which makes more power? slightly lean or slightly rich?

[SET THE STAGE]

title says it all

[usp4u]

lean. be careful.

[SET THE STAGE]

that's what i thought, thank you. i won't make it too lean. no more than it was when i got it at least (backfired and heated up like no other. it was awful)

[GPracer2500]

This begs the question: What or where, exactly, is the tipping point between rich and lean?

[SET THE STAGE]

i'm not saying i'm going to drop my pilot 4 steps down, move my needle clip to the first notch, and put in a size 55 main. i was just wondering.

[storms400ex]

lean is mean but be careful that you dont lean it to much

[GPracer2500]

Originally posted by SET THE STAGE
i'm not saying i'm going to drop my pilot 4 steps down, move my needle clip to the first notch, and put in a size 55 main. i was just wondering.

My question wasn't specifically directed at you or your jetting. I'm just making a general point about "rich" and "lean"....

What is rich? What is lean? What is smack dab between the two?


If you use a stoichiometric (http://en.wikipedia.org/wiki/Stoichiometry#Stoichiometric_air-fuel_ratios_of_common_fuels) ratio (about 14.7:1 for most gasolines) as the tipping point between rich and lean, then slightly rich produces best power in the vast majority of modern engines. This is why you'll often see a reference line at about 13.5:1 on a dyno sheet's a/f scale.

If one considers the tipping point between lean and rich as whatever air/fuel ratio yields the best power, then again, slightly rich is most likely the answer. You'll loose some power vs. your best power ratio but probably not as much as if you went to the lean side. This could go either way though depending on the engine.

Or, if one's tipping point between rich and lean isn't a stoich ratio, or a best power ratio, but rather some other less easily quantified point (like jetting richer and richer until it burbles and then back it down a size or two, or whatever one might do to establish "normal" jetting), then running leaner could yield best power.

This last scenario is more likely to actually apply in an air cooled and/or older design engine that can't operate near stoich for long without overheating. I believe this is where the old adage "lean is mean" comes from. Back before our very effective liquid cooling systems (not to mention modern head and piston design), "normal" jetting was actually pretty rich. It had to be to help keep the engine from overheating. If you took out fuel you'd pick up power. But you'd also add heat the engine might not be able to get rid of. That's not so much of a problem with most modern engines--particularly if they're liquid cooled.



See what I'm getting at? Rich jetting, lean jetting, "normal" jetting....they are all points on a scale. But the scale can be pinned--so to speak--to different things. The answer to your question changes depending on what you consider rich jetting, lean jetting, or "normal" jetting.

[BakerRacing40]

Originally posted by GPracer2500
This begs the question: What or where, exactly, is the tipping point between rich and lean?

right before you burn a hole in your piston!! lol

to lean vs to rich- one burns a piston up and the other will wash out your rings.. gotta be careful your not too lean or a big boom will happen lol

[honda400ex2003]

WOW Gp, very good post thanks for the info on the subject. i just filled a weeks worth of quote for something to learn a day. Unreal, the knowledge in that post. This is an interesting topic. Thanks steve

[oilguy]

lean makes more power,,, however you have to very cautious you can lead to hot cilynder temps and leads to detonaion and in the end boom you have a borken engine.

be carefull do your homeowrk,,, get a wide band and if somehow you can log do as well... do research,, get a tunner