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Thread: Timing control at low RPM cruise?

  1. #1

    Default Timing control at low RPM cruise?

    Greetings, and thanks for a great forum. I've learned a lot from just browsing threads here. I do have a question that I've not yet come across a solution for (here or elsewhere).

    I just finished adding timing control to my week-old Sniper install, and so far it's running mostly great. I am only noticing one aspect of operation that was better with the previous configuration (carburetor with MSD distributor), and I'd like to see if it can be brought up to par (at least).

    My vehicle is a Jeep CJ-7 with a mildly built AMC-401 (9.5:1 CR, 272° advertised cam, Air-Gap dual-plane, ported heads, Tri-Y headers). It has an overdrive 5 speed transmission, and fairly tall gears. Consequently RPM at highways speeds can be pretty low (1200-1400 RPM). The engine makes (or made) great torque in that range, so this hasn't been an issue thus far.

    Anyway, now with the timing control added, I'm noticing that throttle response is relatively lazy in highway driving conditions. Once I dip into the throttle a bit more, I get a rush of torque which feels pretty non-linear compared to what I'm accustomed to happening. So, I watched the LCD screen while cruising at a fixed speed (50 MPH), and noticed that the ECU commanded timing is 17°, which happens to be my idle timing target. I was also able to correlate the non-linear torque rush to the timing advancing quite a bit as the throttle is tipped in. It appears that the Sniper is not using my cruise timing setting during cruise operation. Driveability quirks aside, I suspect this situation will also kill my cruise fuel economy.

    Questions:
    What parameters cause the Sniper to transition between idle timing and cruise timing modes?
    Can these thresholds be changed?

    Does the Sniper attempt to model the basic behavior of a mechanical/vacuum advance ignition, or is it a completely different theory of operation? More specifically, is "cruise" timing intended to mimic vacuum advance?

    I ask this because in my cruise scenario, at 10 inHg of vacuum, I would have expected some amount of "simulated" vacuum advance to be added to the idle timing of 17°. Or, is that not enough to cause the Sniper to apply the cruise targets? Thanks!
    Last edited by stinkfinger; 04-22-2019 at 04:13 PM.

  2. #2
    Join Date
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    Default

    Originally Posted by Danny Cabral
    The Target Air/Fuel Ratio Table & Base Fuel/Timing Table (and MAP kPa & RPM axes/scales) should be configured using the Sniper EFI software:
    In the Sniper EFI software (LINK), Target Air/Fuel Ratio Table (Fuel ICF) & Base Timing Table (Spark ICF), select "2D Table" Type (not "Simple").
    The Target Air/Fuel Ratio Table & Base Timing Table can then be properly configured & tuned for any engine.
    https://www.holley.com/support/resou...Fuel_Injection (Sniper EFI Software & Holley 558-443 CAN/USB Dongle)
    https://forums.holley.com/showthread...679#post100679 (Sniper EFI Optional Comm/Data Cable Accessories)
    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.

  3. #3

    Default

    It can be a little hard to dial in the timing table using the handheld so you might want to pop the SD card out of the handheld and put it in your desktop computer. Using the Sniper software you can open up the timing table and then modify it so that you have full advance at cruise. You might also add some timing at idle. 17° is on the low side for a mild performance cam. You can play with that just sitting in the driveway with the car at idle. Keep adding timing until the manifold vacuum peaks and then lock it in there and go for a drive.

  4. #4

    Default

    Thanks, I figured that I'd eventually need to tune using the PC software. I'm still curious as to how Sniper timing control relates to conventional/mechanical timing advance mechanisms (static/centrifugal/vacuum). For example, I noticed while cruising in high gear with relatively little RPM change that depressing the throttle increased the advance. My understanding of conventional ignition systems suggests that advance should have decreased (less vacuum = less vacuum advance). Hopefully this all becomes self-evident once I crack open the software.

  5. #5
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    Quote Originally Posted by stinkfinger View Post
    Hopefully this all becomes self-evident once I crack open the software.

    http://documents.holley.com/techlibrary_199r11259.pdf (Holley Sniper EFI Help Manual - EFI Software, Tuning & Datalogging)
    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.

  6. #6

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    I found this along with the tuning software download: Tuning and Log View Software User Manual. It certainly looks comprehensive. Are there any other good resources to help understand the ins-&-outs of Sniper tuning (especially timing control)?

  7. #7
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    https://forums.holley.com/showthread...8640#post88640 (Target A/F Ratio Table & Base Timing Table Reference)
    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.

  8. #8

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    Lots of learning to do...thanks!

  9. #9
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    25,060

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    You're welcome.
    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.

  10. #10

    Default

    Quote Originally Posted by stinkfinger View Post
    Thanks, I figured that I'd eventually need to tune using the PC software. I'm still curious as to how Sniper timing control relates to conventional/mechanical timing advance mechanisms (static/centrifugal/vacuum). For example, I noticed while cruising in high gear with relatively little RPM change that depressing the throttle increased the advance. My understanding of conventional ignition systems suggests that advance should have decreased (less vacuum = less vacuum advance). Hopefully this all becomes self-evident once I crack open the software.
    The Sniper timing control does whatever it is programmed to do. If you want it to have the same exact curve as your old distributor then make it so. If you want it to do something else then make that happen. It is just a table of numbers, fill in the table as you wish. There is no magic, it is just table full of numbers.

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