ViribusUnits

Does anyone have the flow rate of the L-jet fuel injectors? Also at what pressure was this measured?

19 lb/min comes to mind, but I'm not sure.

Thanks.

toofast928

24 lbs at 43 psi

John.

The Bosch injector specs are 111-112 cc/30 seconds @ 36.0 psig for the L-Jet cars.

ViribusUnits

OK, working with an online calculator, it tells me that 111-112 cc/30 seconds is about 21.5 lb/min. All at 36 psi of course. (or 2.5 bar)

Going further, it tells me that if I change the pressure to 43 psi I get just 24 lb/min, so your both right. Thats nice.

Now if I'm reading my WSM correctly, the fuel rail pressure should be 36 psi above the mannafold pressure, normaly. So that would mean the engine would recive about 21.5 lb/min of fuel, if the injector duty cycle was open all the time.

Thanks.

SteveM928

That would be lbs/HOUR, not lbs/min. Don't forget that that's the flow per cylinder either, so total into the engine would be times eight injectors.

ViribusUnits

Yea my bad.

Wrote lb/hr on my notes, but got confused between the lb/hr line and the cc/min line in the middle of the typeing.

2V4V

Hugely important to remember the following,

When sizing injectors, they are generally rated at 80% duty cycle - that is, only being open 80% of the time. If they are measured at a different duty cycle you will get different results.

Some people flow rate injectors at 100% duty cycle. This is nice for a baseline, but you must find out what duty cycle they were flowed at as well as the pressure, because it will greatly affect your end flow calculations.

If you are setting up engine management, exceeding 80-85% duty cycle is a recipe for trouble for a multitude of reasons.

Nice thing about the low-Z (peak and hold) type injectors that are spec'ed for our cars is the faster attack and decay times compared to a high-Z (saturated) injector. This leaves more time for the actual fuel pulse, when accounting for the opening and closing of the injectors.

Greg

SharkSkin

Interesting.... I'm no fuel injection expert, but at one point you said 36 PSI above manifold pressure. Manifold pressure is -7PSI more or less, assuming 15 inches of vacuum.

So, if you have a gauge that reads zero when the port is at atmospheric pressure, and it reads 36 psi when connected to the injector rail, then the injector is really seeing a 43 PSI differential.

But if taken literally, 36 PSI above manifold, then your gauge would be reading 29PSI at the fuel rail.

Sort of a strange confluence of numbers IMHO... but according to VU's quote from the WSM, 29 PSI should be indicated on the gauge. I seem to recall that a higher pressure is recommended?

D

ViribusUnits

The recomended pressure, assuming I'm reading my WSMs correct is around 2 bar at idle. Or around 29 psi.

The recomended pressure for the L-jet cars is 36 psi engine off, fuel pump on. Basicly when the mannafold pressure is at 0 psig.

The S4 cars call for higher pressures. Accoring to the WSM around 3.8 bar, or around 55 pia above mannafold pressure.

43 psi seems to be something of a common pressure to measure fuel injectors at. Don't ask me why, but it is. Maybe it's very common for more common cars?

Rez

Holy spell check batman!

John..

L-jet does not run 80% duty cycle....

ViribusUnits

What is the highest duty cycle?

2V4V

True John, our cars do exceed the 80th percentile...

100% is the highest (theoretical) duty cycle.

Some cars I've measured can approach the mid 90% under certain conditions, but they try not to stay there very long.

80%-85% is one of those tuner "guidelines". Can you exceed it? Sure. When you do what are the risks? Locked injector is the biggest potential downside. If that injector fails partially open (can happen) guess what happens to that cylinder getting all it's boost, but half it's fuel.

The other main reason to stay under 100% is simply so that you have something to tune. If you've raised the line pressure to the limit of the injectors, and the injectors are running WFO, then what are you going to adjust to fix a lean spot? You'll be left with putting in new injectors, and retuning the whole system just because you undersized the injectors.

Greg

PorKen

Stock L-Jet fuel pressure is 36PSI (2.5 Bar) with engine not running and fuel pump relay jumpered, and ~29PSI at idle (depending on vacuum leaks).

43PSI is 3 Bar; those metric types love even numbers.

Gretch

"The S4 cars call for higher pressures. Accoring to the WSM around 3.8 bar, or around 55 psi above manifold pressure."

With 19# injectors.

So you get the same flow capability with 30# injectors and a static pressure of 40psi or 33 at idle. Exactly the "at idle" tuning called for in Murphy's kit. Tim's setup, with a rising rate regulator sensitive to boost will then cover the aditional fueling requirements.

At full boost (8lbs in my case, 1/2 an atmosphere) I should need 50% more fuel to avoid going lean, correct?

That means the fuel pressure has to rise to 50 psi, correct? It does that easily. If the 19# injectors were sized for 80% duty rate, there should be at least that much head room in the 30# injectors, at least at 8psi of boost.

Am I all wet here or is it this basic?