One of the things I want to eliminate as a potential cause of my
 high rpm  misfiring is EMI due to unshielded plug wires. I
 currently have Blue Max EMI  sheilded plug wires and just purchased
 Magnecor shielded wires. What makes these  "shielded"? They have a
 conductor with a very thin wire wrapped around the  insulation of
 the core wire, and that is covered by another insulating layer,  and
 that is covered with the outer sheath. But,my understanding is that the
  spiral wrapped wire is supposed to shield the inner wire, and the
 way I have it  configured, with the inner conductor and spiral wrap
 exposed and crimped in  contact with the teminal ends, doesn't the
 spiral wrapped wire also conduct the  spark current and thereby
 defeat the whole purpose? Isn't the shielding wire  supposed to be
 grounded at one end to the engine and drain off any induced  current
 from the high voltage secondary ignition lead, and be separate and
 not  in contact with the    conductor? And if that is the case, how
 am  I supposed to configure or  fabricate the terminals in such a
 way as to ground the spiral wrapped shielding  wire?

  Alternatively, I do have some heavy braided wire that I could slip
 over each  entire secondary lead and ground one end of or the other
 to provide shielding.

  Comments and suggestions invited.

  Brian Trubee

  Yes the shield should be grounded on one end. It is insulated from
  the core. Some plug wires have a core that has some resistance
  winch is supposed to minimize radiation.

  By all means add the braid and ground on one end.

  I think somebody is selling spark plug shields.

http://www.overnightautoparts.**com/brand/msd.html<http://www.overnightautoparts.com/brand/msd.html
  http://www.innerauto.com/NGK_**Brand/<http://www.innerauto.com/NGK_Brand/

  Paul Lamar


 Be careful of VHF radio interference with only one end of the
 shielding grounded. I had dreadful ignition static with my Mooney 20
 J IO 360 after the mags had been off to the magneto man. The bonding
 check was fine, but when the magneto man came back from holidays I
 learned the new leads were only earthed at one end. All the experts
 insisted that this could not happen, but it did, grounding the other
 end cured the static  John Evans


Are you certain the "first" ground was good? If you ground both ends, the
high
voltage can induce a current in the shield that can then cause other grief.

Dale Davies



When it comes to plug wires, always start with something that you know
works. Which may mean stock wires. Bulent Aliev tried to use custom plug
wires on his cozy4 rotary ignition. The wires had a metal conductor core.
(Common on some race cars, and very common on Porsche and other oem Euro
cars where they put a 2kohm resistor in the distributor rotor). In the case
of Buleys engine, the wires created all kinds of trouble for him before he
sorted out that the wires were the problem. He actually sold his whole
rotary engine setup to another cozy4 builder and installed a lycoming type
engine, simply because he could not figure out the wires were keeping his
rotary from running properly.
 Changing to the lycoming type engine did'nt resolve his troubles, and I
read he regretted tossing the rotary. The wires caused it all, both on the
rotary, and on his new lycoming thing.

It is common for oem plug wires to have resistance over 20kohm per foot. I
have checked this with a multimeter on many oem wires. Why so high? Same
reason as aircraft. Radio interference is greatly reduced.

Watch out if you try to us some of the expensive high zoot plug wire sets,
your ignition system, possibly your whole electrical system, may not like
them. Voltages as high as our coils put out will conduct across just about
anything. Lowering the resistance of the wires will probably not help
anything. High voltage electrical current travels in the surrounding fields
of the conductors as well.

Ed Carver