How much power can an engine lose when the A/F ratio is lowered...

[Howard]

... from, say, 13:1 to 11:1? Assuming an engine that makes about 200HP at 13:1...

No exact numbers, just looking for a general guesstimate. Thanks in advance.

 

[Howard]

^

 

[GalvanizedYankee]

The fuel ratio is by weight.

1 part fuel to about 14.5 is generally considered optimal.

1 to 12.5 is best power mix.

1 to 10 is cold start.

1 to up to 16 is super economy.

This is a generalization and very dependent on engine type, spark plug location, compression ratio, carb or injection type, and so many other things its boggling.

Power loss?? As engine and air temp rise, power will fall off. Then the plugs will foul and power will be limited to what the starter can put out.

If it manages to still run when hot at 11 to 1 probably a 30% loss....

 

[Howard]

Originally posted by: galvanizedyankee
The fuel ratio is by weight.

1 part fuel to about 14.5 is generally considered optimal.

1 to 12.5 is best power mix.

1 to 10 is cold start.

1 to up to 16 is super economy.

This is a generalization and very dependent on engine type, spark plug location, compression ratio, carb or injection type, and so many other things its boggling.

Power loss?? As engine and air temp rise, power will fall off. Then the plugs will foul and power will be limited to what the starter can put out.

If it manages to still run when hot at 11 to 1 probably a 30% loss....

Thanks.

Oh, and Mitsubishi's GDI technology (Gasoline Direct Injection) allows up to a 40:1 A/F ratio. Can't do that with American fuel because a higher-efficiency catalytic converter is required, but our sulphur level in the gasoline is too high to work with it...

 

[GalvanizedYankee]

I was thinking about this post during my brisk 5 mile evening walk.

Why did you ask?

Start up a/f ratio is around 4.5 to 1, cold run 10 to 1.

The old gas school buses that blow all that black smoke use Hall Scott engines, they probably run at 11 to 1.

A small high output engine like a 1000cc m/c engine would die at that ratio.

The 40 to 1 you refer to, I can only imagine would be at shift point or throttle off going down hill.

Honda's old CVCC engines use a separate little chamber that held a rich charge that once ignited would squirt into the main chamber that holding a very lean mixture.

If you will post in this thread a link to the info on an engine that will produce acceptable power at 40 to 1...Thanks...John

 

[Lithium381]

Originally posted by: galvanizedyankee
I was thinking about this post during my brisk 5 mile evening walk.

Why did you ask?

Start up a/f ratio is around 4.5 to 1, cold run 10 to 1.

The old gas school buses that blow all that black smoke use Hall Scott engines, they probably run at 11 to 1.

A small high output engine like a 1000cc m/c engine would die at that ratio.

The 40 to 1 you refer to, I can only imagine would be at shift point or throttle off going down hill.

Honda's old CVCC engines use a separate little chamber that held a rice charge that once ignited would squirt into the main chamber that holding a very lean mixture.

If you will post in this thread a link to the info on an engine that will produce acceptable power at 40 to 1...Thanks...John

40:1 seems a little high, not enough compression at that ratio.......


generally speaking, wouldn't it be better for everyone to increase their a/f ratios for daily driving, slightly better economy all around and we'd all be saving a lot! of course you'd have the soccer mom that would rufuse to give up her 30%, but sure as heck dn't need 100% of my power at the ready in bumper to bumper traffic

 

[NeoPTLD]

Originally posted by: galvanizedyankee
The fuel ratio is by weight.

1 part fuel to about 14.5 is generally considered optimal.

1 to 12.5 is best power mix.

How does it make more power by getting out of tune from stoichiometrically correct mixture?

 

[GalvanizedYankee]

Dyno's and lap times don't lie.

At about 14.5 everything burns pretty clean.

At 12.5 lighter elements in the fuel burn better and faster. The partially burned heavy elements go out the tail pipe as pollution or get taken care of in the cat as it reaches
solar temperatures...

 

[Stallion]

Running an engine lean can be very costly. A lean A/F mixture will burn pistons. It is always better to run rich instead of lean.

 

[Howard]

Originally posted by: Lithium381

Originally posted by: galvanizedyankee
I was thinking about this post during my brisk 5 mile evening walk.

Why did you ask?

Start up a/f ratio is around 4.5 to 1, cold run 10 to 1.

The old gas school buses that blow all that black smoke use Hall Scott engines, they probably run at 11 to 1.

A small high output engine like a 1000cc m/c engine would die at that ratio.

The 40 to 1 you refer to, I can only imagine would be at shift point or throttle off going down hill.

Honda's old CVCC engines use a separate little chamber that held a rice charge that once ignited would squirt into the main chamber that holding a very lean mixture.

