Spark Tuning

[Rally Smith]

How does a person drive when tuning spark tables?
I can drive light and get zero's all over the place but once I get on it a bit (less than 80% throttle) I'll get numbers in those same cells. I can keep taking timing out but still get numbers at times in those cells. What am I doing wrong?

Thanks,

[steveo]

by 'numbers' do you mean knock count or knock retard? what ecm are you tuning, and what engine?

if you're monitoring for knock counts, you're generally tuning heavy loaded throttle (in the 80kpa+ range). you need to drive in a variety of conditions to tune timing to the limit.

you generally wont get useful knock information at light throttle cruising range, a lightly loaded engine is really hard to get knock from. you're shooting for 'smooth and efficient' which generally is the point of greatest vacuum but no further, but also is by feel.

if removing a decent amount of timing in an area doesn't remove the knock counts, it's probably false knock. false knock can be engine harmonics that your knock filter isn't equipped to deal with... valvetrain noise, exhaust tapping against the frame, cam drive noise, whatever. if false knock only exists in a single area, some ecms let you disable knock retard in that area.

[Rally Smith]

by 'numbers' do you mean knock count or knock retard? what ecm are you tuning, and what engine?

if you're monitoring for knock counts, you're generally tuning heavy loaded throttle (in the 80kpa+ range). you need to drive in a variety of conditions to tune timing to the limit.

you generally wont get useful knock information at light throttle cruising range, a lightly loaded engine is really hard to get knock from. you're shooting for 'smooth and efficient' which generally is the point of greatest vacuum but no further, but also is by feel.

if removing a decent amount of timing in an area doesn't remove the knock counts, it's probably false knock. false knock can be engine harmonics that your knock filter isn't equipped to deal with... valvetrain noise, exhaust tapping against the frame, cam drive noise, whatever. if false knock only exists in a single area, some ecms let you disable knock retard in that area.

Steveo, thanks for the reply.

Yes, numbers meaning knock retard. I am running $0D, BJYM, 7427? 350 TBI out of a 95 GMC K1500.
I'm just trying to get the spark table optimized as much as I can before going back to the VE Table again.

[Fast355]

Steveo, thanks for the reply.

Yes, numbers meaning knock retard. I am running $0D, BJYM, 7427? 350 TBI out of a 95 GMC K1500.
I'm just trying to get the spark table optimized as much as I can before going back to the VE Table again.

I have given up using knock sensors for tuning with the small block chevy. Plug cuts are a much more reliable method. I have pulled timing until it barely runs and still seen knock counts on more than one engine. Disabled knock, put in a timing table that resembles what a typical small block runs well on and VROOOOMMM. TONS OF POWER! The knock sensor in my Express is disabled, the high and low octane timing maps are set the same, and the thing runs great.

[Rally Smith]

Fast, I don't want to sound like a moron but, what is a plug cut? Is that another way of saying disabling the Knock Sensor? Any suggestions or sample Spark Map Table I could give a shot with? Thanks for the info!

R.S.

[CFI Z51]

I have found the modified timing table in BJYL 700R4 bin a good place to start...

[Rally Smith]

I have found the modified timing table in BJYL 700R4 bin a good place to start...

Cool, thanks CFI.

[Fast355]

Fast, I don't want to sound like a moron but, what is a plug cut? Is that another way of saying disabling the Knock Sensor? Any suggestions or sample Spark Map Table I could give a shot with? Thanks for the info!

R.S.

Plug cut is a method of tuning, involving cutting the spark plug apart and looking at it under a magnifying glass.

[Rally Smith]

Plug cut is a method of tuning, involving cutting the spark plug apart and looking at it under a magnifying glass.

Well, I'm not Bill Nye so I'm thinking that this is not an option.

How would I disable the Knock Sensor?

[steveo]

if you have consistent fuel quality and a conservative timing table with a pretty good tune, there's really no need for a knock sensor. personally i disable mine except for very high MAP; right now it's disabled completely because my engine mounts are worn and my exhaust can touch my k-member on occasion.

before you totally give up on knock detection; keep in mind that substantial lean spots will cause pinging and hit your knock sensor too, as will misfires.