Trying to decide on an ignition coil

[A.J.]

A little background first. On my SRT-4 van I have to gap my NGK V-Power spark plugs at .024" to keep the spark from blowing out at 20 psi of boost. Spec for this engine is .052" but that's at 15 lbs of boost with two coil packs and I'm running a distributor with one coil. I'm also running Rich Bryant's MSD wires and modified cap. I bought an MSD 6A box because it claims it can increase the output of even a stock coil. Before I bought the MSD box I bought this Accel coil: http://www.summitracing.com/parts/acc-140021/overview/. After hooking the box up I couldn't increase my gap any more. At .026" it blows the spark out. I called MSD's tech line and they said it might be the coil. They recommended this coil: http://www.summitracing.com/parts/msd-8253/overview/ but they said I might still have to run a tight gap for the boost I'm running. I really don't want to spend $186 on a coil that "might" work. A friend of mine let me borrow this coil: http://www.summitracing.com/parts/acc-140008/overview/ and he said it'll shoot a 3" spark when he uses it with his MSD box. I hook up the borrowed coil and I can now open my gap up to .050" (I didn't try larger) at 20 lbs of boost and it does not blow the spark out.

So my question is, "Do I buy the Accel coil that I know works for $65 or do I buy the MSD coil for $186 that the manufacturer of the ignition box recommends?" One side of me says, "Stick with the coil you know works" whereas the other side of me says, "Go with the coil the manufacturer of the box recommends because they test their boxes with their coils." If something happens to the box later on and they ask, "What coil were you using?" and I tell them the Accel coil, that might put doubts in their mind about what might have caused the failure. Just like if a customer comes to me with squeaking brakes after doing a brake job himself without turning the rotors. If they turned the rotors I can guess it's probably the cheap pads they chose but because the rotors weren't turned is that the problem.

[turismolover22]

Personally I would run what works, or what you know works.I would also get on the phone and call them to find out if using other brand coils would void any sort of warranty they might give you for a box failure. Also I would check to see what the box wants to see as far as resistance values. For the 8v the accell super stock coil can has the correct resistance, like the stock chryco coil. The MSD requires use of an external ballast resistor to bring their coil to the proper spec. Things to consider when dropping money on something, I wouldnt want to spend 200 bucks to find out the coil will cook itself because its "mismatched"

[cordes]

If it works then it is true.

[johnl]

" . . . . .Also I would check to see what the box wants to see as far as resistance values. . .."

That, is the critical question. Wouldn't hurt to verify their warranty policy either.

[zin]

Like John says, so long as the box is ok with "driving" the load, which is to say the resistance, etc are within its capabilities, go with the one you know works.

There is always the possibility that the 6al just isn't up to the task, I've see "7" boxes not get it done, and that wasn't even that much compression or nitrous...

Also, be sure the box/coils are getting proper voltage, much like fuel pumps, they'll talk back when they don't get full voltage...

Mike

[wallace]

I would use the accel coil since it's proven. I wonder if just the coil with no msd box would work just as well?

[Ondonti]

I would use the accel coil since it's proven. I wonder if just the coil with no msd box would work just as well?

I remember when I was looking at a coil upgrade I was really looking at peak current as something important to me. I dislike that some companies avoid publishing the full facts on their coils. I shouldn't have to look it up outside of the online store.

I have a feeling that it doesn't matter what happens to your box, its not really helping. Either coil might work, therefore I would go for the cheaper one that you know works. I also wouldn't run that big of a gap without being on a dyno and knowing its not blowing out. You can't actually feel blowout until it gets really bad. Blowout kills HP well before you feel it. Its very obvious from the waviness it adds to your dyno chart.
Back to back pulls where the only difference was .031 gap vs .025 gap (clean pull). I still had some breakup 2 pulls later with ~0.5psi more boost. I don't think I could make this kind of power on my current megasquirt dwell settings because our OEM is much more aggressive. Neon 2.4 guys have major spark problems when changing from OEM to megasquirt. The darn MS coil driver freaks out about high dwell as if your coil burning up would be the end of the earth (therefore never push it at all?).
I figure I will go for higher coil voltage rather then coil on plug and expensive/annoying MS upgrades. When I ran an OEM style ECU I gave the coil its own power feed relay and large gauge wiring directly from the battery with a fuse inline. I would not have had such problems lighting off the mixture if I ran race gas and no 32 GPH triple nozzle methanol injection.

