robertbartsch

I recently leaned out my engine (10%) over the entire RPM band and added 5% ignition timing to the RPM band above 3400 Vs. the stock GM tune.

I think this increased power and no knock has occured yet. Is this the standard for increasing power?

Can I go more lean? More timing?

Thanks...

horist

Can't really tell if you can go leaner w/out knowing what you're at now... (wideband) ... lean = power, too lean = boom
Timing = power
Too little timing = less power (igniting mixture after TDC when Piston is already into combustions troke)
Too much timing = less power (igniting mixture while piston is on compression stroke, so piston is moving up and at same time you're trying to force it down... big shock to piston)

As a rule of thumb though I wouldn't change both at once... change the fueling to get it where you wan it... then start adding timing until you get Knock, once at that point you can back the timing down or add more fuel and see if the knock goes away

LS1s seem to like around 28* of timing (some require less timing, others can run more timing and still make power)

jimmyblue

iTrader: (11)

You're trying to find the MBT point (timing for
maximum torque) for given mixture. Traditional
curves show best torque at about 12.5:1 and
best power at 12.8:1 but this varies by motor.
The pressure pulse wants to be positioned away
from valve-open and past TDC, your pressure
profile w/ time is convolved with the crank angle
in creating the delivered torque impulse to the
crank. There is a "sweet spot" for the RPM and
the cylinder charge. The spark has to lead this
by the burn time. Burn time decreases as you go
lean; fat and late blows energy out the exhaust.
But rich means more fuel burned means (to some
degree) more power albeit less efficiently made.
This accounts for the increase in power from
stoich, going richer (for a while). The inefficiency
of combustion steals more and more past the 12.x:1
range, factory settings are like 11.8:1 for purposes
of minimizing the consumer whining about ping.

High compression and purer cylinder charge also
accelerate burn time. Whatever the burn time is,
determines the advance tolerated (ping). In general
it's better to start burn as soon as possible to get
the most "time in the saddle" for the expansion of
the burn. Though popping it early at low RPM, may
mean you are pushing against a cylinder that is
nowhere near maximum lever arm projected at the
crank and so it just pushes without much advantage
and the energy goes into heating the walls instead.
Torque being force*projected_radius pointwise
through the arc.

Seems like the sophisticates like to tune fat in the
midrange of RPM (where you have the luxury of
time, to expand the cylinder burn into torque)
and taper it leaner up top (where you got to git
'er done in a shrinking power stroke duration).
Spark advance positions the pulse but all there
is, is the time between TDC and exhaust valve
open and you have to position it as best you're
able, within that.

There is sort of a "flat top" to both the power/
mixture and power/advance curves. The high
advance and high AFR sides of these "flat tops"
both terminate in ping. Ping seems to be about 2
degrees past best timing but there is not much
penalty for taking out another degree or two if
you like to build in some tolerance.

A stocker with restricted intake and exhaust has
a fair bit of residual gas remaining and poor high
RPM cylinder filling, so its burn time is long and
much leaner mixture can be tolerated especially
up top. Improve this situation with breathing mods
and your pre-spark cylinder pressure will go up
and the purity of charge as well, knocking down
burn time and the required spark, and upping the
degree of enrichment that makes best power.
The stock guidance of 13:1 is probably not the
same point you want to be at, with good breathing
(let alone power adders).

To exhaustively (heh) map the fuel*spark surface
and see the best pairs for power, and arrive at an
overal peaked-up tune would take a fair bit of time
but could be done (say, on a acceleration vs RPM
Excel basis using the VSS pulses if hours of dyno
time at $100 a pop aren't your style). Keep the
curves w/ some sensible tags and corresponding
table archives, and you can Frankenstein together
a "best observed" PE table and spark table by picking
the values based on the top line (one may be better
for midrange torque, another for top end HP, if you
approach it by simple scaling and shotgun the table
settings by some planned series).

robertbartsch

OK - I think I will experiment with the Beta version of the diagnostic program from LS1Edit.

Exactly what parameters should I log? I know i need to log TTrims Vs. RPM and that LTrims should be slightly negative....

Is there a comprehensive narrative to explain the parameters and how to tune?