Hello Hello! I just saw a demo on a MSD 6A ignition compared to a standard ignition. You could alter the distance between the plug and ground and alter the RPM's. Pretty impressive, the stock spark started to fail after moving it a little further while the MSD ignition box made a whole lot more spark and would hold even when the distance was great. Well here is my question..... Will this ignition box make a whole lot of differance when used with an msd HEI distributor? And you guys that have installed it what gains have you seen? It claims better response, power and econemy.

 

With automotive ignitions, there are two components to a spark; strength and duration.

Strength (voltage) allows the spark to span a wider gap. This is useful in exposing the mixture, particularly a leaner mixture, to a larger ignition area and is why the factories went to the electronic ignitions and wider spark gaps.

The other component is the spark duration. Inductive ignitions(points or electronic), where the energy is stored in the coil, have a fairly wide firing line...on the order of 15-20 crankshaft degrees. Capacitor discharge ignitions, like the MSD and others, have a comparatively short firing line due to the coil just acting as a transformer, rather than an energy storage device. The capacitor stores the energy and discharges it nearly instantaneously into the coil.

CD ignitions can generate fairly healthy initiating voltages (the voltage required to jump the gap, also referred to as the ionizing voltage), which is useful if you are using wide plug gaps, have very high cylinder pressure, or a difficult to light mixture(usually very fat). If your ignition isn't capable of generating a sufficient initiating voltage, then the plug just blows out and you have a misfire. Inductive ignitions, particularly a well-designed electronic system, can also develop a healthy initiating voltage, but they have their limits in a demanding performance environment.

But, electricity is passive. You can't force more voltage into a device than it demands. At idle or under lighter loads, it takes about 10kv to light a plug. It doesn't matter if your system is capable of 60kv. It will only pass the voltage asked of it to get the job done. Under more demanding conditions, the voltage requrements go up. As long as your system can reliably supply what it takes, then performance improvements are not likely to be realized.

The other issue is repeatability and where a multi-spark system like the MSD and others can make a difference. No piston engine hits on all cylinders all the time. Not even a finely-tuned NASCAR engine. Misfires are just a fact of life because you can't always have a perfect combustion environment. What you'd like to improve is the rate of random misfire.

There are various ways to do this in the ignition. One method is a feedback ionization spark. This is the most sophisticated method in that it uses the second spark to read the cylinder pressure. If the original voltage fired the cylinder, the pressure will be high and the required ionizing voltage would be very high. The computer reads this as a successful event. If the ionizing voltage is low, the computer reads this as an unsuccesul firing event and sends another firing event to get the cylinder to hit.

The other method, and the one that MSD and others use, is to repeatedly hit the plug whether it needs it or not. This is a brute force method, but it does work. I know MSD says it will hit the plug about six times through 20 degrees of crank rotation, but on my scope, I've never seen more than four hits. These multi-spark events is what people are likely to notice most since it does decrease the random misfire events and shows up as a smoother idle.

As to using a CD ignition with an HEI...under most circumstances, it's a step backward. If the engine is running properly, then you have little to nothing to gain and by switching from an inductive to a capactive system, you loose the long spark dwell, which is the more desireable component of the firing line. It really depends on the particulars of the engine in question, but in most cases, you loose.

The best direction is to use high-quality ignition components and keep the system properly maintained.

 

MSD box for MOST STREET cars: No, it will not make a SIGNIFICANT difference in performance. Seems your 79 C3 came with HEI distributor. For MOST STREET cars, a properly maintained & setup HEI will make ALL the Fire your motor needs. If and when MSD box fails (and they do fail sometimes) ... you will not READILY find anyone who knows how to troubleshoot it or fix it. A good HEI is VERY reliable, has great parts availability & most decent mechanics can troubleshoot/repair HEI. I have & have had several HEI and MSD systems ... MSD boxes are great for a race car. Spend your money elsewhere.

 

Excellent information Gerry, knowing information and knowing how to convey it are two different things. You did a great job of both .

ltlevil

 

If you are running a healthy cam on the street it helps with idle quaility but as stated above it prolly will not net you any peak hp gains

 

I don't know what your future plans are, but an advantage of the MSD type boxes is the accesories that are built in to them. I run a Mallory HyFire VI-it retatrds initial start up timing to give the starter a little break, has built in rev limiter that is programable (no pills), has a place for boost sensor to retard timing for forced induction, as well as programable timing retard for using nitrous. These may be of use to you depending on your long term plans. If you are not interested in these things then a properly tuned HEI and carb would be the best choice in my opinion.

ltlevil

 

The 6A is 20 year old junk. "A" stands for anolog. "D" stands for digital

The whole idea of phony plug in resitors which have a big + and - doesn't enspire my confidence in a rev limiter.

