Air Scoops On Backwards?

[W.O.T]

Just curious why some people run their carb air scoops backwards? ive heard a few different reasons but im still curious. Thanks Guys.

[shaun]

wouldn't doubt if it's just for looks....

[HokeySon]

illegal to run them forwards. supposedly in case of a backfire, don't want it directed towards the passenger area.

[jag2]

I just assumed mine was done that way by the factory to keep out waterspray.

[coopers396]

I dont know if its illegal but its turned around so that if the motor backfires its not shot directly at the passengers

[hotrod56cars]

It's Coast Guard mandated that they're installed with the opening facing the back of the boat.
I point it backwards because of everyone else's reply...

[wsuwrhr]

Mine have always faced forward, illegal or not.
My thought is rear facing scoop will allow the scoop to become a venturi of sorts and suck the reversion fuel right out of the carb venturies and onto the atmosphere.
I pitted eons ago for a real LS6(?) (the 454 model) Chevelle. We picked up a couple tenths by switching to covered carbs, you could see fuel marks at the end of a run on the windshield and roof.
I loved that car. Heavy ass pig flew.
"With enough horsepower you could make a brick fly"
Brian

[Beautiful Noise]

You can run the Scoop forward as long as you are Running Flame Arrestors encase of backfire :)

[BIGAMIST]

You can run the Scoop forward as long as you are Running Flame Arrestors encase of backfire :)
Thats what I've been told.

[Sleeper CP]

It's Coast Guard mandated that they're installed with the opening facing the back of the boat.
I point it backwards because of everyone else's reply...
I believe the rule is: if the Carb(s) is less than 18" above the top of the engine compartment the scoop is to be run backwards in case of backfire. If the carb is 18" above the engine compartment it is assumed the fumes will not egnite by a backfire. In any case if you have a covered engine you must run an arrestor. If you are running a Tunnel ram or a really high intake and the carbs are more than 18" above the top of the engine compartment you don't have to run anything; you should but you don't have to.
Also, some engines will actually run better with the scoop run backwards. An old friend had a 750 HP 468 with a tunnel ram it had a roller cam and 12:1 comp. it made alot of noise in front of the engine and behind. On one trip to the river his wife asked him if the boat would be quieter if he turned the scoop around(reducing intake noise) he said :OK, his boat picked up 300 rpm's and he reduced a bunch of noise coming from the intake.He ran it that way for the next 6 years.
Try it both ways you might be surprised.
Sleeper CP

[Danhercules]

There was a thread on this a while back.
It was also said that running it backwards is like a cowl (sp) induction hood. It accually sucks air better.

[mdunn01]

I am curious if i should switch mine around? I really hate the backwards look but it sounds like a good idea.

[V-DRIVE VIDEO]

I've been coast guard inspected and pulled over by the cops on this subject. I passed the coast guard inspection and received my junior GI badge but they recommended I get lights Lol. The cops (Ca) checked to make sure I had flame arrestors and "recommended" I turn the scoop facing backward.
Some people run the scoop backwards to keep splashing water out of them.
http://www.v-drivevideo.com/jerrysgallery/albums/userpics/10001/normal_Mich%20004.jpg

[HalletDave]

I am curious if i should switch mine around? I really hate the backwards look but it sounds like a good idea.
I could be wrong but I don't think it really matters which direction you face the scoop as long as you are allowing in the coolest air supply possible. I do believe that an air cleaner or spark arrestor is a must to help smooth the air flow coming into the carburetor. Turbulent air plays havoc with the air bleeds on a carburetor. A forward facing scoop ingesting a little bit of fine cool water mist from a roost is not going to hurt your motor.
:idea: If you can see the other guys' roost, you have all ready lost the race.
Run what works for you.
My boat is so slow I don't think it really matters.:D

[GUGS102]

