BlueTwoToneCorvette

I have been tuning my 85, and today I changed the Spark Advance vs Rpm vs Load table to add 1-3 deg of spark advance over 800 RPM across the load level values. The datalog did not show the knock flag being set, but in all I didn't notice any real difference in a few 2nd/3rd gear WOT runs.

You can see I didn't make a big change. Anybody have experience with L98 TPI timing and what it likes? Thanks

Here is my modified table:
32 48 64 80 96 112 128 144 160 176 192 208
400 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04
600 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04
800 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04
1000 28.12 28.12 28.12 28.12 28.12 25.67 23.11 23.11 23.11 21.53 21.53 21.53
1200 29.89 29.89 29.89 29.89 29.89 27.42 25.06 24.96 24.96 22.32 22.32 22.32
1400 32.18 32.18 32.18 32.18 32.01 29.81 27.25 26.27 26.27 24.16 24.16 24.16
1600 36.75 36.75 36.48 35.69 35.16 33.24 31.99 30.68 27.78 25.93 25.93 25.93
1800 38.75 38.75 38.48 37.70 37.17 36.64 34.63 32.97 29.36 27.25 27.25 27.25
2000 39.72 39.72 39.45 38.40 37.87 37.08 35.33 34.28 31.39 28.30 28.30 28.30
2200 40.79 40.79 40.52 38.93 38.05 37.97 36.39 34.81 32.78 29.54 29.54 29.54
2400 42.11 42.11 41.59 40.00 39.03 38.15 37.35 36.30 34.71 31.46 31.11 30.94
2800 43.59 43.59 42.54 42.27 40.00 39.83 37.45 36.38 35.24 32.61 32.51 32.34
3200 47.28 47.28 44.91 44.12 40.08 39.83 37.52 36.30 35.16 32.79 32.69 32.61
3600 47.28 47.28 45.96 46.06 41.59 39.83 37.71 36.13 35.06 32.69 32.69 32.69
4000 47.28 47.28 45.96 46.06 45.54 42.00 38.85 36.13 35.06 32.69 32.69 32.69
4400 47.28 47.28 45.96 45.96 45.54 41.75 38.50 38.33 35.06 33.22 33.22 33.22
4800 47.21 47.21 45.89 45.79 45.54 41.47 38.23 38.23 35.06 34.53 34.53 34.53

Here is my stock table for 1985:
32 48 64 80 96 112 128 144 160 176 192 208
400 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04
600 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04
800 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04 20.04
1000 28.13 28.13 28.13 28.13 28.13 25.66 22.85 22.85 22.85 20.74 20.74 20.74
1200 29.88 29.88 29.88 29.88 29.88 27.42 24.61 24.61 24.61 21.09 21.09 21.09
1400 30.94 30.94 30.94 30.94 30.94 28.48 25.66 25.66 25.66 22.85 22.85 22.85
1600 35.86 35.86 35.51 34.45 33.75 33.05 31.99 30.94 27.07 24.61 24.61 24.61
1800 37.27 37.27 36.91 35.86 35.16 34.45 32.70 31.99 28.48 25.66 25.66 25.66
2000 38.32 38.32 37.97 36.56 35.86 34.80 33.40 32.70 29.88 26.37 26.37 26.37
2200 39.38 39.38 39.02 36.91 35.86 35.86 34.45 33.05 30.94 27.42 27.42 27.42
2400 40.78 40.78 40.08 37.97 36.91 35.86 35.16 34.10 32.34 28.48 28.48 28.48
2800 42.19 42.19 40.78 40.43 37.97 37.97 35.16 34.10 33.05 29.88 29.88 29.88
3200 47.11 47.11 43.95 42.89 37.97 37.97 35.16 34.10 33.05 29.88 29.88 29.88
3600 47.11 47.11 45.35 45.35 40.08 37.97 35.51 34.10 33.05 29.88 29.88 29.88
4000 47.11 47.11 45.35 45.35 45.35 41.13 37.27 34.10 33.05 29.88 29.88 29.88
4400 47.11 47.11 45.35 45.35 45.35 41.13 37.27 37.27 33.05 30.59 30.59 30.59
4800 47.11 47.11 45.35 45.35 45.35 41.13 37.27 37.27 33.05 32.34 32.34 32.34

antfarmer2

They put some thought in this why do you want to damage it?

BlueTwoToneCorvette

You are funny. GM thought they needed to be conservative so low octane gas wouldn't cause detonation problems in high heat or dense air conditions. A little tweaking and you can safely improve your L98 TPI over stock.

