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Old 04-15-2012, 01:40 PM   #21 (permalink)
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If my post offended anybody then I apologize for that, it was not my intent.

The fact remains that any gains in economy will be hard won. By all means go ahead and give it your best shot if you like, but I gathered from your post that you didn't want to spend much money or time on it, which was the reason I replied as I did.

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Old 04-15-2012, 02:13 PM   #22 (permalink)
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Quote:
Originally Posted by steffen707 View Post
Try taking a stock d16z6 si engine and just lean the fuel injectors out to 20:1 air fuel ratio and you're going to destroy the engine. The engine has to be designed to go to lean burn in the first place.
Fuel injectors don't work like that in modern EFI systems. The ECU will still follow its closed-loop programming until the peak capacity of the injector is reached, and then it will lean out, but in an uncontrolled manner.

While small bore engines do better at lean burn than larger bore engines (all other things being equal), and lean burn engines benefit from higher C/Rs, almost any engine can be converted to lean burn without inherent problems. (This is not to imply that it's easy or emissions-legal to do, but it certainly can be done.)

Quote:
Sure leaning out the A/F ratio to like 14.7:1 from 13:1 will realize a gain, but from my limited tuning experienece, you don't want to mess with high AF ratios on a normal engine.
The challenge with leaning an engine is to get leaner than 'peak egt' in a controlled manner. Aircraft engines have been doing this for decades by separating fuel metering from throttle position, but it can be done as well on EFI engines with a Megasquirt or similar controller.

Running an engine at peak egt (A/F ratio about 15:1...plus or minus) long term might damage it, but I doubt it even then. Water cooled engines are pretty efficient at wicking away heat. Running lots of timing advance at peak egt can easily bring on preignition and detonation, which WILL damage and engine if permitted to persist, but modern ECUs sense this and pull advance out, returning the engine to the safe zone.

The lean condition itself is not inherently damaging. In fact, running the Insight's engine way lean of peak egt is one way that car achieves high MPGs. I don't know how lean they can go (anybody know?), but I wouldn't be surprised to learn that it's well over 16:1. As an engine goes leaner than peak, it runs cooler and cooler, and makes less and less power, until proper combustion can no longer be maintained and the engine roughens up and finally dies if you keep going leaner.

Reading between the lines on comments about the Insight engine, and how it won't stay in lean burn above about 75 mph, it's clear that it comes down to the 'power required' equation. When the car's total drag exceeds the max hp the engine can make in lean burn, whether during steady-state driving or while accelerating, the ECU converts to 'normal' mode to provide the power required and FE drops noticeably.
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Old 04-16-2012, 03:25 PM   #23 (permalink)
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Quote:
Originally Posted by E4ODnut View Post
If my post offended anybody then I apologize for that, it was not my intent.

The fact remains that any gains in economy will be hard won. By all means go ahead and give it your best shot if you like, but I gathered from your post that you didn't want to spend much money or time on it, which was the reason I replied as I did.
You didn't offend. I was just being melodramatic. I agree with you in that the cost and time-commitment will likely be too high for me to proceed with this. Maybe I will start saving my pennies for a MegaSquirt or similar device so that I can look at this again some time in the future...

For now, I am trying to see why I can't get a Geo Metro XFI ecu to work with my base Metro car. I am sure there are multiple reasons, but I can't even get it to start
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Old 04-16-2012, 06:30 PM   #24 (permalink)
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Most factory EFI systems will hold the A/F ratio to about 14.7:1 in cruise conditions. Some will allow open loop idle at slightly richer. Most will go into open loop full throttle at about 13:1 or richer.

I've spent a lot of time and effort tuning my Ford 300 CID 6 for lean cruise. This is a low tech, low compression engine, but I find I can run lightly loaded as lean as about 18:1 before I get a lean stumble. In theory that should yield about a 22% improvement in economy. Real world is different. At this ratio the power output decreases significantly, so you have to open the throttle more allowing more mix into the engine to compensate. You are still ahead to run lean, but not nearly to the extent that one might hope for. The other thing is that with the lack of power with lean mixtures, the engine will spend less of it's time in this range, so the benefits are limited by this factor as well.

