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Thread: scoop / air restriction ?

  1. #1
    Unchained
    I have been running a Mr. Gasket / Hilborn style scoop on my carbs since I put the engine together. No air filters, just the coarse mesh screen/foam that they come with.
    Two different engine builders have informed me that the screen/foam is an air restriction for the flow that I need to feed air to the monster. I have two 850dp holleys, 8-71 Hampton blower, 540 ci Arias/Chevy engine. Has anyone else found the scoop/screen to be an air restriction?
    This year I went from 23% blower OD to 38%
    blower OD and am only getting 14.5 lbs.boost
    at 6000rpm. I thought I would get a lot more boost with that much OD. I never concidered that the scoop screen could be an air restriction.

  2. #2
    DEL51
    Unchained,I think an 871 may be a little on the small side for a 540.I am going to test my scoop and my filter on the Dyno.

  3. #3
    DEL51
    I did not intend to have the sad face on the previous post.DEL51

  4. #4
    superdave013
    The scoop is not the restriciton, the carbs are. Put an Enedrle injector hat on that blower and @ 38% over you will get more than 14.5 pounds. When I ran carbs I never ran over 15% overdrive. Anymore made no more boost but it generates more heat. With the injector hat I was running 30% over. It would make 28-30 psi depending on how freash the blower was.
    Put fuel injection on it and you will shit on the throttle response too.

  5. #5
    Unchained
    Thanks Dave, I always wanted to run an Enderle but was concerned about the drivability. The Enderle certainly has the ultimate bad ass look that no carbs can match.

  6. #6
    Infomaniac
    Unchained: This should start some discussion
    At 6,000 engine RPM a typical 8-71 running 38% O.D. moves 2,721 CFM of air. At 23% O.D. 2,425 CFM of air. You should have enough carb to match this or the boost will be limited.
    THIS IS CALCULATED USING STANDARD VOLUME NUMBERS IN THE MATH. This is a very good base line to select carbs with.
    I am sure carbs flow more, the more vacuum you put under them. You can suck the power valves shut under conditions similar to yours. This is one reason some folks boost ref. their carbs. I choose to not run power valves on a blower.
    Injection is great and I would be curious to know how much a bird flows vs a bug etc.
    Hard starting when cold, fast idle and strange part throttle operation are all part of it.
    If you go to twin doms. they are not the best for part throttle operation either.
    I will have to send you the video of my 8 year old son on a tube behind the Cougar. The engine sounds terrible running 35 or 40 MPH down the lake. The butterflies are pretty much closed, only opened a few thousandths.
    After I get where I am going the hat and blower are sweating like crazy. Just part of it when running injection. There are plenty of guys around here jet or v-drive, blown or not that run injection on their lake machines. Once you do it you will never go back.
    Oh Yea: I ran the same scoop with just the screen when I had carbs. I did not use the filters either. I put some black foam filter element used in the Edelbrock Pro Flow triangle shaped breather sandwiched between the coarse screens. Never had a problem with restriction.
    [This message has been edited by Infomaniac (edited November 30, 2001).]

  7. #7
    Unchained
    Info, After hearing about the drivability problems I really don't want injection. My boat is loud and impractical enough now but drivable enough to ski, tube, and cruise with. I won't give up the drivability so I need to do the best I can with carbs. I think that I want to go with a 14-71 blower, crank trigger ign, and two 1050 dominators.
    You know, the typical boat performance plan. Throw more money at it until it does what you want.

  8. #8
    572Daytona
    How about one of the Holley 2000cfm injection units? http://www.holley.com/HiOctn/ProdLin...FMSFI/MPI.html I've never used one but I remember a post by Duane Oberlander at Hi-Tech Performance http://www.hi-techperformance.com/ saying that he used on on his 572ci jet and was very pleased with it.

  9. #9
    1riverrat
    Ron's racing has an 8 port hat type af fuel injection and say that it has excellent
    driveability but that is on tunnel they did not say anything about driveability on the blower. http://www.ronsracing.com/

  10. #10
    Blown509Liberator
    Unchained
    I was talking with Dave from DNE about carb sizing on Blower motors. One thing he said was to check to see if your building vac just under the carbs. if you are then they are to small. This may be the place to start.
    What HP are you making? I am making 850 and have a very good drivability with it. It starts easy and I have about 800-900 rpm idle
    Runs well at ski/ tubbing speeds.
    MikeW

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