blower boost; dyno vs boat?
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blower boost; dyno vs boat?

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    Senior Member LOLYFE's Avatar
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    Default blower boost; dyno vs boat?

    Have a 557 bbf with a mooneyham 8-71 on it. My question is that on the dyno it makes about 12 lbs boost @ 6500 rpm, but with motor in boat, the gauge just doesn't read any boost. Its a Livorisi mechanical gauge (new) with a 1/4 line going to front of boat. Check guage and it is accurate. Any ideas??

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    Senior Member wagspe208's Avatar
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    Boat boost should = dyno boost at x rpm and WOT. If you are at 6500 rpm but 1/2 throttle, no boost will not be equal.
    The engine does not know it is in a boat.
    Wags

    And did you put the boost gauge fitting in the same placeas on the dyno?
    Last edited by wagspe208; 09-09-2010 at 12:00 PM.

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    mo balls than $cents$ IMPATIENT 1's Avatar
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    make sure your farrels didnt shut the 1/4 line and pinch it shut, use regulated air pressure on the motor side of the line and make sure its actually working up frt. dyno will load the engine different than a boat, boat may be alot easier to hit 6500 comparing load to load

    Dare to be different, if it turns out great you can claim you planned it that way.

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    Senior Member LOLYFE's Avatar
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    Quote Originally Posted by IMPATIENT 1 View Post
    make sure your farrels didnt shut the 1/4 line and pinch it shut, use regulated air pressure on the motor side of the line and make sure its actually working up frt. dyno will load the engine different than a boat, boat may be alot easier to hit 6500 comparing load to load
    So, if loads are not the same, (was wondering about that) can you overdrive more? I think that final compression and quality of fuel will still be a determining factor in overall performance right?

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    Senior Member LOLYFE's Avatar
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    Quote Originally Posted by wagspe208 View Post
    Boat boost should = dyno boost at x rpm and WOT. If you are at 6500 rpm but 1/2 throttle, no boost will not be equal.
    The engine does not know it is in a boat.
    Wags

    And did you put the boost gauge fitting in the same placeas on the dyno?
    Yes, same port. thanks

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    mo balls than $cents$ IMPATIENT 1's Avatar
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    Quote Originally Posted by LOLYFE View Post
    So, if loads are not the same, (was wondering about that) can you overdrive more? I think that final compression and quality of fuel will still be a determining factor in overall performance right?
    well at the dyno they have load cells to load within certain rpms and hp levels, so if you told em to pull it to 6500, they did and put more load to it to in order to make boost happen. a 557bbf is a monster by itself. this in a jet or outdrive boat? have you tried goin wfo from barely moving in the boat and see where the boost went?

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    Senior Member LOLYFE's Avatar
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    Quote Originally Posted by IMPATIENT 1 View Post
    well at the dyno they have load cells to load within certain rpms and hp levels, so if you told em to pull it to 6500, they did and put more load to it to in order to make boost happen. a 557bbf is a monster by itself. this in a jet or outdrive boat? have you tried goin wfo from barely moving in the boat and see where the boost went?
    Its in a jet, fairly extensive mpd pump work, has an a impeller in it now, haven't really seen top rpm yet. Has run 96 with pedal left. The motor had a tunnel ram on it before with same impeller, boat with blower motor seems different with the same impeller, have a aa stainless being worked on now to try. Motor with tunnel ram about 750 pump gas 930 with blower and race gas, seems to effortlessly turn "a" impeller like motor really isnt loaded. Trying to write what i am thinking is proving to be hard on this topic, bare with me thanks

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    mo balls than $cents$ IMPATIENT 1's Avatar
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    Quote Originally Posted by LOLYFE View Post
    Its in a jet, fairly extensive mpd pump work, has an a impeller in it now, haven't really seen top rpm yet. Has run 96 with pedal left. The motor had a tunnel ram on it before with same impeller, boat with blower motor seems different with the same impeller, have a aa stainless being worked on now to try. Motor with tunnel ram about 750 pump gas 930 with blower and race gas, seems to effortlessly turn "a" impeller like motor really isnt loaded. Trying to write what i am thinking is proving to be hard on this topic, bare with me thanks
    your 557 is jus strong bro stick it to the wood leaving from a rolling start and id bet you see boost for a bit till you back outta the throttle or pump fully loads the motor down. have a friend we built a flat topped 557bbf for and he's turning a a-cut to 6600 on motor alone, no nitrous, so you jus prob aint loaded the motor nearly nuff yet.

