[Diy_efi] RE: Diy_efi digest, Vol 1 #413 - 12 msgs

[Dave Dahlgren]

Over the last 20 years I have not found this to be true at all. I have never had
the chance to run an engine on an eddy current dyno but I suspect the results
from a water brake to be similar. What I have found is that when the timing is
retarded from optimal that the engine runs richer or indicates it might be a
better selection of words. The NTK wide band will read richer with the same
amount of fuel and if timing is advanced to optimal it indicates leaner to the
point I am tempted to add more fuel. The EGT I have found to be very useful for
timing adjustments as well. Too hot explore a degree or two more timing and see
if it goes down as long as A/F ratio is reasonable. Same goes for too cold take
a couple of degrees out. EGT I have always shot for is about 1300 to 1350 after
5 seconds at load with a N/A engine. I have also generally shot for an A/F ratio
of 13.3 to 14.0 at WOT depending on the combustion chamber design and fuel used
on an N/A engine. This is of course starting at some reasonable timing curve for
the engine I have no idea how it would work if you are miles off in adjustment
as I try not to prove the absurd nor do I start with an aggressive timing curve
as well. If I think it will need about 36 degrees at WOT for a given rpm I start
at 32 or 33.. These are race engines as well and light throttle cruise settings
I have no experience with, we never are at these points, so this method may well
be useless in exploring those settings.

Dave

Adam Wade wrote:

> 
> I concur.  My feeling is that the best way is to use
> an eddy current chassis dyno and hold the vehicle
> steady-state under a given load, and then adjust the
> timing using EGA, and possibly EGT as a backup.  This
> is assuming you have already optimized the fuel map
> for best power across the board.
> 
> My experience has been that when tweaking an engine
> designed for performance (sportscar/motorcycle), you
> should have to do little or no modification to the
> fuel mapping after optimizing the timing.
> 
> =====
> | Adam Wade


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