What spark plugs are you using 38's or 40's?

I think the 38's are recommended for lycoming, some are using 40's a hotter plug. Are 40's better? I had 38's on my o-360 and got sick of lead fouling plugs.:evil: Some locations were repeat offenders. Any issue running 40's in all locations? Run better, harder on engine?

Cal if your talking about your experimental, aren't you using electronic ignition ? If so NGK BR8ES = no lead

I run REM-37BY's and lead is never an issue. Minor bits to pick out of the insulator pocket every year or so.. have never had a fouled plug.

Iflylower said:

I think the 38's are recommended for lycoming, some are using 40's a hotter plug. Are 40's better? I had 38's on my o-360 and got sick of lead fouling plugs.:evil: Some locations were repeat offenders. Any issue running 40's in all locations? Run better, harder on engine?

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I'm glad you brought this up. I get some fouling now and then on mine (can't offhand remember which ones they are but they're not 40's) even though I always lean in out. At every annual there's quite a bit of lead to clean, especially out of the bottom plugs. I've read that you can use hotter plugs on the bottom, but then what happens when you rotate them? I too was thinking of switching to just running the 40's in all locations. My plugs have 500 hours on them and it may be time to switch them out at the next annual.

I run Rem 38s iridium plugs on the bottom, and Rem 40e plugs in the top. the 38's dont lead up nearly as bad, and last a lot longer. I clean my bottom plugs every 20 hours, and always, find lead.

Tim said:

Cal if your talking about your experimental, aren't you using electronic ignition ? If so NGK BR8ES = no lead

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Yes, im experimental, can do anything. I made my decision two years ago when overhauling the engine. Two years ago there was a lot of talk about the end of 100LL. I wanted a plane that would not need a runway, start without a battery, and would burn any fuel. I stayed with 8.5 pistons and just overhauled /yellow tagged the bendixes I have. Just trying to get a plane in the air. I may mess with Pmags at a later date after certification.

I'm curious if 40's are a good fit for all around since I'm buying plugs this week. I've heard 40's run cooler cylinders since they burn all the fuel better/faster. I don't know. Obvious doesn't always work. Doesn't octane help fuel burn slower, thus a more even power stroke? I figure hotter has to start & idle better since mags are week at start and idle RPM. But, maybe there's no noticeable difference in the two plug heat ratings? I would suspect hotter would help in cruise too, thus I defer to y'all in case you know.

I hear the fine wires are good and I've been back ordered on the new tempest $50 fine wires for a year. Now I need plugs.

My experience is the cool cylinder on the bottoms lead up the worst. I used to carry an extra plug and use it occasionally when mag check couldn't burn through a fouled/ shorted plug.

Lastly, I don't plan much auto fuel use, but want the option if I need it.

FWIW I run Unison UREM38E (I bought a bunch before they sold out to Champion) and they stay clean with aggressive leaning during taxi.

I just bought 96 unison UREM 38E plugs from Don George aircraft for 9.95 each brand new in factory packing... Round engines go through plugs fast. my c-90 I run Unison Urem38S and Champion Urem38S on my 0320,,,, love the fine wires for long life and no lead fouling.

Dave

I'm experimental run Denso Racing plugs 5703 fine wire iridium mike o

irishfield said:

I run REM-37BY's and lead is never an issue. Minor bits to pick out of the insulator pocket every year or so.. have never had a fouled plug.

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REM-37BYs are 'extended tip' and really are the ticket. They don't foul, burn cleaner being more out in the flame front, and one reputable engine builder told me he actually measured a small power increase on the dyno. They are the same price the standard plugs and I don't know why they aren't more widely used. I have personal experience with them on two aircraft totalling 700 hrs and would recommend them over the standard plugs.