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Dual spark dethroned


Well Known and Active Forum Website User
VOC Member
I have been running the Comet racer on twin plugs
I have just sorted a new head (better inlet port) but it only has a single plug at the moment otherwise nothing altered
rewiring the B-TH for a single coil is simple -only connect one!
The CR of around 10 is the same as the old head and that had an ignition setting of 28deg (set on a brake)
I want to set her for single spark and was thinking of an initial setting of
32 deg and put the unit at the end of the B-TH slot in the flange so I can advance it towards 28 deg during initial setting and track testing. Later I will budget for a brake session when I can include another machine to make it economic. (and possibly go twin plug again) any thoughts on that 4 deg change?


Well Known and Active Forum Website User
VOC Member
I am not sure that I am smart enough to know. 32 degrees sounds just right to start. I would guess that because there are no improvements to the combustion chamber that the single spark might like 32 more than 28, but 4 degrees is not a huge jump. If the single spark completes its combustion work in 32 degrees it will make the most power there. If it can finish in 27 or 28 degrees it will show more power because the peak pressure in the cylinder will occur 4 degrees too early and the pressure may even peak prior to TDC. Usually, peak pressure should be at 12-14 degrees after TDC. So, when we set the timing we are looking through the wrong end of the telescope. We are really trying to guess where we can light the spark so that will in turn create maximum pressure at 12 ATDC. Not easy when you have all the variables of compression, exhaust, inlet changes as well as fuel and atmospheric changes.

That being said, getting the maximum power with a either a single spark or a dual spark will give you a nice ride.


Kansas Bad Man

Well Known and Active Forum Website User
Non-VOC Member
I found that ignition advance has three variable's to consider depending on the track, Daytona wouldn't be the same as Mallory , you must think the speed in which the fuel burns which is a constant,
the position of the piston in the cylinder when maximum expansion of the fuel occurs which is not a constant, and the number of gears in the gear box and there ratio to each other. The bottom line is to , if possible to have a manual advance and if some one ask you what is the advance you run , tell them its the one that is getting me the fastest lap times.

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