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Old 01-25-2015, 01:33 AM
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BarelyAWake BarelyAWake is offline
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Join Date: Jul 2009
Location: Maine
Posts: 7,212
Default Re: Small Engines cold air and Performace.

Originally Posted by Davezilla View Post
Yup... just look up cylinder head temp gauge on ebay... they run off a small sensor that goes under the spark plug like a washer or better yet, like a ground wire... These are fairly cheap but most of them need a 12 volt source to work.

I'm not totally sold on the spark plug heat range theory for cold weather since the air is more dense, thus leaning the fuel mixture, the last thing ya wanna do in a lean condition is put in a hotter plug.

But really, even with all the temperature swings in the wintertime in some places, do you see everyone changing their plugs and rejetting for the cold then changing back for the warm weather in their cars, trucks, buses, motorcycles etc? Nope... everyone just drives them. Some people block off part of their radiators in the winter, but that's about as far as they go with that.

You *can* do all that for the weather extremes, but it's typically not necessary unless you're just looking for maximum performance all the time, or on race day.

Jus' a FYI - the 'TTO' temp gauges (CHT/plug) & similar (ebay/clones) often have a self-contained battery (hearing-aid/watch type):

I agree w/ya Davezilla. Insofar as winter rejetting & plug range swapouts... well... the American south west gets chilly n'all & folks can ofc do whatever they wish in the quest for HP - but I gotta mention it does get a bit cool up here too from time to time. The winter & summer extremes in Maine are no more then between -20F & 100F usually & granted, that t'aint near as much as some places but to my knowledge no one around these parts mucks about with plug ranges & rejetting in their 'smokers two or four due to the temperature change (including dirtbikes, quads, chainsaws & other year-round uses).

Yea, air density does have an effect & it can even be pronounced enough to "feel" a difference on a cool day with our engines - but consider for a moment small aircraft which routinely experience extreme variations in air density and temperature as they change altitude. At a set RPM in combination with both the EGT and CHT readings (exhaust & head temps) a manual mix control is utilized to maintain the proper fuel/air ratio as they ascend or descend... but no one worries the heat range of their plugs as they do so. This includes the not "computer-controlled" ultralight & sport/experimental classes which often fly two strokes as well as the fours, as I did with a Rotax 440 (two stroke) in a Quicksilver MX (in both winter & summer BTW, same range plugs).

So... you can "sweat" such details if ya wanna but honestly you'll be just fine picking a range/ratio that seems good for the engine & sticking with it no matter the season *shrug*

...& no, I don't bother with engine shrouds or covers either - them lil smokers ain't sufferin' near as much as me in the chilly lol

Last edited by BarelyAWake; 01-25-2015 at 01:43 AM.
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