1471 blower on a 496
+ Reply to Thread
Page 1 of 2 1 2 LastLast
Results 1 to 14 of 20

Thread:
1471 blower on a 496

  1. #1
    Senior Member raysoncraft1's Avatar
    Join Date
    Feb 2008
    Posts
    568

    Default 1471 blower on a 496

    Someone put a 1471 little field blower on a 496 chev. It is 23% under driven. Can the carbs get a false reading at idle due to so much under driven?(BOUGHT IT THIS WAY) Just hving problems with idle it seems like it wants to die until i hit the throttle attle. The carbs are 750s boost ref jets 78 prim 84 second i belive 10.5 power valves.

  2. Remove Advertisements
    PerformanceBoats.com
    Advertisements
     

  3. #2
    Senior Member Hass828's Avatar
    Join Date
    Dec 2007
    Location
    okie, lake Texoma
    Posts
    6,278

    Default

    Quote Originally Posted by raysoncraft1 View Post
    Someone put a 1471 little field blower on a 496 chev. It is 23% under driven. Can the carbs get a false reading at idle due to so much under driven?(BOUGHT IT THIS WAY) Just hving problems with idle it seems like it wants to die until i hit the throttle attle. The carbs are 750s boost ref jets 78 prim 84 second i belive 10.5 power valves.
    If its idleing slow , with that much underdrive you will probably need to check vacuum at the carb to see if there's enough to hold those power valves closed. Probably just needs some different power valves.

  4. #3
    Senior Member raysoncraft1's Avatar
    Join Date
    Feb 2008
    Posts
    568

    Default 1471

    vacuum is at 5 inches power valves should be closed until boost? YES NO MAYBE? I thought with boost reference you want them closed cause when you boost the force of the air opens them? vacuum coming of the intake manifold for the carbs.

  5. Remove Advertisements
    PerformanceBoats.com
    Advertisements
     

  6. #4
    The Hat
    Guest

    Default

    Quote Originally Posted by raysoncraft1 View Post
    Someone put a 1471 little field blower on a 496 chev. It is 23% under driven. Can the carbs get a false reading at idle due to so much under driven?(BOUGHT IT THIS WAY) Just hving problems with idle it seems like it wants to die until i hit the throttle attle. The carbs are 750s boost ref jets 78 prim 84 second i belive 10.5 power valves.

    have you tried to lean or richen the idle screws to get the engine to respond? can you pull a vacuum reading off the throttle base to see what it is?, and I never ran ANY Holley carb with a Power valve one small sneeze and they usually give up, ....and removing them only requires a plug, and up a jet size or two.....but then I am Old School and dont like chasing shit like a dead power valve that have only a small effect on drivability.....unless you backfire and kill it, then the engines run like crap so why bother with them if you can bypass their function. positive floats are correct ?. easy way to tell if the engines to lean at idle is to put your hand over the primary side(s) and gradually choke the engine down, if the engine speeds up.....Bingo....she's lean.....if it has a blown power valve usually makes the engine run rich....

  7. #5
    i'm back!! 1QuickCP's Avatar
    Join Date
    Jun 2009
    Location
    Montana
    Posts
    687

    Default

    Power valves into the garbage can...problem solved.. also at 23 under whats kind of boost r you making? If ur going for a low boost deal all the time id ebay the 14 and get a good 10-71 that you can turn faster. IMHO

  8. #6
    Senior Member Hass828's Avatar
    Join Date
    Dec 2007
    Location
    okie, lake Texoma
    Posts
    6,278

    Default

    Quote Originally Posted by raysoncraft1 View Post
    vacuum is at 5 inches power valves should be closed until boost? YES NO MAYBE? I thought with boost reference you want them closed cause when you boost the force of the air opens them? vacuum coming of the intake manifold for the carbs.
    NO! they're not closing if thats the case.
    Lets understand I'm no carb guru but the 10.5 means it takes 10.5 of vaccum to close them, and you only have 5, so there's your problem. Try a set of 3.5's would be my suggestion, but I'd double check that with a good carb guy.
    As soon as you begin to accelerate the vacuum goes away and then boost comes on, all that time the powervalves will be open and supplying extra enrichment then when you idle and have the vacuum back the valves will close and idle will lean back out.
    For a little lake deal , I wouldnt do away with the power valves as your economy will go out the window.
    My .02

    p.s. You'll probably need to put the vacuum guage back on it & reset the idle mixer screws after you get the power valves closing because if you been messing with them , closing them down to try to get it to idle then fix the power valves, it'll be to lean on idle and you'll have to open 'em back up a little. Best to do it with the vacuum guage though. Good luck, Hass
    Last edited by Hass828; 12-30-2009 at 06:38 AM.

