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Thread: VAFPR and tuning

  1. #1
    Fuel Injected! CDeeZ's Avatar
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    VAFPR and tuning

    Got a 27 PSI marine spring to feed my SBC that I'd estimate is ~400 FWHP. I have that spring in there and I'm now wondering what the best approach is to dialing in the fuel.

    I read a LOT of mixed information on whether or not a VAFPR is worthwhile on a TBI setup. Should I get a VAFPR to bring AFR closer to stoich at idle or can I tune around without it? Idling pretty rich right now at around 10 or 11 AFR with the 27 PSI spring in there. Injector flow rate is setup in the tune as 91.

    If it can be tuned without using a VAFPR, can this be done entirely on the VE table or should I be looking elsewhere as well?

  2. #2
    Super Moderator dave w's Avatar
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    The VAFRP is challenging! Most TBI computers do not a table to compensate for Kpa vs. lbs. / hr

    For example, (I make up some numbers):
    100 Kpa / 108 lbs /hr
    80 Kpa / 91 lbs / hr
    60 Kpa / 78 lbs / hr
    40 Kpa / 65 lbs / hr
    20 Kpa / 52 lbs / hr

    Perhaps Dynamic EFI has a TBI computer system that has a table for VAFPR?

    dave w

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    Quote Originally Posted by dave w View Post
    The VAFRP is challenging! Most TBI computers do not a table to compensate for Kpa vs. lbs. / hr

    For example, (I make up some numbers):
    100 Kpa / 108 lbs /hr
    80 Kpa / 91 lbs / hr
    60 Kpa / 78 lbs / hr
    40 Kpa / 65 lbs / hr
    20 Kpa / 52 lbs / hr

    Perhaps Dynamic EFI has a TBI computer system that has a table for VAFPR?

    dave w
    The EBL has provisions for both Vacuum and Boost to work with a VAFPR. Worked well for me with the Weiand 177 I ran. A Weiand 177 is one of the easiest ways to make a TBI engine crank out decent power and ALOT of torque.

  4. #4
    Fuel Injected! CDeeZ's Avatar
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    Yes the EBL would do it. I have a 4l80 in this truck so I was trying to stay with the 7427 pcm to shift it. So are we saying there is absolutely no way to fuel a tbi at 30 psi with GM PCM? Without it being stupid rich at idle?

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    If I am reading the post correctly you haven’t tweaked the ve table down. If that is correct take idle table and lean it out. Try open and closed to see what you can come up with. Until your table takes you below the min open/close time of the injectors you should have adjustment.
    6395, BHDF, 7.4 BBC lightly modded now 6395 BMHM back to BHDF

  6. #6
    Super Moderator dave w's Avatar
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    Quote Originally Posted by CDeeZ View Post
    Yes the EBL would do it. I have a 4l80 in this truck so I was trying to stay with the 7427 pcm to shift it. So are we saying there is absolutely no way to fuel a tbi at 30 psi with GM PCM? Without it being stupid rich at idle?
    WBO2 tuning is a must have tool for tuning a 30 PSI TBI with or without a VAFPR: http://www.gearhead-efi.com/Fuel-Inj...g)-Spreadsheet

    dave w

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    The most common way to account for AFR is in the VE tables. It may be possible to use excel and an existing correct VE table and scale it based on AFPR changes to pressure. I would ensure both open and closed throttle VE tables are adjusted. But without a correct VE table this exercise may be a waste of time.

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    Quote Originally Posted by dave w View Post
    WBO2 tuning is a must have tool for tuning a 30 PSI TBI with or without a VAFPR: http://www.gearhead-efi.com/Fuel-Inj...g)-Spreadsheet

    dave w
    Over the past 16 years I have tuned plenty of engines without a wideband. It is not a must have by any sense of the imagination. I am not arguing that it is not a valuable tool because it is, but it is also not necessary.

    I usually disable BLM and tune off the integrator alone. History average off the Integrator with the BLM disabled is a quicker way to tune than it is off BLM.
    Last edited by Fast355; 1 Week Ago at 06:49 AM.

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    Fuel Injected! brian617's Avatar
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    I'm running the marine spring with around 25psi and didn't have any problem making the VE table work. Just make sure your actual injector flow #s match injector flow rate in .bin
    89 K1500 Scottsdale 5.7L 5spd 3:42

    Build specs: 97 4 bolt main block 350ci, Eagle rotating assembly with flat tops and 4 valve reliefs, Dart 165cc/67cc Iron Eagle heads, Manely SS valves and springs 110lbs seat @1.7, GM Ram Jet cam 196/206 @.50 .431/.451, stock intake and throttle body, heads and intake gasket matched, Delco EP377 fuel pump @ 22 psi, 427 PCM.

  10. #10
    Super Moderator dave w's Avatar
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    Quote Originally Posted by Fast355 View Post
    Over the past 16 years I have tuned plenty of engines without a wideband. It is not a must have by any sense of the imagination. I am not arguing that it is not a valuable tool because it is, but it is also not necessary.

    I usually disable BLM and tune off the integrator alone. History average off the Integrator with the BLM disabled is a quicker way to tune than it is off BLM.
    It's true, tuning with BLM's & INT is a good proven method.

    In a good / better / best method comparison, tuning with WBO2 is the best for analyzing AFR's during Choke, Warm-up, Power Enrichment, and Acceleration Enrichment. It's totally up to the tuner to decide what a "Must Have" tuning tool is.

    dave w

    Log 17 AFR Averages.jpg

    Log 19 AFR Averages.jpg

    Log 19 PE AFR Averages.jpg

    PS
    Spark Advance is also helpful!

