Thread: Technical Question about Lean mixture

Are we talking Petrol or Diesel engines, Regards Frank.

oh yeah, silly me.... Petrol Engines

Running lean in a petrol engine can be better than running rich, up to a point, a lean mixtute burns hotter and can cause pre-ignition by overheating valves and spark plugs also heavy carbon deposits. These super heated items can act like a permanent "on" spark from a spark plug and ignite the fuel/air mixture out of sequence. This type of pre-ignition can burn holes right through a piston, one of the symptoms of pre-ignition is the engine running on when you turn the key off and you get that knocking sound. A bit lean is ok, as long as you know what's what, ignition timing is critical if you intend to run lean as is the correct fuel, a lot of race engines run on the lean side, but they take precautions to avoid damage, like polishing the combustion chambers and valves, correct timing and plugs to name a few, engine temps. may go up, but if in good nick the cooling system can usually handle it, Regards Frank.

ive got some experience with tuning an SR20DET..

a lean mixture will produce more power then a rich mixture
however, a lean engine runs hotter, as fuel also cools the chambers.

a lean engine wont last as long as a rich engine.
when tuning rich is safe. ive seen too many engine go from being lean.

a lean mixture will produce more power then a rich mixture

Can't say I've come across that before.

http://www.motecome acroos .com.au/a...ambdaoverview/

Running excessivly lean gives you problems with detonation and burnt exhaust valves.

Originally Posted by nobbyclrk

Can't say I've come across that before.


Running excessivly lean gives you problems with detonation and burnt exhaust valves.

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im not talking about excessively lean.

being lean and making high power is dangerous for an engine. really hard to tune right and most tuners side of the caution of rich.

I have also had some experience tuning SU carbs on Rover engines, increasing capacity (in this case from 3.5 to 4 litre) required a needle profile change, the std needles had a less aggressive profile, IE were too lean across the midrange for the increased capacity engine, and caused detonation and overheating. (A 1988 110 County). After the needle change, was able to run 8 degrees BTDC timing, had more get up and go in the midrange, and ran noticeably cooler. Vehicle used less fuel, too.

JC

Thanks Guys, the reason for my question is this, ive had my 93 3.5 D1 for about 9 months, and thetemp guage has always sat on half, no matter what, recenlty (Last weekend) I decided to tu e and clean the MAF and TPS, when I put the meter on it it read 3.6v, so I sdjusted kt back to 1.3, immediately I noticed no rich smell from exhaust anymore, and kt seemed to run better till I went on a longis trip cruising at about 90 the temp rose to 2/3, had to pull over a few times to let it cool at idle, now this was my thinking, if the previous owner did not adjust the MAF only the timing could the timing be out now I have set it correctly, (I dont have a timeing light tl check it yet) I.E would maf setting have any influence over the timing, another thougb I had was the fuel filter now the engine is running better the filter being blocked could cause it to run leaner causing it to heat up.. I have ordered a filter and will change that when it arrives.. think im clutching at straws here but im just trying to fugureout the increase temp when all I have done if tune a few things