theNeanderthol

iTrader: (1)

I want to talk a little about some ignition mod stuff. I know that there is a lot to be gained from ignition upgrades for a carburated car, and most of us use carburetors. So here goes.

Please correct me if I'm wrong, I'm trying to uncover the mystery of the ignition system. It seems that there are 2 main problems that need to be adressed in updating an ignition system.

One is the strength of the spark. As the motor goes into higher RPM's, the ignition coil has less time to charge to charge between firing, so the spark isnt as hot at high rpm. Electromotive answers this by using a multiple coil setup that allows one coil to fire and the others to recharge. Awesome!. The capcitive discharge system (CD) uses a stronger coil to fight this problem. From what I have read, all a CD box does (like MSD or mallory) is (besides the multiple strike stuff which only happens to about 3000 rpm) is use a transformer to take the distibutor signal and turn it to a high voltage signal, so that when THAT signal hits the - terminal of the ignition coil, it puts out an enormous spark, much bigger than it would if it were triggered by the distibutor signal. This is great, but it is a very short spark, a few miliseconds maybe. which brings me to my next main problem

Spark duration. We need more duration, and the only system that seem to answer that really well is the electromotive system (hpv1 and hdv). It pputs out a hot spark (multi coil system) and also can make the spark last much longer, but letting the plug spark , not one huge quick release of energy, but a little less energy during a controlled , longer period of time.


We all dont have the $ for the electomotive system.

I guess the real question is, what is more important, the spark duration, or the strength. If it is the strength, I see no reason whey we cannot rig a multicoil setup ourselves. We have lots of good brains on the forum. I know we can also increase the spark duration, Its been done. It want be as precise and the electromotive setup because they use that 60 minus 2 tooth gear setup thingy that feeds precise info to the system. Without that, we just have a trigger on the dizzy, not as precise, but it does the trick.

What do you guys think? Is there something to be gained by experimenting with a homemade multi coil setup, or is a CD system good enough??

A trigger to switch between coils, one firing, and the other charging cant be to tough or expensive to setup

t_g_farrell

iTrader: (1)

Have you seen the transister trick circuit using the 2g coils ? Might want to check it out.

https://www.rx7club.com/1st-gen-archive-71/ignition-transistor-trick-2gcdfis-478518/

https://www.rx7club.com/1st-gen-archive-71/ignition-2gcdfis-w-tt-transistor-trick-write-up-simplified-design-484176/

gsl-se addict

iTrader: (3)

Basically:

-voltage determines how far the spark can jump under given pressure/temperature in the combustion chamber. People are always looking for more volts, but more volts doesn't really matter as long as it is high enough to jump our given spark gap under the conditions we run.

- energy: You will see this listed in most CD systems (xxx mJ). This is important as it relates to the duration of the spark.

I believe that duration is most important for use due to the long combustion chamber of the rotary. As long as the spark is hot enough to consistantly ignite the air/fuel mixture, increased spark current/temperature beyond that doesn't really help.

Most of the upgrades are more than enough for our cars (MSD, 2GCDFIS, TT, and so on). It just depends on your budget and preference.

It is true that at higher RPM, there is less time for the coil to charge, however, it isn't quite as important for us as our engines fire much like a 4-cyl. If it was like an 8-cyl, for example, we would only have half the time available to charge coils at a given RPM (assuming firing through a dizzy cap). The 2nd gen coil/ignitor pack, for example, can give excellent sparks at high RPM (I tested to 14k RPM on bench). I really don't think you need to rig up a multicoil setup. You may only need something like that for engines with many cylinders and/or operate at very high RPM. Otherwise, I don't see an advantage to it. It would be interesting to design/test such a setup, though.

Kent

theNeanderthol

iTrader: (1)

OK I see what you mean . SO I suppose that a better spark duration would yield more advantage than just a hotter spark. That is the impression I got when reading info from electromotive. The reason I felt that a multicoil setup would help is because our systems will fire once upon combution, and once on the exhaust. So the one coil will still have to fire often at high rpms. So maybe Having not just higher voltage, but higher energy (mjoules), could be obtained my using a multi coil setup. And the better energy would yield more spark duration. WHat do you think?

does anyone here on the forum actually have experience using a multicoil setup like electromotive's?

gsterror

I remember my Uncle looking into a multicoil setup a few years back. I can ask him if you want.

Anthrax Mike

From my understanding.

Spark duration is most effective as far as lean condtions are concerned, the longer the spark the higher the chance that a HC molecule will find its way into it. And this also makes sense with the exceptionally long combustion chamber of rotar motor.

Also as compression pressures increase a higher amount of voltage is required to over come the pressure.

Its kind of a give and take. If your system only fires 10,000 volts. At idle maybe only 2,000 is required to over come compression pressures, leaving more for duration. And the opposite is true as pressures increase, thus giving a shorter duration.

As for hotter spark I'm not so sure. But you'd like the longer the spark occurs the hotter it might become. oh well.

rotaryengineering

I just purchased the Electromotive XDI and will start some testing in a couple of weeks. My application is in a full Drag Car with a P-Port carburated. The reason I bought the Electromotive System was for its accuracy, multi-coil, 0 timing split capabilities. I just received everything but, from what I read and been told by the Techs. at Electromotive this is the most accurate system available on the market today. At high RPM's the last thing I needed was my ignition to not work properly.

Can a cheaper system be put together for a fraction of the cost? Yes

My MSD Ignition system I had on my car worked flawlessly with no problems. Dual MSD 7AL with Pro Coils and a 1985 Locked Distributor with Stock Igniters. This system was definitely not cheap either but, worked well with no problems on my Turbo Setup.

I'll post information about Electromtive XDI when I get some more good information for those of you that are interested.

Thanks

Siraniko

iTrader: (13)

hey Albert, thanks for sharing and keep us posted.

Kentetsu

Bang for buck, I still have to say that the TT system is the way to go. Under $50.00 and the improvement is simply unbelievable. Then you can take the money you saved and get an airdam or something. Kent rocks!

no_name

what is the TT system?

Kentetsu

https://www.rx7club.com//showthread.php?t=411312