The 1L Metro engine spends quite a bit of it's time with relatively large throttle openings which reduces pumping losses to begin with. This will make it harder to get gains in economy from leaning out because the engine is already sized right for the job.

I'm not saying it can't be done, but the gains will be small and it will take a lot of effort to get them. If you're into it though, the experience can be lot of fun.
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Old 04-16-2012, 07:29 PM   #25 (permalink)
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I should just go out and find a VX
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Old 04-16-2012, 07:42 PM   #26 (permalink)
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Quote:
Originally Posted by Stan View Post
Fuel injectors don't work like that in modern EFI systems. The ECU will still follow its closed-loop programming until the peak capacity of the injector is reached, and then it will lean out, but in an uncontrolled manner.
If you remap the fuel table in a modern EFI system and tell the injectors to flow less, then yes it will lean out in whatever manner you program it to.

I'm saying the design of the pistons and valves won't like the lean burn, unless it was designed like that.

If you're saying any modern EFI engine can just run lean as hell like a VX or HX or insight motor, then every manufacturer would have done so from 1992-2000 to get way better mileage at cruise.....but they didn't.

I thought I read that the VX will go to 20:1-25:1 AFR. This is a lot more than the 15:1 you were talking about.

Last edited by steffen707; 04-16-2012 at 08:11 PM..
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Old 04-16-2012, 07:53 PM   #27 (permalink)
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Quote:
Originally Posted by E4ODnut View Post
Sorry to shock you into reality, but unless you are very knowledgeable in the art of engine tuning, and are prepared to spend a lot of time and not a small amount of money in the process, what you are seeking is not achievable.

The bottom line is that all the OEM manufacturers of factory EFI equipped vehicles have done a very good job of compromising power, economy, reliability and emissions concerns. Any gains you will get in one area will be hard won and will negatively affect the others.

I have considerable experience in tuning my engines for economy so I'd like to think that I know what I'm talking about. I also have a 91 Sprint and a 91 Miata in my stable. They work so well from factory that I wouldn't even consider modifying them. My Sprint is a $900 beater with almost 300,000 km on the clock. It averages 58 mpg Imperial in summer, 56 in winter. I don't know how I could improve on that.
58 imperial is about 48 US. I had a carburated 86 Sprint I rebuilt the engine on years ago and when I put it back in it got 52 to 55 US. Maybe you don't know how you can improve on it but I bet you a lot of people here could, me included.
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Last edited by guudasitgets; 04-16-2012 at 08:01 PM..
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Old 04-16-2012, 08:42 PM   #28 (permalink)
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to get rid of your lean stumble, advance the timing

every chevy from about 94 through 2005 has lean burn built into the ecu, but disabled.
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Old 04-16-2012, 09:52 PM   #29 (permalink)
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The lean stumble is after the timing has been advanced to optimize the lean mix. I can adjust timing and mixture in real time to determine optimum. The only way I could improve on it would be lots of expensive dyno time and that isn't practical for me.
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Old 04-16-2012, 09:56 PM   #30 (permalink)
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AFR sensors

did you really think that the OEMs have been using AFR sensors since the early 2000 s
and the systems do not have the ability to be in fuel control when leaner than 14.7 to 1 ?

why else would they have gone to the expense and trouble of using AFR sensors in the first place ?



look where NOX peaks , about 16 to 1 , after that you can swag that combustion temp goes down as lean ness goes up as NOX forms at around 2500f and if the system is lean er than 16 to 1 there is plenty of 02 to combine with the N

so
conditions leaner than 16 to1 can not have higher combustion temps than conditions at stoich , 14.7 to 1

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