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Thread: Retard Timing after acceleration/during overrun.

  1. #1
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    Lightbulb Retard Timing after acceleration/during overrun.

    Hi. I have a 1991 Mustang LX 347 stroker with a full length exhaust (minus cats) and the Holley HP EFI system. I'm interested in retarding the timing once I let off of the throttle while moving, such as running up to 4,500 RPM in first gear, then just letting off the throttle, and getting exhaust crackles, pops & burbles, somewhat like an anti-lag system in turbo cars. This would be only for sound effect until I actually turbo the car at a much later time. The only things I could think of that would be problematic would be the higher exhaust gas temperatures, thus making the exhaust pipes and valves hotter.

    I believe the way to do this would be to look at a datalog and find out what the MAP sensor reads, then take that number (i.e. 38 kPa) and go to the timing table and retard the timing, maybe 5° in that RPM & pressure range that I found in the datalog. I believe this should be able to give me the deceleration pops, crackles & burbles that I'm looking for. If anyone has done this before, knows how to, or knows what me doing this would do, your help would be greatly appreciated. Thanks.

  2. #2
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    There's some information about it HERE.
    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/2800 RPM converter, M4602G aluminum driveshaft, FRPP 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 tires.

  3. #3
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    I tried the stuff on there (except for the free flowing exhaust, I have no cats, an X-pipe, and nearly straight through mufflers), but I couldn't get it to work. I'm afraid to retard the timing too much, since I'm still learning the timing tuning. I changed the Target AFR to 14:1 in the range that I need, but I feel like I need to actually change the fuel flow in that region. How much should I retard the timing by? I have it retarded 5° currently, but I feel that is much too little. I've seen timing tables from Japanese tuner cars like EVOs where they actually go negative with the timing. Does negative timing mean the spark happens before TDC? And lastly, does decreasing the number in the timing table retard the timing? That is what I did, but I'm unsure that's what retarding it and not advancing the timing. Thanks.

  4. #4
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    Quote Originally Posted by paddyrk View Post
    How much should I retard the timing by?
    No one can answer this question for your engine.

    Does negative timing mean the spark happens before TDC?
    No, it means ATDC (spark happens later).

    And lastly, does decreasing the number in the timing table retard the timing?
    Yes, of course.

    That is what I did, but I'm unsure that's what retarding it and not advancing the timing.
    A timing light is used to set & verify ignition timing.
    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/2800 RPM converter, M4602G aluminum driveshaft, FRPP 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 tires.

  5. #5
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    OK thank you. One last thing, would retarding into the negatives be overly harmful to the engine? I have Trick Flow 190 11R Twisted Wedge aluminum heads on a 347 stroker with forged internals.

  6. #6
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    Won't hurt the engine. Late combustion with no load, is simply combustion still happening as the exhaust valves are opening, hence the burning in the exhaust system. Late timing at any time, especially under load can give low power. Not as bad as too much timing advance. Turbo cars are known to run excessively rich, and retarded timing to build boost for launch control. Gary
    Last edited by Gaz64; 12-11-2018 at 07:14 AM.
    Regards, Gary

  7. #7
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    You shouldn't have to tune the ignition timing near zero or into negatives.
    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/2800 RPM converter, M4602G aluminum driveshaft, FRPP 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 tires.

  8. #8
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    Good to know. Since I'm still using old school distributor cap, I'm wondering how much I can retard the timing before it’s too retarded, that it no longer is able to send spark to the cylinders effectively. Before I saw your reply I set the timing to zero on overrun. But when I took it out for a ride and tested it out, when I left off the throttle I just lurched forward like I had slammed on the brakes.

  9. #9
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    Do you have an adjustable rotor? Here's an article: https://www.hotrodhotline.com/conten...n#.XCgG5s8zZuU
    Regards, Gary

  10. #10
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    Yes, I can adjust the cap now, but I’m not going to, since I set the timing with my tuner on the dyno and would rather not mess with that.

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