[Diy_efi] Timing Advance Curve?

Geddes, Brian J brian.j.geddes at intel.com
Wed Dec 18 18:56:16 GMT 2002


So there are basically two timing limints we're talking about.  First is =
the point where torque stops rising or rises very slowly - like a point =
of diminishing returns for timing.  The second limit is the point where =
the engine starts to knock on the fuel/IAT/etc combination that you're =
running. =20

The problem is that these two limits - knock and torque - do not =
necessarily come in the same order on all engines.  On some NA engines, =
the knock limit may be well beyond the torque limit.  On turbocharged =
engines, where the A/F mixture is pressuirized, hotter, and more =
knock-prone, the knock limit is most likely lower than the torque limit. =
 At least that's what I think I heard...anybody else care to confirm?

- Brian

> Help me here. How can you reach the ping limit before the=20
> torque limit. If it
> pings you are at the torque limit for the fuel you are=20
> running. Are you saying
> that if you had better fuel it would not ping and therefore=20
> make more torque.
> Seems nonsensical. I have tuned the Mazda Miata engine for=20
> SCCA GT racing.
> Granted we had good fuel but as a restricted engine best=20
> power on a water brake
> dyno was at around 32 degrees. You could put more in it but=20
> no power came out.
> Why bother carrying a load of timing if it does not make the=20
> torque meter go up.
> It might have a couple of more degrees in first and second=20
> gear only but that
> would probably be the end of the mapping changes from the=20
> dyno. From the years
> of dyno time I have logged you could always slowly add timing=20
> to the point the
> power did not go up if you added a degree or two more it=20
> stayed the same and any
> more it goes down. The place in my mind to stop is the point=20
> where it adds no
> more power not the place where it makes no difference. You=20
> can always add a
> little in the lower gears to make the car snappier and then=20
> still be fine for a
> top gear pull on a long straight.
> Dave
>=20
> "Geddes, Brian J" wrote:
> >=20
> > I was already thinking that what you describe below was=20
> true - good to get confirmation.  I'm running a '90's=20
> designed 6-cylinder turbocharged engine (6G72, Mitsubishi=20
> 3000GT VR-4) with over 1 bar of boost, so I'm guessing that=20
> I'll reach the ping limit at boost well before the torque limit.
> >=20
> > - Brian
> >=20
> > Further a few words to timing advance. Engines of newer=20
> conception (4V, =3D
> > central spark plug, CR~11) will have at loads lower than=20
> 50-70% their =3D
> > best advance before "pinging". At full load, knock limit is=20
> always the =3D
> > best.
> >=20
> >                 --- so long ---, klaus.
> >=20
> > There also remains a problem with late model 4valve engines=20
> in that some of
> > them hardly detonate at all! I have seen Mazda MX5 (Miata)=20
> engines on the
> > dyno which don't ping, or at least give no indication of=20
> pre ignition
> > audibly with well over 40 deg advance, WOT and max. torque. The only
> > indication was a drastic reduction in power.
> >=20
> > I have also seen one F3 engine builder destroy dozens of=20
> Mitsubishi engines
> > (4G63 I think) before they got the timing right. Part of=20
> the reason was that
> > the dyno guys had trouble figuring out where the ping limit=20
> was. Then when
> > they installed the engine and it was subjected to ram=20
> effect through the air
> > box, Kabang! Admittedly, these engines run air restrictors=20
> and CR's in the
> > region of 13:1, so getting the ignition map right is an art=20
> form in itself.
> >=20
> > The really clever engine builders (Neil Brown, Speiss=20
> Tuning) use the method
> > prescribed by Klaus. But the cost of the test equipment is horrific.
> >=20
> > Just a word of caution for anyone trying this theory with=20
> modern 4valve N/A
> > engines, that's all.
> >=20
> > _______________________________________________
> > Diy_efi mailing list
> > Diy_efi at diy-efi.org
> > http://www.diy-efi.org/mailman/listinfo/diy_efi
> >=20
> > _______________________________________________
> > Diy_efi mailing list
> > Diy_efi at diy-efi.org
> > http://www.diy-efi.org/mailman/listinfo/diy_efi
>=20
>=20
> _______________________________________________
> Diy_efi mailing list
> Diy_efi at diy-efi.org
> http://www.diy-efi.org/mailman/listinfo/diy_efi
>=20

_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi



More information about the Diy_efi mailing list