running rich 'n running lean... what are the benefits??

[MMamdouh]

i saw in many articles about running rich and running lean and how they might hurt the engine as well as peerformance and how some times it is better to run rich.

i used to thing that their is this one optimum air/fuel ratio per operating speed for the engine which is 1:9 at idle, 1:14.5 at mid rage revs and 1:11 at high revs... is that still the case or has this changed with the new engine managment and all??

what about messing with those ratios?? is it going to be good performance wise and fuel economy wise? what are the problems of running rich and running lean??

i know i asked too much but by lack of knowledge at this area is killing me.

MMamdouh

[kinkyllama]

I dont know much on the subject either...

but i do know running rich is better.. plus if your car runs rich stock then theres usually more room for tunning

[joseanevo]

That is a good question, if you are running N/A well the ECU can do some adjustments to the mixture and try to run almost perfect 14.7:1 ratio with the simple mods everyone does ,running lean will destroy your engine more faster than rich, anythig that runs from 15.0:1 and up will destroy the engine anytime but richer makes is a little bit difficult , but like i said before this usually concerns turbo and nitrous guys who need to compensate for the aditional stress they are putting to the engine more air needs more fuel .......so everyday driving leave it stock for racing just for insurance go a little rich but not to much.......

[tango]

Neither situation by itself is good. Running rich can foul plugs and cause heavy carbon buildup all over the place. Running lean can obviously cause other problems where one can seriously damage an engine from the inherently hot temperatures that this condition causes. An ECU that varies mixture across an rpm band however can yield very good results because an engine will actually require different mixtures as revs change. Toyota had a system called "Lean-Burn Technology" several years ago on their Euro-spec Carina-E. This is what I dug up:

Most cars run at what is called a 'stoichiometric' air-to-fuel ratio of around 14.5:1 (also known as Lambda 1), and so does the Carina E under hard acceleration. However, it achieves its excellent economy by switching to a 'lean-burn' air-to-fuel ratio of up to 24:1 under light throttle loads. The problem which lean-burn technology has had to face is operating with a catalytic converter, which will only work effectively at Lambda 1. (It doesn't need to catalyse under 'lean-burn' conditions, because the engine is inherently 'clean'). Toyota says: 'the engine needs to revert to stoichiometric whenever the swirl control valves open. Software has been written to smooth the transition between lean-burn and stoichiometric to make it imperceptible to the driver'. However, my experience of both the Carina E 1.8 (the next generation to your car) and the Honda Civic VTEC-E is that there is a very perceptible transition from lean-burn to stoichiometric and vice versa. You could have the car checked at your Toyota dealer to make sure, but I think 'all or nothing' is a characteristic of lean-burn engines. Watch out for a new lean-burn GDI engine from Mitsubishi capable of running at an astonishing 40:1 air-to-fuel ratio. This offers 150 bhp from an engine capacity of just 1.8 litres, yet up to 35% better economy and up to 90% lower NOx emissions than a stoichiometric 1.8i.

[MMamdouh]

thats my point... running rich cause loads of pollution, carbon buildup and bad fuel economy.

now i knew what are the problems of running lean and how to utilize the lean mixture to best serve fuel economy without damaging the engine.

now this post makes me think twice about bypassing my EGR valve... seems like it kicks in when things get really hot in the engine and if it was absent - the EGR - then my engine could blow up... right?

MMamdouh

[PrecisionBoost]

When dyno tuning a turbo car you would normally shoot for 12:1 but with a naturally aspirated it should be more like 13.5:1 for optimum power.

Runing too rich or too lean will decrease power output.

[GsiTurbo]

The actual air-fuel ratio will be very much dependant on an application. Most out-of-the-lot vehicles will be setup for optimum fuel efficiency and emmisions.

In the tuner world, this is not often the case. On a turbocharged cars, its often safe to run engine a bit on a richer scale, and/or retarded timing. This particularly goes to motors that have been coverted to turbo, and often running on stock internals.

Keeping air-fuel ratio richer will prevent the following (on a turbo engine):

- detonation of air charge (knocking). An engine will survive knocking for a few seconds only
- cooling the combustion chamber

The actual safe air fuel ratio should be performed on a dyno with a wideband 02 sensor, and ideally knock sensor readout. This way, air-fuel can be adjusted to get the optimum horsepower (we are talking 15+ horsepower on typical 2.0 DOHC engine). If Air-Fuel is good, but the knock sensor goes crazy, timing should be retarded in the RPM range corresponding to knocking. Sometimes, to prevent knocking, race fuel must be used.

[ShalerPunk]

there are hondas that run 17:1, but they're designed for that sort of madness.