bowtieman81

iTrader: (35)

I just bought HPTuners and am learning to use it (slowly). I have a 2000 TA with basically the stock tune. I deleted the EGR setup, so in the EGR timing advance table I zeroed everything. I have not messed with any A/F stuff yet.

Looking at the high octane timing table I notice the timing is pretty good until about 3800 rpm. At about that speed the timing goes from about 27-28 degrees down to 23-24 degrees and stays that way until 4800 rpm or so. I am just wondering why this is? Why does the timing drop off suddenly right around the time where the engine starts making good power?

Well, I figured I could pick up a little power so I bumped the timing up 2 degrees in the area where it dropped off. Did a WOT run and got plenty of knock retard. Went back in and put the timing back to stock.

horist

I believe the purpose is... that RPM range is peak torque, peak torque = greatest cylinder pressures, higher cylinder pressure = more prone to pre-ignition/detonation ... so they back the timing off at peak torque

txhorns281

iTrader: (12)

From stock you could stand to bump your timing a little and then correct A/F to avoid KR. I've always ran about 30 degrees of timing at WOT and 12.8-13.2 A/F. Car's always ran really strong!

P Mack

iTrader: (6)

Conspiracy theorists say this was gm's way of keeping the f body slower than the vette. It is right at peak torque though.

bowtieman81

iTrader: (35)

Thanks for the responses; horist that is basically what I thought. Didn't occur to me GM would do this on purpose so as not to steal the vette's thunder.

When I did bump up the timing I got some bad knock retard right in that rpm range. Is that because my A/F ratio is too rich (I should point out that I just put LT headers and ory on 2 weeks ago)? I am also basing my A/F being too rich statement off of the stock O2 sensors. They read 905-915 mV at WOT pretty much the whole rpm range.

I plan to get a wideband (probably the LM-1) fairly soon, but for now I am just trying to understand how the factory tune works and why it does what it does.

jimmyblue

iTrader: (11)

With headers you can't make too much of the in-car O2s.
Those voltages could be saying anything from <10:1 to
13.5:1 depending on exhaust gas temp (unknown).

Headers improve extraction and cylinder filling, so a car
may not be able to tolerate more advance while a stocker
like mine took 6 degrees without complaint. Better charge
needs / wants less spark.

Whatever GM's reasons were, you've already stepped off
from their basis. Don't look back