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MG MGB Technical - IRIDIUM PLUGS
| Has anyone used iridium spark plugs in their MGB? I have used Champion , NGK and Bosch. So far the best performance I 've gotten was from NGK. Cheers Gary 79 MGB |
| gary hansen |
| Like platinum I doubt you would see much difference, although some have claimed running problems with platinum, and apparently John Twist has said don't use them. |
| Paul Hunt |
| Hmmm. Curiosity has me. Other than the expense, what could be the reason? Cheers Gary 79 MGB |
| gary hansen |
| Moss also told me not to use them with their supercharger system. Apparently, there were some issues with pre-ignition problems that could damage your pistons. RAY |
| rjm RAY |
| The reason for fitting them? 60-100k life, apparently. |
| Paul Hunt |
| The problem for us is the high mileages are with 'perfect' fuel and ignition control with feedback loop on modern cars. Our olde worlde cars have a harsher environment and 'kill' plugs earlier. We tend to prefer basic NGK BP plugs and change as needed/clean plugs. SCs run better with narrow plug gaps whatever the plugs used. Peter |
| Peter Burgess Tuning |
| Some of the new Fords use iridium here, they are on 120000kl service interval but rarely make it, usually 80000 pulls them up. AND if they do go the distance they are usually frozen in About six times the price of a normal plug here so the option of new normal plugs at say every 20000 is a lot better option They have a use on late model cars where they run so lean and hot and would gobble up normal plugs, specially on cars like some injected v6 cars that you have to pull the manifold off to get at the plugs at great expense for a plug change-For these cars I can see the advantage of long life plugs to save the big dismantle job I tried a set of those tripple earth prong plugs in my old hillclimber once and they just wouldn't go I decided the coil simply wasn't up to the job of driving them compared with later model coilpacks ?????? willy Also just remembered the Fords run 1.5mm plug gap on them to get a bigger spark which promotes a better idle with their very lean mixture The LPG version of the same car runs .8mm pluggap |
| William Revit |
| "I tried a set of those tripple earth prong plugs" I've had a set of Bosch 4-point in my roadster for 33k now and they perform as well as ever and show no wear. Mind you, I have run a set of standard NGK in the V8 for 25k before I started getting any issues ... |
| Paul Hunt |
| Paul In all fairness I haven't tried multi earth plugs in a road going MG but in my racer they weren't much chop as stated above. They would start to play up a bit at about5500 revs under full load and wouldn't rev out at all. Where I normally went to just over 7grand they had pulled the pin at just over 6 BUT as mentioned I suspect the coil wasn't up to the job.and probably not a fault of the actual plugs. With a modern high output coil I suspect they would have been fine.-don't know. I believe they were originally designed fo cars with coil packs that fired two plugs at once,-one being positive powered and the other negative Plugs up till then had been designed to spark from the centre out to the earth tang but on the double firing coil packs one plug fires this way but the other fires from earth back to the centre, hence the need for longer lasting earth posts and the introdution of plugs with two,three,four A bit like some racing plugs that just have a centre post in a reduced diameter base to get a similar result I guess cheers willy |
| William Revit |
| On a multi electrode plug the spark can only jump the shortest gap till it wears and another one becomes the shortest etc. A bit like the horrendous Splitfire plugs. Peter |
| Peter Burgess Tuning |
| The Lucas Fault Diagnosis Manual states "the standard ignition system will quite adequately meet the requirements of a six-cylinder engine up to about 8000 rpm". It's also perfectly adequate for the V8, which has half the coil recharge time of the 4-cylinder, mine revs into the red all to easily if I don't watch it. That equates to getting on for 10500rpm on a 4-cylinder. This is one of my 30k+ 4-points. No sign of erosion that I can see - remember you can't gap them like a standard plug - compared to the Bosch images http://rb-aa.bosch.com/aa-uk/en/sparkplugs/start/super4.htm 
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| Paul Hunt |
| Lucas Fault Diagnosis manual---- that would be a very large book I would imagine Paul The key is as you say with plug gaps probably I would imagine I put them in straight out of the pack just for a try so the gap would probably have been 30 thou or something bigger Thinking back, with the help of my little record book, the plug gap that gave the best result on my car was .022" Any more than that and it would crack up under high rev, high load conditions As I said before a better coil probably would have made a difference but me being a sucker for getting the best out of what there is there already, wouldn't allow that It'd be too easy just to put a coil on, there must be a harder way to fix it lol willy |
| William Revit |
| Gents, a quick question about these iridium spark plugs - can and should the gap be adjusted to the recommended size for the different types of MGB engine. i.e. 25 or 35 thou ? Thanks Andy |
| Andy Robinson |
| Andy In a word yes -if it is a single earth tang plug -- BUT Be very carefull and don't lever against the centre post while doing it, I don't know what brand you are buying but most here have the allocated plug gap as the last part of their part no. - i.e. --------11 or-------15 being 1.1mm or1.5mm -I would suggest that you purchase plugs with a gap close to what you need to reduce the need for too much bending and helping to keep the earth tang at rightangles to the centre post willy MGB -4cyl==.028"==normal road spec |
| William Revit |
| OE plug gap for MGBs is 24-26 thou for the 25D4 distributor, and 35 thou for the 45D4 distributor. |
| Paul Hunt |
| Paul Ok- but I have found that the combination of projected core plugs, like N9Y or N9YC and .028" is a good combo for road use on all 4cyl MGB regardless of which dizzy I have no real proof but it's what works and it has always been a good reliable spec. willy |
| William Revit |
| Peter has it right (as usual). We went through every type of plug available when running an MGA in a stock class where any small improvement was important. I never found anything better than an NGK BP6ES on a pushrod engine. On the improved engines (12:1 and up) you needed warm up plugs if you used Champions, and had to swap out for race plugs. With NGKs the tolerances were broader and the engines would start, warm up, and race all on the same plugs (usually B10EVX) |
| Bill Spohn |
| I just changed the spark plugs on my 1977 MGB. The manual says to gap them at .035". But, I'm not sure that's correct, because I have an electronic ignition. I set them at .025". The old plugs that I removed were gapped a little over .035", and the car ran well, so maybe I should use .035", too. Or, set it as Paul suggests at .028"? Thoughts? Randy 1977 MGB, with twin HIF4's and Allison electronic ignition. |
| Randall Olson |
| The electronic ignition setting calls for a gap of .035". The electronic system can handle the larger gap than a point based system. The custom distributor, on my '67 supercharged B, calls for a .055" gap. RAY |
| rjm RAY |
| Thanks. I set them at .035". Randy |
| Randall Olson |
| Even the 45D4 points ignition gapped them at .035", nothing to do with electronics. The gap could go quite a bit bigger than that and still fire, but that results in higher HT voltages, which can break down other ignition components. It's that which limits the gap. |
| Paul Hunt |
| Last year I installed NGK BPR6EIX Iridium IX plugs and noted, albeit subjectively, an immediate improvement in performance, as if it had been doped with the MG equivalent of red blood cells. My standard plug from that day forward. |
| Gary Kinslow '69B roadster Pale Primrose |
| That would be the lighter wallet :o) |
| Paul Hunt |
This thread was discussed between 16/03/2015 and 10/04/2015
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