Hey guys,

I know a manual 6G75 converted 3rd gen will do 160kw@wheels all day but what injector duty cycle % are people seeing at this load point? i'm just trying to find out if there's any head room for another 30 odd kw's.

Cheers.

About high 60ish% as I was told by my tuner...

The new 6G75 injectors i was using in the built 3.5L engine were maxxed out at around 180kw's at the wheels causing the engine to run very lean.... Increasing rail pressure to 50-55psi helped make it slightly richer until i changed injectors

Here I go again ... picking your brains Sir Donkey :-) CC speaking !! On my new NA build I was thinking of going with 560cc standard 2011 WRX injectors ? what did you use Jason ? Im knowledge scavenging again :-)

Interesting..the car will be on gas 98% of the time and as the LPG ECU intercepts the signal being sent to the petrol injector and then sends the modified signal to the LPG injector,so does anyone have any idea how the LPG ECU would react to the leaning out? would it throw in extra gas to keep the A/F ratio safe or would it just keep trying to replicate (+20% more gas) whatever the petrol injector is being told?

The new 6G75 injectors i was using in the built 3.5L engine were maxxed out at around 180kw's at the wheels causing the engine to run very lean.... Increasing rail pressure to 50-55psi helped make it slightly richer until i changed injectors

How many RPM's were you turning?

Interesting..the car will be on gas 98% of the time and as the LPG ECU intercepts the signal being sent to the petrol injector and then sends the modified signal to the LPG injector,so does anyone have any idea how the LPG ECU would react to the leaning out? would it throw in extra gas to keep the A/F ratio safe or would it just keep trying to replicate (+20% more gas) whatever the petrol injector is being told?

it wouldn't actually lean out... but your gas ecu might need tuning.. and who knows whether the lpg injectors have enough flow for this power level.

if you are on gas 98% of the time the the injector rate and leaning are ultimately irrelevant.


It works like this.. your injector is capable of say 500cc/min. Each time it goes to fire the engine it opens the injector for a certain amount of time to get the right amount of fuel. So for example it calculates based on air through the MAF and all the other values it knows that opening the injector for 2ms will give the right amount of fuel, and does so.

Now there are two situations that will cause you to lean out, either

(a) You get to 100% injector duty cycle and it is basically open as log as it possibly can be, and not enough fuel got in, or
(b) It wasn't open 100% of the time but the fuel pump couldn't maintain flow and/or pressure so the amount of fuel flowed didn't match what was desired.


Usually with stock injectors you hit (a) and not (b), (b) tends to happen with big fat upgraded injectors and a stock fuel pump. Especially on turbo motors where you are also working against boost pressure.


Now what your LPG ECU does is go, your fuel injector is 500cc/min and the LPG injector is say, 700cc (for simplicity). Also account for the fact the amount of LPG you need is slightly different to petrol and you need to translate the fuel required. So why your petrol injector might open 2ms the LPG injector needs 2.5ms.

So the LPG ECU reads 2ms and really sends out 2.5. At this point the actual flow rate of the injector, and the flow rate of the fuel pump/pressure are irrelevant. you could entirely unplug the fuel injector and this would still work. So what you really need to worry about is the ultimate flow capability of your LPG injectors and what the duty cycle of those are.

Great post Trent,LPG fuel system is good for 240kw conservatively and i believe they use these injectors on the XR6T kits so i would think i'll be ok..just.

How many RPM's were you turning?

It started leaning out from 4500rpm upwards and really became too lean (14+afr's) from 5500rpm onwards