MSD Coil

[ssnsltd]

does anyone know what the voltage output of a stock 88 coil is?

 

[Willis]

Voltage output? Not an issue. Here's why: The coil will only put out enough voltage to overcome resistance. If your plug wires have 10k ohms of resistance, and your plug is gapped at .090", you might see voltage spikes close to 30k volts from a stock coil, however, with lower resistance wires and plug gap of .040" you might only see 6k volts. Any coil you put on with the same plugs and wires is going to put out the same voltage a properly working stock one is. Thats why a coil makes no difference.

The only time you would see an improvement, is when the secondary ignition system has so much resistance (like bad wire or plug) that the stock coil can not overcome it, or when the stock coil is going bad (internally shorted) and can not put out enough voltage to overcome the resistance. Aftermarket coils usually have more windings than a stock coil (however the XJ is equipped with an 'e-coil' type coil which is a hi power unit already), so under extreme circumstances where an ignition problem is occurring, the aftermarket unit (if more powerful than stock) may be able to overcome the problem and keep that cylinder running.

I wouldn't go out and just buy a coil. That's what thier advertising department wants you to do. It's there job to convince you that thier coil is better than the stock one.

I maintain that no coil in the world is more powerful than a stock one with a properly working ignition system. The voltage output is directly related to the secondary resistance.

Don't waste your money.

Or better yet, send me $50 and your old coil, I'll paint it red and send it back. It will be a direct bolt on 'upgrade', and you will convince yourself you have much better pick-up and gas mileage because you have to justify your expense.

Steve

As far as MSD goes, you tell me what's better, one spark lasting 10 milliseconds, or 3 sparks lasting 3 milliseconds each (theoretical numbers, but one spark has to stop before the next can begin on the same cylinder)? Don't forget, your rotor is still moving in relationship to the cap, spark can only last so long.

 

[Eagle]

Thank you, Steve, for explaining all that far better than I could. I'm convinced that most of the reported performance gains with these things are imaginary, but people seem to buy them anyway.

Okay, Jacobs and MSD lovers of the western world -- can any of your expensive ignitions beat the 28 MPG my '88 got when it was still fairly new (about 3 years old), running stock ignition and NGK plugs?

Didn't think so. That 28 MPG was not imaginary -- I was more organized back then, and kept written records.

 

[ssnsltd]

Don't recall anyone saying they were only putting in a coil, but thanks for the information. I assume you measured the output of the stock coil under the conditions you described? It gives me the reference voltages I was looking for.

I have replaced 6 coils on “street” vehicles with an after market variety over the years. Every time performance (and yes, mileage) has increased. Come to think of it, I can’t remember a single car or truck I saw (or worked on) at the track running anything other than after-market coils/ignitions. Maybe some of the weekend bracket racers had a stock coil. But, I am sure I am just imagining things.

28MPG, with a 4.0l ?(since that is what the reference engine in the two threads is).Wow. I am happy when I hit 20.

 

[MacGowan-XJ]

Who ever thought a simple question like this would spur so much talk. I believe there was one guy in all 23 responses that actually answered the question. Thanks to all for contributing something.

BTW.. Coil upgrade is to compliment my MSD 6 ingnition. I'm not just buying the coil. I doubt just the coil would make any kind of difference on a stock system.

Thanks again to all.

Greg

 

[MaXJohnson]

I could swear he asked for a part number for the coil. Not a debate on whether its good or not.

Friends don't let friends waste money.

 

[MaXJohnson]

MSD is not just for gas milage....

Multipal Spark Discharge.... Stock can't do that.

If any of you know about MSD you know that there is a series of more powerful sparks per cylinder under 3000 RPM for more complete combustion.

Because of this along with the Higher then stock spark energy, the things you will notice RIGHT AWAY after installing MSD are as follows:

1.) Like he said, better gas milage

2.) Deeper exhaust tone due to more efficient combustion.

3.) Better throttle responce

4.) More Horsepower ( you will really notice on the highway )

5.) longer plug life

6.) Cleaner Burning, Longer Lasting Engine

Anything I'm leaving out?

How about some independently run dyno results running this mod on a stock 4.0L. Butt dyno's don't count.

 

[Markm80521]

Friends don't let friends waste money.

Now, now. If that was the case we wouldn't have any DANA 60's now would we.

 

[Willis]

Now, now. If that was the case we wouldn't have any DANA 60's now would we.

So Dana 60s are a waste of money??? :doh: wish someone would have told me that a long time ago. I think I'm going to trade my D60 for a D27, just think of the weight savings!!!

 

[Willis]

Don't recall anyone saying they were only putting in a coil, but thanks for the information. I assume you measured the output of the stock coil under the conditions you described? It gives me the reference voltages I was looking for.

I have replaced 6 coils on “street” vehicles with an after market variety over the years. Every time performance (and yes, mileage) has increased. Come to think of it, I can’t remember a single car or truck I saw (or worked on) at the track running anything other than after-market coils/ignitions. Maybe some of the weekend bracket racers had a stock coil. But, I am sure I am just imagining things.

I did not measure the output of the stock coil. What I am saying is that output voltage is inversely related to secondary voltage.

