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Dynamohum Dynamohum is offline
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Join Date: Jan 2008
Location: Midland Ontario Canada
Posts: 173
Originally Posted by 911st View Post
A lot of what you are saying is over my head I think.

However, I believe the stock ignition is CDI and hard to beat as to intensity.

I think many of the wasted spark systems do not generate as hot a spark but not sure.

If you are staying single plug adding MSD seems to be an improvement. With this you can also get pressure based boost retard. Or even go fully programmable.

There is a company that taps into the signal from the Motronics to coil for the advance curve and from the crank sensor to know which cylinder is up to feed their own box for driving a twin plug wasted spark system.

Me I would stay with the single plug factory or add on MSD unless going for over 500hp or lowering compression to under 7/1. If I was going to go twin plug I would probably get a twin plug dist or just change over the whole EFI to a programable.
Thanks for your input,

To clarify the 84 - 89 Motronic ignition is an Inductive system using a coil not a CDI unit.
The ignition driver item #9 in the DME from the link Inside a Carrera ML3.1 DME - The Land of NoVA/DC/MD area Porschephiles shows that it is a power transistor on the Digital side of the DME. In hind sight, I think that's where my confusion started lol

From your post, Motronic's turbo conversion thoughts? mentioned using the adjustable MSD boost retard system as a method of controlling ignition boost retard, so I decided to check it out. After reviewing their installation diagram, I questioned whether it would work, since their wiring diagrams show the white trigger wire hooked up to the distributor pic-up and since the Motronic system has no dist pic-up it left me wondering where would the signal come from. So I sent an email to the supplier and apparently according to them it will work and this is what they had to say;

"It will basically wire in between the ECM and coil.
The white wire will connect to the wire that is currently connected to the coil (-)
The Orange wire will then connect to the coil (-)
The small red wire will connect to switched 12v+ or the coil (+)
The black wire to ground."

Nice to know as this looks like a fairly inexpensive solution to having variable control of boost timing externally of the ECM ignition tables.
It's piggyback and and some what of a band aid but a solution, but still a means to the end result.

I know we are getting a bit off topic here, but its all tied together.

One of problems with doing your own turbo conversion is with working out all the variables in managing the new fuel and ignition needs, however for me that's part of the fun.
Thank You for your time, Paul. We do because we can.
87 911 3.2 (Turbo conversion, build in progress, Thermal Barrier Coatings, High Pressure Dry film coatings) Modified heads, boat-tailed case, ARP hardware, OBX Header, 930 clutch disk, G50 Trans
89 5.0 Mustang convertible (For Sale)
Old 02-02-2010, 05:24 PM
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