i've done some searching, saw jeff20b and patmans previous posts, but does anyone have their 20b running sucessfully with a megasquirt? I want to run leading spark only to fire the leading and trailing together. I was thinking of using 3 stock fc coil packs because we have them around, but may switch to 3 aftermarket dual tower coils.

This is going to be controlling a 20b n/a (9.7:1cr) half bridge. I'd love to save the $$ going megasquirt over an e6x / e6k etc, but i'll wait if needed.

Any help / advice / opinions / model selection and options would be appreciated.

 

i dont think there is code for a 20b trailing setup.

 

I don't want to run the trailing separately, just have it fired at the same time as the leading (dual tower coils / somehow with the stock coils maybe?)

 

i guess you set it up to fire every 120 degrees.

 

Ive seen a 13b distributor modified for this, this dissy is only providing the advance, then 3 magnetic pickups stacked veriticly along a peice of pipe, with 13b distributor rotors each with 2 of the arms cut off, so that they where 180 degrees out of phase, as the dissy spins at half engine speed, then the 3 rotors where 120 degrees out of phase from each other. The magnetic pickups where directly running the coils, with 0 split. Fuel was controlled by an old haltech fuel only computer, that is far less advanced than a megasquirt.

 

running a 20b leading only should be fairly easy. You just set it up as if it were a V6 in the code, with 3 triggers and 3 returns on the CAS, and each of the three LED-based outputs going to a coil.

 

thanks, yea thats what i was thinking it would be fine to run it as a v6.

Which megasquirt version would i need to use, with which options to run it this way? Same as running a 13b? Thats where i am confused. I'm planning on ordering a prebuilt unit as time is a factor, so wondering exactly what i would need in the way of trigger setup (removing teeth from the cas?)

Also any recommendations on who to buy a prebuilt unit from?

 

Th e easiest thing to do would be to use ms1/extra (ms2/extra would work as well, but is just now going into beta).

You could easily cut 2 teeth out of the CAS, and use a slightly modified megasquirt to d othe job. Nobody builds prebuilt units set up this way though, so you'd have to get someone to do custom work for you, or do a little bit of modification to the MS yourself.

The MS would need to be modified to turn the LEDs into spark outputs. As far as the trigger wheel setup goes, I'd expect you to use a 60 degree trigger angle, with wheel settings of:

Trig A: 1
Ret A: 3
Trig B: 5
Ret B: 7
Trig C: 9
Ret C: 11

With ms2/extra, you'd just set it up as a 12-1 crank wheel, and enter a missing tooth position of 90 degrees.

In any case, it shouldn't be difficult to do.

Ken

 

You shouldn't use three FC leading dual output coils for this. There seems to be a problem firing these coils on the same chamber, whether the same rotor housing in our case, or the same piston on boingers. These coils prefer a wasted spark setup, for instance on a 4 cylinder where one coil would go to pistons 1 and 4 and the other coil on 2 and 3, or in our case, L1 and L2. These coils work best when one output is in the combustion phase of one chamber while the other is in the exhaust phase. I don't remember the science behind it but it has something to do with the ions surrounding the spark plug in the exhaust side allowing the spark to jump much easier than in the combustion side where it must fire through the compressed air/fuel mixture.

Thinking about the science, I think it has something to do with the nature of the kettering spark. It automatically increases the voltage as the spark plug gap and/or chamber pressure goes up at the expense of some duration. You can either have a small spark with long duration or a much larger spark with less duration. It's a trade off but those 2nd gen leading coils and ignitors are very powerful and can easily jump over a 1" gap in normal atmospheric pressure.

Anyway if you want to fire leading and trailing together, it is best to get two ignitors and two coils for each rotor housing. You end up with a mess of coils on top of your engine, but that's the way it goes with a 20B.

Now if you were going with a 4 rotor, you could get away with two FC leading coils and stock ignitors. One coil would go to L1 and L2, the other would go to L3 and L4. You could get the so called wasted spark (simultaneous firing) on just two ignition channels firing one and then the other 90° apart. Set it as a 4 cylinder.

There is even a way to have these dual leading sparks with single firing trailing if you go to four ignition outputs like a V8 and set each one to fire every 90°. Use some diodes and four trailing coils along with two leading coils. Interconnect the trailing ignitors to the leading ignitors with diodes facing the appropriate direction and wire it up to the MS. The diodes will prevent the wrong trailing coil from firing each time the leading coil fires. So MS output 1 will trigger the leading ignitor and T1 trailing ignitor but the diode will prevent T2 ignitor from firing. Then 90° later MS output 3 triggers the other leading ignitor and T3 but not T4. Do you see where I'm going with this? 90° later (180° total so far) MS output 2 triggers the first leading ignitor again along with T2 but not T1, again thanks to an appropriately connected diode. And so on for MS output 4 90° later (270° total) on the other leading ignitor and trailing ignitor T4 but not T3. Firing order is 1324.

I realize some of the above doesn't help you directly but maybe it will help someone some day... especially if they want to do a 4 rotor with full leading and trailing with only six coils and no split. Too bad us 20B types don't have it that easy.

 

If you need to use seperate coils

You can use Bosch HEC716 coils. You would run wire coming off the leading spark LED to a pair of ignitors, wire them in parallel, and then they go off to their respective coils.

You will need 6 ignitors and 6 coils in this method tho

You will also need a smaller value resistor in the LED circuit. In the FAQ it recommends 4.7k ohm. I found that 800Ohms fires my ignitors (Bosch BIM024) reliably. 4.7k would not fire them at all.

 

i dont know if this is for real but i thing that the 20b could be running like a 6 cil cop and read it somewhere but they need somobody to test it.

 

Yeah, I use 4.7kohm resistors with the stock ignitors because with the normal 1k resistors, I had very odd problems with noise getting back into the MS somehow, causing anything powered by the +5v regulator to be very sensitive... so I'd get problems like accel enrichments triggering when they shouldn't and things like that.

When you change to different ignitors/coils, the 1k (or less) resistors are usually fine.

But yes, I was saying leading only would be very easy to do... I didn't even catch that he was going to drive to plugs in the same housing with the same coil.

COP is the only way to go on that engine... as everyone is saying.

You cannot run it like a 6 cylinder COP though, you have to run the coils in pairs, with the MS set up as a 6 cyl wasted spark engine.

 

muythaibxr, I used 1k resistors on my LEDs and they worked fine with GM HEI and 1st gen RX-7 J-109 but caused some weird problems with the FC ignitors. If I ever choose to upgrade to FC stuff I'll be sure to try out the 4.7k resistors. Thanks!

 

Bosch BIM024 ignitors work fine with the 4.7K ohm resistor. But when you wire 2 BIM024 ignitors in parallel off the one LED output, thats where you need to drop the resistance.