About Fuel Injector Timing

[cooperr53gp]

I have read lots of thread about injector timing but some of them confused me. 

I am tuning my cooper r53 gp and I realized something about injector timing. When I start tuning my car Inj timing was 330 BTDC and position is end of injection that came with base map. Then I calculated my camsaft timings and found intake valve opening 18 BTDC. And set my inj timing from the formula 360 - 18 = 342 BTDC then I made a few runs and realized that engine knock noise lower than before. And play with ignition advance knocking values with 330 degree isnt knocking with 342 degree. I can advance timing about 2 degrees with 342.

I am using 550 cc injectors and at max duty cycle i see is about %60. I think in this case injector timing matters.  But I dont know my settings right or not.

For a theory you have to inject all fuel right before intake valve open. But there is someting wrong with this theory before intake valve open exhaust valve is also open and fuel can go to the exaust without burning.

I think best time for injecting fuel is right after exhaust valve closed. But in this case I dont know is there enough time for injection fuel.

And my other question is why is vipec using 330 BTDC for Cooper S it doesnt match with stock cam specs.

In this picture left side stock cam and right side my schrink cam values. 

 

 

[rrob]

Most piston engines seem to like 360-420 around idle, I ramp it up with engine speed also. 

[Adamw]

Injector spray pattern, injector location, port temp, fuel composition and fuel pressure will all have a significant influence on what is optimum for you.  You cant guess or calculate it theoretically, as what you are trying to acheive is find what conditions create the most usable volume of volatile fuel vapor.  You must do it by experimentation while measuring torque output.  Most engines it makes very little difference once engine speed is above about 3000RPM.  For idle and low speed you can determine it just by adjusting timing so that you get the richest measured lambda for a given pulsewidth. 

As rrob says, for a warm engine at idle with injectors close to the intake valves, common values will be 3-400deg.  For a cold engine/port usually much earlier timing is required - often around 200-300 is best.  

 

11 hours ago, cooperr53gp said:

I made a few runs and realized that engine knock noise lower than before. And play with ignition advance knocking values with 330 degree isnt knocking with 342 degree. I can advance timing about 2 degrees with 342.

Knock level is not really relevant - this could mean the exact opposite of what you are trying to achieve.  Less efficient combustion means lower cylinder pressure, less noise/knock and less torque.  

 

 

 

[RedZED]

From My experience:-

One of the most obvious signs of incorrect injection timing on a petrol (gas) ice engine is not being able to achieve good stable AFR values at idle.

Its always a good idea to map out your intake camshaft lobe openning and closing. Then overlay your injection start point. If you are starting to inject fuel onto a closed intake valve, the atimised fuel will puddle on the head of the valve and get drawn into cylinder making it much harder to ignite. Injected fuel must take place when the intake valve is open.  So we have some questions that comes to mind:-

1) At what point (time / degrees ATDC) after the intake valve opens do I start injecting?

2) How do I adjust it the injection timing?

3) How do I know when I've hit the sweat spot for optimum injection timing to achieve maximum efficiency?

The answer to questions 1 & 2... can be adjusted in the config of an after market ECU. Question 3 can only be anwered by careful torque measurements on the dyno.

As an estimate only, injection could start about 20+ degrees after the intake valve starts openning.

Ah.. what would I know!

[k4nnon]

This often a difficult subject to grasp and understand because there are soo many different factors that will change how an engine runs. Theoretically you can do the math and get an exact point of time to when the valves open/close or when to inject the fuel. But then air temperature, air velocity, engine speed, port design, ignition timing, fuel pressure, fuel temperature, and more will effect how the engine runs at that particular injection timing. The best way to figure out when the best time to inject fuel is mentioned above. Watch your lambda correction value at idle and make small changes to the injection timing either up or down and adjust to its richest value. If you make an adjustment and the lambda correction is going negative keep going until it starts going back the other way. At one of these adjustment points the cylinder will ingest as much fuel as it possibly can during one valve open/closing event. This is usually the sweet spot and injection timing can be populated to this number in the whole map, Or you can play with injecting timing with engine speed above 3k rpms or so. Another big thing to pay attention to is just how the engine seems to like the adjustments. it might seem to run super great in one area and slightly rough in another. Just takes playing with to get right. 

[Laminar]

Would there be value in making a 2D table that varies injection angle based on vvt intake cam position if you're really shooting to synchronize injection with the intake valve movement?

[k4nnon]

21 hours ago, Laminar said:

Would there be value in making a 2D table that varies injection angle based on vvt intake cam position if you're really shooting to syncronize injection with the intake valve movement?

This would be a nifty idea. I even thought about doing this in my vehicle while on the dyno. While tuning different vvt angles ill have the map locked at different angles to overlay tq output and build a map which produces the most. Would also be a great time to find the best injection base timing for each specific vvt angle and build one complete injector base timing map and vvt map at the same time.