[Diy_efi] Timing and dyno pulls

Patrick Cahill patc at opposition.tv
Fri Dec 20 03:28:16 GMT 2002


Peak power can occur on the edge of detonation and in fact many "boost
buttons" on N/A setups are nothing more than an ignition trim which puts the
advance up into the almost pinging region for a couple more HP. Needless to
say that their use is strictly time controlled and the method is only
employed in classes where engine development has hit a plateau so everyone
has much the same HP.

Ditto the bit about cool engines and keeping heat away to avoid detonation.
The temperature variance you refer to has more to do with a question of
tolerances and sealing. I can tell you of  a few engines which currently run
coolant temps of 55-70deg. Celsius with CR's in the 13:1 to 14:1 range and
max advance of 32deg in naturally aspirated format. These guys are also
winning international races and have been for some years like this. I'm not
going to tell you who it is as they would not appreciate the attention.
Suffice to say two are English, one Italian, one French, one German and two
Japanese.

BTW, they are not backyard hackers, in fact one is the Motorsport dept. of a
very large automaker.

In fact, it has been a popular theory for years that cool water and hot oil
are the real way to make HP. Even my liquid cooled Kawasaki KX250 runs quite
cold as you can pull up after a run through the bush on a hot summer day and
still touch the radiators. The big loser with cold coolant temperatures is
emission levels not power.

Someone asked in a post who blew up all the engines on the dyno trying to
get the ignition map right and the answer is HKS when they tried to build an
F3 motor a few years ago.


Message: 2
Date: Thu, 19 Dec 2002 13:12:38 -0500
From: Dave Dahlgren <ddahlgren at snet.net>
To: diy_efi at diy-efi.org
Subject: Re: [Diy_efi] RE: Timing and dyno pulls
Reply-To: diy_efi at diy-efi.org

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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