Injector pairing for batch fire injection in Megasquirt??: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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April 11, 2011 3:30 p.m. DILYSI Dave SuperDork

Honda 4 cylinder. Firing order is 1-3-4-2. Megasquirt will support 2 separate injector channels, meaning I need to inject the fuel for 2 cylinders at once.

Option 1 - Group 1-4 and 2-3. This is the common way to do it. Reason being I suppose that that's the way the crank groups them. But those pairings are 180* opposed in firing order, so if you are timed perfect for one injector, you're completely imperfect for the other.

Option 2 - Group 1-3 and 4-2. Follow the firing order. It seems like you could more accurately emulate sequential injection this way. This way, if you're timed perfect for one, you're only 90* off for the other.

In reality, I realize it doesn't make a damn bit of difference when we're talking about duty cycles of 80% and 8000 RPM, but still...
April 11, 2011 4:50 p.m. alfadriver SuperDork

Option 1 is better.

Have you checked the injection sequence for your computer? I've not found a batch fire that doesn't fire once per revolution- so for each cycle, it injects twice- once "correct" and once 360deg out. (nit pick correction- 1-4 and 2-3 are 360 deg apart in firing order....)

One other note- mixed results from open valve injection. In theory, it will allow you to run more spark, but you need a dyno to check it. The trade off is on a cold engine, you'll inject liquid fuel into the combustion chamber (and possibly on the walls....). For safety, I would start on a timing that does closed valve injection. It works fine.
April 11, 2011 4:52 p.m. fifty Reader

I went with option one on my 4 cyl VW engine (same firing order) - worked fine.

Of course, with MS2 you can have true sequential. You need a toothed wheel on the crank, and then something for cam timing - the dizzy would work fine for this. http://jbperf.com/sequential/index.html#ms2mods
April 11, 2011 5:00 p.m. DILYSI Dave SuperDork

alfadriver wrote:

Option 1 is better.

Have you checked the injection sequence for your computer? I've not found a batch fire that doesn't fire once per revolution- so for each cycle, it injects twice- once "correct" and once 360deg out. (nit pick correction- 1-4 and 2-3 are 360 deg apart in firing order....)

One other note- mixed results from open valve injection. In theory, it will allow you to run more spark, but you need a dyno to check it. The trade off is on a cold engine, you'll inject liquid fuel into the combustion chamber (and possibly on the walls....). For safety, I would start on a timing that does closed valve injection. It works fine.

Thanks!
April 11, 2011 11:18 p.m. DILYSI Dave SuperDork

And done.
April 12, 2011 8:33 a.m. MadScientistMatt Dork

alfadriver wrote:

Option 1 is better.

Have you checked the injection sequence for your computer? I've not found a batch fire that doesn't fire once per revolution- so for each cycle, it injects twice- once "correct" and once 360deg out. (nit pick correction- 1-4 and 2-3 are 360 deg apart in firing order....)

MS can be set for anything from once every other revolution to twice per revolution on a four cylinder.
April 12, 2011 8:39 a.m. alfadriver SuperDork

MadScientistMatt wrote:

alfadriver wrote:

Option 1 is better.

Have you checked the injection sequence for your computer? I've not found a batch fire that doesn't fire once per revolution- so for each cycle, it injects twice- once "correct" and once 360deg out. (nit pick correction- 1-4 and 2-3 are 360 deg apart in firing order....)

MS can be set for anything from once every other revolution to twice per revolution on a four cylinder.

For batched fired, the least compromise would be once per revolution. that way, the pair will get two injections, and one could schedule open valve injection.

The one note that I would make, do make sure that MS is capable of overlapping the injections on the two drivers. Last I heard, it was capable of this, but I ran into this problem on a TECII, which limited a pair batch to half the time it could have. If I put all of them together- as in twice per rev, it would have worked- but for whatever reason, the TEC was not able to schedule the injector drivers at the same time at different timings... odd. I'm pretty sure MS IS capable of that, but you should double check it. No reason to cut your injector capability in half just due to a driver issue....
April 12, 2011 11:11 a.m. MadScientistMatt Dork

alfadriver wrote:

For batched fired, the least compromise would be once per revolution. that way, the pair will get two injections, and one could schedule open valve injection.

The one note that I would make, do make sure that MS is capable of overlapping the injections on the two drivers. Last I heard, it was capable of this, but I ran into this problem on a TECII, which limited a pair batch to half the time it could have. If I put all of them together- as in twice per rev, it would have worked- but for whatever reason, the TEC was not able to schedule the injector drivers at the same time at different timings... odd. I'm pretty sure MS IS capable of that, but you should double check it. No reason to cut your injector capability in half just due to a driver issue....

Kinda surprised an Electromotive ECU would not do this. MS has done overlapping injection since the beginning.
April 12, 2011 11:22 a.m. alfadriver SuperDork

MadScientistMatt wrote:

Kinda surprised an Electromotive ECU would not do this. MS has done overlapping injection since the beginning.

I found out the hard way- my challenge car ran out of fuel at the top end... Thankfully, it didn't break anything. I paniced and cut the tips off the injectors, and then found out that I can batch fire the entire set later.... Oh, well.

Really surpised me, too!
April 12, 2011 11:30 a.m. John Brown SuperDork

alfadriver wrote:

MadScientistMatt wrote:

Kinda surprised an Electromotive ECU would not do this. MS has done overlapping injection since the beginning.

I found out the hard way- my challenge car ran out of fuel at the top end... Thankfully, it didn't break anything. I paniced and cut the tips off the injectors, and then found out that I can batch fire the entire set later.... Oh, well.

Really surpised me, too!

Ahh... the patented Eric Storhok 36lb injector mod!
April 12, 2011 11:35 a.m. alfadriver SuperDork

John Brown wrote:

Ahh... the patented Eric Storhok 36lb injector mod!

I can't take credit for it- someone told me about it. And it only works on some injectors- others- the tip is part of the pintle seal.