Ignition upgrade, done by a cheap SOB (me)

[Patryn999]

It started with my original setup (ground 262 cams and methanol injection), I was starting to get a missfire during peak torque. Balls. I initially solved this by increasing stock dwell, and running 6 stock coil packs (grounding one side, about +15% peak voltage).This was a bit of a hack and looked somewhat similar to a dogs breakfast, but my morals say power does not need to be pretty.

However, Adam had a set of 280/12mm billet cams that were destined to turn over in my lovely VR4. This was the beginning of the end for the stock ignition system.

My understanding is that large duration cams and the resulting overlap allows a flow of exhaust from the cylinder back into the intake at low RPM, causing that lovely chaotic lopey idle. This causes the mixture being sparked to vary, and the resulting lean cycles were misfiring. Only this wasn't just occurring at idle, the car would get an intermittent 'buck' under low load with RPM < 2K. Which, I'm sure you can understand, was a distraction. Normally one would retard/advance the cams to get a better idle especially when idle vac is about 6-7 in-hg , but I kind of wanted to see if it was the ignition.

Thus started my journey with too much internet time and not enough money. So no COP for me. The result, was that I settled on uprated versions of the twin-post coils commonly used in GM engines (HEI, DIS coils). The specs for these are quite nice (the ones selected were not top of the range, but good specs and cheap, haha) and easy to get replacements for.

Coil specs from manufacturer:
0.5Ohm (Can get 0.35 ohm coils which would generate a larger spark with same dwell).
~4.8mH
(Measured) turns ratio: 1:83
(Stock is about 1.4 ohms, 8mH. Estimated using rise-time on a scope, forgot to measure turns ratio).

Ended up buying three of these coils + 40ohm/ft Taylor Thundervolt leads for ~$220NZD shipped

Now I needed a separate igniter - as I was looking for a high voltage output to overcome lean conditions as well as high energy this requires an igniter with a high breakdown voltage. So I settled on buying three of these ICs: FGB3245G2_F085. Nice, high voltage IGBT injector driver IC's (normal BJT voltage is about 280-350V, these are 450V). Complete with a couple of heatsinks, a plastic box, a base resistor each. Now had a high spec'd 3 channel ignitor box for ~$20NZD.

And the waiting begun, almost 2 weeks to arrive from the states But they arrived, and I got to it.

First off was bench testing the coils against a stock item - I'm not going to put them in unless I can prove they are better (OK, I possibly still would've put them in but it's comforting).


Test 1 setup: Two M10 bolts on a wooden board connected to outputs of coils. Measurements were taken when spark started breaking up/becoming intermittent. 12.8V supply.

Test dwell: 3.5ms
Stock coil spark became intermittent at 35mm.
New setup became intermittent at 45mm.

Test dwell, 4.5ms
Stock only made 38mm.
New setup made 50mm.

***** DISCLAIMER. This was an old stock coil, not new. There was no visible arcing when the spark started breaking down with the lights out, but from the sound of it I would've said that this was breaking down internally on the secondary side, not failing due to primary side breakdown. So it's possible a fresh stock unit would jump a larger gap than measured.

Test Setup 2: 4ms dwell (This kept changing between tests as I was having fun changing the frequency and making loud sparking/singing noises to annoy my workmates)
Set up: ~0.8mm gapped standard spark plug, measuring burn time in open air:
Stock coil: 0.8ms burn time.
New setup: 3.9ms burn time (I sh%t you not)

Keeping in mind that under pressure, this should go down.


Welp, that seems to indicate fairly conclusively that this was going to be an upgrade so I set to it. We'll cut down the details but for anyone looking at this:

• If using a 'universal' spark lead kit maybe try to find the right rubber plugs - getting the short boots to clip on the rear spark plugs can be difficult.
• The coils still need to go through the IFS (Ignition fail sensor?), and this adds (measured) 0.11omhs series resistance. So for now I'm running it, but in future I'm going to generate a tack signal elsewhere and get rid of this parasitic POS.
• Also, it takes more time than you expect. Assembling everything and putting it in took me a solid 8 hours, and it's not even pretty yet.
• The coils are mounted on the firewall where my fuel pump resistor used to be. I'll get some pics when I tidy it up a little.

