Technical Tips > Post 84

C4 1987 Owners Manual - Spark Plugs Alloy Heads.

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87Z51:
As you say the original plug was Delco FR5LS (discontinued) which cross references from this chart

https://www.sparkplug-crossreference.com/convert/AC_DELCO/FR5LS

to a Champion RC12YC

I ran the colder RC9YC in my '87- perfect plug colour on the open road or WOT at the strip with a proper tune.

https://www.sparesbox.com.au/part/champion-copper-plus-spark-plug-oe005-rc9yc

or Repco for twice the price
https://www.repco.com.au/en/parts-service/fuel-ignition-exhaust/spark-plugs/champion-copper-plus-spark-plug-rc9yc/p/A7122195
Have also used NGK BCPR6ES

FWIW : the pre made plug lead sets will only fit PROPERLY if the dizzy is in the correct orientation .
Need to set the engine to TDC on No 1 cyl  ,pull the dizzy out and reinstall it back in correct orientation

Vettech:
Well thank you for telling me that, I've seen pics, video's etc which shows exactly that, but when I've pointed this out to people they have said I'm drinking too much. I dropped it, thinking that when I  got the car, it's paperwork included a spec sheet from some mob called "CROW", maybe that causes a change or was it when I threw the Harmonic Balancer. This was repaired, but is it in the correct position, esp since the timing mark is on it. But my 90 definitely picks up and goes like a rocket sled, so maybe a combination of tied plugs, leads and timing, coupled to #8 firing past the plug, yes I got it out along with Alloy, a deformed sealing washer, and a sooty plug.

I just revisited the 90, and its as you say, the dizzy is located at 90° exactly across the intake. But now I have a plug hole to get fixed, to get this car out of the garage, as the wife wants the 3000 tiles laid asap.

The old plug was NGK BCPR5ES-11 same as new ones - see pic below - note the seal washed was bitten or crimped or cross threaded by the last mechanic, destroying the plug hole, allowing blow by.

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