    Summary 1-10-2015_Spark Advance.jpg

  11. #11
    Fuel Injected! CDeeZ's Avatar
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    Quote Originally Posted by myburb View Post
    If I am reading the post correctly you haven’t tweaked the ve table down. If that is correct take idle table and lean it out. Try open and closed to see what you can come up with. Until your table takes you below the min open/close time of the injectors you should have adjustment.
    Yes, I hadn't touched the VE yet. I whacked the entire Idle VE table with a "multiply by .6" and that took me from idling between high 10s and low 11s AFR to 12.5 to 13 ISH AFR range. I wasn't sure if the VE table would be enough to dial the fuel back. It was so rich before that plugs were fouling out very quickly and the place was absolutely fumed up with vapors from being so damn rich.

    Quote Originally Posted by dave w View Post
    WBO2 tuning is a must have tool for tuning a 30 PSI TBI with or without a VAFPR: http://www.gearhead-efi.com/Fuel-Inj...g)-Spreadsheet

    dave w
    I have your spreadsheet and I permenantely installed an AEM WB02 in this thing to always monitor the AFR!

    Quote Originally Posted by 1project2many View Post
    The most common way to account for AFR is in the VE tables. It may be possible to use excel and an existing correct VE table and scale it based on AFPR changes to pressure. I would ensure both open and closed throttle VE tables are adjusted. But without a correct VE table this exercise may be a waste of time.
    In your opinion, should the Idle VE table cells roughly match the same or similar cells in the main, larger VE table?

    Quote Originally Posted by Fast355 View Post
    Over the past 16 years I have tuned plenty of engines without a wideband. It is not a must have by any sense of the imagination. I am not arguing that it is not a valuable tool because it is, but it is also not necessary.

    I usually disable BLM and tune off the integrator alone. History average off the Integrator with the BLM disabled is a quicker way to tune than it is off BLM.
    You also always tune your spark on the street usually don't you? Bump it up till it rattles then back it down a degree or two?

    Quote Originally Posted by brian617 View Post
    I'm running the marine spring with around 25psi and didn't have any problem making the VE table work. Just make sure your actual injector flow #s match injector flow rate in .bin
    What are the specs of your engine you're running this setup with? Care to share your tune in it's entirety or any portion? I'm glad to hear about another person who has made high pressures work with the TBI setup on a 7427 PCM, very encouraging to me. What injectors are you running? I have the stock 61 pounders in there, and if my math isn't wrong then my flow rate is 93.2.. (Old pressure 12, new pressure 28, old flow rate of injector 61 = new injector flow rate of 93).




    Thank you all for chiming in. There is some real talent in this thread and I'm thankful that you guys all have shared info with me. Hopefully I can work through dialing this turkey in and post up some burnout vids soon.

    Two questions:

    Is there any gain to be had in terms of leaning out idle a little bit more by altering the Minimum Synchronous BPW or Minimum Synchronous BPW Allowed values ?????

    Can a VE value be too low? I think ideally (If I'm not mistaken) You want around 85 for a MAX value in VE or you need to up your fuel pressure or injector flow rate. After whacking my Idle VE table with the .6 multiply adjustment the lowest VE value in the table is around 21.... If I hit it again it becomes about 12......

  12. #12
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    In the ve table you can modify the numbers any way you want. In the function box you have multiply, divide,add, subtract, integer and maybe others so you are not limited to a mult of .6. What ever number you want in the ve box, put it there. If I remember the tuner pro will correct any fraction you come up with to a whole integer.
    6395, BHDF, 7.4 BBC lightly modded now 6395 BMHM back to BHDF

  13. #13
    Super Moderator dave w's Avatar
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    Usually, when I have an engine that is running rich EVERYWHERE, I change the injector flow. For example if the injector flow is 93 and the engine is running extremely rich, I would change the injector flow from 93 to 95, or maybe 97. Increasing the injector flow will cause the computer to Lower the Injector Base Pulse Width, causing the injectors to spay less fuel.

    I consider the injector flow as a course adjustment, and the VE table as a fine adjustment.

    Injector flow is like apples / oranges / bananas

    What the injector is rated to flow.
    What the injector is actually flowing.
    What the injector parameter is in the .bin.

    More often than not, All Three are different!

    dave w

  14. #14
    Fuel Injected! CDeeZ's Avatar
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    Great information guys. I'm waiting on Oreillys to test the battery for this thing. Measures 12V and even with the charger on it, it keeps running down. Thinking it's got a cell that is popped.

    Dave, your approach to dialing in flow rate as a rough adjustment and VE as a fine adjustment makes perfect sense. I'm thinking when I get that battery back/get a new one tonight that I will revert back to the stock VE table and attack the flow rate scalar until I'm in the rough ballpark on the WB02..

    I also noticed last night that my IAC is at 0..... Guess I need to set the min air on this turkey also. This would also likely explain why the engine kept killing out on me last night when I was monkeying with the idle and got it in the 13 AFR range.

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    In your opinion, should the Idle VE table cells roughly match the same or similar cells in the main, larger VE table?
    I have found that they really need to match at the points where the transition occurs between open and closed throttle. By the time I'm done tuning I usually end up making the open throttle cells match closed in most cells.

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