I have never gotten too brave always keeping my AFR's in the low 15 area and egt's ~ 1350. Leaner mixture requires more timing correct?

The reason new civics get such good gas mileage is their very lean fuel mixtures. In excess of 20:1. They can get to this point without breaking up because they run pretty advanced ignition at cruising speeds. I had a chance to test this out with my stock h22.

say at 3500 rpm, i was running 34* table timing, unknown actual. The engine would breakup in the high 15's and hesitate. I took what marshall said and added a good bit of advance and it stopped hesitating at those AFR's. I wouldnt put this theory to test anywhere but cruising and light loads, like getting up to speed at a normal pace. From what i got out of it, as long as the engine does not detonate, the higher ignition you run the leaner you can go. take it with a grain of salt but it worked for me. Instead of getting 280-290 miles to the tank, i got around 340-350.

I've also noticed that i get better gas mileage when i dont run closed loop and tune each cell to the proper target afr.

Quote, originally posted by Combustion Contraption »

i am going to beat you up if i ever meet you

Quote, originally posted by Combustion Contraption »

i am going to beat you up if i ever meet you

yes 98vtec has it right, but this would be in terms of a stock narrow band sensor. If you use a wideband sensor to and tune fuel and compensations such as IAT and ECT and many others then there is no need for enabling the stock narrow band.

First of all, it's WAY too general to say that Civics run 20:1, because the ONLY two civic motors that do that are the VX and HX. The VX being the D15Z1 and the HX being the D16Y5. These motors were specially designed to be able to run that lean during light loads. Every other Honda motor will tolerate maybe 16:1 under very light load, and that's still pretty impressive.

Also, you can't assume that a leaner mixture always gives you better economy. It does so only under certain conditions, namely cruise. But if you run lean when you're trying to accelerate, even if it's just a slight incline, you use more throttle and you waste fuel. So it's better to grade your load. Up a not so steep hill might start at 14.7. Slight incline but still accelerating will be about 15.5.

So go with this. 14.7 Idle, and get it to Idle as low as you can and still be stable, ie 750 RPM or so. If your motor has the stock cam then shoot for stock spec (Idle tuning is a whole book on it's own). Mild acceleration shoot for 15.5. (Heavier than that acceleration shoot for 14.5 blended down to about 13.2 for heavy acceleration.) From there down go to 16, try going leaner and see if you get a misfire. And like you said, try playing with the timing.

If it's a stock motor, you can run 13.2 under heavy load and RPM and be careful with timing. If it's modified, run maybe 12.5. High load RPM territory is for experienced tuners though.

After your fuel is optimized you can squeeze a little bit more out with timing, but if timing is already close, it really isn't a justified expense. You do exactly as someone previously stated and tune for MBT on a load bearing dyno.

Right now, I get 25mpg with or without the O2 sensor if I drive it the way I like to. That includes several trips a day to 9 grand and about 20 miles total of driving. If I do not rev the piss out of it and stay off the cam for the most part I have seen 26mpg. This is probably 50/50 city highway driving.

Quote, originally posted by Combustion Contraption »

i am going to beat you up if i ever meet you

Quote, originally posted by Combustion Contraption »

i am going to beat you up if i ever meet you

I have not. Do you think that would help?

i would try interpolating 1750 RPM - 26" to 14" - 1250 RPM. You've made your ignition idle resolution a little higher into the RPM range than it needs to be.

what is your compression?

can you email me your bin? I'll make the changes that i would make and send it back to you. Doesnt mean what i change will fix the issue, but second opinions are always nice

blakesvtec-at-yahoo.com

Quote, originally posted by Combustion Contraption »

i am going to beat you up if i ever meet you

Emailed you a copy of the bin. Check it out if you want. Compression is ~11.2:1. Did 176whp with the exhaust and all, 190whp without the exhaust on the dyno. Not really dyno tuned, but street tuned at this point.

Quote, originally posted by Combustion Contraption »

i am going to beat you up if i ever meet you

For real. Mine goes 0, 500, 900. Idles like glass too.

Matt, you should know better. He is not adding timing to make more power but to start the ignition event earlier so that complete combustion can occur. Combustion occurs most efficiently(ie read at the minimal timing) at 12-13:1 AFR. Anything richer or leaner requires timing advance as the burn takes longer.

Typically the trick is to run lean AFRs with advanced timing. How lean? Well, that is where it gets tricky. If you run too lean, your engine will lose enough power so that you are increasing loading on the engine to get to the same speed thus making fuel economy go down. Typically in the 15's works pretty well.

runs perfect, did 15.0's @ 90

Quote, originally posted by Jschnatter »

civic killer is god

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Over the past years, I have consistently seen better than stock gas mileage from approximately 10% leaner than stoich mixtures below 750mbar load coupled with 2-5 degrees extra timing advance.

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