The much more effective approach for the early 911s with the offset spark plug, was to twin plug each cylinder.
This results in having a higher CR engine without significantly reducing the timing to reduce the likelihood of detonation.
The later Porsche engines with the spark plug in the center have much higher CRs. As of the 996, Porsche no longer
found a benefit of using a CDI vs an inductive discharge ignition IDI. With present day semiconductor technology,
i.e. switching speeds & current capabilities, an IDI can produce a spark equal to any CDI system.

I put a CDI+ on back in 2017 along with plug wires, a coil and a rebuilt distributor (vacuum advance delete). Three years of nearly year round daily driver duty and 35k miles later it hasn't given me the slightest concern or hiccup.

Many original 3 pin Bosch CDIs from the early 1970s are still running their original 911.

I'm better than a HS auto shop student, but darned if I can't figure out where to plug that PC into my SC! Help me out here, Swami.

Inductive and CDI will never be equal. The phase angle between current and voltage is much different between both types and this fundamentally changes the spark characteristics. Furthermore, voltage is self regulating with an inductive ignition while with CDI it needs to be controlled at the source. There are other distinct differences too. No, the sparks are not equal. Fred

love it! L/D is just waiting in the weeds to strike and tell you 50 year old electronics are fine and can't be improved upon.

My original 3 pin Bosch is in a box properly labeled and sealed as a precious relic in the 911 parts cabinet.

I have been running an excellent CDI unit, not a MSD or the one discussed here. Been in use for 12 years and over 100,000 miles on my 2.7 MFI WITH DRAMATIC IMPROVEMENT over OEM.

I am sure Jonnies system is great too, but it was not an option when I did my research made the installation.

Right, the inductive discharge ignition is the de facto automotive OEM ignition for all present day vehicles,
e.g. Porsche, BMW, Mercedes, & Ferrari, and even in racing (F1).

https://books.google.com/books?id=TzqIDQAAQBAJ&pg=PA215&lpg=PA215&dq=Formul a+1+inductive+ignition+system&source=bl&ots=D-zZuAcGsY&sig=ACfU3U3iXm-hE92bIWHetd_lWfqc5Kti4w&hl=en&sa=X&ved=2ahUKEwi4vu mf1fTnAhXxJDQIHRYeAFUQ6AEwDHoECAoQAQ#v=onepage&q=F ormula%201%20inductive%20ignition%20system&f=false



http://forums.pelicanparts.com/uploa...1582910829.jpg


http://forums.pelicanparts.com/uploa...1582910867.jpg


The typical CDI spark duration is 50-150us (Bosch-80us, MSD-40us), which results in a marginal spark as noted in the reference.

Agreed, A good CDI has an effective duration of at least 350µS. Fred

Just advancing the timing is missing a couple of the biggest selling points of the CDI+. The multi spark to 10,000rpm and the ability to customize the advance curve. I’m switching from CIS to carbs on my 82, to take advantage either I need to send out my distributor for a recurve or install the CDI+ and achieve the same results.

The only way you are using a PC to “tune” a 1982 911 is by going to EFI or using the CDI+

It's just been shown that a multiple spark system has no benefit.
You have an engine capable of 10K RPM?

Customizing the advance curve will provide a margin gain over just tweaking the timing.

‘Dave’. Your technical ‘proof’ data appears to be for a modern Ferrari F1 engine. I would imagine that the piston, head, inlet and fuel system and pretty much everything else is a million miles away from an air cooled Porsche.

Btw, McLaren use both CDI and inductive ignition. You cannot say that one is better than the other in all cases. It depends on the engine design.

https://www.mclaren.com/applied/products/download_support_document/

I think it needs to be stated that Jonny's CDI has the multiple sparks close enough together to effectively give a long duration spark. This is different than MSD where the sparks are quite short (40-50µS) followed by a full 1mS without any spark before the next in the series comes along. Obviously, 1mS is far too long an interval between sparks except perhaps at idle rpm. Fred
EDIT: It should also be noted that the multisparking that was tested in the article was done with an inductive ignition, not CDI so the peak power of each spark would be much, much lower than Jonny's CDI.

Need help / advice with CDI+
 

Really love the CDI+ on my '78 930. I do wish they would add support for turbo boost signal as that would allow elimination of the boost retard function on the distributor... but I have a more pressing matter at the moment. Please advise / help if you can. I am upgrading my intercooler, adjusting valves and installing new ignition wires so the car is in pieces at the moment. I read a note in the Classic Retrofit version notes for the 1.38 version (the latest) which said that there was a bug introduced in the firmware in an earlier version by the increase of the clock rate on the CDI+ processor which can cause the box to shut down in high heat circumstances (ugh) so I planned to upgrade the firmware while I have easy access to the CDI+ box. I downloaded the 1.38 version of the software, plugged in the USB wire to the laptop and was able to communicate with the cable. I re-installed the supplied drivers to make sure I had that right. I get to the point where is says 'Connect to CDI' so I plug the USB wire into the back of the CDI+ (black wire to the bottom of the unit) then I turn on the ignition switch and nothing happens - no connection to the box. The software sits at that point and no connection with the box is made. Is it possible that with several ignition components removed from the car (coil for example) that the CDI+ will not communicate? I have tried it several times in slightly different sequence to see if it was an 'order of connecting' issue but no luck... I'm concerned now that my ignition box may be bad and I will be dead in the water after the upgrades are done. Anyone have this trouble with this version and this scenario? Does the car need to be running to connect to the box and upgrade the firmware?

Remember, there are multiple sources for very reliably rebuilt Bosch CDI units which typically last over 30 years. Pelican Parts has some!

The CDI+ boxes are ‘unbrickable’ so don’t worry about that.

You should be able to do the update on the bench with a 12V supply substituted for ‘ignition’ and the USB lead.

Shoot us an email if you still have trouble.

So, with the CDI one needs a conventional old style coil and solid copper wires? Spiral wound Clewett's need not apply?

Our CDI+ boxes are designed to be compatible with the original coil and spark plug leads. We have found most aftermarket coils too slow for our rapid multispark. You can make other coils work with CDI+ by increasing the spark interval in the unit (using the software) but that defeats the object of having the fast spark delivery.

..got it on the coils.... now, will spiral wound Clewitt style wires work as well as the stock solid cores?

Read post #28 & #29. The second spark is too short to have any real effect, and has no effect with most standard coils.