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Hatch scoop, should I build a carb tray?

SneakyPete

SneakyPete

Member
Last year I ran with a hole in my hatch to accomidate my taller induction setup. I am going to use a small mustang scoop, sectioned to fit the hatch to cover the hole. Should I build a tray on the bottom of the carb to seal the carb to the bottom of the hatch so it sucks air only from the scoop, or not bother. I don't imagine I would get much ram air from the setup due to the lower speed of a boat and the turbalance created by the windshield and cockpit, I guess I am just looking for pro's and cons. Are there safety issues I am overlooking, like backfires or fumes? My motor comartment does have vents on either side.
 
Any air that can be forced down the carb without the carb trying to pull air on its own will gane you horsepower and top speed.

Big Red N.C.
 
Pete,

I was kicking around the same idea for a while last winter. I didnt do it for 2 reasons..

1: I couldnt figure out how to make it fit on my hatch and still be able to re-finish the upholstery in a way that looked good.

2: I also wasnt sure how much if any air wouuld be forced into the scoop. I was afraid the windshield would cause most of the air to flow over the top of the scoop. I decided to hold off and test it out. This summer while running at speed, I checked the air flow. I built a mini wind tunnel. While at full speed, I had a friend hold a 30 second smoke grenade at various spots in front of the windshield. Most of the air went whipping around over the top of the hatch. :yell:


The scoop idea is not a consideration for me anymore..
 
At idle my checkmate will gain 200 rpms when the engine hatch is lifted. I call that starving for air. The easiest gain is always looked over.

Big Red N.C.
 
BR-thats interesting about the rpms coming up at idle, have you ever tried running with out a hatch at WFO to see what kind of gains you get.

Vinny-thats funny with the smoke bomb thing, I can picture you ripping across the sound at 80+ with smoke pouring from the boat, must have got some major looks. I kinda figured the boat is kind of like a pickup truck bed, with the cockpit acting like the bed, with low pressure air circling and the high pressure air bouning off of the top of that circle of low pressure air right at windshield hieght. Now you can get high pressure air down into the the cockpit (pickup bed) by letting the tail gate down, but not an option with our boats. Yeah I watch Mythbuster on Discovery Channel.
 
BR,

If your engine picks up 200 rpm at idle just by lifting the hatch, then you have a serious problem there. That bilge must be sealed tighter than a crabs ass. I have never seen any boat with that phenomenon.

Pete,

Yeah, it must have looked weird. I did it early in the a.m when not many people are around. Plus, it was in the ocean, not the bay. I am on the south side of Long Island, no sound here, thats the North side.
 
what if you ran a blower in the bilge from one of the side vents into the flame arrestor. instead of blowing air out it blew it in - just a thought.
 
"Forced Induction"

Chris E said:
what if you ran a blower in the bilge from one of the side vents into the flame arrestor. instead of blowing air out it blew it in - just a thought.
Click to expand...

Just that same idea has sparked a whole industry on e-bay claiming horsepower gains on hondas and such from putting a blowermotor pushing air into the engine.

by the time you put enough blowers together to flow enough cfm to help I think the electrical draw would cancel out any hp gains
(loaded alt will draw as much as 15 hp at full output)
 
I was just thinking of a way to add more cold air to the engine, and was searching posts. If there's not enough air flow where a scoop would go in front of the hatch, what if a guy added a couple more breather vents in the side of the boat. You know the ones that your bilge blower attatch to. I wonder if adding maybe 2 more vents on each side with the fins pointing to the front so they would catch the air and fabicate some kind of channel or air duct to shoot the cold air right to the flame arrestor. It may not be 'forced induction' but it could be a cold air intake. I'm not really sure how hot the air is in the bilge, but it's gotta do something having the cooler outside air to the engine....Right????
 
We all need to remember that carbueration starts and ends with FLOW. The more air and the more fuel, the more horses. As far as "ram air" effects, it's unlikely you'll get any at all w/ the rear hatch. Your hatch has got to be REAL tight for the engine to gain 2R's like that (WOW!). I guess I'm just saying that more air / fuel is good and the air temp. (colder) will definitely change the HP.

Tom
 
Adding an few additional vents on the side of the hull wont hurt your performance. It may weaken the hull a bit, but not enough to make a big difference. Hers where I dont like your idea... I would suggest you dont attempt to duct air from the side of the hull directly into your arrestor. I have seen those vents allow water to enter as well as air. Not too bad if the water splashes in the bilge or transom, but think what would happen if you ducted it into the carb??:yell:
 
There was a boat for sale on scream and fly, a 1979 24' Pantera (I know Vinny...). The guy had airbrushed a wild tropical scene on it, but he had also molded in NACA ducts, it was one of the slickest things I have scene in a long time.
 
I had a Magnum 27 Sport years ago and I put two big Hillborn style scoops on the rear hatch, I would leave scoop plugs in for traveling and rainy weather and I didnt have carb trays built in. The intresting part was if I had the plugs out the air flow would push the engine compartment hot air up around the side gunwalls and up into the cockpit. On cold days it worked like a heater, the hot air would warm the cockpit area. The point is that evan though the air flow to the scoops was very obstructed it still pulled in a lot of fresh cool air.
As far as the carb tray, I would build one in if possible, It will only help.
My brother had a 26' Cobra and he didnt want to loose his sun pad so we built a new deck hatch out of alluminum raised it 3" and added vents down the sides. He also nedded the height for the engine and high performance spark arrestor.
F150GT
 
Spacing just the rear of the hatch to create a 2" gap can create quite a difference in airflow. Similar idea to a cowl induction set-up ( without the added effect that the windshield on a car creates ).
The hinge on my ZT lifts the back of the hatch first allowing this gap, which dramatically changes the amount of fresh air available to the motor. I believe this may have been proven by some performance dealers to be as or more effective as a scoop.
 
dang and i just ate crabs for dinner... try reverse induction, or vent towards the transom, it acts like an eductor, pulling air into the engine room.. some utilize a one inch gap below the engine hatch astern, and dress them out with neon lights for crowd pleasing effects.
 
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