Ignition timing in conjunction with

[Mark Pitts]

Got my Spitfire SUs jetted to cope withthe exhaust/cam/inlet =
trupets/porting/every other bloody thing.

Paid a lot of moneyf for it too. Took the hood off, sat a bit of wire in =
the top of the vacuum pot, looked where it sat, span the needle up in =
the lathe and rubbed several thou' off it with fine wet and dry paper... =
did both.. runs a hell of a lot better now than it did after the tuners =
(who did a brill job of the other cars we got) did it, by guess work and =
sandpaper!

Mark

I don't recommend this!

----------
From:  Todd Knighton[SMTP:knighton at net-quest.com]
Sent:  Friday, September 20, 1996 10:41 AM
To:  diy_efi at coulomb.eng.ohio-state.edu
Subject:  Re: Ignition timing in conjunction with

>=20
> Now, rich is a real problem for me.  It's when you wanna "GO" !  So,
> this is where I thought you'd measure acceleration or torque (strain
> gauge on motor mount).  But, Todd says no. =20

	An interesting experience that may prove a point.
	A car we set up and dyno'd by the power method had some pretty wierd
cams on 8.0/1 compression ratio, and turbo'd.  the thing loved fuel to
make power.  Peak power was found at about 8 or 9/1 air fuel.  put it on
the road and it was extremely sluggish.  Due to the air/fuel.=20
Recalibrated the thing to the correct air fuels for the appropriate
boost/compression ratio/cams and it all of a sudden ran great. =20
	figure this one out.  It made better power with more fuel, but didn't
accelerate as well.  I've seen this one a few times.
	In this case the torque measurement in car (namely seat of the pants)
worked better than the dyno.
	You can take this one either way, but I still feel that there is a
given set of numbers for each combo for air/fuel ratio's that works
best.  Don't work so hard to find them, just program them in, then let
your EGO find them.

> I don't know how he would do a real time feedback system, but he =
apparently=20
> thinks a knock sensor is good for this.

	Again, the knock sensor is good for us in our application where the
knock is so close to peak power.  Especially when we see 18 - 21/1
effective compression ratio's on boost, on pump fuels (92-93 octane),
lets talk twiddle fingers here.
	In other situations, as I mentioned earlier, we've seen peak power and
the knock limit be 20 degrees apart.  It's typically on low compression
ratio or really bad combustion chamber designs, but there's a lot of
those out there.

>  Mebbe so.  Seems to me this is more a function of
> timing than mixture.  [Now, there's a variable I haven't been =
considering
> -- i.e. timing!!]

	Knock sensors are used for timing only.  The only car I've seen that
does anything else with it is SAAB, they decrease boost and enrichen the
mixture upon knock as well as work with timing later.  but the try to
leave the timing up as far as possibly under the other conditions.


>  All I'm thinking of right now is A/F ratios.
>  So, you guys that DO know, jump in here and help us out!)

	Try 14.7 - 15 or even up into the 16's if your engine can handle it, it
depends on combustion chambers and flame propogation.  But at light
throttle run as lean as possible with no misfire.
	Go to 12.8 to 13.3 (pump fuel numbers) for max power and torque
normally aspirated.
	Boosted, lower the air fuel proportionately.  We air cooleds have to
run down in the 11.4-11.6/1 range at 20 psi with very good intercooling
to maintain peak power and reliability.  We get slightly better power at
about 11.8 - 12/1 but the combustion chambers get too hot.  Water
cooled's would probably be happy at 11.8-12.0/1.

Todd Knighton
Protomotive Engineering