mark kibort

it would depend on how the mixture is controlled. lean of stoich works for power levels up to 50%. so, you might have to push the pedal down further, but the power neeeded to pass migh still be enough . if this is done right, you would be right on the edge of running smooth, so it would never really be an issue, as you would be so lean , it would proabably start to lean miss with too much power or just not have very much power. again, look at the chart. they are listing up to near 80% of full power!!!!!!! loook , please just LOOK at the chart! it shows DRAMATIC reduction in temps and ive seen it actually doing this flying as well!!

RFJ

I for one like it when Mark gets going,makes people think. Even if they don't like it.Ray

RFJ

I find the sticker to be very offensive, has no place here. just my .02

Ethre

That's the idea. It would only be really effective with a regulated voltage though. From reading up on the 944 guys AFM information though, it looks like the AFM may be an unregulated signal. Haven't had a chance to test it.

And, as it turns out, I have other priorities on my car before I start tinkering. One of these days. . .

j.kenzie@sbcglobal.net

I think Porken had a variable resistor for this kind of thing. Search his old posts.

waynestrutt

its very different than your example. go look at the lean of stoich chart i just posted. this is from Lycoming!!! guys have been doing this since WWII in airplanes and its the same for cars, but WE and the country , care about the polution of cars, which is worse when you run lean of stoich. (high NOX)

So, if you were burning valves, you were still too rich! CHTs and EGTS will be lower lean of stoich, which means you COULD have beat your competition if you could have leaned out your mixture a little more. gone farther on a gal of gas and not burned the valves.[/QUOTE]

Mark you cannot compare a aircraft flying in thin air at sub temperatures with our gasguzzlers on earth. The reduced ambiant temp alone will mask and prevent overheating. And as for the economy run anything more than a slight touch on the throttle(adding air) would result in the engine quitting,so there was no way the SU's could have been leaned out more. Lets face it your wrong you run your engine as lean as you dare and I guarantee you will be replacing valves or worse seats , but its been fun

dprantl

This time Mark is right. I have run my 928 on long trips (>3 hours) non-stop at ~17:1 AFR. I also just easily passed emissions with high-flow cats for the fourth year in a row; this condition does not "ruin" cats. I have my non-cat maps tuned so that light throttle is 17:1, but as soon as the throttle is pressed more than a certain amount it goes back to ~14.7:1. When I want to run lean cruise, I just force non-cat maps in my ST2. At light throttle loads, even if 17:1 AFR produced higher temperatures (which it does not in such a scenario when the fuel map is actually tuned that lean), it would not cause any issues. This is not the same as a lean condition brought on by a *misfire*.

However, 30mpg would require 17.5 - 18:1 AFR. 17:1 AFR will only increase gas mileage by about 15%. Even the most economical 928 (early 32v 5-speed with 2.2 rear pinion) gets 24 - 25mpg on the highway stock at best. You could probably get close to 29mpg though, but with a 2.7x rear pinion, forget it. I can't get more than ~24mpg with mine.

Dan
'91 928GT S/C 475hp/460lb.ft

Lizard928

Are you sure about the valves and seats......

http://en.m.wikipedia.org/wiki/Lean_burn#section_4

That is but an example. Much more can be found

mark kibort

why would you say this. ive done it. by the way, we are not talking 747s here! we are talking piston engines that are running at 10,000ft, and temps of near normal . (hot summer days). temp has nothing to do with hit. you hear of burned valves with NOS systems, ALL the time, not due to lean, but due to stoich operation. we are not talkinga about overheating, we are talking about conditios to have knocks, detonation, and destroy engines. is that due to lean or due to stoich. I contend its due to stoich!
now , you are making more incorrect assumptions. small throttle possitions with lean above stoich didnt make the engine stumble that much either.
now you say "Im wrong". really, without one logical set of circumstances or any evidence, knowledge???? (and a gurantee to boot!????)
remember, in you example or condition, first, we are at cruise settings , so we dont care that we are at 17:1, or 14.7:1. both will be fine under part throttle conditions. will the mixture lean out with throttle position? certainly not. So, it really is YOU who is wrong. worse that wrong, wrong but claiming they are right without knowledge or any logic to back it up.

Thanks Dan! great information. real proof and logic here!

