% difference between the low and high octane spark tables??

[smslyguy]

I have my high octane tables all set up. Was just woundering for safety reasons what the % difference is between the high and low? Would one be able to assume that -2 to -3 degrees of timming in the low octane table is enough if he came across a tank of bad gas??

[joecar]

I think 2-3 degrees is not sufficient, I would have say 10 degrees difference.

[gmperformancecentre]

I agree with joecar,i generally run 8 to 10 deg lower on my customer's cars

[smslyguy]

I agree with joecar,i generally run 8 to 10 deg lower on my customer's cars

Would that be in all tables all across the board? Or just under the load tables??

[Taz]

I have my high octane tables all set up. Was just woundering for safety reasons what the % difference is between the high and low? Would one be able to assume that -2 to -3 degrees of timming in the low octane table is enough if he came across a tank of bad gas??

Not sure what your intent is - by wanting the spark tables that close together. The OEM spark strategy is to run off the High table as much as possible, while blending the two tables (or spark ranges) when necessary.

If you log GM.ASPARK (High / Low Octane Adaptive Spark Scaler) in a well tuned Gen III engine - this PID is often 100% (full High spark table) all of the time. If any knock is encountered the PCM blends the High / Low spark table values to mitigate knock. This blending may be a 95% bias toward the High table, etc. - the PCM does not run off strictly the High spark, or strictly the Low spark table.

Given this dynamic approach to spark advance, there is really nothing to be gained in a street driven vehicle, and arguably some risk involved - in calibrating these tables too closely together. In a competition vehicle, where consistency is paramount, and some wear / damage is to be expected - removing flexibility from these tables may be necessary.

I generally run a 10 degree spark margin of safety between the two tables - knowing that the PCM will attempt to run off the High table as much as possible, and blend / bias the spark advance when necessary.


Regards,
Taz

[Sid447]

As long as the tune file knock tables aren't corrupted,

I don't see why it would matter what margin there is between the Hi and Lo. The engine will still protect itself using the knock tables strategy even when both are the same value.

HSV GTS cars ran "single spark" tables for years (both Hi & Lo were identical) were Speed Density Closed Loop and were sold with a full factory warranty the same as any other factory car.

[Taz]

Hello Syd,

Holden calibrations do differ from those of North American based vehicles. From what I understand in Austrailia you can purchase 98 octane "at the pumps" and even E85. In my area there is no E85 period, and 87 / 89 / 91 octane (with very slight variance) is your choice at the pumps.

The difference in fuel alone would allow for very different spark strategy between Austrailia and Canada.

Have you ever put low octane fuel in an HSV GTS and logged knock and spark advance ? Does the Holden calibration remove a set amount of spark ? Does it blend between spark tables ?

With the High / Low spark table strategy used in North American vehicles the PCM attempts to always use the High table. When knock is encountered it will blend / bias between these 2 tables - which serves to remove the minimum amount of spark advance (and no more) to stay out of detonation.

As I stated in my previous post, a well tuned Gen III will often use the High table 100% of the time when logged. Also given that the PCM blends the tables on a percent basis, it wouldn't matter if the Low table was significantly less than the High - as these Low values would never be used with consistent quality fuel.

Getting a tank of contaminated fuel, or old fuel, etc., will make any extra margin in the Low tables invaluable.

Just my opinion ... as a cautious person.


Regards,
Taz

[joecar]

The HSV GTS cars also ran speed density... so I'm wondering if both spark tables were still functional (i.e. instead of defaulting to the LO table in the absence of the MAF sensor)...?

Can anyone illuminate me on that...

[Blacky]

The HSV GTS cars also ran speed density... so I'm wondering if both spark tables were still functional (i.e. instead of defaulting to the LO table in the absence of the MAF sensor)...?

Can anyone illuminate me on that...

Its been while since I had my GTS. They were calibrated as speed density tunes from the factory and I'm pretty sure like Joe said they defaulted to the low spark map. That would explain why the HSV calibrators felt the need to pull the low spark map up to match the high spark map.

Shameless plug... EFILive's speed density custom OS for the LS1 restores the full high/low spark mapping for SD tunes for the LS1.

Regards
Paul

[Sid447]

Hi Taz,

I didn't realize Canada used the same R+M /2 octane rating as the U.S.(?) ....as those numbers seem very low for RON Unleaded.

The HSV cars (and any individual who used the factory OS and went "maf-less" as it was termed in Oz) were known as single-spark tunes and used to work understandably off the LOT. There was no Adaptive Spark.

I ran it for a few years (2003 to 2005) and only ever remember encountering burst knock (i.e. quick or rapid tp changes, such as changing gear) which caused an instant timing reduction and a return to "full" timing within a few seconds.**

**Although I mentioned the knock tables were stock, control of the sensitivity and nature of how KR worked was found by manipulating the settings in tables {B6224 and 6225} so that it could be made as soft, hard, quick or slow as you wanted.

The car ran very well in a pretty severe desert climate and encountered no mechanical problems. Though it must be said it only ever used a maximum of 24-25 degrees in the WOT part of the H/LOT (just like the HSV factory tunes) and also a diet of 98 RON UL initially and 95 subsequently when it was found use of 95 caused no KR under any driving conditions after a month or so of careful logging.