with cutting with an acetylene torch know, you heat the metal, but it is when you add oxygen, the metal "burns" away. Same with exhaust valves and pistons. Hot is bad. Hot with too much oxygen is catastrophic. So, we cheat and put in too much fuel, so we use up as much of the oxygen as possible. You can heat the combustion so much things break and melt but it is when parts of valves burn away, that we have sudden and catastrophic events.
The second problem heat causes is detonation. (pinging) Detonation can blow crevices in pistons if you let it rattle long enough.
(Thanks to Matt Colie for tutoring me on these matters over and over until it finally got through my thick skull)
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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