Ron Plugs - A detailed guideThese plugs also called RON plugs (RESEARCH OCTANE NUMBER) - were introduced in 1987 on engines with FIXED IGNITION DISTRIBUTORS. Their main function is to prevent detonation (pinking) when using unleaded fuel.
The plug is wired into the control box so that it can be fitted into one of two positions. Inside the plug are two different value resistors, and these will code the control box to advance up the ignition at different rates. The amount of advance under load is approx 5deg less when coded for unleaded (95) than for premium.
Cars with the Mototronic system (auto adjusts for fuel 2.5 & 2.
have another RON plug installed - again Brown but marked A & B. This was brought up in discussion on the Calibra Mailing List as derived from de-tuning the Calibra at low RPM to meet German noise restrictions. The mod was carried out by a member of ClubCalibra, flipping the RON plug, gaining more power down low where you need it!
(98) leaded fuel.
The resistance value also influences other functions and by using any of the 8 values available it is possible to make minor changes to the running of the engine.
The RON plugs come in nine different colours:
Resistance Value Ron Plug Colour and Number
Zero ohms Blue 95, Black 91
220 " Brown 95, Black 95
470 Brown 98
750 Green 98, White 98, Orange 91
1200 Green 95 (part No. 90276398)
2200 Yellow 95, White 95, Violet 98
4700 Red 98 (part No. 90276399)
Infinity Violet 95, Red 95, Orange 95, Yellow 91, Blue 91
Potential 8v Improvements
The table below shows the changes made by each resistance value-V-Octane rating for the three basic 8 valve engines...
KEY
1= Basic value
2= Idle speed increase by 100rpm
3= +5% fuel acceleration enrichment
4= +5% fuel enrichment throughout range
5= Ignition retarded by 5 deg throughout rev/load range.
2.0 NE non-cat
91 Ron zero ohms =1
infinity =2
95 Ron 220 ohms =1
1200 =3/4
2200 =2
4700 =2/3/4
750 =2/3/4/5
98 Ron 470 ohms =1
2.0 NE cat
91 Ron Zero =1
Infinity =2
750 =2/3/5
95 Ron 220 =1
1200 =3
2200 =2
4700 =2/3
98 Ron N/A
2.0SE/ SER/ SEH non cat
91 Ron N/A
95 Ron 220 =1
1200 =3/4
2200 =2
4700 =2/3/4
Infinity=2/3/4/5
98 Ron 470 =1
750 =2
