Ignition curve

[martinsamuel]

Hey guys,

I've been thinking about changing the cdi out for a microsquirt. For a few reasons, to facilitate can bus data logging/display
and to get rid of the cdi, which is obviously going to fail at some point anyway.

Has anyone ever measured or know what the ignition map is for a non-sp 1990 gk76?

Cheers
Martin

[SevenThreeSeven]

Has anyone ever measured or know what the ignition map is for a non-sp 1990 gk76?

All of the Japanese "super sport" 400cc bikes from the late 1980s into the late 1990s had pretty similar ignition curves (and I use the word "curve" on purpose because that's what they had, not an ignition "map" which infers a fully computer controlled 2-dimensional array).

During my research for my own Microsquirt (version 3) conversion (on my B4, now mostly completed) I collected screen shots from the spec-sheets and maintenance manuals of quite a few of the 400cc 4-cylinder bikes produced during that decade and they all look like this: they idle at around 12 to 20 degrees BTDC and they advance from there to somewhere in the 38 to 48 degrees BTDC range as the RPMs increase, usually going "all in" by about 5,000 to 6,000 RPMs.

Examples:
ZR400: 20 BTDC at 1,300 to 45 BTDC at 11,000 (this engine's CDI had a series of intermediate steps in advance)
FZR400 (with 3FH electrical advancer): 10 BTDC at 1,300 to 48 BTDC at 6,500
The GSX-R400 and GSF400 (the 59 horsepower engines): 15 BTDC to 45 BTDC at about 4,500


There are a couple of "special cases" in this group of bikes and the GSX-R400SP is one of them because Suzuki went the extra distance by putting the Throttle Position Sensor on the carbs. But the only difference this Throttle Position Sensor makes is that it causes the CDI to take off 2 or 3 degrees of advance when the rider suddenly twists the grip wide open (because rich mixtures burn faster than lean mixtures).

So the Japanese manufacturers were running these bikes pretty close to the maximum advance that could be used for an engine of this type and size even without modern digital electronic controls. My experimentation with my GSF400 Microsquirt V3 conversion has resulted in an ignition map that goes to a maximum of 43 degrees BTDC. I started out very conservative at about 38 degrees BTDC maximum and the bike felt "down on power". Then as I cautiously tuned it higher there was a huge difference in the engine up to about 41 to 42 degrees BTDC, then it didn't seem to change much as I took it all the way out to 45 and 46 degrees BTDC (but I didn't get any "knock" either). So I settled for a happy middle-ground solution with 43 degrees BTDC as my final maximum number.

If you need any help modifying/configuring for Microsquirt let me know.

[martinsamuel]

Thanks. That sounds easier than I thought (that doesn't happen often). I'm now waiting for an epic failure for saying that.

Martin

[Variablevalves suck]

Yes 45deg seems to be the standard max for most of the manufacturers.

If you have a dig around on the net you can find a few graphs showing the kit curves that usually have flat section in the midrange then a slightly steeper advance after that but still very simple.

You have no worries regarding cdi replacement as ignitec make aftermarket boxes that are tuneable and have tps etc.

[SevenThreeSeven]

That sounds easier than I thought (that doesn't happen often)

I didn't want to make adapting the GSX-R400/GSF400 engine to a Microsquirt sound too simple, because it's not (but it's not rocket surgery either).

You have to physically change the bike's trigger wheel to something that the Microsquirt can read. The easiest thing is to remove on of the teeth from the stock trigger wheel. The stock trigger wheel has 6 teeth on it, with one of those teeth being a "long tooth" and the other five being "short". You have to take the trigger wheel off the bike, remove one of the teeth, re-balance the wheel by removing material from opposite of the tooth you removed, then re-install the trigger wheel on the bike.

Then you have to figure out the "Base Timing" of the trigger wheel so you can tell the Microsquirt exactly where Top-Dead-Center is for Cylinder #1. To do this I had to purchase an old scraped up engine side cover off of Ebay. Then I cut a "window" in that engine cover so I could see the trigger wheel spinning while the engine was running (without having all of the engine oil pumping out onto the garage floor!). The window is necessary so I could use a timing strobe-light to adjust and verify the "Base Timing".

When you've got the base timing set the engine will idle. At this point you can begin defining the Ignition Map. I can provide you with a pretty good Ignition Map to install in your Microsquirt. But because you and I might not get our two unique bikes set to precisely the same base timing for "0" degrees Top-Dead-Center my numbers might be just a bit off on your bike (maybe a degree or two in either direction). The reason for this is that setting base timing, "0" degrees Top-Dead-Center, is a completely visual thing, it's just a "best guess" visual sort of thing.

And there's more that I can't remember right now...