dimented24x7

iTrader: (2)

I was thinking that if I ever do finally get my car running again Im going to need a new heated O2. Well, why not spend the extra dough and get an LC-1? Well, why bother to run stoich in closed loop if I have the LC-1?

Im thinking that somewhere between 14.7:1 and 20:1 there is a sweet spot for fuel economy for my motor. Ive definatly been entertaining the idea of just running lean when in closed loop and at idle/low load. Running lean at idle is counter-intuative, but after what I saw with my brothers '96 grand-am, it sort of changed my mind.

After I fixed the dead ignition (typical problem with coil housing on quad-4's), he said that the car got nearly 40 MPG on the highway, and over 30 in the city. It turns out that the car was actually not entering closed loop due to the previous owner fiddling with the t-stat. In addition, it also has a very, very weak pump, and runs at nearly 20:1 on the wide band! Obviously its probably not actually that lean, maybe 18:1. If it wasnt for the smell of the exhaust, I never would have known. The later PCMs allow the cars to run very smooth, and the car is quite drivable dispite this problem. High loads are a different story. Sets a knock sensor fault as soon as you hit the gas from all the detonation.

The way I look at it is that with TBI, as long as there is a warm engine and intake, and some vacuum, the air/fuel mixture should be fairly homogenous, so there wont be as many rich/lean pockets in the chamber. Also, by trashing the crap stock O2 routine and adding full PID control along with a nice, steep response around the desired closed loop AFR, I should get fairly good control. In addition, all the various PID idle controls in the PCM I'll be using should keep the engine in check.

I wonder where the peak fuel economy will be? With only around 9:1 compression ratio with stock pistons and vortecs I dont think Ill be able to get anything crazy like 25:1 AFR. Maybe around 16:1-17:1 AFR? Sound too crazy? It works for my brother, goes forever on a tank of gas. Cant say his motor will last that long, he still refuses to replace the pump

DENN_SHAH

iTrader: (1)

i run my car up to 17.2 AFR in Decel by the ECM, highway cruise is around 15.4~16.4. i don't know just how close it really is to those AFRs as i don't have a wideband,.. yet.

one thing about that quad 4, the coils fire really hot on it, so it can light a lean mixture.

Fast355

iTrader: (2)

I ran my stock cammed 305 with TPI heads on it, at 17:1 during highway cruise (pulling 5,300 lbs). No problems, at all. Just the second I started pulling a hill, it came out of highway a/f to a more conventional setting.

With "fast burn" heads, a standard heated aircleaner, and a functioning EGR I see being able to run up to 18:1 no problem.

Smallish injectors at much higher pressures help accomplishing good mileage as well.

dimented24x7

iTrader: (2)

Speaking of that, I was thinking I should probably upgrade my ignition as well before I try this.

The quad 4 definatly does have the advantage of no wires between the coils and the plugs, and no dist., so its a straight shot at the plugs.

Fast355

iTrader: (2)

One a seperate note, Chrysler tried doing this years ago. They were running a/f mixtures as lean as 20:1 @ light loads. The system worked well when it first came out. The problems started surfacing after several years. The carburetors would meter a little differently, the ignition system would degrade, things would get out of adjustment, the car would be a lean stuttering detonating mess.

dimented24x7

iTrader: (2)

Was the system closed loop? I take it the answer is no since it was probably like 25 years ago.

327_TPI_77_Maro

iTrader: (8)

Chrysler Lean Burn setups started in something like 77. Late 70s-early 80s. They were computer controlled carb setups and had O2 sensors. I can only imagine they did run closed loop.

DENN_SHAH

iTrader: (1)

they were closed loop feed back systems.

as Fast355 said, they did have problems with them after they got a few miles on them.
it wasn't a bad ideal over all, just not a good ideal for use with a carb.
they also ran the timing up around 52 degrees when in lean burn.

kevm14

This is probably almost a question for the EBL thread, but I'll ask here: can you elaborate on this please?

dimented24x7

iTrader: (2)

The stock routine is fine for the stock O2, and is set up to allow the routine to perform some diagnostics on the sensor at the same time, but the constant swinging wouldnt fly when running lean. The engines power output changes too rapidly at those AFRs and it would likely cause a surge. The integral term also can only step in the direction of the desired fueling, IIRC.

Id rather have the proportional term drive the integrator and have a derivative term in the main fuel loop so the O2 PID can target the desired AFR and not ocillate around it.

87tpi7749

I read an article on Banks site about Smokey Yunick running afr of 22:1 and getting 40-50 mpg back in the day. I haven't read his patent papers, but the patent numbers are listed, maybe you can find some info. The Smokey paragraph is towards the bottom. http://www.bankspower.com/tech_coolair.cfm

dimented24x7

iTrader: (2)

The concept is sound enough, but having a turbocharger and all that other stuff is a bit complicated.

Getting it to vaporize and mix is definatly key. Otherwise there are high NOX and HCs from the rich and lean pockets in the CC. Its sort of hard to get all of the fuel to vaporize, as the mixture gets quite cold from the vaporization of the gasoline. Ive looked in the intake after the engine was running and there always seems to be a little bit of fuel along the outer edges on the interior of the manifold.

kevm14

I think I read that article, too! IIRC, it was an old C&D, but I really can't remember for sure. Anyway, I think the engine was called "the hot air engine." The "secret" was very high intake air temps. The C&D writer kept saying he thought he heard detonation and Yunick kept either changing the subject or denying it. Then one time he lost an engine and refused to acknowledge that it might have been from detonation. Interesting, at least. I think he used the Dodge Omni with that 2.2L turbo.

Fast355

iTrader: (2)

http://www.impulsengine.com/how/index.shtml

Something similar except no lean burn and no turbo. They claim huge power. The top performer is a 318 with 630 ft/lbs from 1,000-3,500 and 420 HP @ 4,500, NA. The other is a 360 with 710ft/lbs from 1,000-3,500 and 480 HP @ 4,500 The packages start with a 318 at 480 ft/lbs from 1,000-3,500 and 330 HP @ 4,500. The 360 starts at 540 ft/lbs from 1,000-3,500 and 380 HP @ 4,500. Wish they would post actual dynosheets though.