Some information about detonation & prevention with spark plugs

InsidiousMSP

Member
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Black Mazdaspeed
Lately there has been talk on this forum about detonation and how it can damage our motors. Also, interest has arose about different spark plugs for our cars to replace the stock platnium plugs after increasing the boost. So, I thought I would take an opportunity to contribute some info on why we may detonate and how cooler spark plugs might lessen the chance, for those who are interested in the matter. I've done a little research on different plugs and have asked a few knoweldgable people what would work best on this application.

A little info about detonation first.

If you're familiar with the process of internal combustion, you know just before the piston reaches top dead center to start the power stroke, the spark plug is supposed to ignite the air/fuel mixture in the combustion chamber creating a single flame of heat and pressure to produce force on top of the piston. Detonation happens when the heat and pressure in the combustion chamber cause the air/fuel mixture to autoignite, producing multiple flames within the chamber. These flames collide causing a shock wave from the sudden rise in cylinder pressure, that puts a severe load on the internals. 'Pre-ignition' is a contributor to this abnormal combustion, when a point within the chamber becomes so hot that it ignites the fuel before the spark plug fires.

Common cause of pre-ignition? Overheated spark plug -- a reason to consider the heat range and metal of your plugs.

Stock, we have platinum NGK PZFR6F's. Good enough for 6psi, but might be risky in 10+psi territory. On high heat engines, such as our forced induction MSPs, platinum plugs may not conduct enough heat away to prevent pre-ignition because of the sharper tips. Now is where we need bare copper plugs. Because the tip has a better chance of wearing away due to the coppers low melting temperature, the tip is constructed very wide, making an ideal surface that doesn't stay hot. This lessens the danger of pre-ignition & detonation.

Copper NGK BKR7E's (#6097) can be had for under $2 a piece. Much cheaper than platinum and iridium plugs. Our MSP pioneer, Joe P., has recommended and used these plugs on his high boosted 'speed, and it certainly makes sense with it's 1 heat range colder than stock and bare copper construction. I'm waiting to put these in my car while it's getting worked on.

Obviously, these spark plugs alone wont completely prevent detonation. There are other factors aside from pre-ignition that can cause it. However, I definitely think of it as a good preventive way to save the motor, and thought it would be a good topic to post.
 
INGREXCO said:
why do people buy these platnium and iridium plugs then?

They last longer and (probably) self-clean a little better (hotter), but I doubt you'll find any proof of 'gains' by using them.

Peace...(hippy)
 
great post

what about extended reach copper plugs on the msp?

i know lunixracer has then on his turboed mp3. any thoughts?
 
Is it difficult to change out spark plugs..how is it done, and what tools would you need?
 
not too hard
1. unscrew plastic engine cover
2. pop off spark plug wires
3. measure gap of plugs with gapper tool($1.00 at autozone)(i went with .75 mm)
4.Unscrew the two ignition coils(i think two screws each)
5. use deep socket tool to take plugs out and replace one at a time(not sure what size to use)
6. screw it in tight!
put coils back on, then wires, the cover if you use it(i keep it off)

i tyhink thats about it, im in a hurry so bear with me
 
Great info...That info is great for anyone going turbo, supercharger, or nitrous!!

Nice Write up InsidiousMSP!

Chas
 
What if you are running stock boost, would it be wise to use these or maybe just use copper in the same heat range as the stock plugs?
 
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