Jump to content

Recommended Posts


I recently purchased a CDI+ unit for my 1974 911 Targa from the folks at Pelican Parts.  I have been chasing a small exhaust backfire and low RPM bucking/stumbling issue for several months and bought the CDI+ hoping that it would cure my issue.  My original Bosch CDI unit was putting out about 150v at idle (measured with a direct voltage adapter) so I figured it was time for a replacement.  Unfortunately, it did not cure my issue, however, the engine has a different tune to it at idle (sounds stronger) and under high load and WOT it absolutely screams!  It feels like a completely different engine with the CDI+.  I couldn't be happier.  I finally bit the bullet and pulled my CIS and found a severely cracked and leaky air box.   A replacement box (and other bits) are in the mail, and I can't wait to finally get my issues resolved.  Thanks for putting together such a modern and elegant product!

I am curious to find out more about some of the features available in the CDI+ software such as: tachometer smoothing, adaptive multi-spark and distributor input smoothing.  I recently had my tachometer rebuilt by NHS but it still swings around more than I care for especially with high RPM shifts.  I'm told this is normal and due to the large dial and the design of the internal movement.  I am going to hook up the CDI+ to drive my tach and I'm wondering if the tachometer smoothing feature might settle my tachometer down a bit.  Any details on these features would be greatly appreciated.

  • Like 1
Link to post
Share on other sites
  • 2 weeks later...

Hi SD,

Yeah I had a cracked air box in my SC too.   The new air boxes are made of a much stiffer material (PA6).  Car runs a whole lot smoother.

You have found a few features that are undocumented - manual needs an update.  In the meantime...


Fixed Timing.  If this box is checked then the CDI+ unit fires as soon as the signal is seen from the distributor as per the original CDI.  Unchecking the box results in the timing curve on the main screen being applied.

Pulse Output.  The shift light on the red wire is flashing rather than on.

Invert Output.  The red wire output is inverted when checked.

Custom Output.  Currently used to drive the solenoid on an MFI pump.  The operational on and off RPM are set on the main page ( default is 1300 and 1500 RPM as per the original 'speed switch'

Tacho smoothing.  This effectively provides a software damper to the RPM, providing a smoother dial movement.  It's a balance between responsiveness and smoothness.  Obviously you want the dial to indicate the correct RPM so if the damping is too 'stiff', the needle would lag behind the true RPM.  Not enough and you wont get any effect - we've tried to choose a happy medium.   Every gauge is different so results vary a bit but there is no harm in switching the feature on.

Tacho Sweep on Start.  The tacho will sweep from 0 to 7000 RPM when the igntion is switched on.

Adaptive Multi Spark.  The CDI+ will fire the maximum number of spark pairs that can be fired in a 20 deg crank angle for any given RPM.

Distributor Input Smoothing.  This is a similar scheme but applied to the input signal of the distributor.  When you have a 'lumpy' motor (e.g. highly string 2.0L with a light flywheel) the idle can be quite erratic due acceleration/deceleration of the engine on every combustion.   When operating in the timing curve mode.

Number of Cylinders.   This should be set correctly as it affects the RPM calculation.

Triggers Before Start.  The number of distributor pulses to ignore before firing the ignition.   This allows the engine spin up to speed prior to the first spark - prevents kick back.



  • Like 1
Link to post
Share on other sites

Very interesting - and informative.

Funny enough, I too have a 1974 Targa - and will order the CDI+ very soon (my wife has generously 'forced' me to order it as my X-mas present).

I have an idle issue that I believe may be related to the Distributor advance. Using the CDI+ it may (or may not) fix this, if I disable the mechanical advance. And I cant wait to enjoy all the other benefits and adjustments!

P.S. getting the Fusebox(es) as well - Go Combo Deal :)

  • Like 1
Link to post
Share on other sites
  • 3 months later...

ok, I fitted the CDI+. 5 minute job. Car still works 🙂

Starts, drives, idles - all perfect. Plug and play.

Hardest part was to verify timing before and after, that took most of the about 5 minutes it took me to fit the CDI+.

I am not ready to explore the advanced functions - need to book a dyno to get real feedback.

Very happy with the result right now. Fuse panels next ......



Link to post
Share on other sites
  • 2 weeks later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...