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[t_cel_t]

got my shit going on MS pretty good but i feel my target a/f ratios are way to rich.
is it safe to run like 15.5 or 16 while cruising at about 3100rpm and 50kpa absolute pressure?

i keep finding all kinds of conflicting opinions and i dont want to burn my shit up.

also is it safe to run high a/f at high rpms but little load? like under 70 or so kpa.

[Joseph Davis]

70 kPa and under (that's 8-10 in/Hg, right?) shoot for 14.7 for most cars.  A car always idles best at stoich (ASSUming all injectors flow equally) but you can lean things out in the cruise range for fuel efficiency *if* the car wants to operate smoothly there.  I was running 17:1 on my 12.5:1 D16 at part throttle, getting 41+ mpg in open loop.

If you pay close attention you'll notice a lean burn setup will operate at a higher manifold pressure.  At the end of the day you only get so much power from gasoline, and if you run a leaner ratio then the car will require "more air" in order to get sufficient gasoline to maintain a cruise.  I'm curious about tuning part throttle timing to suit, on a loading dyno, as I feel there is something to be gained there on a lean burn setup.

[lilpooh21186]

Agreed if you can source a load dyno, i Would run the car leaner just tune in your timing for optimum results.

[98vtec]

in part throttle, the leaner you go the more timing you will need to add so it doesnt misfire. 

Get to your cruising speed and slowly start to remove fuel til it misfires.  Add some timing and the misfire should work itself out.  If you feel uncomfortable running really lean mixtures then dont.  But 15.5-16 isnt too lean for most engines with a decent set of injectors.

I know i, on a particular trip, got up to 18:1 AFR without misfire on the h23vtec.  this was with RDX injectors at 55psi.  I dont remember how much timing i was running at part throttle back then, but i remember it being a good bit.

[t_cel_t]

yeah i aint paying for a dyno, this is done on the street. can i just find a big hill and drive up it like 50 times at different rpms?

[98vtec]

yeah i aint paying for a dyno, this is done on the street. can i just find a big hill and drive up it like 50 times at different rpms?

sure...

[Joseph Davis]

Why did you bother to answer, Blake?

[98vtec]

Why did you bother to answer, Blake?

i'm on lunch.


FUCK YOU

[HiProfile]

if you run a leaner ratio then the car will require "more air" in order to get sufficient gasoline to maintain a cruise.  I'm curious about tuning part throttle timing to suit, on a loading dyno, as I feel there is something to be gained there on a lean burn setup.

More throttle equates to less restriction. That's one benifit diesels have over gasoline engines. You also get a better mix with mroe air for a given amount of fuel.

One thing to note is a lean mixture tends to burn slower. Using the same timing as a stoimetric mix means you're loosing power for the same amount fuel. The insight will creep above 20:1 (IIRC actually 26:1) if you don't change the throttle angle. There's running lean, then there's runing motherfukin lean.


My low compression d16 runs ~15's for cruising and runs fine. It just needs more throttle. I havent' played with the timing, but I plan to very soon. I want to maximize drivablity since it's my summer driver.