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from what i understand of n/a engines they can have initial static timing, centrifugal advance and vacuum advance pre ecu controls.

my EA82T has an inital of 20 degrees presumably for the low 7.7 comp ratio

it also has vacuum advance unit (does it retard also under boost beyond back to initial?)
i think it has centrifugal advance inside
it also has a knock sensor to retard timing as much as is needed electronically overie of igniter i suppose

did these turbo engines start at 20, increase with vacuum and centrifugal until boost ?
know the timing advance/retard theory for these? or seen it in action on a dyno and timing light ?

part of the knock sensor test is to tap engine block ten times to see if timing is retarded by ten degrees. one degree per tap ?

Jono you could answer many of these questions by disconnecting the manifold communication tube and alternatively sucking and blowing through it . By this I mean with the dizzy cap removed so you can see the breaker plate rotating one way and then the other .
Your WSM should tell you if the base idle speed timing is set with the dizzy's tube connected or not .

The theory behind having more initial advance in a low compression motor is that its dynamic or effective compression ratio is lower than a similar engine with a higher static compression ratio . By the static CR I mean the measured CR . By dynamic (effective) CR I mean what the cylinders actually get when their breathing is restricted by the throttle valve etc .
Lower effective compression means lower charge air density so lighting the fire early ie 20 degrees betore top dead centre means more of the air and fuel can be turned into thermally excited cylinder pressure . Most engines like their peak cylinder pressure to be approximately 15 crank degrees past top dead centre (TDC) so basically firing the piss weak low CR mixture earlier achieves this because the burn (and pressure rise) is slower . The higher CR engine has more to burn and burns faster , if you set these to 20 deg BTDC the pressure rise would be too close to TDC and some of the pressure energy is lost trying to compress the piston and rod .
When you retard the ignition timing you are moving the pressure peak further forward into the power stroke and because the piston is further down the bore the volume is greater and the peak pressure will be lower . This is why retarding the ignition timing lowers or supresses detonation , less pressure - less heat so less opportunity for something other than the plug to start the burn .

The turbo engines of today can use higher CR's because our fuel is higher octane and the turbos have evolved to the stage that they have less oil sheer drag than they used to . Low friction bearings means less exhaust energy to get them spinning so less reversion/charge polution/pre heating . Higher CR's ie 9:1 give crisper throttle response and better part throttle fuel consumption . Effective intercooling makes a big difference . The ultimate engines will have variable valve timing and lift and most importantly divided exhaust manifolds and twin scroll turbochargers . This the road to high volumetric efficiency and broad flat torque curves .

Anyone awake ? Nite all .

Great response!

One thing to add, yeah the knock control can be tested by doing that. The knock control on pre 88 turbos was a separate knock computer. 88 onwards was ECU controlled.

I have a different spin on why there is a 20deg static advance........

20deg is just barely the amount of variation that can be electronically controlled and still have the HT contactor in the dizzy for that particular spark plug still in "contact".
Additionally, 1980s electronics, it far easier to program or calculate a delay amount, ie a retard from the trigger point. So move the trigger point forward,
and allow the initial trigger to be at "-20deg retard". Hence electronically, advance is actually achieved by less retard. Because mechanically you have set it at 20deg static advance.

I surmise this is how it is with the subaru ECU, although I never had one, the microtech digi I had was setup this way. The dizzy I used also had mechanical advance. There is also a dizzy with optical trigger for ea82, but I never seen one.

I think this also makes sense with the knock sensor used with the subaru ecu,if its faulty your stuck with the "retard" amount, someone confirm this?

Yep,yep, yep, Disco - you always write such detailed and understandable explanations - publishable standard! GREAT. Now for the next part of my question - anyone got a chart of typical timing as per revs/load of a turbo of this ilk? The thinking behind all this is fix current problem if timing has something to do with it (may be multiple problems!!) and in the back of all this is the gas guru was telling me that once on gas we would just stake the dizzy internally at one fixed amount of advance and leave it ! Mentioned using another simple igniter bypassing any ECU or knock controller .

It may just be staked at 10 degrees or something, he has loads of turbo gas experience - just not with old chunkers like mine. That said , he does run turbo gas vapour injection on a mid 70's Corona!!