Following the initial change by Rover of the spark plug specification to Champion L92Y (now L92YC) the specified gap was 25 thou. This figure was quoted regardless of the compression ratio, so engines running the 10.5 : 1 CR would run the same plug and gap as those with the 8.5 : 1 CR.
I have been giving thought to the subject of spark plug gap and whether cylinder head changes or engine capacity changes or the addition of electronic ignition would warrant a variation.
The MGB GTV8 which also used the 3.5 litre Rover V8 with a compression ratio of 8.26 : 1, fitted with the Lucas 35D8 points distributor and 16C6 6 volt coil all as used in the 3500 and 3500S also used the same spark plugs, Champion L92Y, but in this case the factory specification called for a gap of 35 thou, a full 10 thou more. Clearly the coil and standard components were more than capable of dealing with the additional voltage required to bridge the plug gap, although I don't know at this stage whether or not any component reliablity issues surfaced as a result of the increase.
The SD1 saw the introduction of a new and improved cylinder head which featured larger valves and long reach spark plugs. In 9.35 : 1 CR form, the spark plugs were Champion N12Y and the gap until the end of 1981 was set at 30 thou. From 1982 onwards the gap increased to 35 thou.
So to question time. If your 3.5 litre engine is fitted with later cylinder heads or your lovely Rover has a nice new engine of increased capacity running under the bonnet, what spark plugs are you running, and what gap have you set them to? Have you experimented with different gaps and found any improvement with one setting over another? If you are now running an electronic ignition system or your engine is fuel injected, did you make a change in plug or gap?
In my case, my 4.6 runs Champion N9YC spark plugs, which I have set to 25 thou. I use Lumenition in a new Lucas 35D8 distributor that I purchased 18 years ago. The original Lucas 16C6 ignition coil manufactured in 1973 continues to provide outstanding service. Being a "Thor" engine, in original form my 4.6 would have been distibutor-less, powered by a Bosch Motronic engine management system and running platinum plugs.
I value and appreciate your thoughts.
Thanks in advance,
Ron.
I have been giving thought to the subject of spark plug gap and whether cylinder head changes or engine capacity changes or the addition of electronic ignition would warrant a variation.
The MGB GTV8 which also used the 3.5 litre Rover V8 with a compression ratio of 8.26 : 1, fitted with the Lucas 35D8 points distributor and 16C6 6 volt coil all as used in the 3500 and 3500S also used the same spark plugs, Champion L92Y, but in this case the factory specification called for a gap of 35 thou, a full 10 thou more. Clearly the coil and standard components were more than capable of dealing with the additional voltage required to bridge the plug gap, although I don't know at this stage whether or not any component reliablity issues surfaced as a result of the increase.
The SD1 saw the introduction of a new and improved cylinder head which featured larger valves and long reach spark plugs. In 9.35 : 1 CR form, the spark plugs were Champion N12Y and the gap until the end of 1981 was set at 30 thou. From 1982 onwards the gap increased to 35 thou.
So to question time. If your 3.5 litre engine is fitted with later cylinder heads or your lovely Rover has a nice new engine of increased capacity running under the bonnet, what spark plugs are you running, and what gap have you set them to? Have you experimented with different gaps and found any improvement with one setting over another? If you are now running an electronic ignition system or your engine is fuel injected, did you make a change in plug or gap?
In my case, my 4.6 runs Champion N9YC spark plugs, which I have set to 25 thou. I use Lumenition in a new Lucas 35D8 distributor that I purchased 18 years ago. The original Lucas 16C6 ignition coil manufactured in 1973 continues to provide outstanding service. Being a "Thor" engine, in original form my 4.6 would have been distibutor-less, powered by a Bosch Motronic engine management system and running platinum plugs.
I value and appreciate your thoughts.
Thanks in advance,
Ron.