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Inductive discharge or Capacitive?

cybrfire

cybrfire

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It would seem, the hot ticket is capacitive discharge. I do understand the differences and for my particular engine, I don't see much benefit of capacitive.

Anybody have experience with both?

Inductive dies off around 5000 rpm, well outside the optimum range for my cadillac 500. I'm running around 10.2:1 compression. No boost, no nitrous or anything else that would increase the resistance to the spark inside the cylinder.

Capacitive is extra cash that may not necessarily have much benefit.

Other big difference, capacitive will hit the spark plug 8 or so times per combustion cycle where as the inductive will hold one long spark. Is one better than the other?
 
You are off slightly. I actually had to stop and think about inductive ignition.
That is what it is, of course, but I honestly do not think I have ever heard it called that.

The inductive ignition does not deliver all that long a spark. Its much longer than CD, but not all that long.
The primary advantage to CD, is not the multiple strikes, since at the higher engine speeds it does not have time for more than one strike.

The advantage is, while a standard ignition system dumps 8 or 9 volts into the coil, a CD will dump in 4 to 5 hundred.
Thus the spark is much higher voltage.
You need current to generate the heat necessary to start a good burn.
And CD systems are often a little low on current.
But, you need voltage to jump the gap, ionize the mix, and allow the current to flow.

So, the higher CD voltage spark lets you run a wider plug gap which has more fuel mix in the way of the spark, so a better chance of a good burn.

The plain fact is, HEI is a pretty good compromise. The spark voltage is higher letting you run wider gaps, and you still keep the current for burn.

Unless you are going to try to run really lean mixtures, or high RPMs, CD is not going to be a big help.
Assuming that your HEI is up to snuff.
 
Fordum said:
You are off slightly. I actually had to stop and think about inductive ignition.
That is what it is, of course, but I honestly do not think I have ever heard it called that.

The inductive ignition does not deliver all that long a spark. Its much longer than CD, but not all that long.
The primary advantage to CD, is not the multiple strikes, since at the higher engine speeds it does not have time for more than one strike.

The advantage is, while a standard ignition system dumps 8 or 9 volts into the coil, a CD will dump in 4 to 5 hundred.
Thus the spark is much higher voltage.
You need current to generate the heat necessary to start a good burn.
And CD systems are often a little low on current.
But, you need voltage to jump the gap, ionize the mix, and allow the current to flow.

So, the higher CD voltage spark lets you run a wider plug gap which has more fuel mix in the way of the spark, so a better chance of a good burn.

The plain fact is, HEI is a pretty good compromise. The spark voltage is higher letting you run wider gaps, and you still keep the current for burn.

Unless you are going to try to run really lean mixtures, or high RPMs, CD is not going to be a big help.
Assuming that your HEI is up to snuff.
Click to expand...

just wow, glad to have people around here like you that are very knowledgeable :waytogo:
 
HEI isn't an option at this point, but on that note, it's also an inductive type system I think.

While having proven itself time and time again for being simple and reliable it'd be a great if it were an option.
 
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It'd be nice to see more of the tech reviews and tech articles come from a "rock crawling" perspecitve. Seems 99% of what you can read is always refering to racing in one form or another.
 
In a rock crawling scenario, you'll typically be at sane RPM, especially with a Cad 500. With a properly working/tuned inductive system, you are good to go...there would be no huge advantage to CD (especially when you consider cost). Yes, HEI would be good - why isn't it an option? They offered it for the Cad big blocks from the factory...

There is a myth out there that multiple sparks produce a "better" burn. The fact is that once combustion is initiated in a properly tuned engine, there is no advantage to additional sparking.

Some engines (like those with really lumpy cams) can be difficult to reliably light on every stroke thru the RPM band. In those cases additional sparking can make the window of opportunity larger to get the fire started.

Something like an MSD could help if you wanted to run lean for some reason, if you needed/wanted a built-in rev limiting capability, or if you wanted a sealed (waterproof) system.
 
Some time ago, We decided to do fuel injection on the cad 500. Some decisions were made and I don't want to go back to an HEI. I have a Pro Billet diz from MSD that's locked out for computer timing control. Yes, I could go back but it seems just a shame at this point.
 
What's your cam duration Kert? If it's around 230 @ .050 or higher then I would say you could benefit from a CD ignition. But since you said you will top out around 5k RPM, I am guessing it's lower. And since you have FI you probably won't notice it as much.
 
folkenheath said:
What's your cam duration Kert? If it's around 230 @ .050 or higher then I would say you could benefit from a CD ignition. But since you said you will top out around 5k RPM, I am guessing it's lower. And since you have FI you probably won't notice it as much.
Click to expand...


