injected BBC won't RPM past 4000 on the line...sometimes

Discussion in 'PSI Superchargers Tech Questions' started by slracing, Aug 29, 2010.

  1. slracing

    slracing New Member

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    I think I put this out here once before but here goes... I stage the car, put it on the trans brake and if I open the throttle real quick the motor goes to 4000 like it's on a chip. If I open the throttle a little slower it goes right up to my 5000 chip or whatever I have in it.
    I'm running a 509, tunnel ram W/ a bird, square barrel with the "32" spool for injected motors, 80A-1 pump, 7AL2 MSD. If I let go of the button when it's sitting at 4000 it goes out like a slug for 60 or 80 ft. then cleans up like someone flicks a switch. I used to run a tight plug gap and thought the problem was gone when we opened them up to .045 , but then last night it did it again after I put 5 more in the main. Don't know if that had anything to do with it? I had one guy tell me my cam profile might be causing it. Any enlightenment from anybody? Thank You.
     
    #1
    slracing, Aug 29, 2010
  2. Mike Canter

    Mike Canter Top Dragster
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    So when this is happening what is your plug gap. Have you tried it with a plug gap of .017-.019? If so what happened?
    Do you have a crank trigger?
    How much boost do you make at 8000 rpm?
    What are your EGTs while staging?
     
    #2
    Mike Canter, Aug 29, 2010
  3. slracing

    slracing New Member

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    I had the plugs gapped at .025 and it was more frequent, yes I run a crank trigger, no boost (it's injected) and I don't have my computer on the car yet so no EGTs right now. Probably not much help I know.
     
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    slracing, Aug 29, 2010
  4. Mike Canter

    Mike Canter Top Dragster
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    What you should first try is closing your plug gap down to .019 and see if anything changes. On your crank trigger are you running the special MSD shielded crank trigger cable from the pickup to the 7AL2? You can tell if it is shielded or not because it will have a separate black ground wire at the end that plugs into the 7AL2 harness. If you don't have a shielded cable or that black wire is not attached to chassis ground then electromagnetic interference from plug wires, or electric motors will cause the 7AL2 to intermittently random fire and make the motor act real funny or take out a piston.
     
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    Mike Canter, Aug 29, 2010
  5. slracing

    slracing New Member

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    I don't have the shielded cable. Didn't even know they offered one. I'll have to look into that. I'll also double check what I have it routed near. As far as the plug gap goes MSD says .045 for naturally asperated .060 if you run the large cap. I know we have to keep them tight on our blown combo because of the cyl pressure but this tended to give me problems more often with tighter gaps. At this point though I'm willing to try anything once. Why me? I've set up a few of these systems for other guys and they work great!
    Thanks again!!!
     
    #5
    slracing, Aug 29, 2010
  6. Mike Canter

    Mike Canter Top Dragster
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    Please get that shielded cable. The intereference has destroyed a lot of motors and maybe causing your problem by random firing of a few sparkplugs. Even with the shielded cable route it away from all other wires. As far as the plug gap goes methanol is real wet because of the AFRs used which makes they are hard to fire if the plugs load up while coming up to the line. The smaller gap really helps in that wet environment.
     
    #6
    Mike Canter, Aug 29, 2010
  7. slracing

    slracing New Member

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    I'll give it a shot. Thanks again!
     
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    slracing, Aug 29, 2010

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