Great product! I have purchased these fine wire plugs before!

O-360-A4M - Much smoother idle than the Champion REM40E plugs that I replaced. Noticeably smoother operation in cruise as well. All plugs measured between 1000 and 1500 ohms.

This is a provisional rating, subject to revision based on operational performance. In the meantime, however, these plugs seem *extremely* prone to cross-threading - with subsequent damage to the Helicoil threads of the cylinders spark plug hole - upon attempted installation. With one cylinder in particular, the top plug was almost impossible to start into the hole without cross-threading - yet two brand new Unison plugs could be engaged in the same hole with ease. Definitely YMMV - but do be especially careful when attempting to install these plugs. Operational evaluation to follow later. FWIIW....

engine sounds and runs great. IO-360A1B6 RV-8A

I will rate it 5 stars as to performance and long life as well as less susceptible to lead fouling. The 7/8 flat area where the deep socket slides over is not as deep as a Champion Spark Plug. In areas near baffling its really handy to use a box end wrench to remove the plug. And if you are stranded away from home with a fouled plug to remove and install with a box end wrench. If you are qualified and experienced with torque.

I have used iridium plugs in my 152 for nearly 30 years, it completely stopped the lead fouling that that particular engine is prone to. But when I got this old 172 recently and had trouble starting it, I was not sure what to try so I went to iridium plugs on it. The students can now start this thing on their own without my help, iridium plugs are magic! There was nothing wrong with the old plugs I took out, they showed signs of a rich running engine but other than that no problems, certainly not problems that would indicate a difficult to start engine. But iridium plugs have cleared up that problem once and for all. The cost is well worth it, Ive been using the same plugs for over a thousand hours in my 152 and they are still great, so it is a false economy to not buy iridium plugs because you think they are too expensive. If there were six stars, I would give them that rating LOL

Im slowly replacing my champion with these. they seem to be less prone to lead fouling. like the other reviewer said, time will tell. so far so good.

Smoother idle, lower CHT... Time will tell.

Following up on my provisional report of last November (2018), my first removal of the Tempest plugs was recently accomplished, after 34 flight hours of exceptionally smooth, trouble-free operation however, to my great surprise one of the removed plugs was missing its center iridium electrode. This plug was from the bottom position in the number 3 cylinder, and a flashlight inspection of the empty hole revealed the detached electrode, still sitting just above the point where the base of the plug had extended during operation. I immediately notified Tempest Aero Group, and that same day they shipped out eight new plugs, via overnight UPS. I returned the one with the missing electrode, as well as the one that had seemed particularly prone to cross-threading, but was advised to retain the other six as spares - a nice and appreciated touch. Amazingly enough, the missing electrode had caused *no* discernible changes in engine operation, including no difference in EGTs, CHTs and individual magneto drops during pre-flight run-ups - *or* during brief in-flight checks. My guess is that the gap between the remaining portion of the center electrode, and the unaffected side post, was so close to nominal specifications that there was no degradation in performance. The new set still was a bit more challenging to initially engage in the cylinder threads than the Champion iridium plugs had been - the latter occurring over 2,000 flight hours of routine removals and reinstallations - but a surgical touch here and there ultimately resulted in proper seating of all eight new plugs. (Tempest recommends use of its T-556 graphite-based anti-seize product, which I now have on order.)

The ones I replaced were less than 2 years old. They were fine and mag checks were a 75 drop. Champ 40E. I always leaned to Lycoming recommendations , but I seem to have lead problems more often than not. Most recent, did a short flight, shut down, restarted after about 10mins and thought the engine was gonna fall off. Did everything I could think of to clean it out with no tools on me and was able to return to home. That left me in a bad way especially if I had been else where. Lead was the problem. Long story short, I went to theses plugs. I have about an 1 1/2 on them. Mag drop was 50 and at cruise they are smooth, but so were the Champ. I feel it was a good investment for the long run, time will tell. The reason for 4 stars, very pricy. I bought the plug socket that fit theses plugs and took my time putting them in and all went well.

Better than standard plugs , but very expensive.

I replaced the bottom four plugs in my Lycoming O-360 and they were an immediate improvement over the older massive electrode plugs. The engine started easier, and there was no detectable fouling which was a frequent problem in the past after engine start. Its a hefty investment, so Ill wait to replace the top plugs, but worth it so far.