KENS_SS_4

Actually the throttle plate is not important. Just the TPS voltage needs to be low enough to not signal for more fuel.

Leaner than stoich is not a benifit. The engine pumps air which requires work be done. Air that is pumped but not used in the chemical reaction is wasted work.

But I don't know why we are into this at all.

This is a stupid goal. Physics says work demands energy period.

There is no way this guy can get 5 mpg more with lower compression heads or a new cam. He can get 5 mpg more if he slows down and limps the engine in the 900 to 1500 RPM range for acceleration and cruises in the 900 to 1100 rpms, that is my point.

Maybe he should just reset the 6200 rpm limiter down to 1400. That will work!

MrDude_1

iTrader: (4)

the physics involved in a running engine powering a car is a bit more complex then fuel = work.

lean cruise does work.. it works amazingly well.

think about this... lets say we take out a bunch of fuel.. now theres less power.
so he opens the throttle more... now we have the same amount of fuel going in.. it all burns.... same power as before we took out fuel... only now the throttle is open more for less pumping losses...


thats not quite how it works either, but its a simple example of how this is alot more complex then it appears at the surface.


btw, the primary reason we meter air into gasoline motors, and not just fuel, is temperature... when exhaust gas temp from lean mixtures isnt an issue, most motors are throttled like diesels.... with the fuel.

KENS_SS_4

MrDude 1
I don't know what your talking about, do you?

This post is about a guy wanting his DD GTO to get him to and from work using less gas. It is not about anything else.

Running leaner than stoich will use more gas in a given distance than running stoich. I don't have to do any testing to verify this. It is the laws of physics. You cannot get something for nothing. The extra air does not move through the engine on its own, work has to be done.

The extra work costs extra gas.

You say lean cruise works. I say that may be the case, if it is the case it will be explainable in terms that we can easily under stand. Like the O2 sensors are not perfect or the fuel map is not actually stoich. Whatever, I don't care!

Can you please come up with a suggestion to get this guy back and fourth from work in his GTO DD at 32 mpg?
That is a 3800 pound car and he is driving 50 miles of mixed. Actually go back and read his original posts, then comment.

I will be looking forward to some meaningful suggestions on that goal.

Awesomeperfmachine

Running leaner than stoichiometric air/fuel ratio uses less gas. If you are traveling down the road at a given speed with a given throttle opening(given amount of airflow) and you lean the mixture(take away fuel) then you are now using less fuel. You can lean the mixture by either adding air or taking away fuel...

383ss

iTrader: (14)

wow.
where do you come up with this stuff? you are making your basis and assumptions on absolutely nothing.
you say the goal is stupid? your arguement is complete nonsense and a waste of thought.
lean cruise works. period. there is no arguement against that. its a FACT. to argue that shows you have no content in anything you say.

2002_Z28_Six_Speed

iTrader: (19)

I argee with the guy that said we need to get this thread back on track. I would love to discuss this all day long but we need to get this Goat up to 32+ MPG if possible! Come on LS1Tech!!!

We have a crapload of smart guys on here. We can figure it out.

1999 SS

iTrader: (3)

just for sake of conversation:
i drove from detroit to grand rapids two weaks ago in my dd 2000 TA automatic 3.23 gears with only mods beeing a cold air set up and cat back and a recent tune up full tank of gas and big sub box out back and i averaged 28mpg with the cruise set at 75mph. last weak i made that same trip with all conditions being the same including weather but cruise set at 85mph and lost 2.5mpg.

im gonna say that with a 408 getting 32mpg on the cheap is gonna be tough if not impossible but im sure he can get close maybe in the mid upper 20's(25-28) at best with a 3800lb car. i wish ya the best of luck.

hammertime

iTrader: (1)

A couple of things from the original poster to get this thread back on track:
not 50 miles mixed, makes a difference trying to get to 30mpg
obviously, leaner than stoich mixtures do use less fuel
given the above statements, I think we can conclude the 408 has gone, and I think we're dealing with an LS1 ('04) as opposed to an LS2.

mr2guru I never saw a response regarding whether or not you still had headers from the 408 you can install.

