6-71 boost
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6-71 boost

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    SLOW MEMBER slowboy's Avatar
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    Default 6-71 boost

    Is 5-5.5 pounds of boost on a 390 cube small block chevy too much boost for pump gas? I am currently running 91 octane with this set up, but dont want molten parts......yet. Timing is set at 32 degrees.

    Thanks, Ryan
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    mo balls than $cents$ IMPATIENT 1's Avatar
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    Quote Originally Posted by slowboy View Post
    Is 5-5.5 pounds of boost on a 390 cube small block chevy too much boost for pump gas? I am currently running 91 octane with this set up, but dont want molten parts......yet. Timing is set at 32 degrees.

    Thanks, Ryan
    what's the motor compression? i got away with pump gas at 6lbs of boost(@5%underdrive) on a 475 with 9 to 1 but i ran conservative timing also, never once had a detonation issue.

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    SLOW MEMBER slowboy's Avatar
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    Compression is 10-1, aluminum heads, I did not build this engine, this is the way I got it. All I changed was the lower pulley, last night, went from 2-3 pounds of boost at 5100 to 5 at 5600.

    I pulled a plug, and it looked good, no signs of pistion.

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    Rollin With Fink fasterthanu's Avatar
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    Quote Originally Posted by slowboy View Post
    Compression is 10-1, aluminum heads, I did not build this engine, this is the way I got it. All I changed was the lower pulley, last night, went from 2-3 pounds of boost at 5100 to 5 at 5600.

    I pulled a plug, and it looked good, no signs of pistion.

    Thanks

    I say it's a disaster waiting to happen. I would be sure I was plenty fat on the fuel. A normaly aspirated 10-1 motor today, is right at the edge on pump gas. If this is in a jet boat where the motor is loaded most of the time- I would be even more concerned. I am sure some are doing it, just depends how fat your wallet is if it goes............... Elevation, jetting, gearing? and so on will play a big role in it's life expectancey.

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    SLOW MEMBER slowboy's Avatar
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    I dont want to run it on the edge, right now it is at -10 percent (underdriven). I like the ability of filling up with pump gas, but do have access to race gas if needed.

    What is a good boost number to be safe on pump gas? This is in a jet. Sure do like the power it makes with the higher boost, but do not want to spend the cabbage after it melts, rather be safe than sorry.
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    Quote Originally Posted by fasterthanu View Post
    I say it's a disaster waiting to happen. I would be sure I was plenty fat on the fuel. A normaly aspirated 10-1 motor today, is right at the edge on pump gas. If this is in a jet boat where the motor is loaded most of the time- I would be even more concerned. I am sure some are doing it, just depends how fat your wallet is if it goes............... Elevation, jetting, gearing? and so on will play a big role in it's life expectancey.
    i agree, 10 to 1 is huge compression for a gas motor. you should be runnin 112 or alky.

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    Rollin With Fink fasterthanu's Avatar
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    Quote Originally Posted by slowboy View Post
    I dont want to run it on the edge, right now it is at -10 percent (underdriven). I like the ability of filling up with pump gas, but do have access to race gas if needed.

    What is a good boost number to be safe on pump gas? This is in a jet. Sure do like the power it makes with the higher boost, but do not want to spend the cabbage after it melts, rather be safe than sorry.
    Sorry I could not tell you what is safe. This is just my opinion by the way. I have built 3 blower motors two in jets and one in a car. 2 have had detonation issues due to my lack of blower experiance, although after spending enough money and years of tinkering I think I have it down, or I hope so, one nevers knows Just my 2 cents but a few pounds if ya like the blower may be an ok number. Or run race gas and still check your plugs and jet accordingly. Lean is Mean but Fat is were it's at. You leave some power on the table fat but you could also leave money in your wallet in the long run. Keep in mind it is not just boost- it is everything else I mentioned and more. Like I say I have heard of others do the unspeakable and get away with it. Guess it's a coin toss........... I would run some NGK R5673-8 plugs or equivelent for your deal. These plugs as I have been told (and I use) by an expert tuner (fiat48). Says these plugs will show signs of detonation- via the cad plating will burn off showing detonation before you burn a piston. If you have headers you will never hear it happen. Good luck and enjoy your boat.

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    Go to BDS's web site. There are a few helpful charts for getting a base line for boost and such.

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    SLOW MEMBER slowboy's Avatar
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    Quote Originally Posted by fasterthanu View Post
    Sorry I could not tell you what is safe. This is just my opinion by the way. I have built 3 blower motors two in jets and one in a car. 2 have had detonation issues due to my lack of blower experiance, although after spending enough money and years of tinkering I think I have it down, or I hope so, one nevers knows Just my 2 cents but a few pounds if ya like the blower may be an ok number. Or run race gas and still check your plugs and jet accordingly. Lean is Mean but Fat is were it's at. You leave some power on the table fat but you could also leave money in your wallet in the long run. Keep in mind it is not just boost- it is everything else I mentioned and more. Like I say I have heard of others do the unspeakable and get away with it. Guess it's a coin toss........... I would run some NGK R5673-8 plugs or equivelent for your deal. These plugs as I have been told (and I use) by an expert tuner (fiat48). Says these plugs will show signs of detonation- via the cad plating will burn off showing detonation before you burn a piston. If you have headers you will never hear it happen. Good luck and enjoy your boat.

    Those are the exact plugs that I am using, I started using them when I was using lots of nitrous, and have had very good luck reading them. I did not think my compression ratio was as high as it is, untill I had a friend plug all of my numbers into a compression caluclator this morning.

    Have any of you messed with water injection?

    Sorry for so many questions, blowers are somewhat new to me, but I am for sure hooked on them.

    Thanks again, Ryan
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    Quote Originally Posted by slowboy View Post
    Those are the exact plugs that I am using, I started using them when I was using lots of nitrous, and have had very good luck reading them. I did not think my compression ratio was as high as it is, untill I had a friend plug all of my numbers into a compression caluclator this morning.

    Have any of you messed with water injection?

    Sorry for so many questions, blowers are somewhat new to me, but I am for sure hooked on them.

    Thanks again, Ryan
    No never have dealt with water or alcohol injection. An Intercooler is my detonation control of choice.

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    SLOW MEMBER slowboy's Avatar
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    I have an intercooler sitting here on the bench. How much will that help?

    I just need to get some longer studs, longer belt, and another gasket and I can install it. Hopefully soon.
    Last edited by slowboy; 06-18-2008 at 09:54 AM. Reason: I Kant Spel
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    Quote Originally Posted by slowboy View Post
    I have an intercooler sitting here on the bench. How much will that help?

    I just need to get some longer studs, longer belt, and another gasket and I can install it. Hopefully soon.
    it'd be a huge help!!! bolt that sucka on there

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