Myth? Lean mixtures will cause engine damage

[suspendedhatch]

Originally Posted by trautotuning

So what is so special about the vx engine that makes it be able to ignite so well?

Piston design? Ignition Design?

I posted a rather large pic.

Honda pistons are pretty much standard. Honda ignition systems are mediocre at best. The pent-roof combustion chamber shape has a lot to do with it but it certainly is not unique to the D15Z1. It's pretty much standard across the entire Honda lineup since the early 80's.

Originally Posted by trautotuning

Oh and if anybody is planning on doing this (like me), it is a very wise idea to go with an aftermarket ignition module like MSD or the such.

These devices can multifire below a certain rpm, which is what you need to be able to light those lean mixtures (and it is exactly what the Honda insight does, multi fires the plug).

Just a heads up on what I have learned through my research in order to get my engine to lean burn safely

I have an AEM Twin Fire (CDI multistrike ignition system) on mine as part of converting it to direct fire.

"Q: What is Multi-Strike?
A: Multi-Strike is the process of firing the spark plug multiple times at low RPM to aid in idle quality, throttle response and engine start up. The AEM CDI can deliver up to 8 full energy spark events sequentially."

[dkjones96]

12.8-13.2:1 is the max power mixture range. Not sure about economy.

[slurp812]

Originally Posted by Erik

Doing a bit of research, it looks like lean mixes alone do no harm, but at low rpms and high load, lean mixes can lead to detonation and its the detonation that can damage pistons, burn valves etc.

My friend melted 2 or 3 pistons in his 250cc mx motorcycle before he realized he had leaky crank seals, making his bike run lean. Of course he was hammering it to death every time. Thing was he said it was running GREAT, really fast, and then nothing. From what I've seen, I concur...

[dkjones96]

Engines always run their best right before they die.

[theholycow]

Gasoline direct injection engines can run as lean as 65:1 according to this wiki:
http://en.wikipedia.org/wiki/Gasoline_Direct_Injection

...ultra lean mode can involve ratios as high as 65:1. [...]
Ultra lean burn mode is used for light-load running conditions, when little or no acceleration is required. The fuel is not injected at the intake stroke but rather at the latter stages of the compression stroke, so that the small amount of air-fuel mixture is optimally placed near the spark plug. This stratified charge is surrounded by mostly air which keeps the fuel away from the cylinder walls for lowest emissions. The combustion takes place in a toroidal (donut shaped) cavity on the piston's surface. This technique enables the use of ultra-lean mixtures impossible with carburetors or conventional fuel injection.

[GasSavers_maxc]

Originally Posted by dkjones96

Engines always run their best right before they die.

Most put out more power when there into a little detonation.

[GasSavers_bobski]

Originally Posted by suspendedhatch

Honda ignition systems are mediocre at best.

Really? I've read that they're pretty good at what they do... That it's not generally necessary to upgrade them for most performance applications. Are you saying that because you had problems when running a modified lean-burn setup, or because you're annoyed that it doesn't fire 15 times every other cylinder stroke?
Really, I don't think it's fair to compare factory equipment to an aftermarket setup when modifying the engine beyond its intended range of operation. If the engineers had expected the engine to run particularly lean, they would have upgraded the ignition to cope. Newer Honda lean burn engines have two spark plugs per cylinder, and each plug has its own coil/ignitor unit assembly. The separate ignition assemblies not only add redundancy and therefor reliability, but also divide up the work load so plugs could conceivably be fired multiple times (maybe they already are?) with just a tweak of the ECU programming.

[GasSavers_Erik]

This graphic shows 16:1 as having the best economy.



On a related note, supposedly NOX emissions go up when you run too lean, but based on the graphs at the beginning of this thread, it seems that running ultra lean would have lower combustion temps and therefore lower NOX emissions than a stoichiometric ratio.

[dkjones96]

Your forgetting that as you go leaner there are more oxygen molecules available to react with the 78% nitrogen in the air and the combustion temperatures are still in the thousands of degrees.

[GasSavers_Pete]

Wouldn't the ratio of oxygen to nitrogen remain the same regardless of the volume?
The "Lean" aspect applies to the volume of air relative to the volume of fuel so although the volume of air is decreased the actual mixture of the air does not alter.

Cheers , Pete.