What kind of spark plugs and ignition.

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cliffrosa

Member
Joined
Feb 5, 2012
Messages
10
Location
Huntsville, AL
Hey guys I cannot find any information about what type of spark plugs to use on my VW type 4 motor with slick magneto. I want auto style plugs since they are alot cheaper.

Now for my second question, I want to use a CDI ignition or electric ignition for the secondary. Are they the same thing? Whats the difference and what would you guys recommend for a reliable and good priced setup?
 

PaulS

Well-Known Member
Joined
Sep 6, 2011
Messages
297
Location
Seattle, Wa., USA
Electronic ignition is any system that doesn't use points to trigger the coil primary voltage - it includes CDI and a lot of others. CDI uses capacitors to store high voltage (200+ volts) to use to fire through the coil with an SCR to provide very fast coil saturation and high secondary voltage rise times. CDI is perhaps the best of the electronic ignitions.

Most aircraft use dual ignition - not a primary and back-up system. Dual ignition uses two plugs and fires them both at the same time - it provides more complete burning and a HP increase. As a rule of thumb, if you want to use automotive type plugs you will have to select plugs that suit your engines needs. Rarely with the recommended plug for an auto work in an aircraft. You will probably want a colder plug than is used in a car because the engine will be under a constant load (making more heat) and more prone to preignition and detonation. You may also need an extended tip plug to keep the plugs clean when running rich during high load rich conditions. It will come down to the aircrafts needs and what is available. Connections of plug wires and shielding for radio noise is also a major consideration.

Paul
 
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