so when you say start with the .045, does that mean that that's what they are already gapped at?

Thanks for the advice on the plug wires and coil pack, will have to look into it....

Cheers,
Elie

 

Elie,

I do not know what they come gapped with (though probably about .040")and there may be some variation due to shipping and handling. I would get a feeler gauge and measure the gaps to check that they are within the .04-045 range. Any car parts shop can fix you up with that and even demonstrate how to do it - perhaps even do it for you... The center electrode is somewhat delicate so do be careful.

Checking plug gaps and distributor points used to be routine in car maintenance but the plugs and electronics have mostly done away with this for most cars. I have similar iridium plugs in my Lexus and they have gone over 50k miles without any issues and still look quite new. So it may be that I was pushing the limits with the larger gap. There are other interesting theories as you saw previously too.

But enjoy the experience, it is part of the joy of owning a Mini in my opinion!

 

oh i see...ok thanks for that, will get them checked out.

I love tinkering around with my car. It's half a year old, and have the warranty, but i've already modded it more than most :D

 

Denso only claims 30,000 miles for their 0.4mm iridium plugs.

The MINI appears to fire 1 and 2 from ground to center, and 3 and 4 from center to ground, so there is no way to avoid the uneven wear with iridiums though they can be rotated (swap the left two with the right) every 5-10k miles. Uneven gaps are undesirable because a larger gap has a similar effect to advancing the timing for that one cylinder (lights off the charge quicker), leading to a rough idle. And pinging for just the one cylinder will prompt the computer to retard all of the cylinders until the rattling goes away, leading to less power output than if everything were matched.

Autolite iridium and the 0.7mm Denso iridium plugs (those are the ones that claim to do 100k miles) have a platinum pad on the side electrode, but are not available in as many heat ranges, and the wear will still not be even because iridium and platinum alloys wear at different rates.

Most DIS with waste spark use double platinums as OEM to produce even wear over 100k miles. You can modify the ground electrode so that only the platinum pad is shrouding the spark like so (right plug is stock Autolite double platinum):



I would probably not use them for a twincharged or racecar (because the platinum discs are known to fall off with serious abuse) but for normal use they do work great for 100k miles even with mods and a stock heat range. I'd use at most one heat range colder with platinum plugs for a street driven car because our cars run so rich. You really just can't get away with running two heat ranges colder like you can with the extremely fine wire 0.4mm Denso iridiums.

 

"Looking at the graphs, the curve was still breaking up in the 6000- to 7000-rpm range. evosport installied a fresh set of Denso Iridium spark plugs, which did a surprising amount of good. The jagged output was smoothed and horsepower rose to 191 at 7000 rpm. From 6900 to 7100, the car gained 4 to 8 hp, with a peak maximum increase of 9.4 hp at 7000 rpm. Although the surprisingly high peak gain corresponds to a small dip in the previous run, these plugs proved that the stock ones weren't providing optimum performance.W"

This is a quote from European Car Magazines Project mini.

 

Nice post. Excellent info.

Edit: removed blah blah blah misread the post stuff

 

I read through these posts and maybe I missed it but, has anyone mentioned "indexing" their plugs? I realize that this topic would be moot with a four prong plug, but last I read about this being done, it was done to fine tune the firing of the plugs inside the cylinder by locating each spark plug so that it is in the optimum position as it fires within the cylinder causing the most efficient burn. Kinda makes sense...but does it really have any effect on overall engine performance?

 

The theory is that combustion does not really get underway quickly until the flame ball reaches ~0.1" and this ignition lag of establishing a flame front and growing the flame diameter to 0.1" is considerably longer than the ignition voltage rise time for the coil. For example, if it takes 1 millisecond for the ball of flame to grow to 0.1" after the spark (which itself may take 1-2 milliseconds to light things off), that alone is 12° of crank rotation at 2000rpm and 24° at 4000. And that is the reason engines need more advance as RPM goes up (think of "mechanical" advance in a distributor, versus the "vacuum" advance needed because things burn more slowly at part throttle).

No problem right? You could just advance the timing to make up for this delay, except that small variations (in gap, compression, local mixture, etc) make this delay highly inconsistent. Big gaps should reduce this variability.

If you subscribe to this theory, then a gap closer to 0.100" would get the flame front going much more quickly, and would greatly outweigh the change in ignition voltage rise time for the coil (which at least is consistently longer). Less variation and faster burn.

Of course 0.100" gaps wouldn't actually work at high rpm unless we ran monstrously high-voltage ignition boxes, and then the timing would always be far too advanced so different software that takes this into account would be needed. Also the plugs would probably be burnt to little nubs rather quickly. I'm surprised that more people here aren't running an MSD DIS-2 box or something (have only heard of John Petrich trying it).

