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Carb Scoop or Velocity Stack?

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TahitiTiger76

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« on: June 23, 2008, 04:40:39 PM »
Want to get either a velocity stack or scoop from CPPerf to dress up my engine a bit, but I also want to get whatever will perform better. 

I've heard placing a scoop facing backwards works better than scoop facing forward.  Is a velocity stack any better or worse than a scoop?

or does it not matter at all?   ;D
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pw_Tony

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« Reply #1 on: June 23, 2008, 04:41:57 PM »
I don't know the answer, but I'm interested if anyone indeed knows this answer or has tested it? I've got both, and as soon as I hit the water I will be testing both back to back.

Edit, I also have a fiberglass scoop I can test out, front and back... hmmmm....

2savage4you

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« Reply #2 on: June 23, 2008, 04:51:33 PM »
I don't know the answer, but I'm interested if anyone indeed knows this answer or has tested it? I've got both, and as soon as I hit the water I will be testing both back to back.

Edit, I also have a fiberglass scoop I can test out, front and back... hmmmm....



You scoop whore..........Why dont you share ;D

2sav

GT Jets

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« Reply #3 on: June 23, 2008, 05:11:17 PM »
OK, I must be thinking of this all wrong, but here goes nothing... at all..How the hell can a backward facing carb scoop work "better" than a forward one? With the opening facing backwards the pressure would be more "negative" than if the opening was facing the velocity pressure of the moving boat.

I thought the only reason the scoops were ever faceing rearward was to try and reduce carb noise for the occupants of the boat, am I retarded? I would really like to here the mechanics behind it if I'm wrong.

My thoughts were always a scoop for single/double carbs on a very fast moving hull (70-80+MPH) and velocity stacks on slower moving hulls or "impeded" air flow i.e. covered engine top.

Any input would be appreciated.
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« Reply #4 on: June 23, 2008, 05:24:29 PM »
i tried my scoop both ways at parker, and as GT said i didnt like to hear the noise so back around it went. i didn't notice any performance gain or loss either way, but, wasn't really testing either. i run my scoop backwards on the race boat so i don't get water down the carb when i get hosed down.

now mechanically you would think that facing forward you would get more air, but the engine is only going to suck in what it can get out. i dunno :-\ The negitave pressure should feed a more smooth rate of air vs it getting crammed down its throat facing forward. once again i have no facts to prove it :-[

all the drag cars face forward, is that because they cant face towards the rear ??? but on some older muscle cars the openings in the hood faced towards the rear. (for looks or performance?) I'll stop rambling now sorry :-[

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« Reply #5 on: June 23, 2008, 05:30:29 PM »
The best reason to face the scoop back is when your circle racing. This helps from ingesting a big wad of water into your high compression engine when you get hosed down by a guy passing you or cutting you off resulting in hydraulicking the cylinders and puking a rod. (I used a forward facing scoop because I felt nobody was ever going to get in front of me.) Velocity Stack or Carb Scoop?... How fast are you going? +80 go Scoop -80 go Stack.  At +80 the scoop should give you a bit of ram air under 80 and the Stack will help smooth the flow.  If you want to impress people that don't really know what to think put the stack inside the scoop!!!


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GT Jets

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« Reply #6 on: June 23, 2008, 05:32:25 PM »
I was hoping someone was going to make the noise argument ::)  The reason most "Muscle cars" had the scoops backward was because of water, and "cowl hoods" tack advantage of the pressure from the windshield.

As far as "cramming" air down the throat of the carb, this is exactly how a "blow through" turbo setup works >:D But get an a-hole in front of you with a good roost, and you now have a 100% efficient water injection system (blows the carbon right out of the engines valves though).
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« Reply #7 on: June 23, 2008, 05:38:57 PM »
now i see about the car thing thanx ;)

now we can cram all the air in we want but if it's not getting out what are we acomplishing ??? the motor is just a vacume pump, (right?) so it can only use so much. on the other side why make it work so hard to get the air when its free. all we have to do is turn the scoop around. does he have an 80mph boat?

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« Reply #8 on: June 23, 2008, 05:48:07 PM »
All this talking about scoops, and i dont have one..........Maybe i can get a velocityscoop combo ;D

What an idiot.......

2sav

pw_Tony

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« Reply #9 on: June 23, 2008, 05:51:25 PM »
now i see about the car thing thanx ;)

now we can cram all the air in we want but if it's not getting out what are we acomplishing ??? the motor is just a vacume pump, (right?) so it can only use so much. on the other side why make it work so hard to get the air when its free. all we have to do is turn the scoop around. does he have an 80mph boat?

That is what I figured, the engine can only take so much, since essentially it is just a pump. The way I figure a velocity stack, is from sprint cars, drag racing, and quads. It's not always how much air you can get into the motor, it's the way it gets in there.  The veolicty stack starts with a large filter, and tapers down to the carb.... allowing a large mass of air to suck through the filter, then increase the velocity of that mass by tapering down to a smaller opening. I've seen dyno results on a Sprint Car, and it's pretty common in drag quads, so it makes sense to me. But I still think the best way to find out is just to try each other back to back on the same day, and jet accordingly. Like MoneyPitt told me, just because it worked well on a dyno, doesn't mean it will be the fastest way in the boat at speed.

LBsuperjet

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« Reply #10 on: June 23, 2008, 05:53:09 PM »
well, the only reason ive heard of the scoop having to face backwards at places like parker strip u have to have it backwards if you dont have a spark arrestor...trust me, it works! my motor has backfired into my ex-girlfriends hair, and also backfired backwards when the scoop was facing rear...so it is actually a safety issue also.

plus!, in order for a scoop to actually make a difference on a naturally aspirated motor, is if ur doing at least 90 in my opinion. then it will finally create a charge...i never saw a performance difference between the two placements.

