Been doing some more data logging..........

With this latest ignition system (my 6 pack DIS), I can reliably fire AFRs, down to like 18.5:1. There's not much power at that AFR, but I can run there without a miss.

Well, one thing that has seemed rather *odd* was a feeling of the engine needing more Throttle to run at a given speed, and in fact it did.

The interesting thing is, that while in this case I can run leaner, one side effect is needing more Throttle. This also has the side effect of higher MAP readings.

So while I can run the leaner AFRs, the actual injector Pulse Widths are almost identical. There's no where near the change in MPG that you might suspect in running at 17.5:1 compared to say 14.2:1.

AND, as far as MPG goes, lower speed, doesn't mean better MPG. An engine has to get to the stage of being *happy*, and spinning fast enough to have the cam *working*. I get several MPG better mileage at 70 then at the lower speeds (2,200 RPM).

BTW, I don't mean this as a universal rule, but, rather just sharing what I've found in this application.

 

Theres going to be a point where fuel economy is maximized. Leaner or richer then that point will cause the fuel economy to drop. If you took a 350, gave it 13:1 compression, a weenie little cam, and TBI with a heated intake, it could probably run at 20:1+ and get 35-40 MPG. Granted it would only make 120 HP and probably would need fly by wire throttle to control the MAP. With a lower compression motor, or a motor that doesnt make good cylinder pressure at low RPMs, you cant run real lean and still get good fuel economy.

 

When I get back on the engine dyno this summer, I'll do some tests along these lines. Something like Constant RPM, Constant TORQUE, and vary AFR and timing and of course throttle to see what comes out as optimum for mileage (lowest PW for same torque and RPM). But, sadly it's not going to be on a small block chevy, or buick v6. The lean will increase the efficiency of fuel burn, and the open throttle will reduce pumping loss, (and increase the actual cylinder pressure before ignition - any benefit?? thinking out loud, or on type).

On a similar note, I was doing some limp home testing on our lil 3 cylinder, and it would fire and pull til off the scale lean (sequential injection, single coil, distributor, 9.5:1 CR, 1L). Like high 20's, according to an LM1. That's with TPS, TMAP, EGO, and CTS disconnected, and just seeing what it could do, and adjusting the default to something that would start and move the car without stalling or fouling at idle. It never really got to the point of herky jerky, even at full throttle, just really couldn't make the (mustang) dyno accelerate.

 

Somthing I have tryed but have not done any data logging on is running on 4 cyl for fuel millage. I ran a simple experment that involved pulling the the 4 injector wires of on the side opposite to the o2 sensor. The computer compesated well and there is enough power at cruise to make it fesiable to run a switch to break the circuit on that batch of injectors or making the ecm drop them using a relay and a output pending on map and highway speed.
The map does go up and you are on throttle more. But the efect of higher cyl pressure may over ride the loss of mechanical friction on the 4 that are along for the ride.

The engine would idle fine with no codes, run smooth at cruise but had other places in rpm that the engine was out of balanced due to power strokes not being in alignment.

I will post my findings after doing some loging and looking at mpg from my cvs files in excel.
Does any body know much about the mechanics and controls of newer engines that do this?

 

It's as much if not more about how much HP it takes to push the car down the road, rather then what AFR you can get the engine to run at. The *pumping loses*, while great fodder for thought has little signifigant meaning in the real world (as far as my application goes). As I said, it's almost a constant 3.5 Msec PW to get the car to go down the road, doesn't matter if it's 17.5:1 or 13.8:1 AFR, the PW was the same..

 

Everyone needs to try and experiment with their engine to find it's happy place. 17.2:1 (with an operating EGR) when I had a stock operating TPI L98 gave me the best gas mileage (and the shortest PWs) when cruising at it's optimum speed (for mileage) which was just a bit above 60 mphs.

As you said, nothing is universal and different vehicles (engine/tranny combos) will behave differently and have a different sweet spot. The key is, everyone needs to experiment and find their engine's own happy place.

 

Please tolerate my ignorance on this, but how do you determine this mileage "happy spot"? Seems like it would take thousands of highway miles pretty much shooting from the hip with HW mode settings to get an idea of where this happy spot seems to fall. Is there some trick to figuring this out (monitoring pulse widths or something like that) that I don't see?

 

Happy spot or sweet spot is starting from sort of like a "feel of ease" for the engine.

When you have everything in order in the car and start drivin the hwys or countryroads with it then at least my opinion of the startingpoint of "the spot" is where you need the least amount of throttle. The feel is then like the car is moving all by itself and you're only the passenger holdin' the wheel. So you have made the engine's life easy. They are alive, right?

Start the leaning procedure from there. Just my point of view here.

 

That's it.
The less fuel you need, without raising the operating temps., the better.
And using the least ammount of timing, consistant with a given level of performance. ie more timing is not always better, and depending on the engine combo., as low as 30d in cruise might work out.
----------
Gotta stay conscience of the timing, and temps., thou, but basically, yes.

 

Great info, guys, Thanks.

From this and another thread I stumbled onto last night, sounds like minimum TPS for a given constant and consistent load at cruise, which watching for detonation and pre-ignition and keeping an eye on the temps, is the way to accomplish this. Definitely have to give this a try in the next few weeks. Appreciate the responses (without making me feel any dumber)!!!

 

vernw I read that thread too. Some of these youngsters are pretty smart huh?

On (monitoring pulse widths or something like that) Rbob's EBL has a MPG screen that is based on pulse width. Pretty kool as you can see what affect your right foot and your tune are having.

