Max spark advance

[cshuman]

I'm confused. I see where most crate engines state to not set the max advance beyond 32 degrees. However most all the tunes I see in tuner pro are above 40 degrees. Can someone explain?

[B52Bombardier1]

Hello,

GM does not want to risk their engines to warranty claims so they recommend less spark advance. Sure, they can take more but the risks increase for lots of other reasons that GM can't control - poor quality low octane fuel, increases in compression, carbon deposits in the combustion chamber, nitrous oxide usage, turbo and supercharging.

Rick

[cshuman]

Hello,

GM does not want to risk their engines to warranty claims so they recommend less spark advance. Sure, they can take more but the risks increase for lots of other reasons that GM can't control - poor quality low octane fuel, increases in compression, carbon deposits in the combustion chamber, nitrous oxide usage, turbo and supercharging.

Rick

I understand that for a crate engine manufacturer, but the factory tune for a stock L98 has the max advance at 42. And has the spark table set up to that maximum. Unless the spark table is different to what the timing is actually putting out. Does anyone know that answer? I assume if the spark table in tunerpro shows 42 it means that is the actual timing requested?

[steveo]

every engine is different with regards to timing advance tolerance at wide open throttle or part throttle, so comparing the timing from one engine to another isn't really too helpful. also i don't think an L98 has 42 degrees of all in timing advance at wide open throttle. are you just looking at cruising range?

besides the differences between engines, there's a big difference between optimal heavy load advance and light load advance

a more efficient engine will often require less advance to make peak torque

some engines surge with lots of advance at light loads, and some engines smooth out


Unless the spark table is different to what the timing is actually putting out.

different types of distributors/sensors have different levels of consistency with actual engine events, and sometimes the spark table needs to be designed around the fact that a few degrees of timing can be gained or lost from the distributor not being perfect. newer engines with accurate cam and crank sensors are usually pretty damn accurate, your ol' l98 distributor, not so much.

[cshuman]

every engine is different with regards to timing advance tolerance at wide open throttle or part throttle, so comparing the timing from one engine to another isn't really too helpful. also i don't think an L98 has 42 degrees of all in timing advance at wide open throttle. are you just looking at cruising range?




No, if you are familiar with tuner pro there is a setting for max spark advance, with the stock tune it is set at 42 degrees. The spark table is different, based on what you are saying below, in different areas of load and rpm, but has some of the settings as high as 42 degrees.



besides the differences between engines, there's a big difference between optimal heavy load advance and light load advance

a more efficient engine will often require less advance to make peak torque

some engines surge with lots of advance at light loads, and some engines smooth out



different types of distributors/sensors have different levels of consistency with actual engine events, and sometimes the spark table needs to be designed around the fact that a few degrees of timing can be gained or lost from the distributor not being perfect. newer engines with accurate cam and crank sensors are usually pretty damn accurate, your ol' l98 distributor, not so much.

I agree with the above

[steveo]

No, if you are familiar with tuner pro there is a setting for max spark advance, with the stock tune it is set at 42 degrees. The spark table is different, based on what you are saying below, in different areas of load and rpm, but has some of the settings as high as 42 degrees.

i'm pretty familar with tunerpro, and that's like saying if you are familar with books, you'd know that books are about dogs, because once you read a book that had a dog in it.

tunerpro doesn't really know what spark or fuel is, it's just table/constant editor. the max spark advance comes from your particular xdf definition file, and it's not guaranteed to be there (there are plenty of XDFs that don't have it)

as far as spark advance goes another thing to consider is that they might be jacked up pretty high in cruise range for emissions purposes and economy numbers, whereas crate engines can easily be labelled 'for offroad use only' or 'for pre 1980 only' or whatever, so they'll have quite a different tune...