[Diy_efi] Timing Advance Curve?

[Grant Beaty]

>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?

This is true on all the Supra and DSM engines I've seen, with pump gas
(2jz-gtes and 4g63).

Who was it that said they've seen 4g63s blow up when trying to find the
knock limit? How the hell do you do that? The 4g36 bottom ends are by all
accounts just as strong as the Supra's but with a weaker head gasket. I've
seen a DSM have his boost controller line pop off, which spiked the boost to
over 30 psi. At the same time, the extra boost blew the FPR hose off. No
noticable damage. This was all on pump gas.

The same car has had the (internal) WG stick and not open at all a few
times. Only damage done was a blown headgasket (again on pump gas).

Grant

----- Original Message -----
From: "Geddes, Brian J" <brian.j.geddes at intel.com>
To: <diy_efi at diy-efi.org>
Sent: Wednesday, December 18, 2002 11:03 AM
Subject: RE: [Diy_efi] Timing Advance Curve?



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.

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
> torque limit. If it
> pings you are at the torque limit for the fuel you are
> running. Are you saying
> that if you had better fuel it would not ping and therefore
> make more torque.
> Seems nonsensical. I have tuned the Mazda Miata engine for
> SCCA GT racing.
> Granted we had good fuel but as a restricted engine best
> power on a water brake
> dyno was at around 32 degrees. You could put more in it but
> no power came out.
> Why bother carrying a load of timing if it does not make the
> torque meter go up.
> It might have a couple of more degrees in first and second
> gear only but that
> would probably be the end of the mapping changes from the
> dyno. From the years
> of dyno time I have logged you could always slowly add timing
> to the point the
> power did not go up if you added a degree or two more it
> stayed the same and any
> more it goes down. The place in my mind to stop is the point
> where it adds no
> more power not the place where it makes no difference. You
> can always add a
> little in the lower gears to make the car snappier and then
> still be fine for a
> top gear pull on a long straight.
> Dave
>
> "Geddes, Brian J" wrote:
> >
> > I was already thinking that what you describe below was
> true - good to get confirmation.  I'm running a '90's
> designed 6-cylinder turbocharged engine (6G72, Mitsubishi
> 3000GT VR-4) with over 1 bar of boost, so I'm guessing that
> I'll reach the ping limit at boost well before the torque limit.
> >
> > - Brian
> >
> > 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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