Ignition advance Roadster 2017

Discussion in 'TuneECU Source' started by rng3, May 22, 2018.

  1. rng3

    rng3"There is no replacement for displacement"

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    Been researching the timing tables. Downloaded the tables the bike was delivered with and find that the advance is delayed a bit or different for 1st and 2nd gear than the rest. Does anyone know why?

    It has been recommended to copy the upper gears table to the lower, which I have done as that gets more timing in sooner.

    Also looking at different tunes they also vary. The tune Penner graciously contributed seems to use a different strategy. I wonder if Penner and others in the know could expand on the reasoning for the setups they are using.

    In old school the theory was to determine the best timing for power say 38 deg. The timing at idle needed to be relativity low say 8 deg. and then the timing was increased by an advance curve as engine rpm increased. The timing was "all in" at max by say 2,500 rpm and stayed there to red line under full throttle. A vacuum advance if installed allowed the timing to advance even further say another 8 degrees under low load conditions for better fuel mileage. So in normal operation the timing was determined by rpm and load. Under heavy load the timing was retarded to avoid knocking.

    The tables do something similar but with much greater control and are still based on load and rpm. The tables probably now also take into consideration exhaust emissions. Too much timing can increase one type exhaust emission and too little timing can increase a different exhaust emission. It also effects exhaust temperature.

    Considering the low compression ratio of the rocket and with using premium gas knocking should not be much of a problem at realistic timing settings.

    As a side note long ago with carbs we would sometimes use a vacuum gauge to set the initial timing at idle. Warm the engine up and adjust the timing for the highest vacuum possible.

    Thanks,

    Rick
     
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  2. Penner

    Penner.060 Over

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    The Rocket has two spark plugs per cylinder and does not rev that high. So 30 will do the job. With some real tuning and higher compression we just needed 20-25 at high revs to get full power.
    The numbers in that torque graph are degrees before tdc.
     

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  3. Neville Lush

    Neville Lushwww.nevillelushracing.com

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    Low compression ratio, yes HIGH CRANKING/CYLINDER PRESSURE YES. Be careful what you do, Ulf Penner is correct in the above post. 38 degrees is waaay too much.
     
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  4. Claviger

    ClavigerHP Junkie extraordinaire

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    I suspect his arbitrary number of 38, total timing, is based on his experience working with Chevy V8s, Gen 3s or similar.

    The Rocket has dual plugs, pent roof, and decent quench area so burns faster and requires less timing, even with it's low static compression ratio.

    The reason the older school of though did low base timing with a rising rate and all in by a set RPM then stayed there is simple: Distributors.

    With full control of timing and rapid timing attack capability to ramp it up and down very quickly, there's no reason to follow the old flawed model. Lean cruise benefits from highly advanced timing, which, is reflected in the stock tunes, tapering off to a safe "never going to detonate", high RPM timing map. The lower RPM retard in 1st and 2nd, are, as you probably suspect, designed to take some "bite" out of the low speed, low throttle areas and make the bike more civilized at slow speeds.

    The Rocket will develop a fairly harsh on/off throttle transition, giving a harsh jolt when cracking the throttle if not tuned right to avoid it.

    With my big cam, big head, stock bottom end I tried

    28
    30
    32

    at full power. There was no difference between the three, identical dyno plots.

    As @Penner mentions, with high comp pistons and big cams, Spinning to 8k, 25 degrees is enough to achieve max power without risking the motor.

    For a good idea of what a Rocket 3 without a Catalytic and TORs likes for timing, look at the VERY old maps put out by triumph. They were much more aggressive than what's been released for the later models. The motors not changed at all, but the timing has significantly. Why? As you say, emissions standards have changed, catalytics have been added, etc.

    The most gain from timing on an otherwise stock rocket will be found in the lower mid to mid RPM area, up top near redline, there's not a lot left on the table in the timing map.
     
    Last edited: May 22, 2018
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  5. Neville Lush

    Neville Lushwww.nevillelushracing.com

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    A Gen3 Holden V8 needs 19 at WOT and 6000rpm......
     
  6. Claviger

    ClavigerHP Junkie extraordinaire

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    Interesting, all over here people regularly run 32-38 for old school chevy motors. I think by Gen 2, we might mean different things lol. I meant Gen 2, as in, pre-1990s LT series motors.

    I had confused my generations of SBC.
     
    Last edited: May 22, 2018
  7. Neville Lush

    Neville Lushwww.nevillelushracing.com

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    My old Buick ( 1964) big block runs 40 deg max total at high vacuum and 21 WOT with no vac adv. That is as per stock. Heaps of difference with fuels as well.
     
  8. rng3

    rng3"There is no replacement for displacement"

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    Yes that was a completely arbitrary number just pulled out of the air from old small block v8s to use as comparison.
    Thanks for the explanation as well as the numbers. I will take a look at the old maps. I was mostly looking at the timing transition rate at low to mid throttle or load as far as throttle response.

    Penner thanks for the info and the chart, it does spell things out. I have downloaded one of your tunes and am studying it.

    So for K&N's, free flowing exhaust on otherwise stock engine 28-30 max WOT and work on a smooth knock free transition from somewhat higher cruise timing.

    Thanks all,

    Rick
     
  9. rng3

    rng3"There is no replacement for displacement"

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    O.K. the curve from off idle is for smooth transition from idle to power and the curve is a concession to emissions and dovetails with the lower A/F ratio of light load / cruise and perhaps to smooth the engine in that range.
    Now making much more sense.

    Was looking at some of the tunes downloaded from tuneecu site. The below Ign table is from R3R_Slip_grafted_onto-20773_base.hex. Sorry for the bad quality.


    Rick 299.jpg
     
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