What's going on?

I found a book in the library containing SAE papers for automotive engine developments over the last 100 years.

One is the SAE paper for the development of the open combustion chambers on the 1968 199 and 232 AMC engines.

It goes on to say the design revision was for emissions purposes, and that the open chambers reduced emissions levels. AMC also says the new open chambers required some fine tuning of the fuel delivery and ignition timing, but the net result was an engine that produced the same power with the same BSFC as before.

Sounds to me like the open chamber was a win-win.

But in 1977, they went BACK to the quench head. The 1977 Technical Service manual says the change was done to allow for more ignition timing for better power and fuel economy. This contradicts what the SAE paper says.

Something happened here. Why on Earth would they go back to a design that couldn't even pass 1968 standards, let alone 1977?

I cannot come up with any logical reason other than perhaps they had already reduced the engine's emissions low enough that they could warrant switching back to the quench head, but why do this when a reduction in EGR dilution rate would have been a better improvement?




Edited by FSJunkie - Sep/04/2014 at 3:42pm

You may be looking at the time period when "lead" was removed from the fuel supply. If that's the correct time period - 1977, then the quench was to reduce detonation with the use of lead-free fuels. 

Don't forget this was the period that ignition systems were migrating from points to "transistorized" and HEI systems.  Instead of a 10-12kV spark it went to 25 then 50 kV with hotter spark and more accurate and consistent timing, all of which improved efficiency and performance thus allowing some other back sliding "compromises" re-introducing performance.

Electronic ignition systems came about to maintain accuracy and to keep firing old tired engines. A physically solid engine will still only use the lower voltages to fire and maintain a spark.

billd wrote: .......It also allows emissions reductions due to more complete burns as, for example, with GM's HEI, the hotter system can fire a plug with a larger gap and fire it longer. GM skirted some emissions issues with that high potential ignition system. .......

That's really the key.  Spark gaps in general are high voltage limiters.  The voltage rises until the 'spark' is initialized and then never gets any higher.  If you increase the spark gap as Billd mentions, then you have raised the voltage level required to initialize the 'spark' and the voltage will rise accordingly.  That's why the firing voltage won't change with an electronic ignition retrofit if no other changes are made.

My experience with electronic ignition retrofits is that starting with a good points system, the only thing I ever really saw change were better hot starts.

With current technology electronic systems give you the advantage of custom real time advance curves and detonation protection which the points units can't.  I wish someone would bring out a retrofit electronic ignition system that had those capabilities.