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-   -   Dwell setting (https://www.miataturbo.net/megasquirt-18/dwell-setting-54221/)

cat10 12-09-2010 05:36 PM

Dwell setting
Hi folks, please can you let me know what the Dwell Settings should be for my 1.8 mk1 1996.

Cranking Dwell,Running Dwell,Minimum discharge period (ms)

I am using a MS1 V3.

Many thanks

Joe Perez 12-09-2010 05:48 PM

A good starting point is 3.5ms running, 5ms cranking. You might need to increase the running dwell slightly if you find that you're getting misfires. Better to start small and work upwards.

cat10 12-09-2010 06:00 PM

Hello Joe, the reason I am asking is the Diyautotune site has a 96/97 msq.for the pnp which has the cranking dwell at 8.0, Running dwell at 4.3 and the discharge period at 1.0ms

Also on the same site it has the C/D at 7.5, R/D at 4.5 little bit confused to be honest...

Does it really make alot of difference?


Joe Perez 12-09-2010 06:22 PM

Do they?

That's interesting. I was just going off of observations which I made years ago with an oscilloscope on a running engine, though the car I was testing was a '92. I wouldn't have though the '96s coils would be that much different, at least the actual magnetics.

Dwell isn't a massively critical number to get "just right". In fact, the actual optimum setting will vary from one car to another based on the health of the electrical system, specifically the voltage available to the coils under load. In this context, the difference between 4.3 and 4.5ms running is fairly insignificant, so go ahead and try 4.3.

Likewise, the difference between 7.5 and 8.0 during cranking is nearly meaningless. Going overboard merely results in some extra heat being generated, and since the engine is only cranking for a second or two, no harm is going to be done even if you specify 10ms. So give it 8.0 and I'm sure it'll be happy.

Minimum discharge isn't really important, since you'll never spin the engine fast enough for the cycle period to approach the dwell period. This is only a factor on V8s with distributors, where one coil has to fire 8 times per cycle. With our wasted-spark ignition, each coil fires only twice per cycle, so it has plenty of off time in between dwell events.

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