MrDude_1

iTrader: (4)

LOL @ KENS_SS_4... mmk dude.


anyhoo back on the actual subject.. i was thinking about his 87 vs 93 experiment for dollars per mile....mr2guru, have you started on the project?
my car currently isnt in a good stage to try this.. lol. all of my friends with the ability to try this also have their cars heavily modded.. so im dead in the water, but very curious.

'JustDreamin'

The dollars per mile doesn't really pay off that quickly.

In this example, he drives 75miles roundtrip per day = 375miles per week.
If we assume that he gets 25 miles to the gallon = 15 gallons a week.

Using current pricing in my area
15 gallons @ 2.85 (for 87 octane) = $42.75
15 gallons @ 3.05 (for 93 octane) = $45.75
Net difference: $3 a week. or roughly $156 a year.

As gas mileage gets better, the difference gets smaller. At 30mpg the difference is only $2.50 a week or $130 a year, but at 15mpg the difference is $5 a week or $260 a year. Also, this assumes that he gets the same mileage on both grades, which may not be a safe assumption and something that so far nobody has proven.

Also, the total savings going from 23mpg to 30mpg is not a huge deal. Driving 375 miles a week, going from 23 to 30mpg on $3.05 a gallon premium saves you about $12 a week or $600 a year. Which is probably why he doesn't want to spend a bunch of money, it doesn't pay itself off very quickly. Certainly over the life of the vehicle, thats a bunch of money to be saved, but short term its only 2 stops at Starbucks a week.

'JustDreamin'

KENS_SS_4

Laughing at me or anyone is counter productive for a forum. I am very thick skined so it doesn't stop me, but, it will stop others from joining in.

Lean cruise does not mean leaner than stoich in reality. If you don't use the word "stoichiometric" I will stop beating this horse. If you continue then I shall though.

The A/F's that you all see at the bottom of dyno sheets are "calculated", not actual.

A good *** sniff test (pre-cat) would find unburnt hydrocarbons even at lean cruise or there wouldn't be a gain in fuel mileage. Friction and wast heat not put to direct work are one place where mileage is lost. So air moved through the engine by the work of the engine is part of the mileage equation. You cann't save by moving more than is needed.

Slowly accelerate and cruise in a high gear at a low speed. Simple!

MrDude_1

iTrader: (4)

i agree its a case of diminishing returns... but ever since i found out that 87 in a LS1 gives you less MPG (due to the excessive timing retard), ive been curious... if you tuned it for 87, what would the MPG loss be? would the cost savings of the gas be enough to offset the additional fuel used?
i think you'll be losing some efficiency in the form of lost power, but the end goal here is a thicker wallet, not a faster car.
but you're right that it wouldnt add up to a whole lot... and its not like im going to do it myself anyway.. i'll live without caffeine and pay the extra $$.. lol

MrDude_1

iTrader: (4)

i just laughed because its really not worth my time arguing with you about it. i think everyone else participating in this thread gets it, so im not going to waste everyones time by tearing it apart.


ok, a quickie explination of the GM PCM fueling without the word "stoichiometric".

there is a goal AFR that is set as a constant in the PCM.
using one of several methods, the PCM calculates the amount of air entering the cyl.
the PCM then calculates the target AFR, starting with this goal AFR and applying a series of corrections to it from modifier tables.
the PCM then takes the amount of air entering and the target AFR for that instant and calculates a required amount of fuel.
that amount is then calculated out to an injector pulsewidth and this pulsewidth is sent to the PCM.
excuse the term stoichiometric here... this is a screenshot i just took from HPtuners.. i crossed it out with a "yellow highlighter".


it just so happens that GM set this inital "goal AFR" to: 14.62857
well one of the modifier tables for the target AFR is the lean cruise table.
if specific requirements are met, such as maintaining a speed range, little throttle input over a peroid of time, ect... then this modifier table is enabled. i can post screen shots of these requirements and tables, but all thats really important is that alot of these take the goal afr of 14.62857 and change it to the upper 15s to lower 16s range... this of course effects the fuel calculation, and the car runs leaner.
if the tune is even somewhat close to accurate, then thats what the wideband reads too.


im fully aware of how a lamba sensor, err... i mean wideband sensor, works.


