Tempest spark plug question

[dcrogers11]

I'm 100 miles away from my 64 m20C and ordering some Tempest fine wires.  Can someone tell me which part # I need to order?  

Thanks

[jetdriven]

Same as my J, either URHM38S or UREM38S.  the first is 3/4-20 threads and the second is 5/8-24.  My J took the UREM38s. 

[dcrogers11]

JetDriven, Thanks.  How many hours on your plugs and what differences have you seen after going to the fine wires?  Don

[jetdriven]

We just got them. Suposedly they are worth 2000 hours.   We went from being able to run just about peak before roughness to 90-100 LOP.  SOP cruise now is WOT, 10-40 LOP and around 8.5 GPH ~65% power and about 145 knots true.  It also idles smoother without popping like it used to.   We had 1200 hours on the cheap champion massives in there from before. Id say its worth .2-.4 GPH for the same TAS and the ability to run as lean as you wish.

[jetdriven]

I just remembered you have a C. Limited ability to use LOP.  But it does run smoother at idle and near peak. I would think you can go leaner before roughnes. They do last longer, so the cost is more up front and less later.

[Shadrach]

I've been thinking about this Jet, and I would never dispute the superiority of fine wires. However, I do not think that your new found leaning ability was due entirely to fine wires.  I suspect that if you'd installed brand new, properly gapped "massives", that you'd have seen a significant improvement as well.  My bird has massives, and like yours, will go to ~100LOP.  Fuel air ratios are balanced or they're not...  A high power LOP combustion event is probably the most strenuous test of an ignition system, if the plugs are marginal, that's where it will show up.

The fine wires plugs have a larger gap,  a more consistent and exposed spark (I've also heard the plug runs a bit hotter). I'm sure almost any engine's operating range would be increased by using them, but I doubt these advantages alone took you from "roughness at peak" all the way to "roughness at 100LOP". No matter how much of the improvement they're responsible for, I am glad they're working well for you.

It will be interesting to see if the more "conventional" nickel plated copper electrodes of the Tempest fine wire plugs prove to be as durable and long lasting as the iridium in the Champion fine wire electrodes...

[jetdriven]

Thanks for the input Shadrach.   I never had new plugs and this is our first plane so thats good to know. Ours were shot. Also, one good benefit is no carbon fouling, the old ones required a runup and burnoff to pass the mag check.  By design the spark is more exposed.  I think the Tempests are platinum electrodes.  I'm not sure how that compares to iridium, but they are cheaper.

[Shadrach]

If they are in fact platinum, then they should perform well. I could find nothing about the construction material on the website. 

Iridium and platinum are both "platinoids" and have similar characteristics. Denso (auto industry) touts the fact that iridium is significantly harder and has a much higher melting point. However, it is hard to separate the performance "wheat" from the marketing "chaff". If you already have a 150% margin above what you need, another 200% is marketing noise...

My old Lexus GS400 went 145,000 miles on a single set of Denso Iridium plugs and they looked OK when I changed them out for some standard Bosch plugs that my dad had lying around. Just crossed 190K and still runs like a top, so if I keep it for another 100K, I'll report back... ;-)

[jetdriven]

Actually they may be iridium as well.  For all practical purposes, platinum and iridium plugs dont wear at all. I had a 93 Trans Am once, it had the 8$ "platinum tipped" spark plugs in it.  60K miles, the (welded on) platinum buttons burned off and the gap was about 3x the limit.  I think these are plated or solid platinum components.

[Jerry 5TJ]

I use the conventional "massive" electrode plugs in the "C."  I change them at every annual at the least.  There's a company in Van Nuys CA who refurbish the old plugs for $3.75 each. They clean them up thouroughly, install a new washer, and regap them to the desired spacing.  They look like new when they come back.