I believe the rule is: if the Carb(s) is less than 18" above the top of the engine compartment the scoop is to be run backwards in case of backfire. If the carb is 18" above the engine compartment it is assumed the fumes will not egnite by a backfire. In any case if you have a covered engine you must run an arrestor. If you are running a Tunnel ram or a really high intake and the carbs are more than 18" above the top of the engine compartment you don't have to run anything; you should but you don't have to.
Also, some engines will actually run better with the scoop run backwards. An old friend had a 750 HP 468 with a tunnel ram it had a roller cam and 12:1 comp. it made alot of noise in front of the engine and behind. On one trip to the river his wife asked him if the boat would be quieter if he turned the scoop around(reducing intake noise) he said :OK, his boat picked up 300 rpm's and he reduced a bunch of noise coming from the intake.He ran it that way for the next 6 years.
Try it both ways you might be surprised.
Sleeper CP
Try putting a single chrome/stainless scoop on the flow bench, they suck literally. And if you install the arrestor, it just gets worse. They look good but don't work very well.
On a 600 flow bench that arrestor created somewhere around 40% additional back pressure. The scoop its self creates an area of high pressure by cramming the air into the scoop and with no outlet packs air until the high pressure area moves to the front of the scoop and thus does not flow well.
I've not tried a double scoop on the flow bench so I can not make an educated comment on those.
I run a 15" stainless dog dish, out flows the scoop by 50% at only 600CFM. Looks good, won't pull water from anywhere and allows the carb to get a better signal by allowing to to pull air from 360*
Gugs

[LGCDEVIL]

Word on the street is the Dooley scoops like most of the ones pictured, when installed with the opening in front, create a bunch of turbulence in the air flow(pack more air than the carb can use?). This really F's with the function of the carburetor. I have seen a few guys drill some holes in the back of the scoop (2 or 3 holes @ 1 1/2" dia.) to relieve the pressure and let the air flow through the scoop instead of getting all backed up inside the scoop. I spun the scoop around backwards on my deal. Ran harder and was a ton quieter (air noise).

[TahitiTiger]

I ran mine both directions. Didn't really notice a difference in power on my 455. I keep it facing forward, more for looks than anything. As for the flame thing yes I have singed my buddies eye brows on a good back fire LOL.
(knock on wood it doesn't do that any more).
http://i43.photobucket.com/albums/e369/Qckslvr/100_0238sm.jpg

[Sleeper CP]

Try putting a single chrome/stainless scoop on the flow bench, they suck literally. And if you install the arrestor, it just gets worse. They look good but don't work very well.
On a 600 flow bench that arrestor created somewhere around 40% additional back pressure. The scoop its self creates an area of high pressure by cramming the air into the scoop and with no outlet packs air until the high pressure area moves to the front of the scoop and thus does not flow well.
Gugs
Hey Gugs,
Every boat and every engine is different. Just like the post after yours, he turned it backwards and his engine ran better and was quieter. If someone is interested they should just take a wrench and try it. The guy with the 468 I wrote about, he and his engine builder were very suprised that it ran that good. It's counter intuitive to think that the front carb on a tunnle ram would get enough air with the scoop on backwards. I guess Cowl induction scoops work for a reason. Your static flow bench test maynot be the way to test it. Were you blowing a fan across the top of the intake scoop at 60 mph to create the venturi effect that would happen in the real world? I guess there is some reason why Cowl induction scoops work. A drag car racing buddy of mine took off the 9" high snorkle hood scoop and replaced it with a cowl induction hood,picked up two tenths. As far as the flame arrestor goes was it a large Barron SS unit or one of those restrictive disc unit's? On a flow bench a K&N filter will show restriction, but on the dyno it can help you make power with the proper base.
I have tried it on my boat CP 19' openbow. Off the Nos it ran the same, 93 mph, but it was alot quieter(intake noise) . It just looks better with the scoop facing forward, so that's how we run it.
Sleeper CP

[GUGS102]

Hey Gugs,
Every boat and every engine is different. Just like the post after yours, he turned it backwards and his engine ran better and was quieter. If someone is interested they should just take a wrench and try it. The guy with the 468 I wrote about, he and his engine builder were very suprised that it ran that good. It's counter intuitive to think that the front carb on a tunnle ram would get enough air with the scoop on backwards. I guess Cowl induction scoops work for a reason. Your static flow bench test maynot be the way to test it. Were you blowing a fan across the top of the intake scoop at 60 mph to create the venturi effect that would happen in the real world? I guess there is some reason why Cowl induction scoops work. A drag car racing buddy of mine took off the 9" high snorkle hood scoop and replaced it with a cowl induction hood,picked up two tenths. As far as the flame arrestor goes was it a large Barron SS unit or one of those restrictive disc unit's? On a flow bench a K&N filter will show restriction, but on the dyno it can help you make power with the proper base.
I have tried it on my boat CP 19' openbow. Off the Nos it ran the same, 93 mph, but it was alot quieter(intake noise) . It just looks better with the scoop facing forward, so that's how we run it.
Sleeper CP
No argument here, static and dynamic testing are totally different thigs, I was not being contradictory(sp) to your post. Just sharing my experience. I have not tried a double carb set up in static or dynamic situations. I was just amazed at how the scoop and arrestor negatively effected air flow.
As for the arrestor. It was the stock USCG approved unit. Maybe 2.5-3" in height and 5.250-5.5 in diameter, just small enough to fit the carb.
The other reason I ditched the scoop set up was if there was a 40% restriction (without air blowing into the scoop) at 600CFM then what was it doing at near 1000CFM I am trying to cram into the motor.
Not arguing and I'm aerodynanics expert just what I've found along the way.
I am thinking of trying one of those air smoothers that mounts with the base plate of the air cleaner assembly just for kicks. The problem with trying little things on the water is that it takes approx 20HP to see any difference in performance. I doubt this trick will net that kind of gain.
I also ditched the scoop after taking a roller over the bow at 5MPH which went straight over the deck, through the passengers and right into the scoop and shut down the motor. Fortunately I was smart enough not to try and start it until I pumped the water out of the cylinders.

