Blower Size & Fuel System

Discussion in 'PSI Superchargers Tech Questions' started by StrokerMcGurk, Mar 8, 2012.

  1. StrokerMcGurk

    StrokerMcGurk New Member

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    Hello

    Can anyone tell me if a 8-71 will fit on a small block Chevrolet without interfering with the magneto? (Joe Hunt H3 Vertex) Years ago I ran a 6-71 with a Super Mag but I don't recall how close the blower was to the mag. Am I correct that an 8-71 is 1 inch longer than a 6-71? I think that the Joe Hunt H3 vertex mag is considerably smaller than the Super Mag.

    What is the correct amount of fuel pressure with an alcohol set up? What percentage of the pump output should be consummed? My Hilborn injection was originally set up for gas and I think that I use (8) .050 nozzles when I switched to alcohol. Does that sound right? The engine was 364ci and I drove the Don Hampton 6-71 supercharger @30%. I never checked the boost with a gauge. I just added and subtracted teeth until it squirted the copper head gaskets out. Thirty plus years ago I knew all of this but like the saying goes; use it or loose it. Like a dummy I chose the loose it option.

    Thanks,
    Ron
     
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    Last edited: Mar 8, 2012
  2. Moparious Maximus

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    We have an SBC with a 6-71 and its really close to the vertex, there would be no way we could fit an 8 without moving the blower forward or moving the mag up front.

    The pump/pressure/ % of pump used, there are many ways to make it work but this is what I like. 140-150psi peak pressure, use about half of the pump.
     
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  3. StrokerMcGurk

    StrokerMcGurk New Member

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    Moparious,

    I enrolled at the fuelinjectionent.com sight and their calculator shows the following:

    Below is with a 60° 6-71 @30% and (8) .047 nozzles.

    Required Fuel @ 8000 RPM 6.415 GPM
    Pump Flow @ 8000 Engine RPM 12 GPM
    Pump Output Required by Motor 53.46%
    Overdrive 30%
    Boost 22.1 psi
    Theoretically Optimal Main Jet Size 0.124"
    Main Jet Area 0.01208 Sq. In.
    System Pressure @ 8000 RPM 142.4 psi

    Ron
     
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  4. WIZBANG

    WIZBANG Member

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    Why such a big fuel pump and bypass all the fuel ?

    Why such a big main jet ?

    Why not a smaller pump, and also keeping the main in the .100 range ?
     
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  5. Dave Koehler

    Dave Koehler Member

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    You will need an offset mag drive or better yet move it to the front with a RCD adapter.
    You haven't said what your goals are but if you are looking at 800 ponies and down you may want to drop back to around 7 gpm pump size. More hp go for around a 9 gpm pump.
    Dave Koehler
    http://www.koehlerinjection.com
     
    #5
  6. StrokerMcGurk

    StrokerMcGurk New Member

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    Moparious Maximus,
    Dave Koehler,

    RBS offers a 8-71 for SBC and it's basically a 6-71 with an additional 1" of length added to the front of the case. Are there any pros and cons with that configuration? Obviously there's an additional 1" of rotors that is not exposed to the discharge opening.

    http://www.rbssuperchargers.com/Products.cfm?pn=1050-0003&pID=5961

    I have decided not to attempt to piece togehter a FI system. Trying to save money usually ends up costing me money. For that reason, plus it's the smart thing to do, I will purchase a new Enderle FI setup that is sized for my engine and has been flowed.

    I purchased a used(up) Vertex magneto from eBay seller alkydigger1. He advertised it as having hot spark and claimed to have spun it on the bench for 5 minutes. On the day that I received the mag I shipped it to Joe Hunt magnetos for an examination and tuneup. Roger called me back and told me that the mag had a bad high tension coil and it had a bearing/bushing that was worn out. So much for the HOT SPARK. The eBay seller alkydigger1 had the balls to tell me that he did not guarantee the mag to work for ever. He is a Joe Hunt magneto dealer so Roger must have had a talk with him because all of his used mags are now listed as being rebuilt by Joe Hunt magnetos. The cost to repair the mag was $400.00 plus shipping cost. Roger told me that the mag was good as new and after they cleaned it up and rebuilt it the mag looked like new. However for just a few dollars more and a lot less BS I could have purchased a new mag.

    My original plan was to run injected gas but after making the decision to go blown alcohol I sent the mag back to Joe Hunt magnetos and had it upgrade it to a Joe Hunt H3. Roger treated me very fairly and gave me full credit for all of the new parts that were previously installed in the mag. Now I have a good as new Joe Hunt H3 magneto, but once again for just a few dollars more I could have purchased a new Joe Hunt H3 magneto.

    New Question:
    Will using port nozzles eliminate the surge at idle or is that just more internet misinformation?

    Thanks,
    Ron
     
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  7. Dave Koehler

    Dave Koehler Member

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    Just more misguided "Cousin Bubba said" baloney. It's all in the idle rpm and BV adjustment.

    Dave Koehler
    http://www.koehlerinjection.com
     
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  8. secondwindracing

    secondwindracing top alcohol

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    if it is a Littlefied blower all the case length is out the back..if it is a mooney ham blower it is 50/50 half front half rear..Dave
     
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  9. TADHemiracer

    TADHemiracer Member

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    Cousin Bubba / Internet Confusion

    My 526 Brad hemi with a 14 HH will idle smooth at 1,450 RPM, no surges. I actually idle it about 1,800 because I use that rpm to roll the dragster into the lights but it will idle at 1,450. Set your BV properly and the idle will smooth out. My idle PSI check is set at 9 psi. You might want to add a guage between the pump and the BV to check your idle psi for fluctuations related to rpm. Just my .02 worth.
     
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  10. Moparious Maximus

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    Port nozzles dont flow anything at idle anyway so they dont have anything to do with hunting/surge, but it is my personal opinion that port nozzles are definently worth having.

    It will run fine without ports but I have never seen a (HAT only) blower motor impress me.

    How fast do you want to go??
     
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  11. StrokerMcGurk

    StrokerMcGurk New Member

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    Moparious,

    I'm financing this project with SS checks so don't expect to see me in TA/D.

    How fast is your blown small block Chevrolet?

    Ron
     
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  12. Moparious Maximus

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    We really dont know how fast it is yet, we are at 10% over on the 6-71 and it went 7.20 with all the cad left on the plugs, im sure it would run 6.8s or .9s with a good tune. Its only been to the track twice, it had some tire shake issues last year and only made one full pass.
     
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