You also have to understand that these multi spark box generaly only function up to 3000 rpm.

I used the Crane digital and have great faith in it.

 

I have to say, you guys are awesome. You just saved me a couple hundred bucks, coz I probably would have bought one (good salesman I spoke to the other night). Well thanks again, and by the way, my zz 383 went in today mated up with a th700r4. Block is red, the rest is chrome, those hooker super comp headrers with side pipes look beautiful!! I just need to shorten the drive shaft (I had a th350 I think before) and should be golden. Ill get pics soon. Oh yeah differant note: I think I will need to cut the hood- Am I better off getting a new hood and painting it, or cutting the old adding and moulding a hood scoop in to it? I've been told value wise I should keep the old original and buy a new one. Im easy either way, just want to know what you think? Cheers!

 

That sounds like a sweet combo.
I think most GMPP zz motors ship WITH a new 4-pin HEI ... seems some of the newer zz ship w/ MSD's 4-pin HEI ... either way, both hei are VERY good.

 

Gerry explained it well... I'd just like to add this:

CD ignitions have an advantage at very high rpm as the capacitors can charge fast and energize the coil very quickly. The inductive system is limited to energizing the coil with 12-13V where a CD box can hit the coil with 400+ volts. Note that this is only a factor well above 6500 rpm.

CD ignitions also do a better job in firing a dense mixture such as super/turbo charged or (very) high compression as they have higher ionization voltage.

CD ignitions are not good a firing a lean mixture such as idle or light cruise. This is the real reason for the multiple strike. They have so many misfires they need to hit the plug multiple times and hope that atleast one lights the mixture. Problem is the second/third etc spark are progressively later so that the effective timing advance jumps around.

Even with the multiple spark an inductive ignition with its superior burn time does a much better job than a CD system with lean mixtures which is why that is what you'll find on a factory system.

 

Hmmmmm So that explains why my car runs like crap! Well not crap, but it ran much better with the stock setup.

Now that I have bought an MSD tach drive distributor which is a thing of beauty, Very well built! How can I best use it? Right now I have a Crane Hi-6. It isn't nearly as smooth as the stock system was. On my car the stock system was a coil and I think what is called Transitorized Ignition.

I bought th MSD distributor for the wrong reason, but now that I have it I really want to keep it because it is so well built and it is so easy to tune.

thanks,
~Jay

 

I am running a Crane HI6 ignition on mine and it runs great. I fire it with a set of heavy duty points and it never misses a beat to 7000 rpm. I set the limiter to 7100 rpm and it randomly shuts off cylinders. I tested this once and set it at 5000 rpm and just left my foot to the floor. It never went over 5000 just stuttered at 5000 rpm. It is the stock dist. that has been recurved.

 

The MSD vette tach drive dist I bought says it has to be triggered by an MSD box, how are you getting it to fire with the Crane unit? Mine runs flawlessly when triggered by a 6A box.

 

I don't think they specify that it be MSD, just a CD type system. I called their tech support and they didn't have any issues with me using Crane, and also the Crane tech support said their unit will work with an MSD dist.

In fact the instructions with the Crane even give an example using an MSD distributor.

~Jay

 

Based on what Zwede said, I wonder if this might be a better choice for me as it is an inductive discharge
http://www.msdignition.com/ignition_1_5900.htm


What do you think? And how would I add a rev limiter?

~Jay

 

I have always understood that the faster rise time of the CD
ign. was one of the big advantages. Supposed to reach the
fire point before the energy could be drained off by plug fouling. This is in comparison to a simple points and coil system.

 

w1ctc: I heard this also but I've experienced the opposite. I have a CD ignition and inductive on my car and can switch between them in seconds. I've found the inductive does better with dirty plugs.

YMMV.

 

I first put in a CD system back in the 70's with my 11-1 350 with questionable jeting and timing. I would start to get full throttle misfire
after about 1000 miles on the plugs. The CD system made the problem go away. That was with leaded gas (don't know the effect that had).
Looking back, the CD was probably compensating for my poor tuning.