Nitrogeno25
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| posted on 15/4/13 at 03:04 PM |
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Duratec: How lean is too lean?
I was tuning the Duratec (2.0 with Jenvey TBs and megasquirt) for some fuel economy in the 2500-3500rpm range. I can see 16.5:1 afr in the gauge
(almost the same in TunerStudio) and the engine seems to be happy. TPS was at 5% so very low load.
Is these dangerous for the engine?
Thanks!
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JAG
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| posted on 15/4/13 at 03:27 PM |
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My understanding of this is that Lean mixtures run hotter - hence it may be an issue. It just depends how hot is TOO hot 
The limit would seem to be the materials in the combustion chamber and the level of cooling that they get.
It's very difficult to tell without specialist equipment and expert knowledge.
Justin
Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!
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Nitrogeno25
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| posted on 15/4/13 at 04:17 PM |
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Yes I saw the engine was running at 85º instead of the 82º using a richer mixture.
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Ivan
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| posted on 15/4/13 at 04:40 PM |
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This is one of those cases where you are genuinely playing with fire - I think you need to find out what the high vacuum air fuel ratios and the
timing is for the original motor. You then need to take an educated look at the what the impact of the modifications you have made on the cylinder
filling and evacuation is at those vacuum levels and then decide what will work.
I would certainly not go any leaner with mixture and any more advanced with timing than what the standard motor runs at when pulling a high vacuum.
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Nitrogeno25
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| posted on 15/4/13 at 04:44 PM |
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I wish I could get the stock map for this engine!
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motorcycle_mayhem
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| posted on 15/4/13 at 04:52 PM |
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I guess the engine won't see much load at 5% throttle (unless you have a really perverse style), plus, if pushed to the edge - perhaps the
antiknock sensors would get involved before anything went bad. A guess.
Hopefully where you are, there are octane levels available that allow exploring the fuelling/ignition. If you've only got access to 80's
octane (RON) perhaps unwise to push the limits. Some of our American friends have very poor fuel.
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Nitrogeno25
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| posted on 15/4/13 at 05:33 PM |
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quote:
Originally posted by motorcycle_mayhem
I guess the engine won't see much load at 5% throttle (unless you have a really perverse style), plus, if pushed to the edge - perhaps the
antiknock sensors would get involved before anything went bad. A guess.
Hopefully where you are, there are octane levels available that allow exploring the fuelling/ignition. If you've only got access to 80's
octane (RON) perhaps unwise to push the limits. Some of our American friends have very poor fuel.
We have 95 (RON) and 97 (RON) fuel, don't know how accurate are these octane ratings. No antiknock sensor. I'm using megasquirt 2 now and
didn't experimented with knock sensors yet.
Thanks!
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britishtrident
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| posted on 15/4/13 at 07:26 PM |
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quote:
Originally posted by Nitrogeno25
Yes I saw the engine was running at 85º instead of the 82º using a richer mixture.
Weak mixtures burn slower so reject more heat to the cylinders walls (and piston) during the later part of the combustion stroke. This also pushes
t he exhaust gas temperature up and when combined with the higher exhaust gas oxygen content can cause exhaust valve burning.
Off throttle (high manifold vacuum) engines will tolerate weak mixture with a more ignition advance, but beware.......................
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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coyoteboy
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| posted on 15/4/13 at 07:33 PM |
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FWIW the hottest mixture is stoic (it has the highest energy output per unit fuel), if all other factors are correct for the mixture, either direction
takes you cooler, one through excess fuel and other causes and the other through excess air and a few other causes. You'll see hotter lean mixes
if you're not advancing the timing at the same time. But you're grouping a whole load of points into a general one - are we talking EGT,
cylinder wall temp, cylinder head temp etc etc. And are you changing the ignition timing to match the differing mixture? Are you talking about at a
fixed RPM and load, or does your RPM and load change with the adjusted mixture and timing?
You really need EGT and torque feedback to tune properly and try to run at extremes, otherwise stick to known safe AFRs.
[Edited on 15/4/13 by coyoteboy]
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