  9. #7
    Senior Member flat screwd's Avatar
    Join Date
    Oct 2008
    Posts
    279

    Default

    I am assuming that your checking the vacuum from the manifold and not the carb plate.My experience with blowers is that you will always have vacuum under the carbs regardless of engine speed, thats reason for boost ref. I agree with QuickCP powervalves in the trash .Get your self two summit jet kits and start from there. But if you decide to run them than go 3 inches less than your idle vacuum . If this was a purpose built blower motor with a blower grind cam you should have more than 5 inches vac. at idle . Check your timing first after all thats free.

  10. #8
    The Hat
    Guest

    Default

    Quote Originally Posted by 1QuickCP View Post
    Power valves into the garbage can...problem solved.. also at 23 under whats kind of boost r you making? If ur going for a low boost deal all the time id ebay the 14 and get a good 10-71 that you can turn faster. IMHO


    A roots blower, is a Positive displacement device, the drive (under or over) ONLY detemines "WHEN" the blower makes max boost....not how much Max....the faster you spin a Roots, the quicker it makes full manifold pressures, the slower, the longer it takes......., both setups, will make the SAME Max boost....one sooner, the other later.....if it's real far under driven, and 23% is a LOT, it may never catch up to the engine and make all it can, depending on sizing, I ran the Blower on our engines in the 61-73% over range, ...73% for a 14mm drive was as fast as you could spin one, how well the Blower is clearanced, or sealed is a big factor as well, if it's loose, it wont make a lot of pressure because it bleeds off internally.

    hope that Helps



  11. #9
    No Sandbar To Far sanger rat's Avatar
    Join Date
    Dec 2007
    Location
    MI
    Posts
    3,276

    Default

    10.5 power valves open at that vacuum. If you are making 5# vacuum they are already open. Change the power valves to something smaller than 5#. Richin your idle up by turn your idle mixture screws out a little. Try 1/4 at a time till it stays running.
    Quote Originally Posted by One More Year View Post
    The only blab's I will even be a part of is just when it is me they are talking about. Aaaah yes I can see a few good looking shiny tall deck motors on the beach, with barely enough fuel to get back to the launch saying, "Holy crap how fast you think that Daytona was going man? That's like the 20th time he's gone by today?"

  12. #10
    The Hat
    Guest

    Default

    The power enrichment system supplies additional fuel to the
    main system during heavy load or full power situations. Holley
    carburetors utilize a vacuum operated power enrichment system
    and a selection of power valves is available to “time” this system’s
    operation to your specific needs. Each Holley power
    valve is stamped with a number to indicate the vacuum opening
    point. For example, the number “65” indicates that the power
    valve will open when the engine vacuum drops to 6.5" or
    below. An accurate vacuum gauge, such as Holley P/N
    26-501, should be used when determining the correct power
    valve to use. A competition or race engine which has a long
    duration high overlap camshaft will have low manifold vacuum
    at idle speeds. If the vehicle has a manual transmission, take
    the vacuum reading with the engine thoroughly warmed up and
    at idle. If the vehicle is equipped with an automatic transmission,
    take the vacuum reading with the engine thoroughly
    warmed up and idling in gear. In either case, the power valve
    selected should be 1/2 the intake manifold vacuum reading
    taken. EXAMPLE: 13” Hg vacuum reading divided by 2 = 6.5
    power valve. If your reading divided by 2 lands on an even
    number you should select the next lowest power valve. EXAMPLE:
    8” Hg vacuum reading divided by 2 = 4 power valve.
    Since there is no #4 power valve you should use a 3.5.