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    Senior Member LOLYFE's Avatar
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    [QUOTE=IMPATIENT 1;1221776]your 557 is jus strong bro stick it to the wood leaving from a rolling start and id bet you see boost for a bit till you back outta the throttle or pump fully loads the motor down. have a friend we built a flat topped 557bbf for and he's turning a a-cut to 6600 on motor alone, no nitrous, so you jus prob aint loaded the motor nearly nuff yet.[/QUOT Thats what I was thinking, thanks much

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    gn7
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    LOLFYE, Rule #1 when it comes to roots blowers is... never listen to a turbo guy! They just do not get it.

    Roots blower boost has no nothing with load. They are not load sensitive. They are insensitive to RPM within reason, 1000-10,000 RPM. Load and Rpm have nothing to do with roots boost. None, nata, zip, zero. They only care about one thing. Available air intake. THROTTLE POSITION!!! When you stand the throttle blades on end at 2500, it has the same boost as when you stand them on end at 7,000. Doesn't matter what the load is. If there is zero load, and you floor it, it will make max boost right until the rods come out. The only thing that matters is the throttle position. Period. So if you want to know you max boost, flor it and look. Don't worry about the RPM, or the load in the boat, or the speed of the boat, or the time of day.

    And what ever RPM your motor runs at WOT, that the max load it can handle at that RPM. If its 6500, that the max load for 6500. Any less load, it would go to 6700, or higher. Any more load, it would fall to 6300, or lower. The max RPM and WOT is totally determined by the applied load.

    So if your gauge is showing no boost, there is something wrong with the gauge, or line, or manifold port.


    OR YOUR BLOWER BELT FELL OFF



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    Quote Originally Posted by gn7 View Post
    LOLFYE, Rule #1 when it comes to roots blowers is... never listen to a turbo guy! They just do not get it.

    Roots blower boost has no nothing with load. They are not load sensitive. They are insensitive to RPM within reason, 1000-10,000 RPM. Load and Rpm have nothing to do with roots boost. None, nata, zip, zero. They only care about one thing. Available air intake. THROTTLE POSITION!!! When you stand the throttle blades on end at 2500, it has the same boost as when you stand them on end at 7,000. Doesn't matter what the load is. If there is zero load, and you floor it, it will make max boost right until the rods come out. The only thing that matters is the throttle position. Period. So if you want to know you max boost, flor it and look. Don't worry about the RPM, or the load in the boat, or the speed of the boat, or the time of day.

    And what ever RPM your motor runs at WOT, that the max load it can handle at that RPM. If its 6500, that the max load for 6500. Any less load, it would go to 6700, or higher. Any more load, it would fall to 6300, or lower. The max RPM and WOT is totally determined by the applied load.

    So if your gauge is showing no boost, there is something wrong with the gauge, or line, or manifold port.


    OR YOUR BLOWER BELT FELL OFF

    x2 you beat me to it. the blower is tied directly to the cranck shaft (via the belt), the only way to change boost pressure is to change pulley ratios. nothing else can change the boost, the only time boost is unstable i believe, is at idle thats why they lope or roll. they are trying to boost but dont have the fuel so it tries to die then it slowws enough for the a/f to become close then it tries to speed up (hence the roll/lope). but i could be wrong.

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    like was said earlier, must have throttle blades fully open!
    when I was running my blown jetboat, w/ a 12-71, and 2 1050's, (on a
    little 468 mind you) I would spin an agressor AA to 64-6500rpm, and would
    be making right around 16lbs. of boost. My wife wanted to drive, and she
    ran it up to about 4500rpm and zero lbs boost before I started screaming
    at her to either put it to the wood, or shut it down, before she hurts
    somthing! won't make boost without max available airflow! I'd check
    my throttle linkage for full opening! have seen same scenario because
    carbs weren't getting full throttle!

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    Senior Member wagspe208's Avatar
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    I was wondering when someone who understands a roots type blower is "positive dispalcement" and load does not matter, woud speak up.
    Wags

  16. #14
    gn7
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    Turbo guys. You can lead them to water, but once there, your only choice is to drown em. The whole concept of instantaneous "on demand" boost is outside their thought process



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