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Thread: Output Wiring & Configuration Questions

  1. #11


    @Jeff F: I run a fixed pressure (at the rails) system in my car and so do many of my customers. However, keep in mind that running a vacuum referenced fuel pressure system is more proper, because the differential pressure at the injectors remains constant as the pressure inside the intake manifold changes. If you want the best fuel system, then I suggest looking at what VaporWorx has to offer. Carl is a very smart guy and his PWM systems are excellent.

    If you're looking at some of the older base TBI tunes, they were all done in Fuel Flow and the VE% Tables look terrible. I wouldn't start with one of those tunes, and if you do, expect to do a lot of cleanup if you switch them to VE% Table.

    If I can be of service with tuning or the wiring questions, please let me know. I can also offer some recommendations for fans to implement PWM control. I recommend it to all my customers.

  2. #12


    I wouldn't say that vacuum referenced is "more proper". It's certainly how it was done for a long time for a lot of good reasons. By keeping the differential pressure between the fuel and manifold constant you have a fixed (but not linear) relationship between PW and flow which saved some computing power (a real issue in early EFI) and potentially the need for fuel and/or MAP sensors. And having the differential not go down at high load is certainly the right direction. But with more computing and sensor power there are a lot of reasons to vary fuel pressure other ways to minimize power consumption, keep the injector pulse widths in ranges where they are most accurate, etc. Of course, my motivations are mostly that I have a very tight car and engine bay so keeping the regulator in the back and a single fuel line is desirable.

    Quote Originally Posted by andrewb70 View Post
    If you're looking at some of the older base TBI tunes, they were all done in Fuel Flow and the VE% Tables look terrible. I wouldn't start with one of those tunes, and if you do, expect to do a lot of cleanup if you switch them to VE% Table.
    I'm a little confused by this. How does it get from Fuel Flow to VE%? Since fuel flow is a function Displacement, VE, RPM & AFR, does it convert it based on a fixed AFR? Or does it pull the value from the Target AFR table? Since the fuel flow table essentially combines the two variables in the equation (VE & Target AFR), to convert it back without a good reference for the Target AFR you will certainly get a goofy result.

    The fan I have is a Derale that I know is capable of PWM control (Derale has their own PWM system). This was the best combination of performance and size (particularly thickness) as I have a tight space to fit it into.

  3. #13
    Join Date
    Dec 2009


    A little more information: (Holley V2 Software Update Overview - Section 4.1 "Base Fuel Table Changes", Page 6 & 7)

    Holley EFI V2 Software Update Overview
    Volumetric Efficiency (VE) Operation – The option of a Volumetric Efficiency based tuning strategy is now optional.
    This changes the Base Fuel Table units from pounds/hour of fuel to VE%. VE fueling calculations are calculated from the following inputs:
    - Engine Displacement (NOTE: Make sure this is input properly in the Engine Parameters!!)
    - Target Air/Fuel Ratio
    - Engine Speed
    - MAP Sensor Value
    - Input from Air Temp Sensor/Air Temp Enrichment Table
    - Value from the Base Fuel Table (VE%)
    - Fuel Injector Size
    - Fuel System Pressure
    From this information, a fuel flow and consequent injector pulse width is determined by the ECU.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  4. #14


    That didn't really have the answer in it, so I did an experiment. I took a base file, went to the Base Fuel Table and did the VE% conversion. Then I unchecked the conversion, changed the Target AFR table, then did the conversion again. Sure enough, different answers. That makes sense, since all else being equal Fuel Flow = VE/AFR (X a constant of course).

    So then in Engine Parameters I changed it from Speed Density to VE% Based, and it asked if I wanted to convert the Base Fuel Table, which I did. The table was exactly the same as when I checked the Conversion box in base fuel. If I then clicked the Conversion box, the Fuel Flow was what I started with.

    So I'm a bit confused @andrewb70, why would taking a base tune from Fuel Flow to VE% be any different? You can convert from Fuel Flow to VE% and it's exactly the same.

  5. #15


    @Jeff F:What I meant is that if you look at those older fuel based tunes and convert them to VE, they are not the smoothest, despite having very a smooth fuel flow table.

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