Reid

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« Reply #11 on: June 23, 2008, 05:57:36 PM »
Never seen a dynomometer with an 80MPH wind blowing toward the engine either, what do you think, did we stumble on something here! I'm thinking Wind tunnel/Dyno combo >:D we'll be filthy rich!!!!

Then again my stuff never works out that way, I think them up then 1 year later I see one marketed (story of my life). :'(
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

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« Reply #12 on: June 23, 2008, 06:15:35 PM »
Never seen a dynomometer with an 80MPH wind blowing toward the engine either, what do you think, did we stumble on something here! I'm thinking Wind tunnel/Dyno combo >:D we'll be filthy rich!!!!

Then again my stuff never works out that way, I think them up then 1 year later I see one marketed (story of my life). :'(

haha good idea!...my buddies brought that idea to light w/ me a couple years back, and they DID notice a difference on their drag cars, mainly because they figured it would be the same thing as a few PSI on a supercharged motor...but who knows?

Nice boat is nice!

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« Reply #13 on: June 23, 2008, 06:56:28 PM »
At least we can have cool scoops..... unlike the clamp on fellas  ;D

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« Reply #14 on: June 23, 2008, 07:26:28 PM »
The dual velocity stack club is very small on this board.  I think Marcsrollin and myself are the only members  :screwy:

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« Reply #15 on: June 23, 2008, 07:35:31 PM »
One carb, one stack, I'm all about simple :sly:
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« Reply #16 on: June 23, 2008, 08:12:58 PM »
I need to chime in on this one.

Scoops can only do two things - bring in cold air, and bring in cold pressureized air.

On a car, the windshield creates a high pressure area, so the chevys went with cowl induction.

Mopars and Fords took the air as it went over the hood, avoiding the 180 degree turn the cowl induction forced.

If the scoop opening is big enough, and as was said before the engines are just a big air pump, there is a positive pressure build which forces more air into the engine. This is why drag race cars have the scoop facing forward - every bit helps.

I know my duster's scoop can create a few pounds of boost at speed. Free HP.

I love when people ask how much HP you see on the dyno with a scoop or ram air - you don't see any - IT'S  A DYNO - you aren't moving!

On a boat, if you went fast enough, the forward facing scoop would give you a HP advantage. With most boats however, the engine hits top RPM long before airflow becomes an issue, so really it would work either way. The scoops on boats are supposed to face backwards so if there a backfire, the occupants don't get fried or catch something on fire, which really isn't that big of an issue in a car. Huge issue in a boat.

Velocity stacks straighten the air to give more HP, so it is not and either or with a scoop. You can have both.


On my boats setup, I oped for two K&N's hanging out of the cover. The tunnel ram after a hard run is around 38 degreees give or take according to my infrared thermometer.

« Last Edit: June 23, 2008, 08:20:28 PM by speedymopars »
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« Reply #17 on: June 23, 2008, 08:16:21 PM »
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« Reply #18 on: June 23, 2008, 09:05:29 PM »
Wow!  well after reading all the replies I think I will probably go with the stack.  The stack is cheaper, and my boat will never see over 80mph.  If I did get a scoop I would surely face it backwards after hearing about the backfire incident.

The stack should look nice. 
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speedymopars

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« Reply #19 on: June 23, 2008, 09:08:00 PM »
This works for me.
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« Reply #20 on: June 23, 2008, 09:50:46 PM »
Good info, I just run a Dooley stainless scoop with a USCG approved flame arrestor inside, it has always looked good and is totally functional, The main reason I like it is I do some boating in the northwest and it seems to always rain on my parade...the scoop sheds water pretty well, whereas the stacks make great funnels ::)

Killer info again..
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

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« Reply #21 on: June 23, 2008, 10:16:45 PM »
I run filters in my stacks and if I do get caught in a summer shower I always have the bonnet to cover the stacks.
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« Reply #22 on: June 24, 2008, 12:59:48 AM »
My scoop used to face forward until this last Memorial day. It was raining on the way to Parker, so I turned it around to play it safe. I have a flame arrestor inside too. Now I am too lazy to flip it back around. On my buddies boat, our friend had a nice little shock when the boat backfired. Needless to say his scoop is now facing backwards too. I don't know if there is any truth to this but I heard the fiberglass scoops are the best ones for ramming air into the motor and the normal aluminum ones don't help much, just more cosmetic.

Sleeper CP 19

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« Reply #23 on: June 24, 2008, 06:22:48 PM »
You can always put a flame arrestor inside the scoop. Have always ran ours forward, it just looks better. As stated at less than 80-90 mph there is not much ram effect.  When I get the time this Summer I was going to do some testing with the GPS and Radar Gun to determine any bennifit. Since I'm fairly certain I can get the CP to run 100 mph off the bottle at 6,200 ( already runs 98 with a bunch of extra weight and full tanks) I was going to run scoop forward, scoop backward and no scoop ( might borrow a Dominator velocity stack from a friend of mine). With the dynamic testing system that is in my radar gun I can read 0-100, 20-100 or any time to speed or distance to speed reading. I just haven't had the time to play with it other than in the yard hitting golf ball's.

I talked to a few people and they thought that if I took a scoop and cut out the back of it (hole saw or cut vents into it) that the forward facing scoop might work better than with wout the holes because the air just stacks up and creates turbulance in the scoop.  One weekend yrs ago I turned it around and it ran the same mph and rpm's.

I'll play with it once I get the hardware dailed in. I'll let you know how it goes.

Here are a few things the Radar Gun can do:





It's a pretty trick tool used along with a lap top. Here are two examples that came with the program. I can overlay 12 test's on the same page.





Sleeper CP  :)

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« Last Edit: June 24, 2008, 06:37:51 PM by Sleeper CP 19 »
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