first blower build couple questions - Reply to Topic

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Topic Review (Newest First)

  • 12-06-2010, 06:52 PM
    gn7
    No matter Old Guy. the one thing we know he doesn't want to do is open the carbs independent or progreesively to each other. they have to open in unison. Because if there is one thing they are sensitive to is front to back fuel loading. But you are correct, the motor will tell him what it wants. The one thing I do know is, it doesn't want the carbs opened seperately.



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  • 12-06-2010, 06:39 PM
    ol guy
    Geez guys, read back and keep in mind he is going to run the blower @ 10% OVER. I don't know if it is a twist rotor or a straight cut. BUT the over-drive makes a big difference in distribution per cylinder. I would say to assemble as planned go make a decent pass, then shut down ASAP and pull the plugs, let them tell you! Everybody has what works for thier application and that does not make it work for every boat out there! IMLAO M
  • 12-06-2010, 01:27 PM
    gn7
    primary to secondary in the carb itself. No matter what linage you have set up on the carbs themselves, the carbs open together.



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  • 12-06-2010, 01:12 PM
    stewvette
    Just so i get this straight when you refer to having carb linkage 1:1. Is that carb to carb, or is it primary to secondary in the carb?
    thanks.
  • 11-25-2010, 05:36 PM
    Blowncat 509
    As is the original gm "53 series" which the b&m was a copy of
  • 11-24-2010, 11:51 PM
    gn7
    Quote Originally Posted by cfm View Post
    Decent animation on roots blower pressure changes. Top is where carb(s) are at and bottom the intake. Take a good look.

    Blue is lowest pressure, then green, yellow, and red being highest.

    That is a 2 lobe straight rotor blower, and the pic tends to be a little miss leading. They pulse horribly which can be seen in the pic. They move a little more air, but the pulsing is a big bummer in those things. Those do in fact need a big ass plenum to help, and even that isn't enough. The The B&M and the Weiands are all 2 lobe straight rotor



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  • 11-24-2010, 10:06 PM
    Gearhead
    Quote Originally Posted by wagspe208 View Post
    I agree. Hell, that was 15 years ago. Sorry. My memory is not that good.
    I can't even remember the chics I slept with back then let alone jet sizes.
    Wags
    I know thats true. I'm still sleeping with the same one... I think.....
  • 11-24-2010, 10:03 PM
    wagspe208
    Quote Originally Posted by Gearhead View Post
    Wags,

    Interesting. It would be interesting to know how the jet spread was in the carburetors and what size the Power Valve restrictions may have been. This would offer us some knowledge of fuel flow during both cruise and WOT.

    Gear
    I agree. Hell, that was 15 years ago. Sorry. My memory is not that good.
    I can't even remember the chics I slept with back then let alone jet sizes.
    Wags
  • 11-24-2010, 08:59 PM
    Gearhead
    Quote Originally Posted by wagspe208 View Post
    BLOWN GAS CARB

    OK... I will give my real world experience. Not something I read, or what a buddy did. Early to mid 90's.
    Blown gas 468, 7.8:1, jet boat, 10-71, pump gas usually, Barry Grant 750's with 850 base plates (back then these were super trick pieces), side mount. 4 power vaves, boost referenced. Back then the boost reference went into the side of the fuel block.
    I ran this piece on the river. I had 1 side running rich, 1 side lean. Now, this was not a WOT problem.. obviously. It was a part throttle issue. Not so lean as to burn down, but leaner than the rich side. I tried this and that. Finally I called a buddy, as soon as I described the problem, he told me to put 1:1 linkage on it. OK, makes sense to me. I did so, problem solved.
    Upon rebuild at the end of the year... the side that was lean had showed signs of pushing the head gasket (copper, o-ring and receiver groove). Not blowing... very slight signs, but obiously moving. The other side was happy (the rich side orignally).
    So, this is why I have come to my conclusion that sideways mount carbs should use 1:1 linkage.
    If I am in the company of "EXPERTS" like Don Bowers and Mike Kuhl.. I cannot think of a couple of other guys I'd rather be wrong with than them.

