The K&N 59-5020 is an oval, tapered marine flame arrestor built around an oiled cotton gauze element and a stainless steel top. The manufacturer lists a base of 8.625 in by 4.5 in, a height of 3.25 in, and an inside flange of 4.75 in by 2.938 in, and it is labeled for GM LT1 marine engines with no vent. Because the element is washable and reusable, it can replace a sealed factory-style unit with a serviceable one that you clean and re-oil over time. The manufacturer says it is marine approved to SAE J1928 and claims it smooths incoming air for added horsepower and torque. Confirm local marine inspection requirements before you buy, because owners on user forums have debated how these units are treated at inspection.
Shoppers searching for a K&N 59-5020 marine flame arrestor GM LT1 no vent, an oval tapered marine air filter, or an SAE J1928 cotton gauze flame arrestor are usually replacing a stock unit that is cramped, dented, or not serviceable. Owners on user forums say the K&N version improves airflow over stock, though the gains depend on the rest of the engine, so expect the biggest benefit on a heavily modified setup. Pre-install checks matter most. The manufacturer's boat sizing guide asks you to measure diameter clearance around the existing unit, confirm height clearance under the hatch, and measure any vent hose inside diameter before you order. Owners also warn that an over-oiled element can foul a MAF sensor, so let freshly applied oil drain fully before you install it.
The 59-5020 is the no-vent version according to the manufacturer. The manufacturer lists a separate GM LT-1 version with a 5/8 in vent as part 59-5019, so confirm your vent setup before ordering.
The manufacturer specifies a re-oiling amount of 0.59 oz (18 ml). Owners on user forums recommend letting the element drain thoroughly after oiling so excess oil does not reach the engine's sensors.
The manufacturer states the 59-5020 is marine approved per the SAE J1928 standard. Owners on user forums have debated how K&N units are treated during inspections, so check with your local marine authority or inspector before installing.
The manufacturer's boat application guidance recommends checking the space around the existing flame arrestor before you swap it, including diameter clearance, height clearance under the hatch, and whether any vent lines are attached. If vent lines are present, measure their inside diameter and match it to the correct vent hose kit. Owners on user forums say the element should be fully drained after oiling, ideally overnight or longer, before the unit goes back on the engine, because an over-oiled element can foul a MAF sensor. The manufacturer's install instructions should be checked for mounting hardware and tools before you start, as those details were not confirmed in this research.
