TheSamba.com :: View topic - best coil on plugs to use with megasquirt

Tue Nov 01, 2016 5:52 pm

There is a formula for setting dwell for a specific coil if you have the specs on it

I found I was WAY over on my dwell with my Accel coils. Dropped it down to what the formula showed, and it still runs just fine.

Be damned if I know where that formula is now. IIRC it was in the DIY guy's EFI book. But not sure anymore

Wed Nov 02, 2016 12:09 am

On type 4 engines I have seen COPs from Suzuki GSX-R 2001, Denso 129700-4400 10440. A friend has run those for some years now, another has the same for the engine he builds, and I will use the same. They are "dumb" two-wire COPs, meaning they need external driver (like BIP373).
If you get some smart COPS, they can be controlled on 5V.

Wed Nov 02, 2016 2:10 pm

With a dumb coil you can measure the primary and secondary resistance and come with a pretty good number. With a logic coil you really have to scope it since the final driver is in the coil and finding the secondary resistance is tough to do without more specialized tools than I have.

When I have tested the pencil type coils the dwell is usually 1.5-2.5 ms, good for sequential and high rpm.

Here is a few different coils and how they look on a scope being driven with different ignition strategies.