Ignition timing drift?

Give input on tuning as well as any tips and tricks you may have. Also feel free to share base mapping files for various engine types.
andytat
Posts: 21
Joined: Tue Feb 12, 2019 4:08 pm
ECU Model: S80 Pro
Firmware Version: 80.11

Re: Ignition timing drift?

Post by andytat »

Thanks Stevie.
Somehow I knew you were going to say that, I don't have experience with DTA
but I've built at least a dozen 911s with Motec engine management and they
handle single coil up to 8,000rpm no problem.
I'll start looking for suitable COP I reckon.
Cheers.
Andy
Rob Stevens
Posts: 1247
Joined: Thu Jul 28, 2011 4:10 am
ECU Model: S100 Pro
Distributor: None-Coil On Plug :)

Re: Ignition timing drift?

Post by Rob Stevens »

Is there any bob weights or anything like in the distributor that could be doing something odd?
A simple coil pack would be one of the Ford 6 cylinder ones, or something like this https://www.dtafast.co.uk/dta_products/ ... coil-pack/
You won't look back once you have one of these.
Are you sure you don't have any crank errors when it misfires?

Motec doesn't do anything more than DTA this instance. So there is still some underlying fault I believe.
Alex DTA
Posts: 1622
Joined: Fri Feb 28, 2014 1:03 pm
ECU Model: S40 Pro
Distributor: DTA
Firmware Version: 79

Re: Ignition timing drift?

Post by Alex DTA »

The 3000 microsecond limit is because very few coils require more than that, and the current rises very quickly.

At 8000 rpm it takes 15 milliseconds for the crank to rotate through two rotations.
8000 / 60 = 133.3
1/133.3 = 0.0075 seconds per rotation, so 7.5ms, and 15ms per engine cycle

If this is a 6 cylinder, that leaves 15/6 = 2.5ms for the coil to charge and discharge at 8000 RPM.
4000 rpm therefor has 5ms, so anything much above 4ms is never going to be used.

The MoTeC uses external amplifiers, which is the only difference. However, as they're both simply charging the coils, there is no difference in the way they operate to charge the coil.

Your symptoms point to spark break down.
Make sure the spark plugs are resistive, and the correct plug leads are being used.
Also double check it's not a fueling issue.

As the others have said, coil packs are a better solution. If you look at the maths above, you'll see the coil is effectively on the entire time. While that's how they run, you can see why wasted spark coil packs or COP will be more reliable.
stevieturbo
Posts: 3577
Joined: Tue Aug 02, 2011 12:08 pm
ECU Model: No ECU
Location: Norn Iron

Re: Ignition timing drift?

Post by stevieturbo »

andytat wrote:Thanks Stevie.
Somehow I knew you were going to say that, I don't have experience with DTA
but I've built at least a dozen 911s with Motec engine management and they
handle single coil up to 8,000rpm no problem.
I'll start looking for suitable COP I reckon.
Cheers.
Andy
As Alex says, the problem will not be the ecu. And there is no reason why a suitable single coil will not work as you describe, with any ecu.

Which would suggest the problem does lie elsewhere. But modern distributorless ignition is a very cheap, and sensible thing to do regardless.
andytat
Posts: 21
Joined: Tue Feb 12, 2019 4:08 pm
ECU Model: S80 Pro
Firmware Version: 80.11

Re: Ignition timing drift?

Post by andytat »

Thanks guys.
Rob: The dizzy is locked and there are no errors at all.
Alex: I agree, when driving the car it feels like spark break down.
I've double checked the fuel pressure which is fine and stable and it's got plenty of fuel
in the tank. The plugs are WR4DC Bosch which is original for a 3.2 Carrera engine running
Bosch motronic engine management. The plug leads are carbon trace from an early 911, the rotor arm is original with a built in 1k resistance. I would prefer to keep the engine bay looking original if possible.
I'll have another look in the morning and give you (Alex) a buzz to chat about it
Stevie: I agree, I need to get to the bottom of this issue, wish me luck!
Cheers
Andy
stevieturbo
Posts: 3577
Joined: Tue Aug 02, 2011 12:08 pm
ECU Model: No ECU
Location: Norn Iron

Re: Ignition timing drift?

Post by stevieturbo »

And is the coil a regular 12v coil, no ballast wire to reduce voltage or anything like that ?

Can you use a different coil ? The ever popular IGN-1A is a very powerful coil that requires very little dwell time, although not sure how applicable it will be in a coil/dizzy setup where duty cycles may need to be higher.

But I did run my Rover V8 for quite some time years ago with a coil/dizzy without issue. First a basic coil, then later a Crane coil and amplifier, before eventually moving to coil near plug.
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