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Spark plug size

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sticky

Regular Contributor
"hi all can someone tell me wh

"hi all can someone tell me what determines the spark plug,is it ignition system,like if you change a block,and use orig.electrics,would plugs stay the same,thanx"
 
"IN MY OPINION,..IT IS-->

"IN MY OPINION,..IT IS-->
1.type of ignition system
2.size of engine
3.Size of combustion chamber
4.max rpm of eng
5.2 strk or 4
6.normal expected eng temp.
7.sustained use,area-- trolling/or 70 MPH
to try to answer ur original question---
u would use...the recommended plug for that hp and year of engine."
 
"ok i just rebuilt 50hp 75 blo

"ok i just rebuilt 50hp 75 block 74 ign. book calls diff. plug 74-75,which plug to use,thanx"
 
"Current recommendations are L

"Current recommendations are L77JC4 or QL77JC4 for both 1974 and 1975 models, gapped at 0.030"

(Q version is suppressed)

See http://continuouswave.com/whaler/reference/BRP/SparkPlugChart2008.pdf"
 
"Why would they recommend a su

"Why would they recommend a supressor plug? whats is the difference between supressor and the regular plug, specially on VRO/OMS???

As per the spark plug chart:

On ALL VRO/OMS equipped motors the "QL" supressor plug is recommended."
 
The QL plug is inductively sup

The QL plug is inductively suppressed and should be used with CD ignition systems rather than a resistively suppressed plug when a suppressed plug is required.

The QL plugs are recommended for use with VRO/OMS systems because the interference or electrical noise generated by an unsuppressed plug can affect the OMS systems
 
"In order to limit interferenc

"In order to limit interference to radio, television and other electronic circuits a resistance (about 5k ohms I believe) can be incorporated into the plug lead, the plug cap or best of all into the plug itself.

However these are not suitable for CD ignition systems and plugs with a low resistance, inductive suppressor have been developed for use with them."
 
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