Let me put it another way. I am not going to do any exact calculations so take the next example with a grain of salt. Lets say, we have 2 coils with the same internal resistance. One is a performance MSD, and one is from a Geo Metro. The spark leaves the coil and travels through a coil wire that is 1 foot long. That wire is 1000 ohms (The average is 1000 ohms per foot for ignition wires). Lets say it takes 500 volts to overcome that resistance. It then enters the cap and goes through the carbon button into the rotor and has to jump the gap back into the cap. Lets say that takes 2000 volts to do so. It then travels down the spark plus wires at another 1000 ohms per foot. Another 1500 volts. Spark plugs have resistors built in to cancel RFI (radio frequency interference). The spark has to overcome the resistance in the resistor and jump the .040 gap at the electrode at the end of the plug. Lets say 3000 volts is necessary. Total that up, and you have 7000 volts necessary to make the spark plug fire.

Both the MSD and Geo coil will put out only 7000 volts. No matter what. They perform the same. Why? Because they only put out the voltage necessary to overcome secondary resistance. Now, the MSD may have a higher maximum voltage output than the Geo coil. If the spark plug is worn, coil wires have way too much resistance, cap has a huge gap, and carbon button is junk, then it may require 60,000 volts to overcome that kind of resistance. The Geo coil may not be up to that, especially if it is old. So from a maintenance standpoint, if you are going to neglect every angle of your secondary ignition, by all means, buy a MSD, it may prolong the inevitable.

The XJ coil is very similar to the coil used on HEI distributors. If I had to make a guess as to the maximum voltage it would put out, it'd be around 90,000-100,000 volts.

As far as all of the racers using them, have you ever priced a stock coil? Big $$$. With that said, if my coil took a crap, I'd probably put in one of the MSD, Jacobs, whatever coil I found. They still have better quality than the Chinese junk you'd buy over the counter at the auto store, and perform similar to stock. Don't forget, the racers add them because it makes the engine bay look cooler, and makes them look faster. You'd expect to see it.

Steve

 

[Greg Smith]

The MSD coil in my zj crapped out after 4 months. It says made in China on the side!!! (MSD made in china!!! Are there going to be any jobs left in the U.S. ?!!!) Got another under warranty replacement and hope it lasts longer. The zj does seem to have quicker response w. the MSD coil however, but this a 5.2 v8. I have the msd blaster coil on my 4.0 89 xj and that and the new 8mm wires and dist cap and colder plugs make is run smoother and idle steadier than ever but I cannot swear what part the coil plays if any. I got my ingition packages from [email protected] who is well know and respected on the grand cherokee forum at jeepsunlimited.com. Greg

 

[Markm80521]

Since this has strayed into a issue session I thought I would relay mine.

1st off I really felt like the MSD box was the biggest bolt on performance mod as far as low end torque is concerned. At least the butt dyno seemed to think.

I did have an issue arise with the box/coil setup. I have a 80 gig harddrive I have rigged up in my jeep to play mp3's (skip free music) The MSD system made short work of the drive. I Can't have the mp3 system on when I crank the car.

That's it. Other than that been in there a year with no issues. I can't support the better gas milage crap though. Maybe if it was a stock vehicle we were talking about.

 

[RTicUL8]

Friends don't let friends waste money.

So does that mean that I shouldn't wrap my fuel line with expensive magnets to polarize the gas in order to improve mileage?

 

[Lou]

The output voltage of the coil of the is determined by the input voltage(and wave shape of the current flowing trough it), and the winding ratio of the primary/secondary. The output voltage is not determined by the gap of the plug. The gap, and the atmosphere in which it resides, would determine the voltage at which the spark initially occurs.

The ratio of the stock coil is probably something like 13000. That would probably takes to the 100Kv(12v x 13000) that Steve mentioned.

The thing about the MSD ignition is that it relies on resonance, using capacitive drive, to develop a 'stronger' spark. So I don't think you can say that you get 3(?) sparks with each at 1/3 the original power. I have 'seen' with my own eyes that the MSD does put out a much stronger spark than the OE setup. In the end does it really make much of a noticeable difference? -- not really. As someone stated, low-end and idle seem better. Also, as stated, this stronger spark will mask any deficiencies you may have in other areas of the ignition system such as bad wires, coil, etc. I just replaced my stock coil, with a stock coil. The MSD masked a fault(leaky dielectric/cracked coil) with the coil that had me chasing my tail.

As for the OE coil, the design is probably just fine. The E-core design of the OE is probably alot more efficient than the rod(?) design of the canister style coils.

I was young and impressionable when I bought by MSD. If I had to make any recommendations(from personal experience, and from the threads i've read).....get yourselves good wires(Magnacor/Mopar Perf), plugs(Champion/NGK), distributor and that is all you need.

 

[AJsArmor]

Dang my eye is twitching and I'm having flashbacks from high school science classes. Just kidding, all good info and even better if it sinks in. A buddy of mine was running the MSD coil and 6 box in his XJ with 4.0, had a lot of problems with distributor crossfiring. Tried quite a bit to cure it but never did resolve it and just runs the coil now.

Supposedly there is a Ford dist. cap and adapter that will swap to the XJ's and has larger spacing between the posts of the cap and better isolation. I talked to someone who actually had done this but they never could give me the correct pn#'s so who knows?

 

[MaXJohnson]

So does that mean that I shouldn't wrap my fuel line with expensive magnets to polarize the gas in order to improve mileage?

I'll remove mine if you remove yours

We can put them on our new GM shocks to stiffen them up.

 

[hjeepxj]

I'll remove mine if you remove yours

We can put them on our new GM shocks to stiffen them up.

youve got PM