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Discussion Starter · #1 ·
When it comes to fuel, I've read that the OEM system is set up to run very rich mixtures at high rpm as a means of cooling the cylinders and also cooler combustion to avoid detonation. These mixtures can be as rich as 10:1 on 87 octane and not neccessarily on high compression engines either. My question is, on a mildly modified H22A4 running 92 octane, what is the leanest I can go without any worry of detonation?
 

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It really depends on what you have done to the motor and tuning. For example, the civic hx can run as lean as 18-19:1 because it is a lean burn motor. Its going to be a combination of fuel selection, compression ratio. rpms, ignition timing... etc.. etc...

However generally speaking, if you are @ WOT, then you should be running rich to give the engine the amount of fuel that it needs. I believe that 12:1 is generally the a/f ratio to shoot for on a N/A motor. I don't think that anything runs as lean as 10:1 because that would most likely hurt power production and just be a waste of fuel.
 

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sorry for this newbie question. is it the leaner u go, the more power u make? but at the same time u dont wanna too lean bc ull detonate correct?

that might explain my huge jump on my dyno, besides the different gear. the 178 3rd gear run had 13.28 ratio, and the 167 4th gear run had 12.58 ratio
 

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Discussion Starter · #6 ·
Right. The leaner the mixture the hotter it burns, and of course the more heat there is the more pressure there is on the piston during combustion. But the hotter you go the more likely detonation is, and the richer you go the cooler it burns and also you release more emissions from the burned mixture including fuel that didn't even burn depending on how rich you go. The stoichiometric (I hope I spelled that right) ratio for air and gasoline as everyone knows is 14.7:1 by weight. Whether you're leaning or enriching it's best to never lead too far from this ratio or you could end up with big problems. :)
 

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14:7 is only good for part throttle/low loads. You need to do whatever it takes to get to 13:1 - 13:3 at WOT for NA motors and 11:8 - 12:1 on boost.

idle can sit right about 15:1-15:5.
 
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