Spark advance questions for boost tuning

[barbermi]

Hi again all.

I'm on the prowl for good information again. I have hired a dyno in 2 weeks time and plan on finishing off my VE and Spark tuning. Im 100% confident doing my VE so that is easy and will be done first. My questions today are based around spark tuning.

I am running an LS1, maggie 1900 supercharger, 224/224/112 cam, dual 3" exhaust, 11.5 PSI boost and AFR's are sweet at 11.5 on boost

I am currently using the stock Holden LS1 high octane table and I would like to know a few things about it.

Firstly why does the spark table have 3 dimensional tendencies until ~ 0.8g/cyl and then timing is only impacted by RPM changes not g/cyl. Please keep in mind im only talking about the spark table at this point. I understand a0010 will pull timing based on MAP but why is this the preferred method of tuning boost?

Secondly after 0.8g/cyl on most stock Holden tunes the timing will increase somewhat to 2800RPM or thereabouts followed by a dip and then increase again until peak RPM. I have looked at HSV tune files and some do not have the dip like a stock commodore tune. Why is this so?

Can anyone suggest a good tune I can use the high octane table from as a starting point for my spark tuning. I understand nothing will be perfect but the closerthe better to save me dyno time.

Thanks for your help.

Mark

[LastCall]

Hi again all.

I'm on the prowl for good information again. I have hired a dyno in 2 weeks time and plan on finishing off my VE and Spark tuning. Im 100% confident doing my VE so that is easy and will be done first. My questions today are based around spark tuning.

I am running an LS1, maggie 1900 supercharger, 224/224/112 cam, dual 3" exhaust, 11.5 PSI boost and AFR's are sweet at 11.5 on boost

I am currently using the stock Holden LS1 high octane table and I would like to know a few things about it.

Firstly why does the spark table have 3 dimensional tendencies until ~ 0.8g/cyl and then timing is only impacted by RPM changes not g/cyl. Please keep in mind im only talking about the spark table at this point. I understand a0010 will pull timing based on MAP but why is this the preferred method of tuning boost?

Secondly after 0.8g/cyl on most stock Holden tunes the timing will increase somewhat to 2800RPM or thereabouts followed by a dip and then increase again until peak RPM. I have looked at HSV tune files and some do not have the dip like a stock commodore tune. Why is this so?

Can anyone suggest a good tune I can use the high octane table from as a starting point for my spark tuning. I understand nothing will be perfect but the closerthe better to save me dyno time.

Thanks for your help.

Mark

I had a similar set up before, just an older Maggie. I believe timing is determined by air mass, not rpm. WHat table are you looking at?

Usually, there is a dip in timing in peak torque, that may be what you are seeing.

Timing for each set up will be different, and fuel dependent. I ran 12-13 degrees in boost on my 11.1 compression motor on 91 and 17-18 on the same motor at 9.5:1 compression same fuel. I have always used the high octane table for all timing calculation, but it makes it a dog out of boost. So I am going to add more timing into high octane table and take it out in boost using the timing boost table. Hopefully that will help.

[barbermi]

Thanks LastCall.
Very helpful indeed. I now understand why there is a dip in the spark table. Im talking about the high octane table also. Currently im getting 8-10 degrees final spark advance after all of the spark modifiers have done their work. Plenty of room for improvement!

Thanks again