[Diy_efi] RE: Timing and dyno pulls

[Dave Dahlgren]

I have no clue what the beginning of this was alluding to as I could not follow
it. The part about decreased air density requiring less timing lost me. Are you
suggesting if the map sensor reads 20 kpa you would retard the timing from what
it is set at at 40kpa?? Air temperature increases need less timing yes but it is
not air density related at all.

If you have never worked with an ecu that has gear compensation then you don't
know how it works only how you would do it. Do yourself a favor. Next time you
are on the inertia dyno make a pull in first gear and one in high gear and data
log  the O2 readings for both runs. Show me the part where they are the same.
Detonation is so far removed from tuning racing engines that if you get to that
point you have truly lost the rabbit so to speak. Peak power +- 0.5% is quite a
ways from detonation. There is also no rule I have ever heard about keeping heat
out of the cylinder heads. It is a heat engine. more heat more power. If you
keep the heads cool you lose power warming them up. Make a pull at 130 degree
water temp and one at 190... see for yourself. same goes for oil temp.. Keeping
the engine cool only makes you more comfortable not the engine. If you are
keeping the heads cool to stay out of detonation then you are running too much
timing....


Dave

Shannen Durphey wrote:
<Major snip>


> Gear ratio compensations _should_ be time compensations.  I've never
> used an ecu with a gear ratio compensation function, so they might be
> just that. 

 But the time compensation should be (imo) to first reduce
> spark then add additional cooling media (fuel, water, alky, whatever) as
> the amount of time under load increases.  For control systems which do
> not have time compensations, the tuner must estimate if and when
> cylinder heating will cause detonation.  And the tuner must add the
> necessary amount of fuel to prevent detonation before it happens.  Which
> means that if the tuner is wrong, or if the conditions under which he's
> made his estimation are substantially different from the operating
> conditions of the vehicle, his tune is less than the best.
> 
> <whew>
> 
> Shannen


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