bob58o
SuckSqueezeBangBlow
I was looking for info on the coil gap for this flywheel and came across this. Shows how you can tune with the coil gap (at least with the ARC flywheel and small carb on gasoline if you have a dyno LOL).
Not what I was looking for, but worth sharing.
JPR57 JPR57 is offline
4 Cycle Advanced User
JPR57's Avatar Join Date
Oct 2013
Location
The Engine Room @ ARC Racing
Posts
844
It is not about more or less voltage to the coil, because it can only handle so much before they fry. We are accomplishing two things with more coil gap. (One), less magnet drag. The magnets in our flywheels are very strong and will produce some resistance when passing under the coil. This is more beneficial with smaller plate engines. (Two) and the most important is we are trying to time when and how much timing retard we have a high RPM. Every OEM coil no matter if its a Clone, Honda, Predator, Kohler or a Flathead briggs they will retard as the RPMs go up. If you set the timing at 30 deg it will still be at 30 deg while at idle, but as the RPMs rise the timing will begin to retard because the magnet is passing under the coil faster than it can charge and fire. <This is a known fact. Our flywheels have a magnet design that charges and fires the coil much better and more accurately at higher RPMs that does not retard as much as other flywheels, but does still retard. Now factor in that we are running a carb on Gasoline that has a .615 venturi that will reach the point of maximum suckage around 5500 RPM +/-. Because of the cam package and the size of the carb that is where it begins to lean out. We set up these carbs to have a very rich bottom end so they will accelerate quickly and that will require more timing to burn the excess fuel. So we set the timing in the 32-36 deg range to help with the rich bottom end. Now as I stated these little .615 carbs will begin to lean out around 5500 or so RPMs and you do not want to have high timing with a leaned out carb. running pump Gasoline. Therefor we widen the coil gap so the timing will begin to retard a little sooner to try and match the carb leaning out so the engine will continue to make top end power. This is something we worked with for many months while developing our new magnet design and why you can run more gap with the new style design and less with the oil style design. From our testing with the AKRA Clone engines a coil gap of .060-.065 works best on unrestricted engines, .065-.070 works best on blue and purple plates and .070-.075 on green and red. These coil gap numbers not set in stone you may find that more or less will work for you but will require the use of a Dyno, this is what works best for us with our engines on our Dyno. You results may vary...
Not what I was looking for, but worth sharing.
JPR57 JPR57 is offline
4 Cycle Advanced User
JPR57's Avatar Join Date
Oct 2013
Location
The Engine Room @ ARC Racing
Posts
844
It is not about more or less voltage to the coil, because it can only handle so much before they fry. We are accomplishing two things with more coil gap. (One), less magnet drag. The magnets in our flywheels are very strong and will produce some resistance when passing under the coil. This is more beneficial with smaller plate engines. (Two) and the most important is we are trying to time when and how much timing retard we have a high RPM. Every OEM coil no matter if its a Clone, Honda, Predator, Kohler or a Flathead briggs they will retard as the RPMs go up. If you set the timing at 30 deg it will still be at 30 deg while at idle, but as the RPMs rise the timing will begin to retard because the magnet is passing under the coil faster than it can charge and fire. <This is a known fact. Our flywheels have a magnet design that charges and fires the coil much better and more accurately at higher RPMs that does not retard as much as other flywheels, but does still retard. Now factor in that we are running a carb on Gasoline that has a .615 venturi that will reach the point of maximum suckage around 5500 RPM +/-. Because of the cam package and the size of the carb that is where it begins to lean out. We set up these carbs to have a very rich bottom end so they will accelerate quickly and that will require more timing to burn the excess fuel. So we set the timing in the 32-36 deg range to help with the rich bottom end. Now as I stated these little .615 carbs will begin to lean out around 5500 or so RPMs and you do not want to have high timing with a leaned out carb. running pump Gasoline. Therefor we widen the coil gap so the timing will begin to retard a little sooner to try and match the carb leaning out so the engine will continue to make top end power. This is something we worked with for many months while developing our new magnet design and why you can run more gap with the new style design and less with the oil style design. From our testing with the AKRA Clone engines a coil gap of .060-.065 works best on unrestricted engines, .065-.070 works best on blue and purple plates and .070-.075 on green and red. These coil gap numbers not set in stone you may find that more or less will work for you but will require the use of a Dyno, this is what works best for us with our engines on our Dyno. You results may vary...