[n8dawg]

I thought the only reason you ran the scoop backwards was to keep all the ladies long hair from going into the carburator!

[go chiefs]

a friend of mine had a dooley scoop on his nordic, always started the day with it facing forward but eventually spun itself around backwards, he got tired of fighting it so he left it backwards, no difference in sound or performance that we could notice, and didn't have to mf it anymore because he accepted that it wanted to face backward

[Sleeper CP]

Hey GUGS,
We are on the same page.:) Yes, the only way to find out is to do dynamic testing. Run it on your boat and see what happens. Some engines will like it other won't. I'm still surprised that the front carb on a tunnel ram can actually get enough air with the scoop on backwards, I guess that venturi effect is bigger than I thought.
Sleeper CP
P.S. Edit
GuGS you mentioned one thing that does suck on a jet boat. At some point you hit the wall (ie) H.P vs Drag equation and it takes a bunch of H.P. to see any change in speed. Once we got the open bow CP to run over 100, it would run 102-103 with the 250 hp shot or 300 hp shot of Nos. The extra 50 didn't help. Who knows what dynamics we were up againt: aero,hydro or pump efficiency.
The new combo I'm hitting the river with this year should be far more efficient. I'm hoping to get the stationwagon real close to 100 with out the Nos.

[patrolman808]

There was a thread on this a while back.
It was also said that running it backwards is like a cowl (sp) induction hood. It accually sucks air better.
Cowl induction works because air pressure builds up at the base of the windshield. On an open boat, there's nothing behind the scoop to cause the pressure to build. There would be a slight vacuum if anything.

[jetovatorjeff]

i quiets things down quite a bit running them backwards, looks lame though.

[Sleeper CP]

Cowl induction works because air pressure builds up at the base of the windshield. On an open boat, there's nothing behind the scoop to cause the pressure to build. There would be a slight vacuum if anything.
Patrolman,
I don't think there is a vacuum, I know of to many boats that either run the same or even run faster. My CP open bow has a 800+ HP 565" BBF in it with a single Dominator Carb. Off the nitrous it would run the same with the scoop forward or backward.I don't think there was vacuum because the engine pulled the same; it wasn't being starved for air. Now that was some years ago when we were pulling an American Turbine A3 at 5,250 rpm's and running 92-93 mph.
I just re-read your statement:There would be a slight vacuum if anything. Yes created by the venturi of the scoops trailing edge. If that's what you mean we are on the same page, I think?
Just for kicks I'll try it this summer with the new combo and see what happens. But ,ultimatley I'll run the scoop forward, because it looks better that way.

[raped southwind]

Ive agree with the statement that every motor is going to be diferent so either way may work better for you but to my testing there is something called good air and bad air ..and found that running backwards gets me the best air... just my 2 since

[patrolman808]

I just re-read your statement:There would be a slight vacuum if anything. Yes created by the venturi of the scoops trailing edge. If that's what you mean we are on the same page, I think?
Yea, that's what I was saying. Kinda like when you are driving a car/truck, there is a slight vacuum (or negative pressure) immediately behind the vehicle. I run mine foward for more of a 'ram air' function and it just looks better IMO.

[squirt'nmyload]

i ran mine backwards today and didn't notice any difference :)

[pw_Tony]

It just looks to gay backwards....:D

[W.O.T]

It just looks to gay backwards....:D
i agree even if it made my boat slightly faster it looks like crap backwards