The sounds of music
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The sounds of music

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    Senior Member Deweydaddy's Avatar
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    Default The sounds of music

    Hey guys,
    I spent a day at a car show/cruise a couple weeks ago....another 1 1/2 hours posting pics in the open water section....some of you may have seen them.....while sitting in my area.... Amongst fellow hotrod-comrades....we, mostly me...said as some blower motors went by....." With the sounds of music...."blower surge"......that's caused by fuel dripping in the engine at near idle.....just off cruise conditions and said....some cam firing sequences can cause that too.......then some would go by.....just hearing the whirl of the blower.....we had a great spot.....very crowded and most had to wait for a light......is my input to these guys correct? I did have an old timer tell me it was his carbs....not the cam in his case.....I'm not a mister know it all....that's kinda why I'm here.... Thanks
    I’d rather live with a good question than a bad answer.

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    Senior Member Smallblocksperry's Avatar
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    Quote Originally Posted by Deweydaddy View Post
    Hey guys,
    I spent a day at a car show/cruise a couple weeks ago....another 1 1/2 hours posting pics in the open water section....some of you may have seen them.....while sitting in my area.... Amongst fellow hotrod-comrades....we, mostly me...said as some blower motors went by....." With the sounds of music...."blower surge"......that's caused by fuel dripping in the engine at near idle.....just off cruise conditions and said....some cam firing sequences can cause that too.......then some would go by.....just hearing the whirl of the blower.....we had a great spot.....very crowded and most had to wait for a light......is my input to these guys correct? I did have an old timer tell me it was his carbs....not the cam in his case.....I'm not a mister know it all....that's kinda why I'm here.... Thanks
    i dont know it all either, but based off of my experience my blower motor surges from 900-1400 and by leaning out the idle air mixture it calms it way down. But then itll die when i put my boat in gear with the big prop on it.

    on my buddies 26 daytona with a 500inch 14-71 blower motor it idles like an NA motor, i've twisted on the carbs every which way to make it lope (what he wanted) and it just wont surge, the differences between our motors are i run a intercooler/he doesnt, and i have an actual blower cam .252/[email protected] on a 114, his cam is some hydraulic roller marine cam for an NA engine, so maybe the cam does play a part in the surging. the other difference is i have an 8-71 and his is a 14-71

    maybe somebody can chime in with some good info

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    Senior Member Deweydaddy's Avatar
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    Thanks.....sounds like there are a few variables that could cause surge.....maybe a higher idle speed may remove some of the surge and prolly the choice of stall converter in street apps.....
    I’d rather live with a good question than a bad answer.

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    Senior Member wizbang's Avatar
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    " Hunting" for air !

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    Senior Member bbqcruising's Avatar
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    A guy I know with a street rod told me that his surge was created by his power valves. Didn't really ask if he went big or small.

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    Senior Member Deweydaddy's Avatar
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    Quote Originally Posted by bbqcruising View Post
    A guy I know with a street rod told me that his surge was created by his power valves. Didn't really ask if he went big or small.
    that's interesting.....opening and closing at or near idle????
    I’d rather live with a good question than a bad answer.

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    Senior Member bbqcruising's Avatar
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    Yes, at idle. Kind of acted like it was some hot rodders secret. It was purely done for effect and not performance.

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    gn7
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    Quote Originally Posted by Smallblocksperry View Post
    i dont know it all either, but based off of my experience my blower motor surges from 900-1400 and by leaning out the idle air mixture it calms it way down. But then itll die when i put my boat in gear with the big prop on it.

    on my buddies 26 daytona with a 500inch 14-71 blower motor it idles like an NA motor, i've twisted on the carbs every which way to make it lope (what he wanted) and it just wont surge, the differences between our motors are i run a intercooler/he doesnt, and i have an actual blower cam .252/[email protected] on a 114, his cam is some hydraulic roller marine cam for an NA engine, so maybe the cam does play a part in the surging. the other difference is i have an 8-71 and his is a 14-71

    maybe somebody can chime in with some good info
    The fact that your buddies is unaffected by adjusting the idle mixture screw just proves that his butterflies are open to far to get to idle, and once they are open enough to activate the transfer slot, the mixture screw is rendered useless. Having a surge with an I/O can be a good thing with big power because you can put it in gear on the RPM drop and its not as hard on the drive. Yeah, leaning it out will get rid of the surge, but does usually result in a stalled engine when you load it.
    Quote Originally Posted by wizbang View Post
    " Hunting" for air !
    More accurately, searching for fuel. In a MFI deal, the engine Rs climb from the low because the fuel pressure and flow falls, and the engine leans out. Then as the engine speeds up, it goes rich and the R's fall again, and it just bounces back and forth between rich and lean.

    Quote Originally Posted by bbqcruising View Post
    A guy I know with a street rod told me that his surge was created by his power valves. Didn't really ask if he went big or small.
    That's bullshit. There are thousands of engines that surge big time and have blocked power valves. PVs feed the main circuit, not the idle circuit. PV fuel is fed to the booster, and the booster is not OR should not be active when idling. PVs are nothing more than adding a main jet to the carb when the vacuum falls when the throttle goes open. Even if it opened at an idle, which it shouldn't, the fuel has nowhere to go because the booster isn't active. If PVs effected the idle, then just changing the main jet size would effect the idle, and it doesn't.
    Carbs seem to be most affected by the placement of the idle restrictor in the metering block. Blocks that have the restrictor high seem to surge much worse than metering blocks with a low, below fuel level restrictor. Both can surge, but the high restrictor seems to surge much worse.

    High idle restrictor. Common with almost all billet metering blocks except Bo Laws' blocks. Found in many later Holley blocks. This practice got started with the release of emmissions carbs and found its way into almost all newer carbs. Not everything new is better.





    Low idle restrictor. Found in all earlier pre emission Holleys, and almost all carbs modified by a shop that know what they are doing.



    Comparison of the tow idle restrictor locations.





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    Last edited by gn7; 09-05-2013 at 08:22 PM.

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    Senior Member ol guy's Avatar
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    This will be a fun read being that nobody really knows why blowers surge! And no I am not going to get into a pissing match explaining the how and why! Let er rip kids! I will love to hear this!!!!!M

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    Senior Member Deweydaddy's Avatar
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    Quote Originally Posted by ol guy View Post
    This will be a fun read being that nobody really knows why blowers surge! And no I am not going to get into a pissing match explaining the how and why! Let er rip kids! I will love to hear this!!!!!M
    LOL........Its prolly as simple as.."Why does a dog lick his azz?......"Bcause it can"......
    I’d rather live with a good question than a bad answer.

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    Senior Member SHAWN DAVIS's Avatar
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    Probably a million different theories on the subject. Mine is the fact that the supercharger is drawing air thru a restriction and hunting for air.
    I had a twin turbo setup in a flat several years ago that would surge as much as any blower.

    People on facebook may like this little video

    https://www.facebook.com/shawn.davis...type=3&theater
    Last edited by SHAWN DAVIS; 09-06-2013 at 09:50 AM.

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    Senior Member Deweydaddy's Avatar
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    Does the 4/7 cam swap play a part in the sound with a blower app?
    I’d rather live with a good question than a bad answer.

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    No.

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