Considering MicroSquirt for and EJ-25

[Pete Sullivan]

I am considering using MicroSquirt on a newer Subaru EJ-25.
The engine has the 6 crank / 7 cam VR system. I've read on
the forums that others have tried code mods to support it and
perhaps extra2 may support it, but I would like to keep the install
more mainstream and if simple hardware mods will work then they
are preferable.

I could grind down 4 of the 6 teeth on the crank wheel (leaving 2
teeth 180 degrees apart) and all but 1 tooth on the cam wheel.
This setup would give one trigger event per cylinder and one
cam sync event per cam rotation. This setup looks like it would
be compatible with the dual spark feature described in section
2. A. of Dual Spark page in the MicroSquirt manual.
Does this seem reasonable?

If it is reasonable, the question becomes which tabs should be removed.
The crank wheel has tabs at 97*, 65*, and 10* BTDC (crank angle) for
each cylinder. I do not know enough about how MicroSquirt uses the
tach trigger to know which tabs to leave, perhaps it does not matter
which tabs are left. It seems that if you wanted an event prior to any
spark event you would want the 65* tab, but if you used the 10* tab
it would be very similar to having a distributor clamped at 10* BTDC.
Any insights here would be very valuable.

Next there is the issue of the cam sync signal. The tabs on the stock
wheel are at (all ATDC of cyc1 in cam angle) 5*, 27.5*, 50*, 110*,
200*, 230*, and 290*. The manual suggests that the sync needs
to occor some time between the last and first tach pulse, does this
mean anywhere, so long as its once per cam cycle, or specifically
after the last cam pulse (of 4) and the first cam pulse of the next
cycle. This makes me think that the 290* tab is the one to keep.
Again, I need more insights.

Has anyone in the beta group tried triggering MicroSquirt and
using wasted spark in this way?

Also, any new word on the ETA?

Thanks in advance,
Pete

[newtyres1]

The crank wheel has tabs at 97*, 65*, and 10* BTDC (crank angle) for
each cylinder. I do not know enough about how MicroSquirt uses the
tach trigger to know which tabs to leave, perhaps it does not matter
which tabs are left. It seems that if you wanted an event prior to any
spark event you would want the 65* tab, but if you used the 10* tab
it would be very similar to having a distributor clamped at 10* BTDC.
Any insights here would be very valuable.

At the moment I don't think the code is finalized, and it may be that a negative trigger angle is prefered, best to wait at this stage.

The manual suggests that the sync needs
to occor some time between the last and first tach pulse, does this
mean anywhere, so long as its once per cam cycle, or specifically
after the last cam pulse (of 4) and the first cam pulse of the next
cycle.

As long as it occurs between any 2 crank pulses the rest can be configured through firmware and hardware. I would think that a cam pulse that falls close to being right in the middle of 2 crank pulses would be the ideal choice, but it is not that critical. The tooth you keep on the cam will therefore depend on which teeth you keep on the crank.

Has anyone in the beta group tried triggering MicroSquirt and
using wasted spark in this way?

If they have, they'll probably let you know. The new uS code and MS2 codes are one and the same thing, so the development is mostly covered on the msefi.com site - MS2 beta testers thread. I think this site will get busy once the uS is released.

Ian.

[grippo]

For the crank wheel, I would use either the 65 or 10 deg tooth. Either will work - so would 90. The advantage of 10 deg is that it will probably be good for starting, using trigger rise mode. Trigger offset can always be made negative by using, for example, -10 deg instead of +170 deg.

For the cam, the single tooth has to come in somewhere between cyl 4 tach pulse and cyl 1 tach pulse. As Ian said, the mid point is ideal, but all that is necessary is that it be reasonably inside the band so that cam twist at hi rpm or sloppy mechanical tolerances never allow the cam to arrive befor the cyl 4 tach or after the cyl 1 tach.

As far as the ETA, we are satisified with the hardware and software is done except for fixing any new problems that might arise. We plan on starting a production run in the next week or two, plus we will sell the existing test units at a reduced price.

[Pete Sullivan]

So if I keep the 10* tabs on the crank and the 290* tab on the cam
It would place the cam sync signal 25* after the last crank signal and
65* before the first crank signal of the next cycle
(in cam degrees... this gets confusing)

Using 65* crank tab causes the 290* cam tab to come 52.5* after
the last crank signal and and 37.5* before the first crank signal
of the next cycle.

Using 97* crank tab causes the 290* cam tab to come 68.5* after
the last crank signal and and 21.5* before the first crank signal
of the next cycle.

It seems like using the 290* and any of crank tabs would probably
work, 65* is the most in the middle, but 10* would make for
a decent cranking trigger, and would show up on the engine's
timing marks well.

I think that 10* and 290* are the tabs to keep. If anyone
wants to help "refine" my understanding of what is going
on please chime in.

I looked up the costs to replace either the crank pulley or
the cam pulley and they were both under $40 so even if I
do mess one up I am not out that much.

thanks
Pete