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 :facepalm: for low revs thx for your thoughts |
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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Anything above 16:1 and you will lose power big time, to the point of misfiring.
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Originally Posted by Reverant
(Post 706727)
Anything above 16:1 and you will lose power big time, to the point of misfiring.
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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 ;-) |
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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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.
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There was a P-40 pilot in WW2 that figured out how to set his shit 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. |
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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Matt what was your spark timing in this cruise area?
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Originally Posted by Matt Cramer
(Post 707456)
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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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. |
damn. Ok. I'll have to bring this up with the old timers at work.
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Originally Posted by danotakulus
(Post 707649)
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. |
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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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. |
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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Originally Posted by danotakulus
(Post 707766)
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.
Can't seem to find the full article any more though. |
Originally Posted by Techsalvager
(Post 707542)
Matt what was your spark timing in this cruise area?
Originally Posted by Techsalvager
(Post 707656)
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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Originally Posted by TurboTim
(Post 707777)
I forget what goes sky high when you go lean but something was off the chart.
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