K66 ignition

[Ray G.]

If your car has the K66 transistor option does it provide a better spark for better burning of fuel like a MSD might do? If I remember right, in the 60's we had a much higher octane available which would work well with the muscle cars of the era. Is it best to use an octane booster even with the 93 octane we buy today? Ray

[Edward B.]

Re: K66 ignition

Ray, I have K66 on my 69 L36 and I run regular 89 unleaded (no "snake oil" additives) and I've no problems. I DID reduce the compression ratio to (approx.) 9.75:1 instead of the original 10.25: when I had the engine rebuilt though. Ed

[Ray G.]

Re: K66 ignition

Thanks Ed, I appreciate your input

[Mike E.]

Re: K66 ignition

Octane was rated differently in the 60's than it is now, so apples vs. oranges to a certain extent.

[Duke W.]

Re: K66 ignition

If your car has the K66 transistor option does it provide a better spark for better burning of fuel like a MSD might do? If I remember right, in the 60's we had a much higher octane available which would work well with the muscle cars of the era. Is it best to use an octane booster even with the 93 octane we buy today? Ray

Once the ignition system provides sufficient spark energy to create a spark that lasts at least 120 microseconds combustion will begin and additional energy does not help.

The TI and HEI provide about double the per spark energy as the single point system, so they have more reserve energy to create sufficient spark even with worn or fouled plugs or excess shunt resistance paths from the secondary components that bleed off energy.

The TI and HEI will not make more power than a properly functioning single point system, but the latter is much less forgiving of degraded components due to poor maintenance.

Lean, low density, and exhaust gas diluted mixtures that are typical of road engines need the long duration spark typical of inductive systems. The MSD system is a capacitive discharge type. They have lots of energy, but short spark duration - less than 50 microseconds, which is very effective in igniting rich, high density mixtures typical of racing engines that spend most of their time at WOT, but not so good at igniting the lean, low density,exhaust gas diluted mixtures that are tyical of automotive engines that spend most of their lives throttled at idle and part load.

For the above reason, no OEM uses a CD type ignition, nowadays, . They are a poor design architecture for a road engine.

Sure, MSD offers "multiple sparks", but only at relatively low revs and the second and (maybe) third sparks are severely retarded from optimum.

The best strategy is to fire the plug at the optimum point for the operating condition with sufficient energy that combustion is initiated 99.99999999999999999999999 percent of the time, and for typical road engines that means an inductive system.


Duke

[Michael F.]

Re: K66 ignition

I believe oldsmobile had a CD system on the 66-67 442 back in the 60s as an option, didn't see it after 68 or so, do you remember anything about those Duke?

[Duke W.]

Re: K66 ignition

Yes. In fact I have the SAE paper that was written on the development of this system. It used the same magnetic pulse distributor as the TI system, but had a unique cap with higher dielectric strength, red in color, due to the higher open circuit 35kV it could generate compared to the approximate 25kV open circuit maximum voltage of the single point and TI. It generated considerably more per spark ignition energy than the TI, but, as with all CD systems, spark duration was short - only 35 microseconds.

The CD system may have also used unique plug wires, but I'm not sure.

To the best of my knowledge the Delco CD system is the only capacitive discharge type system ever offered on a production car. As you know, it was a short lived system, but I don't know why. Cost? Reliability? I don't remember the RPO code or cost, but I think it was more expensive than the TI, so lack of customer acceptance due to high price may have been an issue. (Does anyone remember the option code and price?)

Or maybe GM figured out that a CD type ignition engine is not the best choice for a road engine.

Duke