4.8 Spark Tuning

[67Wagon]

Hi Everyone,

I have my car running pretty well at this point and want to finalize my spark table. I currently have the stock 2005 4.8 tables loaded with a couple degrees added as shown below. First question I have is why the factory has negative values in the spark table? Second, the engine feels a little jerky when accelerating/decelerating at low speed and curious if it may be in the timing table and the deltas between idle and main spark table, but again it appears the factory has this as well. Any input would be appreciated.

Engine is stock with the following exceptions:

• Summit Stage 1 Cam
• headers
• dual exhaust w/o CATS. No Emission Equipment
• Car weighs 3000 lbs.
• K&N air filter
• Daily Driver in 67 Nova using mainly 87 octane

Main
spark table.png

Gear/Park Idle

Park-Gear Table.png

[SiriusC1024]

Negative values are there to maintain combustion stability.

Good observation about the transition between main and idle tables. I had that problem, too. matching them resolved it.

You're probably wondering whether to match negative numbers to the idle table. It's not anything to worry about because you'll never jump into them right off idle. It's more important to blend the idle/main transition where it occurs. That's usually up to around 1000 rpm by 0.44 g cyl air.

[kingtal0n]

A little jerky with a cam if you have 5.55 in the "normal" table under a fuel tab. Try changing to 6.65 and see if that helps where the coolant temp is warmed up.

Spark timing the map looks very smooth. But at low RPM there can be some large jumps from one cell to the next- see if you can smooth that out.
Also 24 around idle is too much, it may feel like a misfire or jerking. Try 18* to see if that helps around idle.
and make sure the a/f ratio isn't jumping around at low speeds. Keep the VE table as smooth as the spark is.