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I Think I've Hit The Ignition Limit - What Are The Symptoms

Gareth87

By Gareth87,
in Engines & Forced Induction

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Gareth87 Community Regular

Gareth87

Posted
Posted

Had my car on the dyno and as the power levels rose, we found it wasn't revving out to the set limiter.

Had the limiter at 8500 and on low boost it would hit a wall (sounded like a missfire) at 7500.

When we lifted the boost, it hit the missfire earlier at 6400rpm.

Tuner and I think it's pretty straight up and down ignition issue, however, there is some concern that it could be a trigger issue.. I run 1 coil with my distributor and standard FJ20 leads and It's making around 450hp.

Who's had ignition issues and what seems to happen?

I can convert to run 4x LS1 coils but it's going to be a pain in the arse wire in. I am considering an MSD 6A CDI to make sure it's that and not a trigger disc issue or something.

Looking forward to your thoughts,

G

Scott Black Rising Star

Scott Black

Posted
Posted (edited)

What coil are you using, as using one stock coil to fire 4 cylinders at 7000 rpm makes me think that there isn't enough time for the coil to reach saturation and there for weaker spark that's easier to fail to ignite at higher loads. So I'd say either replace the coil with one that needs less dwell for full saturation while still putting out a decent spark or yeah 4 ls coils. What ecu are you using and what sort of signal does the dizzy give, and what outputs does the ecu have as the ls coils with inbuilt ignitors are pretty simple to wire up in most cases, also I wouldn't think it's a trigger issue as if it was it wouldn't be affected as much by varying boost levels

Edited by Scott Black
Scott Black Rising Star

Scott Black

Posted
Posted

At 7000 rpm you have the coil firing 14000 times a minute or about 233 times a second, or about once every 4ms so that 4ms the coil needs to charge and fire( discharge). For peak performance a ls coil needs 5ms just for the charge. If you went to 4 coils even in wasted spark you still have 8ms so a decent amount of time for dwell, or sequential igniting giving you 16ms for dwell so heaps of time.

Gareth87 Community Regular

Gareth87

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Hi Scott, The coil I am using is an old Bosch coil. I'm not sure on the numbers. I tend to agree with you in regard to the spark issue, It certainly seems related to boost which I'm fairly sure is telling me it's a lack of spark when the coil has less time to reach saturation as you mentioned.

My concern with swapping to run 4x LS1 coils is that it requires new leads, wiring, different trigger disc etc.

Will an MSD CDI get me out of trouble and provide enough spark to get me to the rev limit?

Gareth87 Community Regular

Gareth87

Posted
  • Author
Posted

Just saw your calculations in the second post Scott, even if I do run an MSD with a single coil.. Does this mean the coil still needs that sort of time to recharge? which leaves me with the exact same problem.. or does the CDI system allow it to recharge faster? (I don't know a great deal about ignition systems yet)

Scott Black Rising Star

Scott Black

Posted
Posted

All coils need some time to charge, however some of the more powerful coils can still output a very powerful spark before there fully saturated so work better than a stock ignition system, it's what they use on old.gts that rev to 7k yet only use the one coil for 8 cylinders, weather that's enough with the higher cylinder pressure from forced induction I cant answer 100% because I'm used to using ls2 coils with wasted spark as minimum

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