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Thread: Feedback or Recommendations for EFI Tuning

  1. #1

    Default Feedback or Recommendations for EFI Tuning

    Hi All. First time poster, but a big fan of the Sniper QuadraJet EFI!

    I'm very new to the aftermarket EFI game and have a very unique application that I've recently installed the Sniper in. This was for an engine replacement and EFI upgrade on my '76 GMC motorhome! Believe it or not, this is a front wheel drive motorhome with an Oldsmobile 455 rocket powering the old beast.

    I installed the HyperSpark ignition system as well and had great success upon first startup. I've broken the engine in with about 700 miles thus far and things run well, but I know it could be better. I can certainly tell it's going through a bit more gas than expected and I feel the timing could be tweaked to make her run perfect.

    My question is this: Would the group be willing to look at my driving datalog file to give some feedback/pointers on things that I could tweak to get this dialed in 100%?

    Here is the setup:
    Engine: Oldsmobile 455
    Aluminum intake
    Headers (unknown brand)
    WBO2 sensor after passenger side bank headers.
    3 speed Transmission
    Max RPM of about 4500
    Front wheel drive pulling about 13,000 lbs of awesome 1970s style.

    Cranking - 15° @ 400RPM
    Idle - 15°
    Cruise - 36°
    WOT - 34°

    Idle: 600 RPM

    Target AFR:
    Idle - 13.5
    Cruise - 14
    WOT - 13

    My datalog file and exported .csv of the datalog file have been uploaded here:
    Thanks in advance for any feedback and input. I greatly appreciate the help.

  2. #2


    First glance, I suspect you could take better advantage of running the HyperSpark and dialing in your timing a bit more aggressively. I have no idea what a 440 likes, but 36° at cruise on an old cast iron pushrod engine seems on the low side to me. I bet you could add in another 10° or so before it pings.

    Lean out cruise and idle and add in some timing and see if your MPG improve.

    I'd run idle at 14.3 (stoichiometric for 10% ethanol) and try to bump up cruise to as close to 15.7 as you can go. Because of the HyperSpark, you can advance the timing to fire off that lean mix without detonation.

    I wouldn't change WOT as that seems about as lean as I would feel comfortable with, especially on a 13,000 lbs RV, which would probably spend a lot of time WOT just to get moving and up any sort of grade.

    Once you find the timing curve that your engine likes, and this is affected by AFR - lean mixes require more timing and the closer you can get to the detonation threshold, the more efficient your engine will become, the better your MPG will be.

    Additionally look for ways to improve airflow to the engine and block out any hot air as much as possible. This will help with thermodynamics a bit. Hot air becomes less dense and in turn doesn't make as much power, this in turn results in more fuel needed, or more throttle needed to achieve the same level of performance.

    Large displacement is great, headers are great, 800 cfm Snipers are great, but if you choke the engine off with a crappy filter setup and have it breath hot engine bay air, performance and economy suffers.

  3. #3


    Thanks for the quick response & feedback, Gen2Van! What you've outlined makes a lot of sense and certainly helps point me in the right direction. I appreciate the insight & recommendations.

  4. #4


    Buy the special cable from Holley and hook up a laptop to the Sniper as you drive that motorhome on the freeway. While cruising down the freeway open up the Gauge Panel on the laptop, and note how much fuel is being used. Keep the speed steady on a flat road then slowly add more timing while you watch the fuel usage. Do the same thing with the Target AFR.

  5. #5
    Join Date
    Oct 2020
    Ontario, Canada


    GMCMI has an Ignition Manual that has suggested Timing settings. You could use the Timing Table generator from this post to make different timing tables quickly.

    Also, this post details tuning a Terminator EFI on a GMC motorhome, timing changes made a big difference. Perhaps you'll find something useful there even though you have a Sniper. Good luck.

  6. #6
    Join Date
    Dec 2009


    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. I always suggest taking notes of your current distributor's ignition timing specs/curves beforehand, and then program the Base Timing Table accordingly. (Sniper EFI Software & Holley 558-443 CAN/USB Dongle) (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.

  7. #7


    Depending on how much you want to learn and/or treat this like a hobby, you may want to contact one of the pros that post on this site that offer remote tuning help. If you want to learn it for yourself you need to become a student of the game. Ask away and we'll help as much as possible.

    Does it feel sluggish when you try to accelerate? The datalog shows that it's way too lean during those events. I didn't look at your GCF, but the Learn Table Compensation is most likely maxed out in several areas.

  8. #8


    Look for Fast Man EFI. He can help get you where you need to be. Personally I agree with leaner idle, but richer WOT. I run 12.3 to 12.5. If I was you, I'd switch it to run at 12.5 vs 13. Economy at WOT is not what I look for MPG. It's better to be safe than sorry. I agree the cable to hook up laptop makes tuning changes happen so much faster to see what engine actually wants.

  9. #9
    Join Date
    Oct 2020
    Ontario, Canada


    @fr0sty84: I sent you a question about your datalogs in a Private Message. It'd be great if you had a look and got back to me.

  10. #10


    I'm here.

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