[Diy_efi] A/F mixture, EGT and engine damage

[Tim Marsteiner]

Yes, for this engine the 13.2:1 is a good deal leaner
than need be at wot. I have run as low as 11.5:1 at
wot with good power and EGTs below 1400. That's a no
brainer.

At cruise it gets a bit more complicated. The table I
posted was running with a narrow band O2 sensor. I am
pretty sure this is the worst case EGT as 1663 F is
the highest I have ever seen on this bike.

I guess my question was not so much if either of these
is ok, but rather which might be causing the most
problems. What I am hearing is that to optimize engine
life I ought to eliminate both and as long as I stay
above 10:1 or so I should be ok in terms of wall wash.

Here are the results of my fix (pretty fast huh!?:). I
attacked both issues. WOT stays below 1400 F and
cruise stays below 1450 F. 

http://www.superxtune.com/images/EGT0505Cyl2_egt.jpg

I will be honest though I have not seen a huge
reduction in cylinder head temps. Perhaps 10-15 F
reduction. It does take longer to heat up though. This
agrees with John Deakin's article "Mixture Magic".

http://tinyurl.com/cb287

So I think the WOT part of the above tune is good
except for maybe some fine tuning on a dyno and maybe
some more ignition advance.

As far as cruise I have experimented with running LOP
15.6:1 or so. I get some surging at lower speeds and
some pretty high EGTs. A/F seem to be all over the
place(~14.5:1 - ~17:1). Probably due to the ECU using
alpha-N control or perhaps that pesky IAT heat soak
problem. I will keep working on this to see if I can
stabilize the mixture LOP and lower CHT a bit as Mr.
Deakin's results indicate.

Thanks,
Tim


--- Michael Richards <michael at fastmail.ca> wrote:
> > I have heard that going too rich can damage the
> engine
> > by "washing" the oil film off the cylinder walls.
> Is
> > there a safe lower limit on A/F or EGT ?
> 
> If there were a magical number that gave you the
> best economy or the 
> best power for all engines then the numbers would be
> well published and 
> recited by everyone. Your 13.2 number sounds like a
> happy medium 
> between cruise and power. 
> 
> Personally I would try going a little richer under
> load and a little 
> leaner under cruise. Some engines don't mind being
> run high into the 
> 15's for cruise but others will not tolerate it at
> all. Some engines 
> make more power NA into the 12:1 AFR but some are
> better run lean 
> around 12.8:1 or 13:1. Everything is a balancing
> act. If your EGTs are 
> too high try advancing the ignition and/or richening
> it up a little.
> 
> I wouldn't worry about washing the cylinder walls at
> these ratios. Run 
> it 10:1 and richer and you could have a problem.
> 
> -Michael
>
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