To Advance or Retard

[Ksyrium11]

Dear all,
I've been bothered by this for quite some time, as far as I know,
ignition advance would mean moving the ignition timing further away
from BTDC and retard would be getting it closer to BTDC. After
referring to most of the maps uploaded here, I've noticed that most,
or rather all the maps that I've seen had their ignition timing
retarded. I've sent my car for dyno tune recently and the tuner
advance all the timings from 3-6deg. I gained only about 2hp with
this setting. I'm driving a 4g18 SOHC NA Engine.

My question is, where do most factory ecu set their ignition timing
at with reference to BTDC? I've came across one article which says
around 10 - 12 deg BTDC. Since most(or literally all) of the maps
here had their timing retarded, I would also like to remap the
piggyback with retarded timing. Any advice on this?

Thanks
Jeff

 

[Joeker]

Advancing the ignition means lighting the AF mixture sooner. In this case, as you put it "closer" to TDC.

Retarding igntion means lighting the AF after TDC. IN this case, ideally for Forced Induction applications.

You probably misunderstood the defination of advance / retard.

 

[Zeroed]

Well technically closer to or further from TDC depends on whether your ignition is originally ATDC or BTDC. :p

Advanced timing moving it away from BTDC would be correct.


As for the question, wouldnt retarded timing be benficial for only semi-heavily tuned engines? And only because they cannot safely support a more advanced ignition timing without pinging at high load...

Combustion would just take way too long to complete on higher loads for an average engine if the timing is retarded too much, IMO. Less piston wear though I suppose.

 

[SkYwAlKeR]

but if ignite BTDC, it will oppose the movement of the piston... thus, cancelling out the inertia and the explosion force...

i guess the range is from TDC to ATDC.... BTDC cannot be arr...

correct me if wrong...

 

[Zeroed]

At high revs ignition BTDC might be necessary, infact most modern engines idle with the ignition BTDC.
Else, before the combustion reaches its significant level, the piston has already travelled downwards by a lot.

Combustion is a kind of fluid movement which takes time to happen compared to the mechanical movement of the piston, hence ignition before TDC. But we're talking only very small degrees though, ignition still happens when the piston is very close to TDC.

At very high revs, piston travel speed is so fast its quite unbelievable... to the extent where an explosion cannot catch up. It is also on such principles of the 'slowness' of combustion and gas movements that valve overlapping work on.

Pinging / knocking is what happens with what you mentioned, the timing too advanced igniting the fuel to create an opposing force against the piston.

As far as I know lah, correct me if Im wrong.