Lean burn-thoughts, theorys, and discussion
 

Ok guys I have a 1999 honda civic that has a programable engine managment system(crome). I have been messing around with lean burn and seeing what I can fiddle with to up the mpg. the main thing i am wondering about it is how lean is too lean.. I'm sure there is some point where leaning requires more manifold pressure and thus more fuel to keep accelerating I just wonder if its in the realm of afrs we can acheive?

I have a non-vtec y7 engine and with the manifold pressure around 10-12 inches is around 18-1. Any higher manifold pressures (14"-18") where i normally cruise are leaner than that, guessing 22ish to 1 with no indication of breaking up.. anyone know any gauge type widebands that will read higher than 18 or 20 to one? Also the factory timing in those areas of the tune are around 38-42*. In my tune i'm running anywhere from 48-50 degrees of timing.

I'm considering trying out a set of vx spark plugs(one stage hotter than whats in it now, stock) and leaning farther, but I currently don't have an instaneous mpg gauge so it makes fine tuning difficult to have to drive a few hundered miles to see what changes i've made.. I just started keeping a log on here, but over the past few months of testing i've been getting anywhere from 35mpg driving to work and home(5.5 miles 35-45 mph 5 stop signs) to a few tanks in the mid 60's doing highway trips.

anyone have any ideas or thoughts or concerns about lean burn lets hear what you think!

what I would be worried/concerned about is burning the valves with such lean mixtures and high advance. running even hotter plugs only makes it worse. Not sure there are wide bands that lean on market (other than emission type sensors ).
I would check what your exhaust gas temps are , seeing if its getting much higher than stock and seeing what plugs look like before leaning further or running hotter plugs .

The Insight goes to 25:1, so its O2 sensor must also.

that might be but most aftermarket wideband A/F meters only go to 18/1 . The LM-2 says it can go to 22/1 .

I just tested out 25:1 at < 20% throttle, and around 16% MAP load. on a d16y8. NO BUENO. Ended up melting the electrodes on the plugs. Decided it would be safer to further mod the driver, and not risk melting pistons. I would say 18:1 is about as far as you would want to take the car under light loads.

Try a set of NGK ZFR4F-11 plugs. That's what's spec'd for the '97 Civic HX, which uses lean burn. It's not the same plug as the other Civics of that vintage. Your '99 should be the same generation as the '97.

By the same token, you might try using the same primary wide band oxy sensor as that car. A friend has an '04 HX and he says he found the wide band oxy sensor for about $150ish.

If you are burning components under light loads you are not lean enough. If you watch EGT as you get leaner it will go up to peak (which is where you will start burning valves/pistons/other things) then as you go leaner (50*F at least) temps will drop off. The throttle will have to be opened more to get the same power but you won't have to be sucking air past a throttle plate, which is where a fair bit of efficiency can be gained.

So what your saying is you have to jump to a very lean mode where power feels lower so temps run cooler , so like 17/1 >22+/1 . that might be hard to do for DIY .

These engines that run lean mode , I would guess also have better components (valves, seats ,etc) to handle higher temps .
Do you know about the EGT they run ?
more than 1400F ?

from what I have read and understand, peak cylinder temps occur at 14.7-1, peak egts occur slightly richer than that around 14.0ish but anything after that should start significantly dropping, I know theres quite a few pilots on here, and theres a lot of debate in the aviation world about flying l.o.p. (lean of peak, ie leaner than 14.7 to one) some even suggest running wide open on the throttle and leaning until you acheive the correct cruise rpm.. and most of those engines are dinosaurs with piss poor cylinder head designs air cooled detonation magnets..

Does anyone know the threshold of lean burn for the vx? I currently start richining past 14.7 at around 10" of vaccum and run around a 13.8 at full throttle for power reasons... it makes 106 hp to the crank on a good day, it needs all the help it can get overtaking cars on the highway..lol

About the o2 sensor I know a vx sensor(l1h1 or a ntk sensor) will supposedly read 25-1 but the only controller i've seen that utilize them (ngk... anyone know of any other ntk controllers?) only reads to like 16 or 18-1...

Keep the thoughts coming guys!

Ben

There is a wiki started on this mod as i am looking at doing this mod myself. It hasn't really been filled out well yet but it has a few useful links to threads and external link to some good info
Lean burn - EcoModder

Also when i have been researching i came across a graph which showed the cylinder temp compared to air fuel mixture. I cant find it now of course but i do remember temps going up with a slight increase but then decrease when going leaner.

I wonder does anyone know a good method to measure cylinder temperatures?
Can a temperature sensor just be put into the exhaust stream close to the cylinder?