Is there a timing How-to?

[rang-a-stang]

79 Jeep, AMC 401, 6197427, 454 throttle body, $OE, Tunerpro RT, Iron heads, 87 octane fuel, ~9.5:1 compression, forged pistons, Mechanical advance is welded, vacuum advance removed

I am working on my timing tables but there is not a lot of info on how to tune for timing.

I basically started with a stock 454 timing table, added 4 degrees to the whole thing, then drive it looking for any knock retard. I take my history table for knock retard, remove the amount of knock retard from my main timing tables, and repeat the process.

Is this the correct way of tuning timing tables? Is there a better way?

I posted a similiar question here:
http://www.gearhead-efi.com/Fuel-Injection/showthread.php?8868-What-should-I-do-about-my-main-spark-table

[dave w]

Timing is not a simple how to. Adding or Subtracting a couple degrees of Spark Advance (SA) can have significant changes on how the engine performs.

Knock sensor tuning showing spark retard has the benefit of tracking the effects of adding or subtracting a couple degrees of SA.

Understanding RPM;s easy, Understanding Kilopascals (Kpa) is necessary to SA tuning. Engines under heavy load are more than 80 Kpa (the exception is an engine starting is at about 100 Kpa so keep the starting, less than 800 RPM's, SA close to ZERO). Engines under light load are under 40 Kpa. Tuning SA for Kpa above 40 and below 80 Kpa are the most challenging.

As a general rule of thumb, a light load on an engine (like cursing an empty pickup weighing 5400 lbs at 60 MPH on a flat level grade) can have more SA than an engine under heavy load (like a pickup towing a trailer on a 6 mile long 6% grade with the pickup and trailer weighing in at a gross weight of 12,000 lbs). The original 454 SA table was likely a compromise for the two expected uses mentioned above for a 454 powered pickup.

The plan to add 4 degrees the 454 table makes good sense. The challenge is the 454 knock sensor might not be optimally tuned for the AMC 401 bore?

History tables showing spark retard is a good tool, clearly showing what RPM's and Kpa's to experiment changing the SA. Changing SA only a degree or two at time is a good plan. Reducing SA might not be the best plan, sometimes adding SA is the best plan. SA tuning often requires several or maybe dozens of changes to figure out the correct SA.

dave w

[rang-a-stang]

Exactly what I was looking for! Thanks, Dave! That is pretty much how I have been working it; A little change here and there based on retard, then re-log and watch.

[mecanicus]

Hello,
could you succeed with your SA table.
My Cj7 with 401 and the 16196395 is running but it could do better in the range of 1000 to 2000rpm.
mecanicus

[rang-a-stang]

Hey @mecanicus, just posted how I built my table and what it looks like here:
http://www.gearhead-efi.com/Fuel-Injection/showthread.php?8868-What-should-I-do-about-my-main-spark-table/page2

[84Elky]

79 Jeep, AMC 401, 6197427, 454 throttle body, $OE, Tunerpro RT, Iron heads, 87 octane fuel, ~9.5:1 compression, forged pistons, Mechanical advance is welded, vacuum advance removed

I am working on my timing tables but there is not a lot of info on how to tune for timing.

I basically started with a stock 454 timing table, added 4 degrees to the whole thing, then drive it looking for any knock retard. I take my history table for knock retard, remove the amount of knock retard from my main timing tables, and repeat the process.

Is this the correct way of tuning timing tables? Is there a better way?Might try this. Works every time: https://www.thirdgen.org/forums/diy-prom/761049-spark-advance-table-example.html#post6301288

[rang-a-stang]

Might try this. Works every time: https://www.thirdgen.org/forums/diy-prom/761049-spark-advance-table-example.html#post6301288
Where have you been all my Spark Tuning life?! I wish I had seen this about a year ago!!! Honestly, I may start over using your table and comparing it to mine and see where I can adjust. This is awesome! I wish my truck wasn't broken and I wasn't leaving for 2 months!