EFI and ventilation

I know there are two main reasons for plenty of ventilation under the cowl; heat and fumes. If I were converting to EFI, wouldn't the fumes be eliminated? No bowls or open fuel. Wouldn't that also mean I could skip the spark arrestors on things like the starter and alternator? Fuel tank is vented topside.

signed, noob outboarder

 

WOw you are opening a can of worms. No on the first. You still must ventilated the compartment because most fuel leaks are at fittings, not just the carb. So EFI doesn't eliminate the possibility of a leak.

Where the worms are is the flame arrestor. Some EFI systems claim they can't back fire. I have heard arguments on both sides of this. Currently the Coast Guards policy on this (I wrote it) is that you still have to have a flame arrestor. No one has conclusively demonstrated that an EFI system can't back fire. Theoretically they shouldn't. But the jury is still out.

By the way, if you have ventilation that only meets the letter of the law it is generally not enough for the engine to breath right and remove heat. The regulation is only designed to remove fumes. No consideration was given to heat and breathing. If you have a big block engine you probably need more air. Start your engine, and then lift the engine hatch. If the rpms go up you need more air.

 

Ok, that makes sense about the leaks. The EFI that I'm talking about sources its intake air from outside the cowl, so (theoretically) backfires would be one small step safer provided they don't blow the elbow off the throttle body There is also an intercooled turbo involved, so the chances of a backfire reaching hatch air are pretty slim, but I'll take that under advisement. This particular application uses coil-on-plug ignition with a magnetic trigger so it should be as safe as possible. So I guess the main concerns are heat and starter/alternator ignition sources, right? Correct me on that one if I'm wrong.

This is the Subaru engine to which I referred in the other thread and believe me, its not the first time I've been met with such resistance. I do have very specific reasons for this and I'm not stupid... just not too well versed on marinizing oddball engines since all of my experience is with outboards. The technical and engineering parts I have down, I just need you guys to help me with the stuff that I might overlook.

 

If the air intake is outside the boat, and can't backfire into the boat, and the backfire would be direct away from any occupants then you aren't required to have a flame arrestor. Heres a quote from the regulation:

"An arrangement of the carburetor or engine air induction system that will disperse any flames caused by engine backfire. The flames must be dispersed to the atmosphere outside the vessel in such a manner that the flames will not endanger the vessel, persons, on board, or nearby vessels and structures. Flame dispersion may be achieved by attachments to the carburetor or location of the engine air induction system. All attachments must be of metallic construction with flametight connections and firmly secured to withstand vibration, shock, and engine backfire. Such installations do not require formal approval and labeling but must comply with this subpart."

 

Ah, OK. The intake would be on the front of the cowl under the gunwale on the port side, so to be safe I'll make sure some kind of proper flame arrestor is used. I was going to try and source air from somewhere completely safe, but there is nowhere that is totally safe from ingesting water. By the way just so you have an image of what we're working with, its a 19' Baja bowrider I/O. Thanks so much for the help.

 

Never underestimate the power of human stupidity" Robert A. Heinlien

Sorry, but it's "Heinlein" - not picking nits - sort of a spiritual father to me, and he'd like this forum. Thanks for all, Uncle Bob....

Nice idea on the Subie motor. boxer motors keep the cog lower. And I have had backfires on an injected engine that would put flame out past the cold air intake, thru the intercooler AND the turbo AND the TB. Wire screen is your friend, along with a good bilge blower....

 

This is the Subaru engine to which I referred in the other thread and believe me, its not the first time I've been met with such resistance. I do have very specific reasons for this and I'm not stupid... just not too well versed on marinizing oddball engines since all of my experience is with outboards. The technical and engineering parts I have down, I just need you guys to help me with the stuff that I might overlook.
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The tiny homebuilt aircraft guys LOVE the Subarus.

They might be a source for realistic numbers for power output on a long term basis .And any "problems" & fixes for long term operation at high power levels.

EAA is one source.

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