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Old 03-26-2011, 07:22 PM   #1
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Default Lean Burn engine

Hi there, got a stupid question...

anyone ever tried to tune the engine below 2.5k to 3k rpm like a lean burn engine:
this means afr above 20:1 to max 28:1
it's only possible under low rpm, cause such lean mixture would burn quiet slowly --> at high rpm the mixture would still burn when the exhaust valve opens...
therefore high ignition advance would also be a must...
furthermore knock sensors...
and a wideband lambda which is possible to detect levels above 20:1
anyone tried so far?

what I am aiming for is:
better fuel economy for low revs

thx for your thoughts
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Old 03-26-2011, 07:42 PM   #2
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Are we talking about a stock n/a engine on 91oct? 20:1 is ridiculously lean I highly doubt it would work, but I'm definitely keeping an eye on this thread for possible explanations proving otherwise
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Old 03-26-2011, 07:45 PM   #3
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Anything above 16:1 and you will lose power big time, to the point of misfiring.
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Old 03-26-2011, 07:56 PM   #4
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Quote:
Originally Posted by Reverant View Post
Anything above 16:1 and you will lose power big time, to the point of misfiring.
This... well 16 ish... i run 16.5 and when it is hot, I miss alot. I also get great milage, but when it is hot, I am hosed, so I had to richen up a bit. Good luck with 20 breah.
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Old 03-26-2011, 08:02 PM   #5
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i have a stock engine, but turbo charged (95 ROZ)
of course i know that igniting the leaner mixture is not a simple task, i already have a better ignition system
the loss of power is cause the ignition has to be extremly advanced, otherwise the peak pressure is reached beyond the optimal point (10-20 degree after tdc)
probably a cylinderpressure sensor would be useful...

but i want to know if any1 tried so far?

thx for your thoughts ;-)
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Old 03-26-2011, 11:26 PM   #6
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One of the problems with Miatas is 2500 rpm is like 40mph or something. Don't seem likely to be cruising at that speed.
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Old 03-27-2011, 12:03 AM   #7
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I was thinking about this, using table switching for this, having a cruise map and when you punch it a "go" map. But I want to get an EGT sensor before I start messing.

Last edited by Techsalvager; 03-27-2011 at 12:20 AM.
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Old 03-27-2011, 01:35 AM   #8
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There was a P-40 pilot in WW2 that figured out how to set his **** to lean burn, then he went and taught all the other P-40 pilots about it. They noticably extended the range of the P-40. The concept is proven, but it's prone to making mistakes. The ignition is advanced significantly to start the burn early, and the burn completes shortly after TDC, effectively providing more power for the down stroke than the resistance of compression on the up-stroke. The problem can be the transition from lean-burn to stoich burn (where you have to bridge the detonation range of the AFR) - WW2 planes that were just cruising pretty much set the RPM and stuck to it.

IIRC, I thought the prius was set as a lean-burn engine. The EPA doesn't like them though.
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Old 03-28-2011, 05:16 PM   #9
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I had a "semi lean burn" fuel table on a MegaSquirted Civic a while back - that car liked to cruise at 18:1 to 20:1.
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Old 03-28-2011, 07:38 PM   #10
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Matt what was your spark timing in this cruise area?
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Old 03-28-2011, 10:53 PM   #11
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Quote:
Originally Posted by Matt Cramer View Post
I had a "semi lean burn" fuel table on a MegaSquirted Civic a while back - that car liked to cruise at 18:1 to 20:1.
damn that's impressive. I can get just around 17:1 in my miata then I get misfiring. My old subaru would misfire at like 15.5:1 haha. 20:1 would be sweet.
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Old 03-28-2011, 11:06 PM   #12
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This topic was featured in hot rod i think?
Yeah it was:
http://www.hotrod.com/techarticles/e...ine/index.html
Also:

http://www.legendarycollectorcars.co...clusive-video/
There is more to it than better mpg; Smokey Yunick actually made power with his setup.

