is the MS-I with all the rx7 mods required for the 13B going to be powerfull enough to run the 20B as well?

 

right now it could probably do leading only, and I might be able to add code for leading and trailing now that msns-extra 027a and above support 6 ignition outputs...

I believe mike20b has an MS running leading only on his 20b.

 

I have leading only on my NA 20B with the late leading mod on the MS I CPU, v2.2 board and MSnS-Extra022i6. I may do a turbo some day, but it's an early engine (#756) so I don't know yet. I only got as far as firing it up on renns' tables (adjusted for 12x12) and have not attempted to tune specifically for the 20B yet. It could be driven, but it needed tuning.

The late leading mod consisted of tricking the MS into thinking it was running a V12 instead of a V6 as that was the only way to double the spark output back then due to it having been a function of input trigger signal vs injector squirts. In other words, I had to double the incoming trigger events to double the outgoing spark events. Meanwhile, the injector events remained the same. It was a nice trick I discovered.

I wanted late leading for a handful of reasons.

To get that awesome 20B exhaust note with a unique tone that only late leading can provide.

No need for an aftermarket tach because each leading coil still sparks twice per engine revolution, which is exactly the same as the stock 4 cylinder/2 rotor tach requires.

I've found the late leading mod, when performed on a 2 rotor engine, is always an improvement over the stock cap and rotor (or single leading spark per rotor face) system; easier starts; cleaner emissions; more power; smoother running; less flat spots in the power band, and I'm sure there's some more.

This worked for me on the earlier codes. I am unfamilier with the latest codes. There is a chance that the latest code would not work in late leading mode. You'll probably be locked into single leading and trailing sparks, which is what all the other 20Bs out there are running with expensive aftermarket ECUs (split or no split). I'd honestly prefer to keep the late leading spark rather than swapping it for a trailing spark because I'm not running forced induction, and trailing sparks through a tiny hole which adds hardly any power. I've also done some casual testing on my early 4 port 13Bs running DLIDFIS (a late leading mod for 1st gen RX-7 distributor-equipt engines) switching trailing on and off while driving through various conditions, and trailing's influence was unnoticeable. However, there was always a noticeable improvement in the areas mentioned above when a late leading mod is added.

In conclusion comparing late leading without trailing to a single leading+trailing setup on the MS, the benefits outway the drawbacks as far as I can tell.

 

Just to clarify something I said earlier. The late leading mod itself was performed on the CAS and not the MS. I didn't want to confuse anybody. The only mod I did on the MS was to convert the LEDs to ignition outputs by adding a pull-up resistor to each, and then I added a jumper wire from each to the DB37 connector for easy output with the rest of the wires in the wiring harness.

The regular 20B leading firing order is:

1-0°
2-120°
3-240°
One spark every 120° of eccentric shaft rotation.


The late leading mod adds an extra spark to each rotor face 180° after each regular spark:

1-0°
3-60°
2-120°
1-180°
3-240°
2-300°
One spark every 60° of eccentric shaft rotation.

 

.. is there enough dwell time at higher RPM for this ? are you getting losses by 5500 or around there?

Interesting timing. I wonder how it would work with the std 13B-turbo..

 

it already happens in a way on a 13b... the leading ignition Fires every 180 degrees, which means on one rotor it's causing the fuel to ignite, and on the other rotor, it's firing into spent exhaust...

 

yep I've seen the animation on that kinda took me by surprize that '3rd' spark.. so now, why bother with the trailing coil in, given peoples experiences without it.. ( better performance it seems )

 

well, it's not better without it... the trailing just doesn't help that much for power...

Supposedly, according to some rotary design docs that were posted here, the trailing helps with fuel economy on NA applications

I think on turbo applications, the trailing ignition split also has a large effect on the spool time of the turbo.

 

That jives with what I understand about rotary ignition.