pit_celica wrote:Here are some points that came from a thread here on MS forums (I can't find it right now) :
- You want all the fuel to be injected before the opening of the intake valve.
- You want the end of squirt to end about 10° earlier for each 1000 RPM (the fuel still take about the time to evaporate on a hot intake valve, so you need to compensate for that).
- At mid to high RPM, injection timing doesn't have a lot of impact, so do not spend a lot of time to fine tune your injection timing table.
- The first step is to play with the injection timing in a single cell at mid load and crusing RPM. Find the spot where the AFR is at its richest. This is your ideal injection timing value. Extrapolate in the X axis as per point #2.
- After injection timing tuning, you will need to retune your VE table because it will be a little too rich (that's an indication that you did a good job with your injection timing tuning : combutsion is more efficient because it require less fuel to stay at the same load/RPM).
Sam
So we want the numbers (Degrees) to decrease in order to end the squirt sooner in the rotation???
Thats how I have my map setup, but everyone says that is the wrong way.
1968 Dodge Charger, 446ci 513HP/542ftlbs,Full sequential fuel/Spark using MS3X. Jeep CPS, Ford Crank sensor, 36-1 wheel, Coil near plug with D-585 ls2 coil packs. Edelbrock pro-flo intake, 600cc injectors, GM MAP, TPS, IACV, CTS, MAT. 92mm Throttle Body.
Yves wrote:I ran the engine a couple of times on sequential.
Seems that she runs a lot richer than what I was seeing on batch fire with the above settings.
With the same pulsewidth, your O2 sensor was telling you it was running richer? Doesn't that mean that the fuel is atomizing better and you get the same power out of less fuel, thereby having more left over in the exhaust stream? Or am I misinterpreting this?
It's using up more air, so the mixture does burn better and this means the engine produces more power imo. To get to the same AFR, I need to reduce the fuel.
Yves wrote:It's using up more air, so the mixture does burn better and this means the engine produces more power imo. To get to the same AFR, I need to reduce the fuel.
This does not make sense. Going to seq does not make the engine use more air. It is richer because the fuel is atomizing better. You can lean it back out to the same AFR from before going seq and get the same power on less fuel.
Megasquirt is not for use on pollution controlled vehicles. Any advice I give is for off road use only.
"Using up more air" was important in what i wrote. This was aimed at the amount of air in the chamber. If the fuel burns better because it is atomized better it will convert more air to co2
I was going to start a new thread, but figured this would be a good thread to just post this in as a reply...
Holley EFI released v4 recently and with it they included a similar option to what is being discussed in this thread.
I was going to try to cheat and just use their calculated values then from there see if it could be improved on, but the problem is their table is in relation to BDC whereas tunerstudio is looking for values in relation to TDC. So, if I am thinking about it right I will want to add 180, but based on numbers that were calculated earlier in this thread that doesn't seem like enough. Maybe add 540? I've been thinking about it way too hard. Time to try to get some help. lol
If you want to use this table form Holley and apply it to MS, first, use absolute values (remove the negative from the table) and add 180° to the value. In my setup, I was using something like 330° to 380° (linear transition in the X axis from idle to redline RPM). So, if we translate the first row in the screen shot above, you would get 251.8° to 290.8°. These values are in the ballpark of a functionnal injection timing table based on end of squirt. They correspond approximatively to the facts on injection timing :
- You want all the fuel to be injected before the opening of the intake valve.
- You want the end of squirt to end about 10° earlier for each 1000 RPM (the fuel still take about the time to evaporate on a hot intake valve, so you need to compensate for that).
- At mid to high RPM, injection timing doesn't have a lot of impact, so do not spend a lot of time to fine tune your injection timing table.
- The first step is to play with the injection timing in a single cell at mid load and crusing RPM. Find the spot where the AFR is at its richest. This is your ideal injection timing value. Extrapolate in the X axis as per point #2.
- After injection timing tuning, you will need to retune your VE table because it will be a little too rich (that's an indication that you did a good job with your injection timing tuning : combutsion is more efficient because it require less fuel to stay at the same load/RPM).
I will just add that the table I used (see page 1) gives me excellent results. However my injection angle is the worst you can possibly have because of space constraints (90° at airstream), which implies I need time to get the fuel to vaporize from the walls.
How does this calculation work in relation to cam timing or port velocity? Would it be fair to say 8ms is a fairly aggressive number and perhaps could be higher when port csa increases (sluggish port at low rpm) and cams that have an early IVO?
krisr wrote:How does this calculation work in relation to cam timing or port velocity? Would it be fair to say 8ms is a fairly aggressive number and perhaps could be higher when port csa increases (sluggish port at low rpm) and cams that have an early IVO?
A sluggish port will have a slow airspeed and therefor the amount of fuel going into the mixture will decrease. It will depend heavily on how good the injection angle is, how hot your port is, how far your injector is from the port etc. If you have a less than optimal injection angle, you will need more time. If you have a higher running temperature (i.e. 195°F vs 185°F) you will need less. If you have an injector further away from the valve you have more time to get the fuel to vaporize etc. Apparently the 8 ms was a number that was arrived at after testing and seems to work for me. I understood this was for an injector at the port entrance into the head and pointing at the valve. I still have issues when the engine is cold however.
As you are injecting roughly during the time the intake valve is closed (exhaust valve opening) and your intake valve opens earlier, you need to use a higher number in injection timing imo.
It will also depend on what your engine likes. Mine doesn't like fuel that isn't vaporized very well, it ran better at a higher temp than 185°F and has issues when starting up during WUE.
In a way tuning the fuel injection timing is like tuning the ignition timing. I can also see how one could effect the other in this regard...but I haven't seen a test done on the dyno as far as this is concerned.
pit_celica wrote:If you want to use this table form Holley and apply it to MS, first, use absolute values (remove the negative from the table) and add 180° to the value. In my setup, I was using something like 330° to 380° (linear transition in the X axis from idle to redline RPM). So, if we translate the first row in the screen shot above, you would get 251.8° to 290.8°. These values are in the ballpark of a functionnal injection timing table based on end of squirt.
Thanks for your input, but plotting numbers using absolute values just doesn't seem logical to me. Especially looking at the higher boost areas of Holley's table.
I did a mistake. You should not do an absolute then add 180° from the Holley table. You need to multiply by (-1) to invert the sign and then add 180°. This way you will be converting correctly from the Holley table to MS table.
But, keep in mind that injection timing have less importance at high boost and high RPM (basically at high injection DC%). I think you should focus only on the low load/low RPM cruising load/cruising RPM to fine tune the injection timing.
I don't think to multiply by -1 is the answer either. To do that would put the value at the top of the rpm/boost at 43°.
I ended up having a little chat with Scott Clark a couple nights ago and what worked out to his liking was adding 360 from holley's values. So that's where I'm going to start. I get what you're saying about WOT timing. 24 psi and 7000 rpm (my highs) are still only at 75% duty cycle though with the 2000 cc injectors so I would imagine there may still be some room for improvement being that they aren't hung wide open.
