Plug & Play Megasquirt?

Topic: Plug & Play Megasquirt? (Read 4965 times) previous topic - next topic

Plug & Play Megasquirt?

Reply #30 – April 04, 2008, 10:28:07 AM

Batch fire in truck 5.0 Speed density SEFI in passenger car 5.0 speed density applications. All Mass Air was SEFI AFAIK.

Cougar5.0 -- I see you're still running over 100% duty cycle....or did you finally swap the injectors?

Plug & Play Megasquirt?

Reply #31 – April 04, 2008, 11:49:12 AM

That plot is deceptive - it shows that in order to fire the injector after the exhaust valve is closed, the end of the pulse would be after the intake is closed AND even beyond the 720 available degrees. This is not the case - if you subtract the largest number from 354 (where the exhaust valve closes and where I have set the pulse to "start" at), you will see that the pulses are no longer than 540 degrees or about 75% duty cycle.

So what happens in reality is that I set the "off" point for the injector at 560 degrees - just 19 degrees before the intake is closed (the cam is actually mounted straight-up, not 4 deg advanced as shown). This means that the injector starts firing at about 20 (560-540) degrees at high RPM & load. I'm sure I've created more questions than answers :hick:

Plug & Play Megasquirt?

Reply #32 – April 04, 2008, 12:32:52 PM

Quote

This means that the injector starts firing at about 20 (560-540) degrees at high RPM & load.

At which point the combustion events in the chamber happen within a short duration (each one). This would in effect require less spark or more? And correct me if I'm wrong but this promotes a rather clean burn @ high RPM, right?

Plug & Play Megasquirt?

Reply #33 – April 04, 2008, 12:53:16 PM

Quote from: Cougar5.0;212508

That plot is deceptive - it shows that in order to fire the injector after the exhaust valve is closed, the end of the pulse would be after the intake is closed AND even beyond the 720 available degrees. This is not the case - if you subtract the largest number from 354 (where the exhaust valve closes and where I have set the pulse to "start" at), you will see that the pulses are no longer than 540 degrees or about 75% duty cycle.

So what happens in reality is that I set the "off" point for the injector at 560 degrees - just 19 degrees before the intake is closed (the cam is actually mounted straight-up, not 4 deg advanced as shown). This means that the injector starts firing at about 20 (560-540) degrees at high RPM & load. I'm sure I've created more questions than answers :hick:

A couple questions:

Have you tried injecting the whole pulse before the I valve even opens? This will greatly improve your vaporization and may reduce unburned fuel in across your O2 sensor. Fuel needs the heat to vaporize well. The goal is to start injection soon after the I valve closes so it can sit on the valve and absorb heat.

Why the excess overlap with a blower? I would've thought your overlap could be reduced since you are forcing air through the exhaust valve.

Plug & Play Megasquirt?

Reply #34 – April 04, 2008, 02:45:27 PM

I used the fast-ramp Comp "XE" cam because of the 35+ HP improvement that Richard Holdner saw in his testing with a KB blown 5L engine. I have done everything possible to reduce the off-idle torque of the blower as there is still way more than I need! This involved using a 112 LS cam (overlap leaks a little boost at low RPM and also helps cool the exhaust valve), retarding it 4 degrees (pushes the torque curve out a bit) and I pull timing in 1st gear based on load (i.e., if the tires slip the engine load will be reduced, but I pull MORE timing at medium loads (none at light loads so normal driving is not affected). I have considered injecting onto the back of the valve longer (it still happens quite a bit anyway) but the arguments for and against made me keep it where it is (which still has it spraying on the back of the intake valve for 380 degrees of crank revolution!) Adding 140 more degrees of of time to the back of the intake did not seem worth the risk of possible carbonization and pulling of fuel past the valve guide. Of course when I had injectors that were too small and I was at 100% DC, this became irrelevant :hick:

Plug & Play Megasquirt?

Reply #35 – April 04, 2008, 04:55:56 PM

I really don't think you'll have to worry about the fuel evaporating off the wall as late as you're injecting it.

Is your open loop cal good enough to put it in OL when alot of fuel is passing through the exhaust valve?

Plug & Play Megasquirt?

Reply #36 – April 04, 2008, 06:29:02 PM

Why would fuel be passing through the exhaust valve? The car runs open loop for the first few minutes just fine.

Plug & Play Megasquirt?

Reply #37 – April 04, 2008, 08:28:56 PM

You said that when fuel passes through to the exhaust it screws with your AFR reading at your O2 sensor. I'm saying that under these conditions, put it in open loop and it will ignore the O2 sensor. I'm assuming these conditions are high PW which is high load.

Edit - Just reread your other post. Sounds like its everywhere but light load.

Edit II - Your only under boost above a load of 1 right? This means that this is the only possible time that pressure would force fuel out the exhaust during overlap. Any other time the manifold is under vacuum and would force it out during the piston coming up, which is when the valve is almost closed. I don't think your erroneous AFR readings are coming from overlap. I think its from you inj timing not being retarded enough. This definitely true when your load is under 1 because you are not under boost. Above one you may get some.

BTW I'm having a hard time figuring out which is your cam profile is on that page. The open/closed numbers show overlap of 1 degree. Are any of those numbers accurate?

Plug & Play Megasquirt?

Reply #38 – April 04, 2008, 10:27:07 PM

The cam profile seems to account for the 1.7:1 rockers - making the events seem different than rated. The XE270HR-12 is 218/224 112LS (270/276 @ .005). It's cut to be advanced 4 deg, but I retarded it 4 deg so it's straight-up now.

The only reason I mentioned gasoline blow-through was at idle/very light cruise loads - I ensure the injector fires after the exhaust valve is closed, that's all. I don't care much about this issue at higher engine load & RPM's where I'm mostly concerned with performance.