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  1. #1

    Dyno w Air Fuel Ratio standard practice Why no Ignition Timing and Knock Data

    Tuning was always about mixture and timing.

    Why no timing included with A/F?

    And some acoustic log to post process to detect knock (waterfall plot or simply listening to that signal.)

    Further, since electronic, can I have a timing gauge along with my A/F?

    In the old days, I set total timing and pretty much didn't worry about what happened at low speed. What timing does the Viper like? SBC was 40, Paxton Studebaker 34-36, LS1 heads/cam/headers 30 (or at least that is what the tune yielded.)

  2. #2
    Enthusiast Steve M's Avatar
    Join Date
    Oct 2013
    Dayton, OH
    Because in order to get the timing info, you have to be able to pull the vehicle's data off the bus, and sync it up with the data stream from the external sources (in this case, the WOT A/F ratio and dyno torque readings). Most dyno shops don't have the resources to do that, and especially not for a low production car like a Viper.

    You also can't just generalize "total timing"...the timing varies based on load. For the Gen 4/5 Vipers, that is a 3D table that varies with airflow (in grams per cylinder) and RPM as the axes. What is commanded at peak torque is not what you'd want commanded before or after that point. For my car, I can get away with about 24° at peak torque, and as much as 30° closer to redline on 93 pump. That's about 4-6° more than what was commanded stock. Timing values under light load while cruising range from the upper 30s to upper 40s depending on where you are on the map.

    Truth be told, I've never had my car on a dyno...I've tuned it all on the street, but I have my own wideband that I run full time, and can merge that in with knock and/or timing vs. RPM. I know what it traps in the 1/4 mile (on average about 127-128, and as high as 129-130), so I know the car makes decent power, especially considering the only power mods are a Gen 5 intake manifold and a set of high flow cats (still stock exhaust manifolds and stock muffler).

    Keep in mind that my experience is with Gen 4 cars...Gen 5s are VERY similar with how they work. Earlier Gens may very well be different.
    2008 SRT-10 Coupe - Venom Red Metallic w/ White Stripes
    High Flow Cats | Gen 5 Intake Manifold | HPTuners | 3.55s | MCS | DSS Axles | Nth Moto Clutch | 11.04 @ 129.7, 1.81 60' (-100 ft DA, w/ 3.55s)

  3. #3
    Thank you so much for the 24 and 30 values. I wonder if 30 is sort of universal with OBDII performance engines since they were all designed with EPA constraints?

    In a way, even with carburetors, timing was not tuned as much as fueling Back then we would set total timing and forget about it. If someone had an automatic (didn't know any people like that) they would screw with advance weights. The Mopar guys were notorious for installing a switch to kill a set of points to get a few degrees of retard on big end. But that was all for most.

    With that in mind, the people selling SCT canned tunes probably have enough data to take a good guess at timing so they don't need to know that information to pick a tune.

    Just discovered they make scan gauges. Lifted from another site:

    "The one you have will work with your Scan Gauge II and a FZJ-80 just fine. My point in my previous post was your cable is not an "ISO only" cable. That's the benefit/beauty of the OBD-II standard. It's supports all OBD-II "required" protocols. So the cable you have works with J1850 VPW, J1850 PWM, CAN, and K-line/L-line protocols. And the Scan Gauge II works with all of those protocols."

    And the SGII displays 4 parameters so TPS can be added. But it looks like IAC is not in the list. (I have idle hang issues and I would kill to have this info when it hangs.)

    Even with the tune, I plan on keeping my VEC-1 to tweak timing/fuel given fuel octane and altitude. (In some elevated places, you can only purchase 91 octane. Then you have to deal with coming back to sea level on the same tank of gas.)

  4. #4
    Maybe canned tunes don't ask for timing because without some kind of knock data, you can't really assess that timing. Still, it's not that hard to log that data vs rpm during a dyno.



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