Engine Vent Duct - Which One?

[76SeaRay]

Before I put the "shelves" back in for the side storage pockets at the back of the boat, I need to run new engine vent ducting above the pocket area while I have open access under the gunwale. I have two intakes, one on each side, and one outlet at the center of the stern. I plan to use 3 runs of 3 inch ducting, two for passive air on port and starboard sides, and one to the blower for drawing from low in the engine bay and exhausting through the aft center vent. So, researching the available duct, IBoats has three types available (progressively more expensive). It appears the cheapest one is probably for cabin venting as opposed to engine venting. The other two are type 400/402 and type 420. Are both of these approved for the engine bay? 400/402 says resistant to flame and 420 says resistant to oil and gas so which is recommended to use? Also, is 3 inch the correct size? My engine is a 5.7L GM with full closed cooling and mid-rise dry joint exhaust. Thanks.

 

[alldodge]

Use either, the hose doesn't come in contact to oil/gas enough to worry about. That is so long as there are no flames then all bets are off

3 inch sounds right, its what I used