Chim Spark Plug Gaps

[debaron]

Anyone have any thoughts on gapping out the plugs (NGK B7ECS) on a standard 4.0 Chim? I've seen the figures 0.8 mm / 35 - 40 thou for 'factory' but gapping out the plugs a bit more is said to help burn efficiency and power?


Ryan

[griffter]

Bigger gap needs a higher voltage. This reduces current and hence spark intensity (although the spark may be 'bigger'). Possibly also reduces spark duration. Also needs your ignition system to be in good condition (coil, amp, LT & HT wiring). You may notice an improvement in e.g. part throttle mpg, but not necessarily top end bhp when the ignition system is worked that much harder, or starting. No harm in trying though.

[GreenV8S]

The recommended gap is 0.9mm / 35 thou. If you have an HT system capable of generating a higher voltage spark you could increase the gap accordingly. The benefits would be minimal unless you are having trouble getting the charge to light. If you have a standard HT setup and try to run at a wider gap you will get a weaker spark and maybe no spark at all sometimes, most likely at high revs/high load when it is hardest to get a spark. If you are having problems which you suspect may be caused by a weak spark then after fixing any external hardware problems you should be looking at reducing the gap not increasing it.

[dwgriffith]

Unless you fit standard projected nose plugs such as BP6ES you will have trouble getting a wider gap than 0.8 (as supplied and recommended by NGK) or at most 0.9 : the shrouded tip design of the B7ECS has a very short earth electrode. My Griff is running on BP6ES with the gap set to 1.1mm, the only advantage to the wider gap is that it appears to make the idle a little smoother with the piper 285 cam fitted. After I got the car I fitted the "correct" B7ECS plugs and started to get running issues within a couple of weeks, slow speed shunting, power loss when hot etc etc. Substituted the AFM, TPS, ECU, ignition amp, coil, distributor, leads, changed the timing all with no real effect. The local track car guy told me to put some BP6ES back in gapped almost as wide as I had found the original one's fitted - problem gone. His opinion was that unless the car was regularly driven hard the shrouded plugs choke up.The car had been tornado chipped and set-up by Mark Adams on a set of rollers, I guess he knew what he was doing!!! Other advantage of using BP6ES is that they cost less than £10 for a set of 8.