Direct Injection - bigger bore high pressure pump and larger injectors

Hey guys,

I'm trying to be as efficient with my time on our dyno as possible, so I'm asking for help or if anyone has done this a couple of times and has some words of advice here :)

FI late model GM engine, still stock and on stock ecu (-> HPTuners).

The plan is to change the injectors for bigger ones with data beeing supplied. I'm unsure if the data is accurate enough, given the fact, that aftermarket DI injectors are fairly new.

Also, the pump will be swapped out for a big bore one - other than this unit flows ##% more than stock and ##mm bore size, there's not much more info on that. Also talking to the manufacturer, that's about as much as I'm getting.

Next, camshaft with bigger fuel pump lobe and of course the forced induction system will be swapped out - hence the change in the fuel system, because the stock system will definitely not be able to cope with the power goals.

So, basically I'm about to change the VE completely as well as all the known fuel parameters.

My initial plan, was to put in the injectors, punch in the data and run the car on the dyno at certain load and rpm points and double check against the same load / rpm points as I've run it in stock form.

That should give me enough confidence on the injector data.

Now here's the part I'm not sure -> high pressure pump with bigger cam lobe.

I'm I beeing too fussy about that all, should I just throw it all in and get her on the rollers?

Or is the "change one thing, calibrate it, then change the next thing" the right thing to do here and just accept the fact, that it takes that process to get perfect results.

thanks a lot.

As yet we haven't been involved with the late model GM DI engines so I can't speak from experience. As far as the pump goes, in the aftermarket world you do need quite a lot of data around the pump volume etc to provide stable control of the fuel pressure but I don't know how GM deal with this or if these tables are defined by HP Tuners. If this data is wrong you're likely to have difficulty controlling the fuel pressure but of course it comes down to how far beyond the factory spec you've moved. If you can maintain solid control over the fuel pressure, the normal aim would be to increase the pressure targets at high load/rpm to reduce the required pulse width to achieve a target lambda. The ECUs fuel model will account for the effect of fuel pressure on the injector flow so this shouldn't require any work from you.

Beyond this, you're theory is sensible - Check the tune with the new injectors/fuel pump and see if you're still hitting targets. If you skip this and make the rest of the engine mods it can be hard to decide where any potential error is coming from.