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I am currently trying to do a little fine tuning of my spark table in tuner pro. I have a generic auto parts store rebuilt 350 with 70s smog era heads with a small cam. In other words nothing special. Currently the spark table is very basic. My question is about the part throttle spark timing. From what I have read the leaner the mixture the more timing you want. It takes longer to burn a leaner mixture so you want more advance. So this would be one of the few scenarios where you would want more than 32-38 degrees of total timing you would max out at normally. From what I have seen you want around 50 degrees of spark timing at part throttle low kpa (high vacuum) is this correct? I have no knock sensor so I will stay on the safer side of things. Below are some of the spark table fundamentals as I understand them. I am not as concerned about the exact numbers in the spark table. I am more wondering if my table is taking the right shape. Lower kpa less load and more advance. I believe I am on the right track just want some people who know more than me to confirm that I have the right idea.
Spark Fundamentals
Stock SBC 350 Total Timing: 32-38 degrees
Stock SBC 350 Initial Timing: 8-12 degrees
Total Timing all in at about 3000-3500RPM
Richer Air Fuel Mixtures: Require Less Advance
Leaner Air Fuel Mixtures: Require More Advance
Low KPA Number: High Vacuum Throttle Open Less
High KPA Number: Less Vacuum Throttle Open More
From what I have seen you want around 50 degrees of spark timing at part throttle low kpa (high vacuum) is this correct?
completely depends on motor and fuel and head chamber characteristics.
its kinda hard to do without a way to measure changes and maybea knock sensor
you can use kpa and throttle open positions during cruise scenarios to see what timing gives lowest kpa and lowest throttle opening to maintain a speed but its hard to do sometimes on streets of varying conditions
but your trends are ok. Lower kpa lower load so more timing can work
lower rpm less timing. More rpm more timing typically.
Thanks for your input Orr89RocZ. I have went ahead and made some adjustments to my spark table and took the car for a spin everything seems to be working fine with the new spark table that I have created. No knock that I can hear, and I am aware that there is knock that is you cannot hear. I tried to keep things conservative. If there are any other suggestions on changes I should make let me know.
Mostly a driver preference, the 20 KPa column can be reduced to get the car to slow down better when off the throttle. The IAC throttle follower can also be changed to suit the driver.
10-10-2018, 09:47 PM
