Modifying flame arrestor

[JasonB]

Re: Modifying flame arrestor

Ok, here is a pic of the engine compartment. The cover fits very close on all sides of the engine. There is one 2"x6" louvered vent on either gunnell. a couple feet on either side of the engine. There is one blower that pulls air out of the lower bilge. At high RPM, you can hear air sucking into the engine compartment. Just for the record, the two 18gal fuel tanks are amidship under the back/back seats popular in older boats. There is a ski locker above the engine that take up much of the extra space. Behind each seat in the pic is mostly hollow air space.<br /><br />I'll make it a link since the pic is almost 200k.<br />Is shows the engine compartment with the cover off, but shown in the pic.<br /> Engine Compartment <br /><br />Here is a smaller pic that is justr the compartment. Le link above is a much better pic.<br /><br />

<br /><br />I believe there isn't enough air coming in. I also believe the air in the compartment gets too hot as the engine stumbles at idle when the compartment is hot. Opening the cover helps level the idle out. as a side not, the carb on this 302 is the factory 2bbl rochester of unknown CFM. The engine is not stock, but is only mildly built, nothing radical, just solid parts. Winter maintenance will include a rebuild/polish of the carb.<br /><br />Here is a pic of the boat: Boat Pic

 

[navigator336]

Re: Modifying flame arrestor

Nice clean engine! Yes, that looks like a very restricted and well sealed engine compartment (especially with the carpet on the floor). I assume the louver pictured (port side) is the bilge blower one since it is facing aft. If so, you really only have one louver working to get much air in as the back facing one has a fan blade and the negative pressure created by it's orientation to contend with. If you are hearing a sucking sound at high rpm around the cover or the starboard louver, anything you do to vent the compartment is going to help. If you partially obstruct the starboard louver at high rpm's do you loose rpm's? I'll bet at idle, it is getting pretty warm in that compartment.

 

[JasonB]

Re: Modifying flame arrestor

Thanks for the compliment on the engine. My brother helped me build it last 4th of July. We know every bolt, seal, gasket, and bearing. If I can just get the rest of the boat cleaned up as well... Here is a pic that better shows its shape:

<br /><br />As you surmised, the blower is on that side. I started leaving the blower on while the engine is running and it seems to help.<br /><br />One of my thoughts is to remove the backs of the seats, install an air port and hose of some sort, maybe with an inline blower, and reattach the seat with a spacer holding it off the fiberglass backer a bit. That should increase airflow a bit and I can pipe it near the intake.<br /><br />Unfortunately, with the Ski locker above it, any air scoop type louvers are a tough plan.

 

[OMARiverRat]

Re: Modifying flame arrestor

I like the idea of having 2 blowers, blowing fresh air into the engine compartment. I'm new to this, so bear with me here. However, shouldn't the bilge blowers be sucking air out of the engine compartment, rather than blowing it in for safety reasoning?

 

[jklett]

Re: Modifying flame arrestor

Maybe I'm not seeing this right, but there appears to be a pocket of sorts on the top part of the engine cover? Have you thought of just cutting that open and putting some screen in there to act as a hood scoop? Just a thought.

 

[Doug Durako]

Re: Modifying flame arrestor

You might also try "finned" vents in both sides of the boat, just above the rub rail, about 4 inches ahead of the transom plate. You get lots of air into the compartment and your passengers won't hear the noise.<br /><br />These vents fit in a hole approx. 3X12 inches---about the size of forced air floor vents in a typical house furnace.\<br /><br />Not sure who makes them for boats, but my old Cobalt had them and its engine cover was much the same as yours---very close to the motor.

 

[oldboat1]

Re: Modifying flame arrestor

I added an inline blower to help cool down the compartment (and the engine) in my old Chris Craft. I don't think it had any effect on engine temp, but I'm sure it adds fresh air to the compartment and circulates the air better, particularly when the bilge blower is on to exhaust the hot air out of the compartment.

 

[Squirterguy]

Re: Modifying flame arrestor

Clarifications of a thing or two. Navigator, please check your math. A 454 turning 4500 RPM draws in 1182 cubic feet of air assuming an 80% fill rate. There are 1728 cubic inches in one cubic foot. Well designed intake systems without boosters often draw over 90% at full throttle, if the carburetor is big enough to flow this much.<br />I can attest to the improvement of cooler air. I have a '78 Taylor jet, 454 Chevy. At mid-day, 100 Degrees, she is flat out at about 4800 RPM. At 8AM, at 75 degrees or so, she will run nearly 5000 RPM. The ONLY variable at those times, is heat of the ambient air.<br />Otherwise, looks like really good and solid advice, in my opinion. Nice looking boat Jason. Hope you get your engine quirks solved.