lookup how a diesel works, and you might be suprised..
you dont NEED a clean emissions perfect burn.. if a 14.6 AFR was ideal for power output in a gasoline motor, we wouldnt run richer on race motors... but it turns out, that number is perfect in lab conditions to fully burn all of the fuel. thats it. running an engine insnt quite the same situation. the only reason most motors dont run leaner to begin with is heat. it burns alot hotter after that point. in the US, lean cruise was removed in the early 90s, not because of emissions or anything like that, but because of politics... in a nutshell, theres CAFE (corperate avg fuel economy) regulations, and they considered lean cruise to be "cheating"... so its better for the car makers to just not use it.. even though it would help MPG... however, theres no such BS in ausseland, and they have the lean cruise enabled from the factory.
it works great there..... jsut like my lean cruise worked great on my stock TBI motor, and on other earlier GM ECM cars.

with the MPG hes getting, you can be sure hes already doing that.

87calais

Before I even finish reading all the posts, I would have to ask a stupid question, How does ethanol raise the price of gas if E-85 is 30cents a gallon cheaper, and theoretically should only be around $2 a gallon, if E-85 is 85% ethanol, vs standard gas, which is typically 10%. As for the remark about it being higher priced in the city, there's two thoughts that come to mind, price gouging, and supply and demand.

BJM

iTrader: (1)

I am not laughing at you but you are way off base. Prior to EFI people simply tuned engines to what worked well and the word stoichiometric was used a lot less. OEMs ran carbs leaner than stoichiometric at cruise all the time because it worked. Leaning the mixture works for mileage but moves the engine off its emissions sweet spot where the catalytic converter does its best work and became illegal in the US at some point. Does leaning it out work? Certainly. As you yourself mentioned, as long as some measurable HC is coming out of the engine, some fuel is wasted. You can lean it out until the engine runs really badly and you should still see improvements. Peruse the SAE technical paper libraries for lean cruise and you can see for yourself what people have studied. Generally a lean ratio of 17:1 up to maybe 18:1 is the practical limit for lean cruise traded off against engine smoothness on typical engines. Special purpose engines have run up to 22:1 up to 25:1 or so quite happily.

As far as real world results go, I wrote my own lean cruise code in my Grand National and settled on 16.2:1 at my leanest setting with a small amount of EGR (better heads might have let me go leaner). I ramped mixture according to load up to stoichiometric when a number of parameters were met. I data logged extensively and recorded average cruise fuel savings of 7-10% (the cruise portion only). The cool part was when the lean cruise kicked in you could feel engine power drop slightly and I had to open the throttle slightly to maintain speed, reducing the pumping losses caused by the throttle. I used lean cruise for over a year with no problems at all and saw a small but consistent fuel savings.

ezrollin

Is'nt this called "lugging the engine" and is bad for bearings? Otherwise I would do it

BJM

iTrader: (1)

Not sure why bearings would get hurt, High RPM loads are the enveloping design load for the bearings. Under strong detonation you can hurt bearings yes but it is regardless of RPM. "Lugging" is more a personal thing, the engine can run quite roughly at slow RPM without damage, but people don't do it because they perceive they might be hurting something. The owners manual says to shift in 6th at 50 mph, the CAGS forces you to shift down to 800 RPM from 1st to 4th. Yes it lugs but unless you floor it, you won't harm it.

silverTA2002

iTrader: (1)

Wow, five pages. I don't have time to read them all, but I think the answer's pretty simple....

Leave it stock, or buy another car.

Outside of free mods, I seriously doubt any aftermarket modification will actually SAVE you money (even in the long run).

Yeah, gas is getting more expensive, but do the math, you're not going to save money.

If you REALLY want to save money, DRIVE LESS!! (carpool, public transportation, bicycle, etc.)

ZL1Killa

iTrader: (17)

buy a freakin 4 cylinder and leave this as your fun driver.

it will end up being cheaper in the end and you can go for 'fun' drives.

you don't buy a V8 sports car to get good gas mileage, however in stock form and nice easy driving we do get good gas mileage(unmodded/slightly modded car) but still,
ITS A V8


also, if you want good gas mileage and power, get the VW turbo diesel and mod it, cuz i'm damn sure there are mods

SmokingWS6

iTrader: (1)

Why would you buy a car designed for premium only to run 87?