The OEM plugs are NGK BKR6EQUPK with four ground electrodes that shield the spark in every direction but one. Conceivably, projected-nose plugs with only one ground electrode and that move the spark nearer the center of the combustion chamber, could have a similar effect of "advancing" the timing by reducing the flame propagation delay. That and the ability to run a larger gap due to the pointy tip may be why the Densos seem to work well.

And Rich B, indexing should also help to reduce variations in ignition lag to allow all cylinders to be timed optimally (not to mention produce a smoother idle). The MINI's plugs are angled toward the exhaust valves, so it would probably be best to index the gap downwards toward the piston (single electrode facing exhaust valves and combustion chamber roof).

 

Gotcha.
You're actually talking about flame propagation and I was talking about spark initiation. 2 different things aren't they?
After a re-read I understand your post better.

 

Yep but remember this is all rather theoretical and things look different from here in the Ivory Tower.

From a more practical viewpoint, Petrich did point out he tried gaps up to 0.080" with the MSD DIS-2 and was unable to overcome a high rpm miss (General Motors did specify factory gaps of 0.080" in the 1970s so it isn't unreasonably large, but that was only for smogger motors that didn't rev over 4000rpm). It is possible that even a more powerful box than the MSD would not solve this problem because of the small 14mm shell diameter of our plugs. See, only the tip of the porcelain is burned clean and the rest gets filled with conductive soot. If you make it too hard to jump the gap to the side electrode, it can instead spark down the side of the porcelain which may result in some percentage of misses.

For this reason, I wouldn't recommend using a gap greater than 0.65" even with an ignition box. And I'd rather use an ignition box than some super-fine wire plugs to make up for a marginal stock ignition system. If you're willing to replace plugs every 10k miles anyway, plain $1 Champion copper-core plugs sound like winners. And if not, double platinums are what I'd use.

Since we are discussing controversial ignition topics anyway, I'll point out that Nology wires convert a long, low current inductive spark to a very high current (hotter), but very short duration capacitive discharge (CD) spark. This passive conversion is not 100% efficient (hence the grounding wires and recommendation for using Beru Silver non-resistor plugs) so less spark energy is delivered to the plug, and the rise time is slightly prolonged. Nevertheless the hotter spark may indeed show a power increase at steady-state on a dyno, from the decreased variability in flame propagation allowing more advance (for the previously mentioned flame kernel/nucleus reason). However the extremely short duration leads to miss problems if the local mixture around the plug is not perfect at the moment it fires. The mixture frequently isn't as homogenous as you'd expect, because liquid gasoline is sprayed in just milliseconds before the plug fires. The problem is probably most acute when conditions are changing rapidly, and most acceleration-type dyno results I've seen do show a net power loss. But they also might not be technically lying in their ads!

A CD ignition box like the MSD gets around such problems by firing multiple hot sparks over 20° of engine rotation. Since energy is added, more total spark power is provided, and the ignition rise time is much faster because the coil primary is fed 480v rather than 12v plus it is not dependent on the OEM inductive spark. Unlike...

The Plasma Booster just chops up the long inductive spark into a series of diminishing CD sparks. It cannot produce the really big spark the Nology wires do (since the energy must be divided up into a series of sparks) and cannot make a series of really big sparks like the MSD because it is a passive device. The only time I could see such a pattern being useful is if the plugs are slightly fouled, since a CD spark will fire under those conditions while the slow coil voltage rise time of the inductive spark would allow too much time for voltage to be bled off. The moral? Don't use plugs that are too cold and save your money for an ignition box rather than gimmicks.

Actually, you could even wire up two conventional boxes like the 6AL if you have them lying around or can get them for cheap.

This is just my opinion, and I now retreat to the Ivory Tower with my flameproof suit.

 

Niiiiice

I ran a 6AL years ago and loved it. Along with .060" gap it was a good setup for a V8. Helped with the plug fouling you get with a pretty big cam on a street driven motor. Pre-elctronics

I'll have to bug John about that DIS-2 unit. I looked good but I like real world experience on something with a price tag like that.
Won't be trying any .080" gaps though

 

Thanks! BTW I see my car's coil has flat terminals so the correct MSD coilpack for that DIS-2 would be 8239 and the "cut no factory wires" harness is 8883.

Each coil actually drives two plugs in series, but it's probably not as bad as a 0.130" gap (0.065" x 2) because the waste spark is firing through the exhaust stroke on one cylinder.

I replaced my 20k mile stock plugs with the modified ones from the picture and get the DSC overboost light again I'm not sure why the worn plugs affected the boost but they sure did (I had thought the belt was slipping). I indexed them using crush washers from four different brands of plugs, because the copper indexing washers I have aren't retained on the plug and fishing them out later would have been a pain. See, having a large pile of junk parts does pay off!

 

I may have finally convinced my wife that statement may have some value.