Difference between an odd fire and even fire ignition?

[justinr54321]

Was wondering if anyone could explain the difference between the odd fire and even fire ignition systems. Its confusing for me, and my time is limited to do research. So please, someone help, thank you.

[speeder]

Odd -Fire engines are those that do not have an even angle between TDC events.

 

Harley motorcycle engines are a good example of an odd-fire engine as is my Buick Stage 2 V6.

 

My engine is essentially a V8 block with 2 cylinders cut off. In the classical V8, the block has a cylinder bank angle of 90* and a crankshaft with throws spaced every 90* (2 rods on each journal), producing an evenly spaced firing sequence with 90* intervals.

 

In the odd-fire V6, the 90* block is mated with a 120* crank, still 2 rods sharing a journal, so the firing angles are uneven: 90*-150*-90*-150......

 

Even fire 90* V6 engines have been made by splitting the crankpins to give 120* between TDC events, but this comes at the expense of a weaker crankshaft.

 

I have learned that there have been many odd-fire engines built over the years, including F1 designs. My crank and rods came from a long track NASCAR Busch GN motor, where the good ole' boys valued endurance. You would think that there would be a huge power loss using this seemingly screwball scheme, but whatever loss there may be has evidently been made up for by strength and packaging advantages of the odd - fire configuration.

 

I really can't wait to hear what my motor will sound like - will definitely be unique. I'll not be using an experimental Megasquirt on my expensive new engine, however - Going with an Electromotive TEC3r that supports odd-fire.

[justinr54321]

Awesome info, thanks for that, for it cleared up a lot. I know with the engine I have in mine, which is basically stock with a N42 head, I'm going to upgrade it to EFI and electronic ignition. Going MSD with both. Doing the ignition first, then convert it from the carbs to EFI.

Odd -Fire engines are those that do not have an even angle between TDC events.

 

Harley motorcycle engines are a good example of an odd-fire engine as is my Buick Stage 2 V6.

 

My engine is essentially a V8 block with 2 cylinders cut off. In the classical V8, the block has a cylinder bank angle of 90* and a crankshaft with throws spaced every 90* (2 rods on each journal), producing an evenly spaced firing sequence with 90* intervals.

 

In the odd-fire V6, the 90* block is mated with a 120* crank, still 2 rods sharing a journal, so the firing angles are uneven: 90*-150*-90*-150......

 

Even fire 90* V6 engines have been made by splitting the crankpins to give 120* between TDC events, but this comes at the expense of a weaker crankshaft.

 

I have learned that there have been many odd-fire engines built over the years, including F1 designs. My crank and rods came from a long track NASCAR Busch GN motor, where the good ole' boys valued endurance. You would think that there would be a huge power loss using this seemingly screwball scheme, but whatever loss there may be has evidently been made up for by strength and packaging advantages of the odd - fire configuration.

 

I really can't wait to hear what my motor will sound like - will definitely be unique. I'll not be using an experimental Megasquirt on my expensive new engine, however - Going with an Electromotive TEC3r that supports odd-fire.