Took 347 to dyno - running lean

Discussion in 'Fox 5.0 Mustang Tech' started by KB91Notch347, Dec 5, 2003.


  1. KB91Notch347

    KB91Notch347 Member

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    Took my car to the dyno on Thursday. I'm running big time lean so I only did one pull. Also, because of the MSD box the RPMs were jumping all over so I couldn't get a very accurate torque number. Had I done another pull they said they could have changed the hookup for the RPM reading but since it was so lean I didn't want to take a chance.

    Anyways, I had 300 corrected, rear wheel horsepower at 5,000 RPM. We shut it down early because it was so lean.

    How lean you ask - how about almost 16:1 and according to the computer 19:1 at its worst! The strange thing was 3 of us didn't hear any detonation but when we pulled a plug it looked like it just came out of the box it was so white. I had checked the same plug last Saturday and it looked normal then. The only change since then was I replaced the old h-pipe that had rusted out where it met the tubes before the mufflers with a new x-pipe.

    My timing was set at a conservative 12*. The consensus was that with a 13.5:1 air/fuel or less, 15* timing, and going to 6,000 RPMs I should be near 375 HP.

    Fuel pressure was 40 the entire pull which should be plenty with 30lb injectors, right? I am running the stock computer so maybe I need some custom tuning???

    If anyone has some input I would greatly appreciate it.

    Kevin
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  2. bgjohnson

    bgjohnson Founding Member

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    hhhmmmmm. well maybe your computer isn't sending the right signal to your injectors, but have you tried upping the fuel pressure. Is it sending any codes at you?
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  3. KB91Notch347

    KB91Notch347 Member

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    Before we did the "official" pull, they had me run thru the gears at half throttle. It was showing very lean so I increased the fuel pressure from 37 (vacuum line off and plugged) to 40. Then I did the pull in 4th.

    Today I'm going to bump the FP up to 46 and see if I notice it in the "seat of my pants".

    Thanks for your input.
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  4. needforspeed440

    needforspeed440 New Member

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    let me know what you find....

    I am in the process of building about the same thing, 347 lotta air running 30lb injectors with a 255 pump. let me know what you find, i am expecting a hard time tuning myself. thanks
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  5. KB91Notch347

    KB91Notch347 Member

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    Besides the lean condition tuning has been simple. It idles at 900 with no hunting or surging. About the only thing I've noticed is that when I pull up to a stop sign or red light the idle floats to about 1200 until I come to complete stop and then settles to 900 and holds. The computer and all sensors (including both O2s) are original.
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  6. ninjacoupe

    ninjacoupe New Member

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    I've made a total of 9 pulls on my 347. Once you get it tuned don't make any changes LOL. Last change I made was removal of cervinis ram air box and the addition of Andersons powerpipe and Pro-m instead of CnL.
    Needless to say the increase in airflow resulted in a lean condition similar to yours. 17.5 at tip in 16.5 across the board. Once tuned it netted me 39 more horse at the wheel. Needless to say don't be surprised at the kick in the ass you'll get once that thing is tuned right. My combo made best power on every tuning session at 13.1.
    I'm waiting for some 1 and 3/4 kooks to replace the 1 and 5/8 longtubes on there now and some magnaflows to replace the flowmasters. That in addition to an electric fan and waterpump in place of the stock pieces should net me a cool 400 at the wheels, all under 6000.
    You have a similar combo as me ,you're cams bigger but so are your heads so that should be a good match.
    No reason you should not hit the 375, probably moreso
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  7. KB91Notch347

    KB91Notch347 Member

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    What is your fuel pressure set at?
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  8. ninjacoupe

    ninjacoupe New Member

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    Fuel preesure is set at 40psi all the time. All the changes were made in the chip. Joey the dyno operator said fuel pressure alone would not be enough to get my AF back. The duty cycles had to be increased. The gains I made were across the rpm range not just at peak.The entire curve moved up. Also I made best power with total advance at 35. They also set me up with a nice timing curve.
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  9. KB91Notch347

    KB91Notch347 Member

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    Was the custom tuning done at the dyno or offline?
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  10. ninjacoupe

    ninjacoupe New Member

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    Done right at the dyno. 1st session was 5 pulls. 2 for a/f 2 for timing and the final for timing and air fuel. Then i made some changes went for a dyno day made a pull and found out why it was not faster after the changes, air fuel went real lean. Went back for a quick adjustment and another 2 pulls. Now the car hauls ass again. I just got a call from KOOKS and my headers are done :)
    #10

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