Ignition advance, was Re: alternative engines, WARPED

[rr]

Bruce (or is that Grumpy?) wrote:

>Kinda depends on the WOT pressure drop across the carb., and spring rate of
>the vac, advance used.   Even with the same no. degrees per amount of vac.,
>by different spring rates/dia. combinations things could vary.  Going from
>6-10 start to 20 something at 700rpm, 30 something at WOT (@3,000 rpm), and
>40ish at cruise with a OD kinda hard to do thata way (mechanical).   Hence
>the real beauty of ecm's, IMHO.
>  Grumpy


Bruce is speaking huge amounts of wisdom here, nothing can come close
to how an ecm handles spark control.

I've installed a '747 ecm and spark control system on a carb'd car,
what a difference. Drivability, power, mileage, have all improved.
(Yes, I'm still working on the write-up. The cutoff is next week,
as I'm going back to school, along with working).

Couple of things that mech/vac distrib's aren't/can't do:

  A 210 point table, based on rpm and manifold vac, that defines
  the main spark advance value. This in itself blows away any
  centrif/vac-adv distributor.

  Startup spark, additional timing added for a short time after
  the engine is first started. Keeps engine from stalling (choke).

  Coolant compensation spark, additional timing added/subtracted
  as a function of engine temp.

  Hi-way spark, after a set period of time, above a set speed, 
  additional timing added for better mileage.

  Knock detect and retard, along with testing of the ESC system.

  PE spark, at WOT, additional fuel is added, and spark is also
  added to take full advantage.

Well, more than a couple, but I hope I can get the idea across.
I'm sold on this...

BobR.

>>|      I could be wrong at this, but what I have seen is, ported vacuum is
>>dead
>>| at idle, because it is above the butterfly....and as throttle is
>>increased,
>>| vacuum is generated at the "port" and does not go away at full
>>| throttle,,,,,great for emissions but terrible for performance,,,,,the same
>>| for MPG....
>>| -Carl Summers

>>>|   You sure about that?  I have always understood that a vac advance can
>>>|  reads ported vacuum in order to affect a curve that begins as the
>>>throttle
>>>|  is opened and increases as more throttle is applied, up to the point at
>>>|  which all vacuum (manifold and therefore ported as well) fades under
>>>heavy
>>>|  throttle openings, at which point the advance will decline again and the
>>>|  engine will see only mechanical advance.  This is apparently to provide
>>>|  extra advance for economy at part throttle.  Anybody who can further
>>>|  illustrate this concept, please do because if I am wrong here I'm going
>>>to
>>>|  have some serious rethinking to do!
>>>|   Aaron Willis