  13. #11
    Senior Member Hass828's Avatar
    Join Date
    Dec 2007
    Location
    okie, lake Texoma
    Posts
    6,278

    Default

    Quote Originally Posted by Hass828 View Post
    NO! they're not closing if thats the case.
    Lets understand I'm no carb guru but the 10.5 means it takes 10.5 of vaccum to close them, and you only have 5, so there's your problem. Try a set of 3.5's would be my suggestion,
    but I'd double check that with a good carb guy.
    As soon as you begin to accelerate the vacuum goes away and then boost comes on, all that time the powervalves will be open and supplying extra enrichment then when you idle and have the vacuum back the valves will close and idle will lean back out.
    For a little lake deal , I wouldnt do away with the power valves as your economy will go out the window.
    My .02

    p.s. You'll probably need to put the vacuum guage back on it & reset the idle mixer screws after you get the power valves closing because if you been messing with them , closing them down to try to get it to idle then fix the power valves, it'll be to lean on idle and you'll have to open 'em back up a little. Best to do it with the vacuum guage though. Good luck, Hass
    like I said

  14. #12
    Senior Member Hydroguy's Avatar
    Join Date
    Jun 2008
    Posts
    292

    Default

    If that boat is not a full on race boat running on Alcohol you have TOO much blower. Get rid of it and get a 8-71. Even if you were racing I dont think I would go any bigger than 10-71. You are going to use too much HP to turn that beast and you won't get any kind of good performance out of it.

  15. #13
    B.A.M aka "Black Azz Mike 396_Ways_To_Spit's Avatar
    Join Date
    Feb 2008
    Location
    Mesa,Az "Da Eastsiiiiiiiiiiiiiiiiide"
    Posts
    2,925

    Default

    Quote Originally Posted by The Hat View Post
    have you tried to lean or richen the idle screws to get the engine to respond? can you pull a vacuum reading off the throttle base to see what it is?, and I never ran ANY Holley carb with a Power valve one small sneeze and they usually give up, ....and removing them only requires a plug, and up a jet size or two.....but then I am Old School and dont like chasing shit like a dead power valve that have only a small effect on drivability.....unless you backfire and kill it, then the engines run like crap so why bother with them if you can bypass their function. positive floats are correct ?. easy way to tell if the engines to lean at idle is to put your hand over the primary side(s) and gradually choke the engine down, if the engine speeds up.....Bingo....she's lean.....if it has a blown power valve usually makes the engine run rich....

    I agree 100%!!!!!!!


    Good info here
    G H E T T O F O E L I F E
    Quote Originally Posted by cave View Post
    They bout shit themselves when yelled in Messican, "No brakes no brakes."
    I showed them all the sticker on the side that reads "Driver Ricky Bobby" They just looked at me and nodded yes yes
    Quote Originally Posted by Kyle View Post
    Some peeps just build it 1 part, 1 week, 1 paycheck at a time

  16. #14
    B.A.M aka "Black Azz Mike 396_Ways_To_Spit's Avatar
    Join Date
    Feb 2008
    Location
    Mesa,Az "Da Eastsiiiiiiiiiiiiiiiiide"
    Posts
    2,925

    Default

    Quote Originally Posted by 1QuickCP View Post
    Power valves into the garbage can...problem solved.. also at 23 under whats kind of boost r you making? If ur going for a low boost deal all the time id ebay the 14 and get a good 10-71 that you can turn faster. IMHO

    Yup, can the Pv's!

    BUT, keep the 14-71 and speed it up!!!!!! Make some power and enjoy it!!!!! there isnt too much difference between the 14 and 10. I would speed her up and let it rip. or, get ballsy and overdrive it and get NASTY and WILD!!!!!!!
    G H E T T O F O E L I F E
    Quote Originally Posted by cave View Post
    They bout shit themselves when yelled in Messican, "No brakes no brakes."
    I showed them all the sticker on the side that reads "Driver Ricky Bobby" They just looked at me and nodded yes yes
    Quote Originally Posted by Kyle View Post
    Some peeps just build it 1 part, 1 week, 1 paycheck at a time

+ Reply to Thread
Page 1 of 2 1 2 LastLast

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

Please select your insurance company (Optional)

Log-in

Digg This Thread

Posting Permissions

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
  •  
 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95