Churchkey

You can add some initial advance. The knock sensor will pull timing to avoid detonation if poor fuel, high altitude, desert heat or high engine load @ low rpm is encountered.

BlueTwoToneCorvette

I created my modified spark map off of a 1985 C4 map in this post.
https://www.corvetteforum.com/forums...nce-table.html

It is described as used with 95+ octane gas in cooler weather for racing. I used excel to create a new map using 1/4 of the cell to cell difference between the two maps. So if he added 10 deg of advance to the cell I added 2.5. Since the max I was adding was 3 deg I thought it was safe to try out.

I am adding the graphs of the maps. The 32-208 axis is your engine load, you have the RPM axis in the front and the spark advance axis going up. The stock map was rougher than I expected. The modified map looks smoother. Especially the middle load range. I guess in use, at full throttle/highest load (160-208+ load value) you would be in the last third of the table and that is the smoothest.

I am using Tunerpro RT, Moates APU1, and AEM Bosch wideband. The learning curve is steep for these tools, but they have worked perfectly for me. The APU1 especially, lets you do everything you need in one device.

bjankuski

You are fine, the 1985 will usually make max power between 34 and 36 degrees of advance at WOT. When I tune them I usually target 20 degrees by from idle to 2000 RPM and then ramp from 20 degrees to max advance from 2000 to 3000 RPM and then hold the max to the end at WOT. I see that your lower RPM regions (Both yours and the factory) are more aggressive then that but your upper regions are less aggressive, try what you are doing and log results and see what works best for you. I have not scanned a 1985 in a while, does it show you spark advance and timing retard? I did not think it did (But I could be wrong).

dizwiz24

yea you prob could make some more power on stock heads with more timing.

BUT

if you ever go with more efficient heads (ex. afr comp ported), then LESS advance *might* make more power.

i ran into this with my supercharged 93 on the dyno. i got more prob 15-20 more rw TQ around 2800-3400 rpm by retarding timing about 4 deg from factory.

-and no, my 'control' comparison wasnt getting knock activity . as i was monitoring the dynopulls with datamaster v351

the lsX motors run way less timing than gen 1 sbc due to a more efficient heAd/cam setup....

food for thought

Gibbles

For fun, do some searching for layer timing tables.

Really you want to setup the timing for the fuel and heads, but different timing tables may give you some reference to work with.

vader86

Advancing timing tables is how these aftermarket chips claim to make the power they claim. They're not doing much else.

But they've been proven to not make what they advertise, time and time again. While I think there is some benefit to playing around with timing tables, I don't think the gain is appreciable. Real power increases require more air and and out of the restrictive engine intake and exhaust.

Tom400CFI

Of course an OEM tune is going to be safe. Has to be. When we change the operating criteria (engine temp, air temp, quality of fuel etc), then there is opportunity to explore more timing.


Increasing altitude lowers the possibility of detonation...not raises it.

GREGGPENN

BlueTwoToneCorvette: How do you KNOW what the stock OEM timing values ARE? Did you pull them from your ECM or find a table on the internet?

FWIW, I've found 3-4 versions of the 89 spark table -- and that's on sites that sell tuning software. Are their really multiple versions or are some sites "wrong"?

Point is, changes you make might not necessarily be felt UNLESS you try what you THINK is supposed to be there FIRST. IOW, load what you think is a stock table and see if you can tell a difference vs your stock ECM?

It may be possible your changes ended up closer to what's actually WAS in the car.

FWIW, changes on the 89 BINs have as much as 5 degrees difference in top row timing. Though one is for an automatic and the other for a stick, it doesn't make sense. (Unless GM designers noticed differences in how spark is "needed" above the peak of long tubes?)

When you look around, you'll see there are reasons that more/less timing CAN be better. IOW, more timing isn't always better. THERE IS AN IDEAL AMOUNT for specific rpms/fuel/etc... in YOUR car. It has to do with flame-front speed, turbulence, compression, etc...

If you REALLY want to know what makes the most power in YOUR car, put it on a dyno and SEE the results of changes.

Tom400CFI

This or the drag track. Something objective. GREGGPENN is right that it depends on the car/engine, what has been left on the table.

BlueTwoToneCorvette

The bin should be stock, I pulled it from my chip. The car has never been modified before.

Thanks, I appreciate the input. I'll try 34-36 in the higher load region.

But you are right that I need to have 3 or so bins set up with slightly different timing, then go try them out on a dyno. I don't know if I could feel a difference just driving.

Vader's comment was interesting, as chip upgrades are supposed to do something. Who knows if they are are a scam really?