My DC looks wrong!

[saqmaster]

Hi Guys.. quick question.. MS 2.2.. MT 717.. MS&E/edis 25

At 5500rpm, my injector time is ~19ms, and my DC1 is showing 89%.. From 4000 to 5500 it rises linearly from 70ms to 90ms.. All may look correct you think..

However.. I am using 300cc/min injectors.. Theres no, no way it's using 90% fuel (of which the injector is probably hard on anyway!).. For the amount of flow it's running presently, it's only around 170bhp or so. Shouldn't really be using anything more than 200cc/min of fuel! (AFR is correct and confirmed and the car is performing as expected).

I'm running the injectors with 2 squirts + alternating (to kinda simulate sequential flow amounts). So each injector squirts once per cycle. Right.

Technically switching to 2 squirt sync should make things worse as it'll have to consider two open-times instead of one, per cycle.

Okay. I know I need to do some preliminary checks. I need to ensure fuel pressure is raising with boost. I need to make sure i've got fuel pressure a tall. I need to test the basics.

But.. can someone clarify that the DC1 is actually what it says, just incase something occurs when you run alternating squirt, maybe you have to divide the DC by 2 in this scenario. I'm just not sure.

Thanks,

Stu

[efahl]

But.. can someone clarify that the DC1 is actually what it says, just incase something occurs when you run alternating squirt, maybe you have to divide the DC by 2 in this scenario. I'm just not sure.

Stu,

You can verify this for yourself, the calculations are all in the ini file for all those quantities.

Your 5500 RPM = 21.8 ms/cycle and 19 ms PW does indeed come out to 87% duty cycle, so I don't know what else to say.

Eric

[Bernard Fife]

Stu,

Just to add a little to what Eric has said, the duty cycle is a function of more than just the total flow capacity of your injectors. It depends critically on the amount of time available to inject, which decreases with rpm.

For example, at 5500 rpm, you have:

5500 revs/min * 1min/60 sec * 1 injection / 2 revs = 45.83 revs/sec

or,

0.0218 seconds/injection (= 1/45.83), and DC = 0.019/0.0218 = 87%

at 3500 rpm, you have 34.2 millseonds, DC = 0.019/0.0342 = 56%

So the same pulse width gives different DC, depending on rpm.

For rpms below 4800, the maximum 25 millisecond pulse width of MS-I is always available. Above that, time gets short, and you may need to shorten your req_fuel with larger injectors...

Lance.

[saqmaster]

Great, thanks guys.

So if the numbers add up, there must be something mechanically wrong. I'll look into it.