Gary Z

These plugs each saw one 150-shot (0.062 jet) quarter-mile pass followed by an easy downhill coast back to the pits. Two plugs (cyls 5 and 6) from each of two runs are pictured. These were my first 150-shot passes and the car ran well – 131 mph trap. Previous best was 129 with 125-shot. Both plugs from the first run looked rich to me so I removed fuel for the second run. My wideband showed run1 afr 12.0 and run2 afr 12.2 WOT timing was 18 degrees (24-6) for both runs. I have two questions: 1) Was the second run too lean? 2) Should I put back some timing (pull less)?

The pictures from left to right are: plug5 run1 / plug5 run 2 / plug6 runs 1and2

Thanks, Gary

ATVracr

iTrader: (5)

1st pic slightly rich, 2nd plug slightly lean.
1st pic shows timing mark on tip about 1/8th inch, 2nd pic just starting to put a timing mark on it.

you are in the ball park, which one ran faster MPH?

From here I would make small changes and what ever combo of fuel and timing runs the most mph is where you want to leave it.
There is no perfect plug or magic number, every combo is different and will want slightly different fuel & timing numbers.

Carter01

iTrader: (11)

Pic 1 looks rich, good call. Pic 2 looks lean, typically when you lean it out you need to pull timing as well (to be safe until fuel is close). Focus on the fuel first then the timing. Don't chase the timing mark on the strap, focus on mph. Once the fuel is right and the timing is low then i would add back in 1 degree at a time until it barely shows up on the strap. Then as you monitor mph keep adding a degree until mph stops climbing, when it stops climbing then back out 2 degrees. Make another pass and if it runs the same within .10 leave the timing alone.

Carter01

iTrader: (11)

tree'd by ATV!!!

ATVracr

iTrader: (5)

I can cut a lite when I need to.

Gary Z

The second run was slightly faster (131.0 versus 130.6) I'm running out of gear and was hitting my 7100 rpm nitrous cutoff in the traps so speed may be inconclusive until I get a bigger tire.

Thanks to you and Carter for your comments and suggestions. You've answered my questions and then some.

Gary Z

I hadn't thought about this point and I want be be sure I understand it. Here is my reasoning: Within limits, richer burns slower so more timing advance is needed. Conversely, leaner needs less advance (pull more). Is this correct?

Edit: A more direct way to think about this starts from the familiar fact that more nitrous causes a faster burn hence less advance (pull more) is needed. More nitrous -> more oxygen -> leaner mixture -> pull more. I now see the gap in my thinking. I knew we need to pull more timing as we up the shot. I wasn't making the connection that a leaner mixture is equivalent to more nitrous.

And thanks much for the recipe for going faster.
-Gary

ATVracr

iTrader: (5)

You are correct... when you lean it out pull timing.

Also I would make sure you pull #7 & 8 plugs and tune off of them, they will be your hottest plugs most of the time on a LS1 motor.

Gary Z

I decided to circumcise another plug. Here is plug 6 run 2 - lean like 5.

Gary Z

Does this rule apply for both wet and dry? I'm dry by the bye. Dual nozzles downstream from MAF sensor.

camscam02

iTrader: (21)

I'd like to add there looks to be very little heat on the plugs from the second pass. How much did you change the fuel side?

Gary Z

I changed Commanded AFR from 10.0 to 10.2, wideband went from 12.0 for run 1 to 12.2 for run2.

3YLSYKR

iTrader: (2)

Nice color of plugs.