North American Turbocoupe Organization

Spark Plug Gap
tylerport Offline
Senior Member
What is the effect of either increasing or decreasing plug gap?

Jim Portteus
86 Turbo Coupe, 128K Miles, 140MPH Speedo, Gillis Valve, 2 1/2" Downpipe to 2" Duals w/ 12" Glasspacks, 245/50R16's and new paint.
Jim Portteus

GaryS#2 Offline
Posting Freak
[QUOTE]Originally posted by tylerport:
[B]What is the effect of either increasing or decreasing plug gap?

Increasing will give better gas milage but you will not be able to run higher rpm or boost unless you upgrade ignition.It will blow the spark out at higher rpm with big gap.
Grocery Getter/Rice Cooker.

Nate K Offline
Posting Freak
Insufficient spark plug gap can cause pre-ignition, detonation and even engine damage. Too much gap can result in a higher rate of misfires, loss of power, plug fouling and poor fuel economy. It is always best to check the gap against the manufacturer's specifications. Another consideration that should be taken into account is the extent of any modifications that you may have made to the engine. As an example, when you raise compression or add forced induction (a turbo system, nitrous or supercharger kit) you must reduce the gap (about .004" for every 50 hp you add). However, when you add a high power ignition system (such as those offered by MSD, Crane, Nology)you can open the gap from .002-.005".
NATO Member
90 Mustang LX 5.0L Notch

Cars I wish I still owned:
69 Coronet 440
70 Torino 351C
79 Bronco 351M/400 on 35's
79 Trans Am 403 (6.6L)
88 Cougar XR7 5.0L
93 F150 Flareside Mark III Custom 5.0L

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