I'd have to look at those numbers again. I know the cam peaks pretty low.
 
cybrfire said:
It would seem, the hot ticket is capacitive discharge. I do understand the differences and for my particular engine, I don't see much benefit of capacitive.

Anybody have experience with both?

Inductive dies off around 5000 rpm, well outside the optimum range for my cadillac 500. I'm running around 10.2:1 compression. No boost, no nitrous or anything else that would increase the resistance to the spark inside the cylinder.

Capacitive is extra cash that may not necessarily have much benefit.

Other big difference, capacitive will hit the spark plug 8 or so times per combustion cycle where as the inductive will hold one long spark. Is one better than the other?
Click to expand...
Inductive ignition systems are used on the majority of stock vehicles, due to their simplicity and inexpensive production. For stock applications, these ignitions are adequate, but when it comes to gaining performance, factory inductive ignitions fall short. The primary weak link in an inductive ignition exists because the coil serves double duty. The coil must act as a step-up transformer to create a higher voltage spark, plus it needs to store this power until the ignition is triggered As engine rpm increases, there isn't enough time to completely step-up the voltage before the ignition is triggered, resulting in a weaker spark. This low voltage spark may not be enough to light the fuel mixture in the cylinder, which will result in a misfire and loss of power. A CD ignition is capable of producing full power sparks throughout the entire rpm range. It draws its voltage supply directly from the battery and uses a custom-wound transformer to step up the voltage to over 460 volts. This voltage is then stored in a capacitor until the ignition is triggered. At this point, all of the voltage is dumped into the coil where it is transformed into even more voltage, capable of reaching 30,000 to 45,000 volts, depending on the coil. The ability to produce high power sparks throughout the entire rpm range of your engine is why you need a CD ignition. The payoff is complete combustion of the fuel mixture, which results in more power, increased throttle response, a smooth idle, quick starts, improved economy and reduced plug fouling.
 
Well, I'll throw my 02 cents in , I dont have any of the Technical knowledge on the subject BUT I can provide you with some real world experience.

I run MSD distributors and 6AL boxes and Blaster 2 coils on 5 of my gas powered trucks

1980 K20 ( AKA "the Duck" hence my screen name ) with a 510 stroker BBC

75 Dodge W300 with a 408 Stroker Small block mopar

75 Chevy Stepside with a 377 destroker

79 K20 with a 406

87 K20 Burb with a stock Fuel injected 350

( pattys truck has one too but I didn't install it )


Anyways all these motors are done by 6000 rpm when I installed these setups on the motors ( replacing re-curved and rebuilt HEI's and factory mopar electronic ignition) I didn't notice any power difference what so ever. ( and I did open my plug gaps) but I noted that they started easier and got marginally better fuel economy.

My next motor I build will get a Davis Unified Ignition , because I've heard good things about them, But I still like MSD products and the built in Rev limiter is nice
 
K5er4Life said:
haha, I thought what was being said sounded a little like marketing hype...good catch.:haha:
Click to expand...

Did you notice they are from El Paso, which happens to be right where MSD is located? Kind of funny. They would of been better off just admitting it.

With that said, I like MSD products, I have a couple V8s running on MSDs and they work excellent. And when you start getting a little bigger cam and/or higher compression, they help immensly.

Kert, does your FI system allow running a seperate MSD box? I have no idea what you are running for FI. 10.2:1 compression is getting up there, and if you have a small cam with that compression your dynamic compression ratio is going to be pretty high. It can't hurt to put a 6A or 6AL on there (if you FI has a rev limiter, the 6A would be no different), but whether or not you want to is going to be up to you and if you are happy with the performance and the spark without it.
 
Yep, my system allows the use of an ignition box and was recommended by the guy that has been helping me with the injection system.

I started this discussion to help wrap my head around how each system works and their respective benefits and weaknesses. Also to get the opinions of some people that have used both.

I was kicking around two different boxes, the 6A and an inductive box. Both from MSD. I purchased a 6A from a member on here. The deal was too good to pass up.
 
If it really is a matter of value for the dollar then I don't see where capacitive would benefit your particular truck.

If you are interested in always over covering all your bases regardless of cost than capacitive is the way to go, if you want something that works just fine without spending more than inductive is the way to go.

Ironically our MSD quoting friend hit the nail when saying "simplicity and inexpensive"
 
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