If you have MoTeC (or equivalent), do you need CD system

CamB · CamB's Garage

If you are running MoTeC or equivalent engine management control in place of factory systems, do you need a capacitive discharge system (eg Bosch factory-style or MSD)?????

What do the Motronic cars use?

And if CDI system not needed - why not? I know CDI helps to charge the coil quickly and fully at higher revs and when voltage drops at idle. So why wouldn't this be an issue with a computer controlled system? I assume the computer triggers the coil, but why wouldn't CDI help?

Natchamp · 11-13-2001, 08:25 PM

The ems's like Motec send an ignition signal to an ignitor which fires the plugs. You can use a CDI like a MSD, or whatever, as the ignitor. Wether its worth it or not depends on what type of coils, ignitors you use and if you need the extra sparking capability. On my system I just went with the smart ingitors and wasted spark coils. With a twin plug setup I thought it was a little overkill and increased cost and complexity not to mention the packaging issues.

CamB · CamB's Garage

Probably a better question is:

I am buying a twin plug MoTeC equipped SC engine which uses a modified 964 distributor. Once that goes in (and it has been used in the past for racing applications using 2x 944 coils) should I:

a) buy a second MSD (or is this overkill)
b) sell my MSD and use the moeny to fund the next 5 years of extra spark plugs

I assume if it was fine for racing with the 944 coils it is fine for me. The seller did not indicate what the "ignitors" were? I am somewhat confused.

Cam

Randy W · Randy W's Garage

Cam, I would think the Motec engine you are buying should have a CD unit included with it. The Motec M-48 mated to the 3.2L in my 911T autocrosser is comprised of two boxes - one is the Engine Management System and the other is a Capacitive Discharge System. We used a 993 Twin Turbo Distributor and a coil to finish the ignition system.

Randy Wells

Natchamp · 11-14-2001, 08:54 AM

Cam, it is better with a CD ignition but kinda overkill with twin plug so its up to you. An MSD or Permatune, etc have ignitors built into them. The ems's can not fire the coils directly so they send the ignition signal to either a stand alone ognitor or an MSD/Permatune so they can fire the coils. My setup is a little different because I went with crank fire where as yours is using the distributor for crank signaling and ignition distribution. If I wanted to use MSD it would have taken 2 MSD DIS-4 boxes which are kinda spendy and rather larger to fit physically. On your existing setup what is the Motec sending its signal to?

CamB · CamB's Garage

I actually don't know. I know the broad specs on the engine - 3.0, twin plug, MoTeC through converted MFI stacks, S cams. Around 250hp.

And it has been "lightly" raced - 2 meetings only. This is how I know it worked with the two coils. The engine builder/racer is very highly regarded and I trust him.

Randy may be right - the MoTeC box could have a separate CD box too. I will figure it out in time. I can't get it in the car to either January or March, so no big rush. I am confident it will work, and will explore 2x MSD if necessary but will sell to a friend (Lotus Elan plug fouler) if not.

Cam