Ignition timing questions

[Mikey Antonakakis]

Hey guys, if anyone wants to share, there are a couple small pieces of info I'd like. We're running Megasquirt II/extra on an F4i this year, and so far I'm loving it. However, I'm having some trouble with very low RPMs/idle conditions. I'm basically wondering what the idle portion of people's ignition maps look like. Right now, ours is set at 24 degrees at 100kPa and 1000rpm (we're using MAP for load). It pulls about 88kPa at idle right now, and it seems like the less advance I run, the higher the MAP gets, and the more difficulty it has idling. Anyone have any good base values for timing? If you'd like to share, your max advance at full load and high RPM (which I'm fairly certain shouldn't be too much more than 40 degrees or so), advance at idle conditions (ie 1000 rpm and 100 kPa box would be enough), and max advance anywhere on the map, I'd really appreciate it. I have done a LOT of googling, but have come up with no definitive answer (I know it's different for every engine, but I'm having trouble finding good starting values for a 600cc sportbike motor).

[Mikey Antonakakis]

As it turns out, it was a timing offset issue. That said, would an inertial dyno cause approximately a 50% decrease in wheel torque? We went to a Dynojet today, and made about half the power I was expecting (according to the dyno). When I drove the car though, it certainly didn't feel like half the power...

[consig]

Hey Mikey,

Try taking a look at SAE Paper Number 2002-01-0887.

It has some very good details comparing testing on a chassis dyno with inertia rolls versus testing on an engine stand.

That being said, doubt that you would see a 50% decrease in measured power when moving from an engine dynamometer to a chassis dynamometer. To compare measured torque, however, you have account for your gearing and your final drive ratio and your rolling radius. On the chassis inertia rolls dynamometer you are of course measuring torque at the wheels after the gear reductions.

[kapps]

For reference... Our engine made 80hp, 47 lb ft torque at the output spline on the engine dyno with temperatures in the 60's. It made 67 hp and 39 lb ft torque at the wheels in 95 degree weather on a chassis dyno this past week.

I can't really help with tuning since we're using TPS. Max advance is around 46 degrees.

[Grant Mahler]

Three thoughts:

Always always always check your timing with a light/gun. Always. If/when you get the engine running on your map, your friend's map, a stock map, or a professional tune - you need to know what it is.

You can start almost any engine with 10 degrees of fixed advance(I've started singles, inline 4s and a wide variety of v8s). It won't run great, and it won't blow up. On the other end, V8s tend to max out around 30" advance, and I4s tend to max out around 45-50" advance.

Don't ever compare your final timing values to any other teams or "tooners" in an attempt to determine exactly what is safe! Use a dyno! Who knows if they got their CRIP/Offset value correct; who knows if they reversed polarity on their crank/cam sensors; who knows if they can't read a map? On this note, check your timing again at various RPMs throughout the range, to ensure that the timing light and the cell are the same number.

There's a lot going on in starting from a blank map; I'm not saying I'm the expert here, but I wish I had known those three things when I started.

[Mikey Antonakakis]

I did feel that I knew some good starting values to put in for our setup, and after I checked with a timing light yesterday, I now know why it wasn't working. We were offset 25 degrees or so, which would explain why I had to run 25 degrees advance at idle just to get the thing running. After several hours of trying to straighten that out at the dyno place, I still wasn't able to just enter an offset value in megasquirt, the change never "stuck." Let's say I'd put the offset at a value like 10 degrees. The engine would not run because the timing would be off, so I would then decrease the entire timing map to compensate, but then the engine still wouldn't run, and the only way to get it to run would be to go offset the timing another 10 degrees; I could repeat this as many times as I want, and it would never permanently fix the issue (I double checked that I was going in the right direction). And yes, I burned it to the ECU permanently, or so megasquirt told me. In the end I just offset the whole map by about 25 degrees and checked with a timing light a few more times. A little less than ideal, but this close to competition, with half a semester's worth of schoolwork to finish, I don't have much choice...

[Mikey Antonakakis]

As far as power output goes, according to the dyno our torque curve was VERY flat at around 20-23 ft-lbs across the range. The power curve reflected these torque values, or vice-versa. If you're not familiar with megasquirt, it uses a VE table to control injector pulse width, along with MAP values, and any compensations that are active (including EGO comp). As far as I could find, stock F4i injectors are 230cc/min, and this is the value I entered into to MS for the "required fuel" value... i.e. at room temp and atmospheric pressure (MAP) and 14.7:1 AFR. It uses this value for calculating PW, so it is something like MAP*VE*reqfuel*compensations. So at high RPMs, say, 9000rpm, I was having to increase the VE table value to around 125%, to have an AFR of around 13:1. This value seems to make sense. Now at somewhere close to 100% VE, a 600cc motor should be making around 40 ft-lbs of torque.... not 20. After checking that the timing was correct, and adjusting to compensate, there was no noticeable change. The car FEELS considerably faster than last year's car (we do have a more agressive gearing than last year, so wheel torque should be higher assuming the same brake torque). And last year we made 38 ft-lbs to the wheels (and 57hp). This car certainly isn't half as fast, first gear was done in around two seconds if I remember correctly (I don't, but it was definitely quicker than last year, where the entire acceleration event run was done in first gear to around 11000 rpm). At 13000 RPM, to maintain 13:1 AFR at 76 kPa MAP, VE was around 95%. This estimates to something like 70 hp, not 37... So I don't really trust the numbers the dyno gave. I know I am making some big assumptions with these numbers, but the car has to be making more than 20 ft-lbs from 4000 to 14000 RPM. Last year's car wouldn't even free-rev past 12000 rpm, and made 20 more hp, according to the dyno.