Now, does theory add up to actual results? Yes it did. I now no longer have the bucking under low load conditions - the car is significantly smoother to drive. I can even cruise in 5th gear at 50kph again without feeling like I'm riding a god damn horse. Have been running this setup for about 5 days now. Also used to bog really badly if you engaged the clutch (twin plate) too low with these cams i.e. RPM < 1.2k once clutch released, which it no longer does.

After the physical testing above I adjusted the stock dwell settings to give 4.5ms base dwell, reducing to about 2.5ms at 8Krpm (hoping the VR4 has the same dwell behaviour as the Evo's). Trying to avoid saturating the coils at high RPM and burning them out while still maintaining a damn good spark - this is higher across the whole range compared to stock, just hedging my bets.

Cons: I have some slight EMI being picked up on the stereo that can be heard if it's turned up without music playing. At 40ohm/ft these leads will be contributing to this, despite still running resistive spark plugs. But the wiring on the stereo is not fantastic so I expect this to go away if I clean this up, as it picks up the wideband O2 as well.

Picture of coils with custom ignition driver:
I apologise for the quality, my phone is what one might call 'broken'. Then I got stuck in and forgot to take photos after I hit the 'I've been at this so long I just want to get it done' stage.
IMG_20150523_153623.jpgIMG_20150523_153631.jpg
(Also, not the same coil under test - the one above was floating around in a box)

[lateshow]

Sounds good. I'm planning those same 262's from Adam. I too have a set of extra coils. You wouldn't recommend that setup (2x standard coils) for 262's?

How much did your new set cost?

[Adam.Findlay]

Sweet good to hear that the better spark has gotten rid of the low rpm cruise misfire. Should make it a much better car to drive in traffic!

[Patryn999]

The extra set of coils was how I fixed the missfire when I was running 262s and water/methanol. Single coil set was fine for 262s alone with a 0.8mm gap.

Worked fine then - even the 280's were good under high load, it was only low load on the 280s.

The coils I got here are about 35usd ea.

[Patryn999]

Sweet good to hear that the better spark has gotten rid of the low rpm cruise misfire. Should make it a much better car to drive in traffic!

Yeah, quite stoked with the result myself! And it does make a difference to drivability haha.

[Davezj]

Yeah, quite stoked with the result myself! And it does make a difference to drivability haha.

Nice bit of investigation. i like it when people go the extra mile and explain the reasons and arguments for and against the stuff they do.

can i ask one question, why did you not want to go for the COP option? was it purely cost or just to see if you could do it your way with all your own theory.

you can do a relatively cheap COP conversion as well, taken from the evo boys COP conversion. I have all the parts i just need some time to do it.

[Davezj]

It started with my original setup (ground 262 cams and methanol injection), I was starting to get a missfire during peak torque. Balls. I initially solved this by increasing stock dwell, and running 6 stock coil packs (grounding one side, about +15% peak voltage).

I was under the impression that the VR4 coil packs where a single primary coil and double secondary coil, rather than the single secondary like a lot of other coil packs are like.
So my real question would be, is it better to ground the unsed output or to leave it floating and pot the output with an insulating glue (electrical potting compound rated for 50KV) so more of the energy created within the coil pack could discharge to the used output?

[Patryn999]

I was under the impression that the VR4 coil packs where a single primary coil and double secondary coil, rather than the single secondary like a lot of other coil packs are like.
So my real question would be, is it better to ground the unsed output or to leave it floating and pot the output with an insulating glue (electrical potting compound rated for 50KV) so more of the energy created within the coil pack could discharge to the used output?

The ones in mine (Diamond FL0017) are not centre tapped or separate coils. The outputs have about 17k resistance between them, and do not have a connection to the chassis or to any primary pins. So for mine it was definitely ground one side to get full energy - it wouldn't work otherwise.

[Davezj]

Thank for the reply much appreciated.

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[FLPGACITUA]

We need a like button. Good read! Good luck

[Adam.Findlay]

We need a like button. Good read! Good luck

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