yoeddynz

DIY Fuel injection thread.

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19 hours ago, scooters said:

Remember a common missoma is that sequential injection is tied to valve timing and fire when the valve is ope or about to open.

Lets say your injectors are at 85% duty way the fuck up in the load cells.. well a lot of that fuel will be sprayed while the valve is shut anyway. 

I agree however the further you have the injector from the head, as is being propositioned. The more relevant injector timing becomes because you have inlet harmonics trying to push fuel back out top of the runners. Which doesnt really matter when the injector is right by the valves, but a very big problem if they arent.

I have found that on a cold start the engine will start waayyyy nicer when you use an injector timing that sprays when the valve is open, in order to minimize wall wetting. As it takes so bloody long to evaporate when engine is cold.
A friend of mine tried the same thing with E85 which is notoriously awful for cold start and found massive improvements.

The recent idling improvements that AJG193 recently found by going to 2 squirts per cycle is basically a crude way of circumventing the problems of batch injection's asymmetrical injector timing.

If you have your engine idling and slowly advance through the injection timing range it makes such a difference it can either make your engine rev a lot higher or make it stall. As the combustion quality changes so much.

When I tried having a fuel map using 100% staged outer injectors (even though fully sequential) it was an absolute shit show for idle and transient conditions, even after a lot of time trying to optimize it.

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1 hour ago, Roman said:

I agree however the further you have the injector from the head, as is being propositioned. The more relevant injector timing becomes because you have inlet harmonics trying to push fuel back out top of the runners. Which doesnt really matter when the injector is right by the valves, but a very big problem if they arent.

I have found that on a cold start the engine will start waayyyy nicer when you use an injector timing that sprays when the valve is open, in order to minimize wall wetting. As it takes so bloody long to evaporate when engine is cold.
A friend of mine tried the same thing with E85 which is notoriously awful for cold start and found massive improvements.

The recent idling improvements that AJG193 recently found by going to 2 squirts per cycle is basically a crude way of circumventing the problems of batch injection's asymmetrical injector timing.

If you have your engine idling and slowly advance through the injection timing range it makes such a difference it can either make your engine rev a lot higher or make it stall. As the combustion quality changes so much.

When I tried having a fuel map using 100% staged outer injectors (even though fully sequential) it was an absolute shit show for idle and transient conditions, even after a lot of time trying to optimize it.

Wasn't me that found that. I've been running 2 squirt since day 1. Tried one squirt for a minute once and instantly regretted it. I think 4 squirt would get me too far into nonlinear range at idle.

 

edit: actually went 2 squirt in December, it was the simultaneous thing that I only tried once 

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4 shots per cycle make much more sense to me since with only two shots, one injector per batch will be firing say on valve opening event, while the other will fire with the valve closed 360° out. With 4 shots you'll be firing half and half, meaning each cylinder will see the exact same fuel conditions.

Just make sure you adjust your req_fuek to suit or you will be running twice as much juice and mess everything up.

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my engine runs wayyyyy better on 4 squirts. megasquirts adjusts required fuel automatically when fiddling with that setting 

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It's kind of weird how it all behaves large injectors on small Pulse width will have mostly no effect as a lot of the time they will be spraying on the back of shut valves. 

Only way to nail it down is to get a wide band get the idle stable... you can pull full in out out with the VE table to suite.

however if you do it pre throttle you are just adding another phisical object for the fuel to get around and mess you up.

 

I tried years ago to tune some independent throttle bodies on a 4age. Could not do it with VE.. Had to speed density it. I think because the throttle open up and the 

air flow was really exponential. Another story meh . 

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3 hours ago, Roman said:

The recent idling improvements that AJG193 recently found by going to 2 squirts per cycle is basically a crude way of circumventing the problems of batch injection's asymmetrical injector timing.

If you have your engine idling and slowly advance through the injection timing range it makes such a difference it can either make your engine rev a lot higher or make it stall. As the combustion quality changes so much.

I found this made a huge difference on the 124,  likely due to oversized injectors and very short runners

2 squirts per cycle alternating I think is what they call it. with two injector drivers each one firing every 360 degrees but 180 apart.

each cylinder then gets half of its fuel at the right time and half 360 deg out at the wrong time.

before my engine would get to somewhere around 4500rpm and just pop and fart and not run for crap but if you held jandal it would clear up over 6000rpm somewhat.  also the tailpipe always stank of raw fuel at idle.

switching to this and timing the half of the fuel at the right time to finish injecting just after exhaust valve closing made the engine rev clean right out and I had to pull out about 20% fuel or something.

just now it has some other issues, less fuel going through and I think the ridiculous IAT's at low and no load with no air bypass valve around the supercharger are causing random intake backfires, probably off the hot surface of the back of the intake valve or something like that.

 

CAM%20TIMING-FULL.pngPicture.jpg

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I've heard that some people find an approximation of the injector deadtime by alternating between single then double pulse (per cyl) until the AFR matches for both results 

But as you say the fact you're making that change changes how well it combusts etc anyway so not really a reliable test I guess. 

But if it's 20% difference (at presumably low load) perhaps it could be deadtimes being a little off?

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the excess fuel was because it was injecting during overlap, and with the large injectors that time during overlap was a large proportion of the total fuel being injected getting blown out through into the exhaust. Worse with it being a supercharged engine, so a lot of exhaust blowdown during overlap from intake pressure > exhaust pressure

its a bit messy on my sketch but what I think I was showing there is

red \\\\ hash exhaust valve open period

blue //// hash intake valve open period

yellow highlight is overlap

$ish scribble is spark event (wasted spark setup)

light blue highlight is injection 

360 deg takes 8ms

numbers are cam and ignition timing

cylinder pairing for injection and ignition 1+4 and 2+3

total require fuel is I think 6.68ms per cylinder there, and overlap is something like 1.5ms so injecting during overlap means 20ish% could disappear, splitting the injection up this way means only half that amount has the potential to go out the exhaust as the second half is all injected while the intake valve is open so should almost all end up in the cylinder.

at lower rpm this could be even worse as the overlap time is much longer.

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Anyone have any VAST coils for sale/know the best place (or vehicle) to source them from?

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