I run a parts store Ford 5.0 style coil but your experience with a better coil draws me back to the spending table (rather then just buying a "boost a spark" for a stock type coil). I have not read much of anything that compares with your coil upgrade success. I like hearing about significant differences. You basically doubled the gap at the same boost with nothing else changed but the coil.

[Reaper1]

I wouldn't think that the warranty would be voided on the box by using a coil other than an MSD simply because the box is meant to be an "add-on" that can work with other hardware as long as it resided within a certain range of specifications. Resistance across the primary side of the coil is the main thing to look for.

BTW, running an ignition system in open air means absolutely squat. All it does is show that there is a spark. OK...so the spark "looks" better with product "A" vs. "B", but what does it do in the combustion chamber environment? Keep in mind that voltage is like pressure: how hard is something being forced along. Amperage is like volume: how much is being pushed. Both are important, but given "normal" ignition system operating voltages, the amperage is where the gains can be made. Just like welding...you change the amperage to adjust the amount of penetration the arc can achieve. The voltage is usually constant (I think very high end machines can actually change this).

Another thing to consider is that coils will only produce the amount of voltage needed to make the arc (up to their maximum capability). The environment in which the arc is being made determines the amount of voltage needed (the environment is a resistor). So just because a coil says it makes 75,000V doesn't mean that's what it's always doing. This also depends on the dwell time. For the most part we don't have control over this. It might be in the calibration someplace, but who knows if the hardware in the computer can handle certain changes. The MSD unit can sort of make up for this. Also keep in mind that the "multiple spark" part of that box only happens below 3500rpm (I think that's the cut-off). Above that cut-off the spark only happens once...just like normal.

[Ondonti]

Any decisions made? I am thinking about buying the Accel coil you borrowed and also the yellow Ford TFI Accel coil and comparing them.
I can't find any inductance numbers on the Accel coils which is annoying when I want to calculate dwell time.

[HSKR]

I'm running this coil on my truck with my MSD 6AL. http://www.summitracing.com/parts/msd-8207 Granted I'm not running boost, but this is on a 10.5:1 V8. Has beeen working fine for me. Something to consider. I've also ran the older cube style Jacobs Ultra Coil that sold with the Pro Street ignition using my 6AL with no issues.

MSD is going to recommend more than you need, and of course them recommending the "newest" and most expensive parts is in thier best interest financially. I'd shop around before spending more than you need to.

[A.J.]

Any decisions made? I am thinking about buying the Accel coil you borrowed and also the yellow Ford TFI Accel coil and comparing them.
I can't find any inductance numbers on the Accel coils which is annoying when I want to calculate dwell time.

Yes, I'm going Mega Squirt so I can run the 2 in 1 factory coil and ditch the single coil and distributor. That's probably not the answer you were looking for. Sorry.

The Accel coil did allow me to run 25 lbs of boost and I got 13.3 in the 1/4 mile if that helps. I did start to get spark blow out a couple weeks later at 25 lbs of boost. I was done racing because of the heat so I didn't investigate it further.

[johnl]

The finer the point the easier it is for the spark to jump, that's why the iridium electrode plugs are superior. And iridium, not platinum, of course.

Touch the front lower edge of the ground strap with with a file too. That's what the V groove ground strap plugs are about - lots of sharp edge while retaining enough mass in the electrode to provide a sufficient heat path to carry heat to the plug body and thereby to head off pre-ignition.

Another thing, shortening the ground strap shortens its heat path and that also helps with concerns about "glow plug" ground strap sourced pre-ignition and frees you up some to file a slightly more pointy profile for that sparking front edge.

[Reaper1]

I prep my plugs by filing the ground strap so it only covers about half of the electrode. I also make it into a "V" shape with a flat bottom. This uncovers the electrode so there is more exposure of the flame kernel to the rest of the charge as well as the other reasons mentioned. If you look at NGK race plugs they look almost the same. The only side effect that I have found is that the plugs don't last long. I only use copper plugs. Iridium is better than platinum for a few reasons, but ultimately both are simply a way to increase the service life. Some new vehicles "need" the special plugs as the ignition system uses the electrical feedback to determine fuel requirements, and even knock. That stuff will be thrown off if the wrong plugs are used.