Open loop speed density tuning - LS Jet Boat with L96 VVT 6.0L

Hi all,

Have a factory Hamilton 161a jetboat with a 2016 factory marine L96 6.0L driving a HJ212 pump. The L96 has a cast iron block, rect port L92 heads, 9.6 cr, VVT, with very docile cam timing 196/208, 0.467/0.469, 116 LSA, and is rated at 360hp/380ft/lbs. Looking to upgrade cam/springs to unlock its potential (https://gwatneyperformance.com/product/l99-vvt-cam/ - stage 1 version) and I will need to tune it.

The factory set-up is a speed density open loop tune with wet riser manifolds and wet exhaust and no 02's or provision for them, or any easy way of running them. I am familiar with the Gen IV LS platform and standalone tuning on Link and Holley. HP Tuners will be new but I've watched the relevant tutorials and courses on here. I expect it to be a fairly simple configuration with no MAF, no CLL, and a true VE table driving spark and fuel, however I'll be a bit blind dialling it in.

Questions:

1. I'm expecting that fuel requirement (VE) changes will approximate the % diff in torque curves between cams? Once I deal with idle airflow, I expect it will be a bit fat down low where VE may have deteriorated and will cross-over to a steadily increasing lean condition at around 3k rpm where VE starts to improve, and that I will need to adjust for that, particularly up top.

2. Can I use the jet unit like a crude dyno to identify MBT timing and fuel for a given throttle opening? For example if adjustments resulted in more RPM for a given throttle opening I would be closer to MBT?

3. Given that the engine will be pretty highly loaded in normal operation, can I simplify VVT tuning to a 1D approach where I command cam position based only on RPM?

Appreciate your thoughts and advice.

Cheers, Andrew

I would advise against this entirely, you might as well put a carburetor on it and tune by ear if you have no o2 reference for fueling. Carbs will respond better to changes in airflow than a "tuned by ear" efi system. Best bet is to figure out a way of getting o2 sensors and tuning the conventional way