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Old 11-24-2016, 07:47 PM   #1
Mykk540i/6
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Has anyone locked out their ignition timing?

Years ago in bracket racing we would weld the distributor shafts to the reluctor rings/rotor mounting and then leave the vacuum advanced unplugged. Then we'd set the ignition timing between 34-38 depending on what the engine liked. The ignition timing was then stuck at that timing all of the time; Idling, light throttle cruise, mild acceleration and of course hard/WOT acceleration.

I did this to an 11.5:1 compression Small Block Chevy, Aluminum headed 190cc Int runner 2.02"/1.6" valves, Full roller valvetrain 276/282-110 cam. It ran 11.78 @118 1/4 mile in a 4,000lb pickup with a 2800RPM stall converter, 4.10 rear gears, locker, 75hp wet shot nitrous, street tires.

This truck was my daily driver. I tried all kinds of ignition timing curves finding what the engine wanted. When I locked out the distributor for a solid timing it felt much better on the street. Low end torque picked up, and throttle response would snap your neck if you weren't prepared.

Fast forward a couple of years and now I'm playing with the M60B40 in my E34 540i/6. I've done the normal go-fast parts; Lightweight single mass flywheel. Home made high flow intake/filter. Early B40 velocity stacks intake manifold. Ford "Blue" 24lb Bosch GenIII EV1 injectors. Custom cam timing for 249/241 on a 106ICL & 106LSA. 2.5" Y-pipe into single 3" exhaust all the way out back.

For tuning I'm using the 404DME with an Ostrich 2.0 that I flash with TunerProRT...and the painstaking never ending process of building the XDF from scratch.

Today, just for fun I wanted to see how my little fun street project responded to locked out ignition timing. So I've got the engine idling with 17 (were it idles best) then all other load cells and timing tables are set to 32 with zero'd out timing modifiers.

You never really hear of locked out ignition timing in fuel injection applications, it's usually old school american carbureted iron. On my test drive, I found similar results to my previous experience. Off idle torque felt better and throttle response snappier. High RPM pull felt about the same as the previous tune. Admittedly 32 seems high for this combustion chamber design, and I'll test 30 & 28 & 26 to see if there is a "sweet spot". I just figured I'd start with more timing since I live in a high elevation.

I completely understand that not all RPM's, engine loads, AFR's and driving conditions mandate all the same ignition timing spec. But, I thought it would be interesting to test and see how it responds on this given application....so far, it's good.

What are your thoughts on it? Ever tried locked out ignition timing?
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Old 11-24-2016, 08:28 PM   #2
digger
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It's a step backwards
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Old 11-25-2016, 07:15 AM   #3
varg
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Only to get a car started on initial tuning and verify that the trigger angle is correct. It's a bad idea for any sort of street driven vehicle. You don't hear of this in fuel injected applications because accurate control of advance across the rev and load range is just superior to fixed timing and "all in by 3,000rpm" curves. I don't even see bracket racers doing it anymore, they're using rudimentary computer controlled ignition boxes and distributors from MSD and the like, even if these things only have pre-defined and swappable curves. I've spent too much time tuning cars to do anything other than obsess over every cell in the ignition advance and modifier tables.

Lost torque and power everywhere except where the fixed timing advance number is optimum, increased potential for detonation, jerky low load behavior, worse emissions, etc.
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Old 11-25-2016, 08:55 AM   #4
nando
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it was a bandaid for the poor tunability and reliability of distributor based ignitions. For an EFI car, it's completely pointless.
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