    GN... I can "influence" the cylinders below a hat nozzle with that nozzle. Not great, but if 1 and 3 are lean and I have big port nozzles to compensate... I can fatten up 1 or 3 hat nozzle to get the port nozzls back in line. It is not 1 to 1 or 3 to 3, but it is a general influence. This is a work in progress soemwhat as my port nozzles were staggered from .026 to .042 and hats were ??? (no tune up book in front of me). Now I am working on staggering the hat nozzles a little (no more than .004 ish) to get port nozzles in line. (really trying to get rid of the stuff under .032 ish).

    Hit me.
    Wags
    Wags,

    Interesting. It would be interesting to know how the jet spread was in the carburetors and what size the Power Valve restrictions may have been. This would offer us some knowledge of fuel flow during both cruise and WOT.

    Gear
  • 11-24-2010, 03:15 PM
    cfm
    Decent animation on roots blower pressure changes. Top is where carb(s) are at and bottom the intake. Take a good look.

    Blue is lowest pressure, then green, yellow, and red being highest.

  • 11-24-2010, 03:14 PM
    sanger rat
    Quote Originally Posted by gn7 View Post
    A high helix with a delta, needs to be set back big time.
    Thats what I thought till Mert and Spud told me not to set mine back. Maybe cause it's a 8 and not a 14? Haven't run this one yet so we'll see.
  • 11-24-2010, 02:56 PM
    wagspe208
    Roger GN. I only half assed readyour post regarding carbs and jet changing. Sorry.
    Wags
  • 11-24-2010, 02:29 PM
    gn7
    Quote Originally Posted by gn7 View Post
    Wags, the above is much more true than the side to side lean/rich deal from progressive linkage. The front/rear is a much bigger issue.


    But this is not to say that the blower is the mix master every one thinks they are. I have seen cylinders burn down because one hat nozzle plugged and always takes out a cylinder on the side of the motor the blocked nozzle was on. But this is because the hat nozzles are off set from the center of the blower, and the nozzle spray almost straight down on the rotors right where they are sweeping the fuel to the outside of the case. .
    Quote Originally Posted by wagspe208 View Post
    BLOWN GAS CARB

    Blown gas 468, 7.8:1, jet boat, 10-71, pump gas usually, Barry Grant 750's with 850 base plates (back then these were super trick pieces), side mount. 4 power vaves, boost referenced. Back then the boost reference went into the side of the fuel block.
    If I am in the company of "EXPERTS" like Don Bowers and Mike Kuhl.. I cannot think of a couple of other guys I'd rather be wrong with than them.

    GN... I can "influence" the cylinders below a hat nozzle with that nozzle. Not great, but if 1 and 3 are lean and I have big port nozzles to compensate... I can fatten up 1 or 3 hat nozzle to get the port nozzls back in line. It is not 1 to 1 or 3 to 3, but it is a general influence. This is a work in progress soemwhat as my port nozzles were staggered from .026 to .042 and hats were ??? (no tune up book in front of me). Now I am working on staggering the hat nozzles a little (no more than .004 ish) to get port nozzles in line. (really trying to get rid of the stuff under .032 ish).

    Wags
    Wags, I agree you can make big changes in the fuel distribution with hads nozzels, and said as much in my post. But we are talking about raw, un-emulsified fuel being dumped directly onto the out side of the rotor, just as it is sweeping it to the outside of the case. I have seen big changes with hat nozzles. But you will play hell tyring the same thing on a carb deal. richen up one side of a carb setup, and you end up with 8 richer holes. Maybe a little richer one one side, but not much. Like I said, carbs tend to feed the center of the blower rotors, at the meshing.

    If progressive didn't work, Holley blower carbs would probably be 1to1 and they aren't. And there are literally thousands of blower deals on the street out there with vac secondaries and they work fine.

    I have heard this is a much bigger problem with low profil street type manifolds like the B&M 420. But I have never seen in it my deals.



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  • 11-24-2010, 02:04 PM
    wagspe208
    Now, if we want to argue about cyl to cyl dist on N/A engines, start another thread. I'll be happy to show my ignorance again. LOL
    If anyone thinks a singe 4bl on any engine other than a cup engine has equal cyl to cyl dist. they are FU. Cup teams have spent thousands of hours to balance cylinder power output. 4/7 swap, different ratio rockers, etc.
    3 and 5 are always the leanest on chevys. You always had to tune the leanest cyls to not burn it down. At least this is how it was when I was running a dyno... but then again that is back in the mid to late 90's. (this is a lifetime + in engine development I know)
    Wags

    Come on... hit me with both barrels.
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