If you will post in this thread a link to the info on an engine that will produce acceptable power at 40 to 1...Thanks...John

40:1 seems a little high, not enough compression at that ratio.......


generally speaking, wouldn't it be better for everyone to increase their a/f ratios for daily driving, slightly better economy all around and we'd all be saving a lot! of course you'd have the soccer mom that would rufuse to give up her 30%, but sure as heck dn't need 100% of my power at the ready in bumper to bumper traffic

Mitsu's GDI engine runs at 12.5:1 compression ratio.

 

Howard ;

Spark ignited engines will produce the desired performance only within a relatively narrow range of AFRs(air/fuel ratio). Best power is usually obtained with an AFR of between 11.8 and 13.0 on most engines. The lowest average emissions are obtained with the AFR around 14.7 to 1 (stoichiometric) and best fuel economy is at AFRs between 16 and 18 to 1. Most engines do not idle happily unless they are setup to run richer than 14 to 1 AFR.


If you would really like to understand, read each and everyone of these very good tech articles

 

[GalvanizedYankee]

Originally posted by: Stallion
Running an engine lean can be very costly. A lean A/F mixture will burn pistons. It is always better to run rich instead of lean.

The most heat is produced when the mixture is spot on. Pistons burn primarily because of preignition or detonation, the latter is hellish. Lean mixtures are difficult to ignite, that is why modern engines have very powerful ignition systems. Some fire spark plugs w/.090 gaps. Twenty years ago .035 was the norm.

There are considerations when running rich, pollution, the law, loss of economy, no real gain in street use, wear to cylinder walls and piston rings from wetting, and polluting of crankcase oil with gasoline. The day of the carburetor is over, injection is king now.
:sun:

 

[GalvanizedYankee]

Sorry d/p

 

[Eli]

Yeah. Best power is achieved slightly lean, but you risk cooking things.

 

[GalvanizedYankee]

Originally posted by: Roger
Howard ;

Spark ignited engines will produce the desired performance only within a relatively narrow range of AFRs(air/fuel ratio). Best power is usually obtained with an AFR of between 11.8 and 13.0 on most engines. The lowest average emissions are obtained with the AFR around 14.7 to 1 (stoichiometric) and best fuel economy is at AFRs between 16 and 18 to 1. Most engines do not idle happily unless they are setup to run richer than 14 to 1 AFR.


If you would really like to understand, read each and everyone of these very good tech articles

Thank you Roger I bookmarked it and will study.

The only gas tuning I have done was with a Heath Kit sniffer I put together many moons ago. More recently with a K&N O2 senser and their provided bar gage.

 

[Eli]

Have you guys ever seen those.... damn, I forget what they're called, but IIRC it's basically a spark plug with a little window and some fibre optics, so you can see the color of the flame in the combustion chamber.

Orange = rich, white = lean, blue = good or something along those lines.

A friend of my dads let me play with his when I was like 12, it was fun screwing with the carbs on the lawnmowers with it.

 

Yeah. Best power is achieved slightly lean, but you risk cooking things.

Incorrect sir, best power is achieved when the air/fuel ratio is between 11.8 and 13. (rich)

14.7 is stoichometeric, this allows catalytic convertors to operate at peak efficiancy, the best gas mileage will be obtained with ratios between 15 to 18.

 

[Eli]

Originally posted by: Roger

Yeah. Best power is achieved slightly lean, but you risk cooking things.

Incorrect sir, best power is achieved when the air/fuel ratio is between 11.8 and 13.

14.7 is stoichometeric, this allows catalytic convertors to opwerate at peak efficiancy, the best gas mileage will be obtained with ratios between 15 to 18.

Hmm. You're right, for some reason that was my experience with 2-cycle engines speaking. They will generally rev the best slightly lean(Instead of getting to a certain RPM and going BRAAPPAPAPAPAP), but it's really easy to cook them that way.

 

Eli;

You are confusing idle mixture with high speed enrichment mixture, just because you leaned out the idle mixture, it does not mean that high speed mixture will lean out as well
Now, if you canged high speed jets, that would be a different story.

 

[Eli]

Originally posted by: Roger
Eli;

You are confusing idle mixture with high speed enrichment mixture, just because you leaned out the idle mixture, it does not mean that high speed mixture will lean out as well
Now, if you canged high speed jets, that would be a different story.

Yes.. I am talking about the high speed jet mixture screw. I was just thinking narrowly at the moment.

They do work together at the high RPM range though. Adjusting the idle mixture will change the final ratio.

It's been my observation that 2-cycles like to idle a bit rich and will rev sky high slightly lean - but make the best low end grunt rich. It's always a tradeoff with engines.. lol. For example, the 33cc engine that used to be on my scooter would rev to 10,000(highest I ever had 'er was 10,120.. heh) at 2 1/4 turns out, which is great for a straightaway.. but if you tried to go up a hill like that, it would bog down.

Conversely, at 2 1/2 - 2 3/4 turns out, it had great hill climbing power, but would "stall" into a rich roll at about 8500rpm.

I always carried a small screwdriver in my pocket, and would adjust the mixture based on how I felt, what was comming up next in my path, the position of the moon, etc...

That engine only lasted a year...