Fuel limiter at 50% duty cycle of direct injectors - C7 Corvette, LT1, supercharged

[GME]

Hello everybody!

I'm from Germany, please excuse if my English might not be perfect... I'm tuning my Vortech supercharged C7 (LT1 engine) at the moment and I realized a problem that I can not solve by my own. I tried a lot of changes in the calibration, but nothing helps:

The direct injectors won't open more than ~50%. No matter if I command an WOT AFR of 12, 11 or less than that, the volume of fuel does not increase above a certain rpm and the injectors run into a plateau at 50% duty cycle. When I comand an AFR of 12 (which the C7 likes much more than richer mixtures), than the fuel is just to be enough to meet the required quantity so that the measured AFR can follow the commanded AFR until it hits the RPM limiter. But when I command less than 12 for WOT, you can see more and more that there is a limit at 50% duty cycle. That isn't a problem right now for the 5psi of boost at a WOT AFR of 12 that I'm running at the moment (~630hp at the crank), but I want to increase the boost and will need more fuel soon...

Did I do something wrong? Did I forget to tune a certain map? Is there somewhere a limiter in the software that I need to switch of? Or is the fuel system of the C7 simply maxed out at this level? I can't believe that because I've heard of supercharged C7's with LT1 engines making 700hp at the wheels.

Here is a screenshot where you can see the 50% duty cycle plateau in the top chart:
direct injector duty cycle.JPG

You can see in the second chart that I command an AFR of 11, but the measured AFR is not able to follow it (it's not my MAF table, that's calibrated perfectly) and stays at 11.8, the AFR error rises and the injectors show a 51% duty cycle in the upper chart which remains at this value.

Please help me! Thank you a lot!

René.

[Higgs Boson]

The duty cycle is calculated differently on the DI cars. Most recommend not exceeding 35-40% so at 50% I would say your are just out of fuel. You need a different HPFP cam lobe or more pressure or bigger injectors.

[DSteck]

Duty cycle for direct injection isn't the same calculation as for port injection.

About 48% is maxed out based on how the scanner calculates it.

[GME]

OK, that was also my first thought. But than I've heard about other guys making 650~700hp out of the LT1 engine with stock injectors and pump. Therefor I thought that there is a mistake in my calibration. Can't I "stretch" the SOI and EOI angles a little bit to enlarge the window where the injectors are allowed to spray? There are maps for the SOI and EOI angles, but I'm not sure how far I can modify these values without causing a damage to the engine. Does anybody know the earliest angle to start spraying and the latest angle to end spraying depending on rpm, load and ignition advance?

[Area47]

pull timing, lean it out to 12.5 and try again.

[DSteck]

People are getting more power by using aftermarket cams with enlarged lobes for the high pressure pump.

[GME]

pull timing, lean it out to 12.5 and try again.

What will I learn from it? Please tell me in advance. With my WOT AFR of 12.0 I have exhaust gas temperatures between 830°C and 850°C when running the Corvette at constant high speeds (and high loads) on the German Autobahn. We need to take care not to overheat the pistons, therefor I was already a little bit nervous with 12.0, but your 12.5 sounds a little bit lean to me for a stock engine. Or what is your idea about it?

People are getting more power by using aftermarket cams with enlarged lobes for the high pressure pump.

For example from "Crower Cams"? What happens when I install these cams? Will the fuel pressure increase? Or is the fuel pressure controlled by an electronic valve and can be adjusted in the calibration? In that case the fuel pressure should not change after the installation of the cam as long as the calibration stays unchanged. Am I right or how does the fuel system work?

[DSteck]

There's a dump valve that maintains pressure. Larger loves allow the pump to actually maintain pressure at high load.

[Ben Charles]

Big things to change
Z06 pump is available bolts right in under the intake
Larger Fuel Lobe on an aftermarket Camshaft
Always increase fuel MPA in tune to gain some room
Inject Fuel Earlier with SOI

No all are required above, but will certainly help. I would try the later before the first.