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Thread: Understanding A/F Ratio At Idle

  1. #11
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    Thanks 383_StealthRam. It's hard to keep these links updated when the manufactures change their websites. I wish they would automatically redirect their changed website addresses. Anyway, I updated that link's URL in all my posts.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 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, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, 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 MT tires.

  2. Default

    Quote Originally Posted by Danny Cabral View Post
    Thanks 383_StealthRam. It's hard to keep these links updated when the manufacture's change their websites. I wish they would automatically redirect their changed website addresses.
    Agreed, that's why for most products I personally purchase/own where documentation is important to have access to I try to always download a copy to my own system, just in case it disappears from the manufacture's website.

    HP EFI V4, 388cid Stealth Ram, 1000 CFM 58mm throttle body, Holley Dual Sync Distributor. LS Coil Near Plug, 1 bar MAP, 48 lb/hr Holley EFI injectors, 43 psi

  3. #13

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    This is almost always cylinder imbalance, not the effects of a camshaft. How much does your AFR vary at idle? Here's an SBC with a 285 duration at .050" cam. Closed Loop is on, notice how stable the AFR is: https://www.youtube.com/watch?v=S0XLbI-Brn4

  4. #14

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    Allan, how did you get the AFR so stable? I've got a Holley Terminator system w/Dominator ECU and my AFR is all over the place, from 12.1 to 16.8 at idle in closed loop.

  5. #15
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    Quote Originally Posted by allan5oh View Post
    This is almost always cylinder imbalance, not the effects of a camshaft. How much does your AFR vary at idle? Here's an SBC with a 285 duration at .050" cam. Closed Loop is on, notice how stable the AFR is: https://www.youtube.com/watch?v=S0XLbI-Brn4
    That is an excellent example of how even an engine CAN run. Note how the ignition timing is a mirror of engine RPM. Gary
    Regards, Gary

  6. #16
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    Quote Originally Posted by skizot722 View Post
    Allan, how did you get the AFR so stable? I've got a Holley Terminator system with Dominator ECU and my AFR is all over the place, from 12.1 to 16.8 at idle in Closed Loop.
    NOTE: This a methanol engine, not gas. Gary
    Regards, Gary

  7. #17

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    That has more to do with the engine build. I don't recall doing any cylinder trims.

  8. #18
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    Exactly. Good cylinder heads, camshaft, throttle body & intake manifold with multi-port fuel injection.
    http://forums.holley.com/showthread....5480#post45480 (Read "Potential Causes of L & R Bank AFR Differences")
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 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, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, 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 MT tires.

  9. #19

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    Quote Originally Posted by Danny Cabral View Post
    Exactly. Good cylinder heads, camshaft, throttle body & intake manifold with multi-port fuel injection.
    http://forums.holley.com/showthread....5480#post45480 (Read "Potential Causes of L & R Bank AFR Differences")
    The biggest thing to avoid is those 4BBL style TBs. They always starve the rear two of air at idle.

  10. #20
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    Yeah, especially if the rear two throttle blades are nearly closed due to a progressive secondary linkage. When I converted my previous 1000 CFM 4BBL throttle body to 1:1 secondary linkage (LINK), I set all four throttle blades equally open at idle. Also, aftermarket Ford cylinder heads have almost symmetrical intake ports (better air/fuel distribution).
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 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, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, 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 MT tires.

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