6.0 Tuning challenge

I am wrapping up the last bit of assembly on my 6.0 LQ4 marine build. This is the 4th LS i have dropped into a boat and let me say, all 3 of the others were incredible. ANYWAY, heres what i want to know:

Is it possible to nail down a decent tune without a wideband OR front o2s? the reason i say this is; a typical marine exhaust system is wet. the last swap i did i tried to put front o2s in and they almost instantly fried from the water. I had them in the dry side but you still get steam/ moisture as far in as the exhaust ports in the head. I wiped my wideband the same day trying to use it instead.

I still have the option of running the MAF and MAP as they are still installed. if it is possible to do this how would i go about it? i have never tried tuning without using the front o2s.


Low mile LQ4
SS2 Cam
PAC springs
TBSS intake manifold
Holley rails with aeromotive pump and regulator



Thank you!

It's impossible to know what is going on in the exhaust without a sensor.

Even standalone computers still use a wideband because it needs something to get information from.

I think the only way to get something like this tuned when you can't run a sensor is to toss a carb on the intake or take the engine and dyno tune it and put it back in the boat.

I cant run the engine without water coming out the exhaust and a carb will completely reverse the entire reason for going LS in a boat.

i agree best way would be put in on a dyno. either that or run a cooling system with heat exchanger and dry exhaust.

call kodiak marine and ask them about the ls wet manifolds. they wont be cheap but its one of the only ways i know of to use the oem sensors in a wet system. they use them on their supercharged package with great success.

I tuned about 20 LS3 525 motors on boats. I'm under NDA but what I CAN tell you is... they had custom manifolds made that still had water through them but kept the sensor dry and exposed to exhaust stream. It would work with my wideband, but the manifolds took out TOO MUCH HEAT for the NBO2's to work well. Eventually I stayed open loop with all of them once they were tuned.

Also, FWIW, be super, super conservative on spark... you can't run anywhere near the advance that you would see in a car/truck under any load.

I'm thinking open loop is the way to go. I'm running the Pleasure craft Marine manifolds, they are the only reasonably priced LS marine manifold. I dont want to drill into the manifolds as I dont really know where the water jackets are. It is possible to run water through the heat exchanger to keep the engine cool and bypass the manifolds but not for any length of time and not on the water. I havent dropped it into the boat yet.

I'm not looking to go crazy on fueling and timing. It's going into a 30ft cruiser. I would just leave the stock file in and let it run in OEM open loop the rest of its life BUT it has the SS2 cam and TBSS intake manifold. The tuning would be way off to the point it likely wont run.

One of my friends who dropped a 5.3 in his ski boat left it completely stock, slapped the PCM manifolds on and let's the engine stay in the factory programmed open loop mode with no o2 sensors pinned into he ECM. It has been running strong for 7 years now, CEL and all 🤣. Still gets better mileage and has more power than any carbed marine engine I've seen.

I read about open loop tuning using the knock sensors...any truth in that?

I’ve ran boats always in OL... they usually run around 130 ECT anyways so I usually setup that temp in OL tables to reflect stoich... most time that’s part of the warm up enrichment temp and little extra fuel being used