Re: Ignition Coil for 1970 LS-5

[Jack H.]

Terry's correct. External, discrete ballast resistor disappeared in the Shark era across the board on Chevys. Function (maximize spark voltage during engine cranking and reduce during run) was accomplished INSIDE the ignition wiring harness using controlled resistance wiring runs (like was done with earlier TI systems with their special wiring harness).


For grins, EE's simply HAVE to explore/tinker, two of us disassembled coils to see what's what inside. One was a burned up '091 (HP coil from days of discrete ballast) and the other was a passenger car 'B-R' series from '69-70 era.


Inside the '091, there was magnetic continuity in the core lamination circuit coupling primary to secondary (a very conventional transformer design). In the 'B-R' coil, there was a VERY SMALL air gap in the core lamination that was 'stuffed' with plastic. While the magnetic circuit has to 'jump' this gap to couple primary to secondary, due to its VERY short distance there is only minor efficiency loss. Appears the design was intended to control transient decay and fully isolate primary from secondary electrically. Interesting....

[Terry M.]

Re: Ignition Coil for 1970 LS-5

Jack,


Do you suppose it might be a safety related issue? That is prevent the secondary (high voltage) from getting back into Primary (low voltage). Since primary wiring is not engineered for the secondary voltages.


One of the thoughts that has intrigued me is that I can not imagine what the differences are in coils designated for Mark motors or small blocks - seems to me a coil ought to be a coil. With the Kettering ignition system I can not understand why a difference. I can see if the number of cylinders are different one has more or less time for the coil to reach saturation - so I can grasp the need for some different design for different number of cylinders, but seems to me any 8 cylinder coil should work on any 8 cylinder engine with Kettering system.


Is there a simple explanation or is this along the lines of either FM = *^%&$@# Magic or "If I tell you I'll have to kill you".


Terry

[Jack H.]

Re: Ignition Coil for 1970 LS-5

Typically, an air gap in the core laminations of a transformer serves two purposes: (1) provides increased isolation between primary/secondary and (2) allows precision 'trim' for coupling efficiency between the two sides.


The first item doesn't make a lot of sense as we're dealing with a system that typically does NOT have human interface (threat of shock hazard). Plus, individual windings are insulated and that's usually a sufficient isolation technique to satisfy most designers/safety approval agencies....


The second item is probably more germanine. You control transformer gain with primary/secondary ratio. Variance in wind wire composition (and core lamination material) generates unit-to-unit precision drift. By, overdesigning the transformer and introducing an air gap, you can 'tweak' individual coils to achieve higher precision by varying the amount of core material (gap size) that's removed.


Might well be this internal difference has little/nothing to do with the integral ballast feature of these later Kettering (ever meet KT?) systems. Might be they just adopted a mfgr 'trick' to prevent wind, test, physical sort/bin secondary operations before final packaging of the coil!


The air gap DOES affect a transformer's transient response (core saturation). Improves it at the expense of introducing unnecessary primary/secondary coupling inefficiency. This might be the angle too....

[Terry M.]

Re: Ignition Coil for 1970 LS-5

Thanks Jack,


I knew I shouldn't have asked. I'll stick to transformers I can be lowered into, I'll leave the designing to someone else.


See you in Florida.


Terry

[Jack H.]

Sorry about Florida....

Just bought my ticket for UK Chapter meet in September and made 'loose' commitment to fellow Rocky Mtn Chapter member to run with him on repeat Founders drive to Bowling Green. Two major events per year is my limit until officially retired.... But, I have faith the 'good guys' will show up in Florida to carry the torch and get the job done, Terry. Any interest in seeing JOE (Jolly Olde England)?

[Terry M.]

Re: Sorry about Florida....

Interest? Yes


Resources? No


I list under resources, in no particular order:


1) Time - I now have two jobs, only one of them includes Corvettes. 2) Money - reason for two jobs. 3) Encouragement (tolerance) of spouse - I wish I could talk her into England (she will not fly over water even to go to Long Island). If I could convince her there might be a way to solve #1 & #2.


Enjoy.


Terry