[Diy_efi] Timing Advance Curve?

[Patrick Cahill]

Message: 3
Subject: AW: [Diy_efi] Timing Advance Curve?
Date: Wed, 18 Dec 2002 00:30:04 +0100
From: "Schaffer Klaus Maria" <schaffer at vkma.tu-graz.ac.at>
To: <diy_efi at diy-efi.org>
Reply-To: diy_efi at diy-efi.org

> -----Urspr=FCngliche Nachricht-----
> Von: Geddes, Brian J [mailto:brian.j.geddes at intel.com]
> Gesendet: Montag, 16. Dezember 2002 19:11
> An: diy_efi at diy-efi.org
> Betreff: RE: [Diy_efi] Timing Advance Curve?
>=20
> Any other advice on this?  If a dyno is not readily available=20
> (I have an all-wheel drive car), could one infer a increase=20
> in torque from a decrease in EGTs? =20
>=20
> > The DIY way is to advance until torque drops, or until it pings,
> > whichever is first.  If it pings first, drop it back a notch, or use
> > higher octane.
> >=20

The way which professionals are going:

An engine cycle has his highest efficiency (best torque) when the timing =
of MBF50% (time when 50% of the fuel is burnt) is set to 8deg-ATDC. =
Sounds easy, you only need a device that tells you when 50% of the fuel =
is burnt ;-)

The only way to get the information, is to calculate the heat release =
rate. Therefor you need at least information about the incylinder =
pressure. You need a incylinder pressure sensor and a trigger device =
(resolution of 0.5deg works good enough). A good incylinder pressure =
transducer costs ~$2000,-, bad one ~$1000,-. Low cost sensors are in =
development since years, but not available today. Equations for =
calculating the heat release rate can be found in the Heywood book and =
in many SAE-papers.

There are some indicating system on the market that will do this for =
you. Best will come from a company located at my hometown www.avl.com =
;-). But don't ask for prices or better: before you get a price: fasten =
your seat belts.

Further a few words to timing advance. Engines of newer conception (4V, =
central spark plug, CR~11) will have at loads lower than 50-70% their =
best advance before "pinging". At full load, knock limit is always the =
best.

		--- so long ---, klaus.


There also remains a problem with late model 4valve engines in that some of
them hardly detonate at all! I have seen Mazda MX5 (Miata) engines on the
dyno which don't ping, or at least give no indication of pre ignition
audibly with well over 40 deg advance, WOT and max. torque. The only
indication was a drastic reduction in power.

I have also seen one F3 engine builder destroy dozens of Mitsubishi engines
(4G63 I think) before they got the timing right. Part of the reason was that
the dyno guys had trouble figuring out where the ping limit was. Then when
they installed the engine and it was subjected to ram effect through the air
box, Kabang! Admittedly, these engines run air restrictors and CR's in the
region of 13:1, so getting the ignition map right is an art form in itself.

The really clever engine builders (Neil Brown, Speiss Tuning) use the method
prescribed by Klaus. But the cost of the test equipment is horrific.

Just a word of caution for anyone trying this theory with modern 4valve N/A
engines, that's all.


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