Let me check on this! thanks!

mark kibort

Good Find Lizard,

of course they are wrong too, huh!

Lean burn refers to the use of lean mixtures in an internal combustion engine. The air-fuel ratios can be as high as 65:1, so the mixture has considerably less fuel in comparison to the stoichiometric combustion ratio (14.7:1 for petrol for example).

Principle
A lean burn mode is a way to reduce throttling losses. An engine in a typical vehicle is sized for providing the power desired for acceleration, but must operate well below that point in normal steady-speed operation. Ordinarily, the power is cut by partially closing a throttle. However, the extra work done in pumping air through the throttle reduces efficiency. If the fuel/air ratio is reduced, then lower power can be achieved with the throttle closer to fully open, and the efficiency during normal driving (below the maximum torque capability of the engine) can be higher.

The engines designed for lean burning can employ higher compression ratios and thus provide better performance, efficient fuel use and low exhaust hydrocarbon emissions than those found in conventional petrol engines. Ultra lean mixtures with very high air-fuel ratios can only be achieved by direct injection engines.

The main drawback of lean burning is that a complex catalytic converter system is required to reduce NOx emissions. Lean burn engines do not work well with modern 3-way catalytic converter—which require a pollutant balance at the exhaust port so they can carry out oxidation and reduction reactions—so most modern engines run at or near the stoichiometric point. Alternatively, ultra-lean ratios can reduce NOx emissions[citation needed].

Chrysler Electronic Lean Burn
From 1976 through 1989, Chrysler equipped many vehicles with their Electronic Lean Burn (ELB) system, which consisted of a spark control computer and various sensors and transducers. The computer adjusted spark timing based on manifold vacuum, engine speed, engine temperature, throttle position over time, and incoming air temperature. Engines equipped with ELB used fixed-timing distributors without the traditional vacuum and centrifugal timing advance mechanisms. The ELB computer also directly drove the ignition coil, eliminating the need for a separate ignition module.

Lizard928

MK, look specifically at the Honda lean burn. AFRs as lean as 22:1 requires a certain combustion chamber to work effectively though.
I found 17:1 to be about max on the stock system, distributor less ign systems which allow a bigger gap (.050") you can get down to 18:1 AFR.
I did see 35MPG with an 86.5 engine using EDIS 8 and MS but was running 18:1 AFR or leaner with 27" rear tire diameter.
So the gearing was really tall.

mark kibort

that is flipping AWESOME! thanks!

now, got to find a way that a hack like me can do it so when on Hyway 5, on flat cruise, i can flp a switch to dial in the mixture to 17:1. do you think just pulling the 02 sensor connection intermittantly, is a step in the right direction?
I thought when you pulled it, it actually went pretty rich.
so , temp II wont do it, right ?

good stuff!

123

If he was burning valves, it was because the ignition timing wasn't tuned correctly. Some people in this thread are just asking for trouble and expensive engine problems. People who don't know how to correctly tune the ignition timing, and don't know how the air/fuel mixture relates to it, really shouldn't be messing around with the air/fuel mixture in some of the ways mentioned.

Want to quickly and easily increase your miles per gallon? Buy gas that doesn't have any ethanol mixed in with it, and buy it in Canada. Canadian gallons are larger than US gallons.

RKD in OKC

My dad and brother each had one of those Chrysler Electronic Lean burn cars when they very first came out, they were a 72 grand fury III. Replaced a transistor on the ecu board and got both more power and better gas mileage. The replacement was pretty common. Not idea what the transistor actually did.

waynestrutt

[QUOTE=Want to quickly and easily increase your miles per gallon? Buy gas that doesn't have any ethanol mixed in with it, and buy it in Canada. Canadian gallons are larger than US gallons.[/QUOTE]

Our price for premium today is 1.49/litre or 5.63 /us gal



Mark check this
http://www.sacskyranch.com/bvalve.htm

My experience is as a mechanic for British Leyland MG.Austen Healey,Jag, Rover etc in the late 60's then V W /Audi in the 70's. So customers vehicle were always set to factory spec. My comments are from my experience and not unfounded. Our 928 engines unless just rebuilt are getting on in wear so things like worn guides ,original valves ,carbon deposits etc can accelerate poor seating of valves and result in them being burned. Running a hotter burning mixture just exacerbates this scenario.
and allow the hot gasses to eat away