Last edited by danotakulus; 03-28-2011 at 11:06 PM. Reason: grammar
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Old 03-28-2011, 11:25 PM   #13
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damn. Ok. I'll have to bring this up with the old timers at work.
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Old 03-28-2011, 11:28 PM   #14
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Quote:
Originally Posted by danotakulus View Post
This topic was featured in hot rod i think?
Yeah it was:
http://www.hotrod.com/techarticles/e...ine/index.html
Also:

http://www.legendarycollectorcars.co...clusive-video/
There is more to it than better mpg; Smokey Yunick actually made power with his setup.
Yes I've been heavily interested in the adiabetic engines smokey has built, but that in itself in a whole another way to go about it. Hes heating up the fuel to 400f+ tempatures before it goes into the engine.
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Old 03-29-2011, 09:18 AM   #15
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True, but heating up the fuel enough vaporizes it, allowing the air and fuel to mix properly, avoiding detonation allowing higher AFR. It is one way to skin a cat, but I think I read something about honda using lean burn technology.
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Old 03-29-2011, 09:23 AM   #16
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One time I drove on the highway following Saint_foo here up to a dyno day. in the rain going +80mph my fuel map needed work and I was hitting over 17:1 before it would need more fuel. Got pretty good mpg IIRC.

I typically highway cruise at 16.5:1.
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Old 03-29-2011, 09:35 AM   #17
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I read about the honda "lean burn" at one point. It wasn't as extreme as Smokey's IIRC, just sorta using vtec in an economy mode and leaning it out bigtime like we try to do with our standalones, but with honda's better tech. cylinder head and cam timing. Worked great on those old civics but then the EPA didn't like the emissions and killed that idea. Back when I was ignorant of emissions and had my link ecu I went thru the NJ inspection with a very lean 17ish AFR, thinking it'd pass no problem as I wasn't using much fuel. WRONG. I forget what goes sky high when you go lean but something was off the chart.
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Old 03-29-2011, 09:51 AM   #18
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Quote:
Originally Posted by danotakulus View Post
True, but heating up the fuel enough vaporizes it, allowing the air and fuel to mix properly, avoiding detonation allowing higher AFR. It is one way to skin a cat, but I think I read something about honda using lean burn technology.
I read an article a while back where Honda had developed a test engine that could run at an equivelant 65:1 afr. What they did was machine a cup into the top of the piston then using direct injection they squirted into the cup. This gave them around 20:1 afr in the cup but the average for the cylinder was 65:1. When you wanted more power the engine would run in normal Stoich mode on the full volume of the cylinder.

Can't seem to find the full article any more though.
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Old 03-29-2011, 10:04 AM   #19
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Quote:
Originally Posted by Techsalvager View Post
Matt what was your spark timing in this cruise area?
I can't remember exactly where it was, but it was nothing special. I suspect the cylinder head design was more important - the Civic CX could go even leaner.

Quote:
Originally Posted by Techsalvager View Post
Yes I've been heavily interested in the adiabetic engines smokey has built, but that in itself in a whole another way to go about it. Hes heating up the fuel to 400f+ tempatures before it goes into the engine.
If Smokey's hot air engine wasn't a hoax - which I'm not ruling out either - there were a lot of details about that motor that Smokey kept hidden from the media. My own guess is that the engine was a homogenous charge compression ignition engine. That would fit a lot of the published details - that the engine ran extremely lean, and that the air was heated to almost the point of autoignition - as well as some educated guesses - such as that the engine appears to have been a total bitch to tune, given how several companies he'd licensed the technology to couldn't get a production version working.
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Old 03-29-2011, 10:04 AM   #20
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Quote:
Originally Posted by TurboTim View Post
I forget what goes sky high when you go lean but something was off the chart.
Nitrogen oxide emissio(NO, NO2) from the higher EGT.
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