Setting up an initial ignition timing table

[burgo90]

thats awesome thank you very much kirk

[burgo90]

right after having a play and a read from what i understand below 100kpa has to be more accurate than above. if this is correct then i beleave i am correct in thinking that i should have 6 or 7 kpa points below 100kpa on my spark map??

[MiseryQ]

Is this formula good for all Megasquirt versions (MSnS, EDIS, Extra...) or just for some of them?

When I paste the results in a MS2 vex it's actual.
Am I doing something wrong or are these for MSNS-E only?

[QldRobbo]

I must be missing something....

I'm assuming that 20kpa at 800rpm would be able idle, using the formulas above I get 31 degrees of advance at idle.... shouldn't this be more like 10 degrees?

[blk 02]

I must be missing something....

I'm assuming that 20kpa at 800rpm would be able idle, using the formulas above I get 31 degrees of advance at idle.... shouldn't this be more like 10 degrees?

I was wondering the same thing.... Maybe I missed something

Graham

[jsmcortina]

I must be missing something....

I'm assuming that 20kpa at 800rpm would be able idle, using the formulas above I get 31 degrees of advance at idle.... shouldn't this be more like 10 degrees?

Try more like 60-80kpa at idle.
The formulas are intended as a good starting point and will never be perfect.
Use whatever advance works on your engine, like you say 10-15 deg is more reasonable for idle.

James

[edmcguirk]

It seems to me that after you take into account CR, squish, chamber design, etc. the next items affecting advance are VE and turbulence.

It looks like below 3000 RPM the advance would be dictated by the number of milliseconds it takes to build maximum cylinder pressure from the ignition point to optimum peak cylinder pressure which is supposed to be about 15-20 degrees ATDC. That would give your ignition curve a slope downward from the advance at 3000 to the advance at idle.

Your advance is also affected by cylinder pressure so that you are adding "0.3° per 1 kPa drop". I would assume that if your VE is lower, you could use more advance right? Does VE have enough effect to be worth adding to the advance calculation?


On the other hand, above 3000 RPM your advance does not appear to be related to milliseconds to peak cylinder pressure, it appears to be a constant angular advance. I assume that is somehow the result from turbulence in the combustion chamber. Would VE have any effect above 3000 RPM? Like should advance start to rise again as VE falls off?


I like to have my calculations based on physics but I can't seem to understand the underlying rules of ignition advance.

ed

[Uncle Bob]

just to add a little data for others, motorcycles seem to run more timing than cars.

In general, a 2 valve per cylinder air cooled engine is usually happiest between 40-45 total timing.

water cooled 4 valve engines are usually between 35-40 total timing.

retarding timing with boost, I'd personally say 2* per psi is an awfully large amount of timing reduction. Assuming you're running 30 total timing, that means you'd max out your timing by 7 psi (15* timing)....if you still had another 13 psi to go, that would be interesting

Lot of variables in ignition timing, I realise these are just attempts at getting SOMETHING to work with....

[fastereddie1011]

I threw a timing light on my stock efi chevy truck and it idles at 20 deg btdc. If you rev it up slowly, the timing steadily climbs from 20 up to 36 deg btdc at about 3000-3500 rpm. But if you stab it from an idle it drops from 20 to 5 and then back up to whatever rpm your at so im going to try a map similar and see how it runs.

[SSDD]

Hi all can someone tell me what the equivalent of your US:

- regular - subtract 2°
- mid-grade - subtract 1°
- premium - no adjustment

is in Europe, we have here:

Unleaded 98
Unleaded 95
super

the super is lead replacement fuel that is basically unleaded with some sodium additive for older cars that cant use unleaded

Thanks
Steve