jrnorman

I have an essentially stock O2 Z-28 and using HP Tuner, at WOT at around 4200 rpms and if the spark is much above 20.5 degrees, the KR comes in with enough reduction to get back to about 20.5 degrees. When it hits it often audible sounding like a can full of rocks.

A friend has a highly modified 98 Z-28 with cam, headers, head work, high capacity radiator and 160 thermostat, but stock compression and via HP Tuners he can get 29-30 degrees advance without knock but max power seems to come at 28 degrees.

We have tried everything we can think of to try to get mine higher like larger capacity radiator and 160 thermostat without much luck - at most 1 degree above stock. We are about to come to the conclusion that the advance readout by HP Tuners is somehow on a different basis for 2002.

Does anyone know why we are having this anomaly? Is there a difference in VCMs to account for this?

Also while I am here can anyone tell me if the KR I get from 1500 to 2500 rpms at about 33% throttle and mild acceleration HP Tuners reports large reductions like <4 degrees. But I don't feel a thing or hear anything. I am beginning to think this is a something mechanical like an exhaust rattle or something. The Knock settings are all stock.

Any words of wisdom about that symptom?

Thanks in advance for all your words of wisdom!

jimmyblue

iTrader: (11)

Try looking at misfires, maybe you have a single-cylinder
lean problem or something.

The O2 voltages would be about 900mV, all happy?

Corrupted MAF (ported, K&N spooged. etc.)?

Mentioned cooling mods but not the fan settings.

gameover

your timing is on the low side, but i wouldn't call it abnormal. Some engines just won't take the timing others will. Short of tearing down the engine and inspecting everything, i doubt you will find out why (unless you got a bad tank of gas).

Oil contamination/blowby, carbon deposits on pistons, variations in compression ratio, blocked injector, fuel pressure issues, lean fuel mixture, bad gas, crank reluctor wheel moved, head gasket issues etc.

Tuners see this variation between engines quite often and they all have at least one story about "the engine that just wouldn't play by the rules"...

Chris...

SSpdDmon

iTrader: (10)

I think it has to to with the cam and 241 head design. I have to run stock timing until about 4800rpm to avoid knock retard. But, with the stall I'm not there that long. This is a bit conservative....it's what I'm running now:

............(.76grams/cyl)..(.80grams/cyl)
3600 rpm - 17.995606.....17.995606
4000 rpm - 17.995606.....17.995606
4400 rpm - 18.500977.....17.995606
4800 rpm - 19.489746.....18.259277
5200 rpm - 21.247559.....20.017090
5600 rpm - 23.247070.....21.752930
6000 rpm - 25.004883.....23.510742

jrnorman

SSpdDmond, your advance is about the same as mine, maybe a degree or so less in places and you have an 2002 so maybe it is a characteristic of the 2002 LS1 or the PCM or some combo.

I don't think I have any problems with O2 sensors or MAF because the car dynos on a Dyno Dynamics at 291 HP (these dynos do not use the spinning drums and generally report 15 to 18% lower numbers than the DynoJets which is consistent with results previously on a DynoJet) and peak torque of 304 with an steady average AFR of 12 from 1500 to 6000 rpms using the Dyno's Wide Band. So the car seems to be performing about as it should but with only around 20 degrees advance at WOT at 5200 which on this near stock car is around 0.7 g/L DYnAir.

jrnorman

jimmyblue

No misfires reported and cylinder balance is 95 on all cylinders, could be a single injector not opening I suppose but the over all AFR is a steady 12 from 1500 to 6000 rpms at WOT.

O2 voltages are pretty steady 930mV during WOT dyno pulls.

MAF is original stock, never modified. Did run a K&N filter for a while but switched back to Fram mainly for convenience.

The fan settings have been lowered to 196 for fan 1 (low speed). This is somewhat higher than I could run them but I have A/C and live in Houston and if I lower it any more driving around town the low speed would never turn off.

For the dyno runs I forced the fans on at high speed and of course there was a big fan flowing into the front of the car, but by the last of 4 pulls the ECT was 194 degs. Ambient temperature was around 84 degrees. That is down considerably from the pulls back in April before the cooling mods the last pull was 216 degs, ambient 81 degs.

Do you see anything abnormal with this?

white2001s10

iTrader: (4)

When an engine doesn't play by the rules it generally means something is wrong... usually mechanical.
Do the more obvious checks first. Look for a hot plug or failing injector.

Sometimes it comes down to things like a clogged coolant passage in a headgasket, or a collapsing lifter.
It might take a while to figure out.

Does the engine do this when it's still cold?
How about when the octane is increased?

SSpdDmon

iTrader: (10)

I live in MI (where it's always cold - don't think we've hit 80* yet this year) and I've been having the same issue since the car had less than 30K miles. There's a reason why our timing tables look so drastically different than the older years. When we have different heads, different cam, different intake, different injectors....I'd expect a different spark curve/graph, wouldn't you? After all, the stock curve/graph can't be that wrong....the 01's/02's are supposed to make more power in stock form according to the numbers. Why would the General pull back the timing so much if there was more in it?

white2001s10

iTrader: (4)

No I wouldn't. They aren't that different.

NicD

iTrader: (7)

It's like every other 01-02 f-body I have ever seen. None of them take much more timing than what they come with from the factory. Chalk it up to different heads/cam or whatever. Looks normal to me.

jrnorman

Maybe the question should be broaden to does anyone know of or have a stock or near stock 2002 that can carry more spark advance than about 20 degreess at WOT and around 4200 rpm?

Seems to me that all the replies from other 2002 owners have the same results.

ringram

When all is said and done the less timing you need the better.
Good heads mean less timing as turbulance etc is maximised, hence the vortec fast burn style of head for GenI etc. You dont need as much timing.
Unless you check on the dyno you wont know if you need or want more or less timing. You can get close but thats all.
Afterall why start burning fuel when the piston is still rising in the bore and slow its rise down if you dont need to? Fuel octane also has an effect along with the rest of the intake and exhaust system.

white2001s10

iTrader: (4)

So are you running your car on 87 octane to take full advantage of this?

98redorangeta

iTrader: (10)

I just put over 30* in a 2002 cam only car and never had kr could have probly put more but it want helping the power any so we lowered it back down.

white2001s10

iTrader: (4)

How were you testing the power output?

98redorangeta

iTrader: (10)

I had the car on a Dyno

fast98

iTrader: (16)

my 98 can't handle more then about 20 at wot if it makes you feel better

white2001s10

iTrader: (4)

That's what I thought.
That explains why you saw what you saw with the advance.