Oh and like Grumpy says watch oil temps. Seems like oil temp would be good to data log also.

 

As a function of PW, yes.

If you see the PW getting longer, reguardless of TPS, your mileage will drop (or that's what I've seen so far).

This is a time when a Prominator can pay for itself. Being able to hot swap .bins on a *trip*, is invaluable.

 

Please note: this is another view on the whole MPG item. It may or may not apply to your situation.

When looking at PW, the engine RPM also needs to be taken into account. A smaller PW at a higher RPM can mean more fuel, or less fuel. It is fuel consumption over distance that matters. And distance traveled to get from A to B.

So if using the PW comparison test method, be sure to keep the RPM the same.

A daily drive to work and back offers an easy comparison from BIN to BIN. I thought I was doing great for reducing fuel usaged. The MPG was increasing so I figured it was a good deal. Until I looked at gallons consumed. Better mileage over a greater distance doesn't always mean less fuel consumed. When I found from A to B can be done over less distance and a lower MPG. But less fuel consumed.

Obvious once looked at. But, without the gallons consumed data, who would know?

RBob.

 

PW was a guide, but I actually drove THOUSANDS OF MILES (with MANY COMBOS) to find the combo that yielded the best fuel economy on my (then) stock TPI. And ultimately, only by monitoriing your fuel consumption and noting the results will you find your "sweet spot".

Now, without an EGR setup, the combo is COMPLETELY DIFFERENT. I found my car did NOT tolerate too much leaning of the AFR, especially on "load" situations. Unfortunately, since then, health and financial priorities forced me to stop driving the car and find ways of making money (instead of spending money).

But, if oil goes to $100/barrel this summer, then I will be in good financial shape to resume working on my car and continue doing testing.

 

OK, time to put my "I's Stoopid!" hat on again. Actually thought I was starting to get a handle on this until this post....

RBob - I envy your knowledge and abilities on these cars and coding (EBL is phenomenal!), but I think you lost me on this comment:

Better mileage over a greater distance doesn't always mean less fuel consumed.

I must have missed something here (gimme a break please, it's late and my restless legs won't let me sleep). But better mileage means less fuel consumed since it's MILES divided by GALLONS of fuel. So if the distance is the constant, then higher mileage can only come from less fuel, right?

So what did I miss in reading your post? I know there has got to be something!

As for the other posts, thanks guys. I'll be doing some testing over the next couple of weeks, watching TPS and pulse widths for a given speed/RPM and trying to squeeze out a little better mileage on my 'Bird. Oh, and watching the temps, too. Don't image I'll be able to lean it out too much though since (as Glenn pointed out) my heads aren't drilled for EGR.

If I ever am satisfied with my apparent split AFR problem on my SuperRam I may try some different heads (like AFR) with EGR risers and angled plugs. Gotta win the lottery first though! (or some goody ship come in, for sure). Or if I give up on it and go with an LT1.

 

He's saying that a shorter distance is usually better than a longer distance, hehe. I had to read it a few times also. Shorter distance even with worse economy can be less fuel used than a longer distance with better economy.

So, take the short way to work, unless it's stop and go.

 

In my 93 Typhoon, I dont think I have an oil temp sender. I know Ive got one on the 'vette. Whats the easiest way to log or at least read my oil temp (besides a mechanical gauge). Im running $58 and a nearly stock bin.

 

Dunno, but in my truly honest un-experienced method, don't care about oil temps too much. Heck, the higher the better during "cruise". I'd honestly love to see some logs of contant x's variable y's and oil temps. no joke, i'd literally drool over them, unless it's quick to see not significant changes, but I guess, it would still yield drooling if no to little change.

 

Yeah, I see that now - I knew there had to be something I was missing!!!

Thanks, Jeremy, for settting me straight.

 

I would like to share my findings from today.

Using a formula in Excell and cvs files I found the following.

Highway mode at aprox. 16.8 afr is worth 4 extra miles per gallon over 14.7afr.

Running in over drive is about 3miles per gallon better then drive.

Running one bank of 8 cyl. (drivers side injector wires disconected) is about 2 more mile to the gallon more then running at 14.7. (the map is so high you never see Highway Mode)

Running one bank of cylinders has a vibration that is very anoying. Could be harmful to the engine as well.

I think running a v8 as a v4 would get rid of the vibration, but I would have to run in open loop. Highway mode with above stock settings is worth more any ways.

 

Yeah, running that inline 4 probably isn't the best solution...

 

Just out of nowhere....
I have just been changing the timing around for milage reasons, it had been getting 21 1/2 to 22MPG and with the last change (6 deg less from 43 down to 37) at maps 50 and under. My last run to town was 24.9 Mpg for 24 miles.

 

I am interested in your mpg display. Does it hook to the aldl? Where did you get it?

 

That comes with the EBL along with many other goodies.
RBOB

 

RBob.

 

Once you start worrying about engine life, you will.
Too hot, or too cold of oil, cuts down on engine life.
Running too hot, just about will mandate running a syn., to have an engine last.

An oil temp. guage, is no less important, the a WB, EGTs, or plug readings, for tuning. Not to mention that you can build up ALOT of heat when doing a few back to back runs, enough that even with otherwise having a good handle on them, to cause serious problems.

 

Here was a log with 43 total timing.

 

Not to brag, but here is mine from my G20 VAN. 5,500#, 3.73 gears, 2,800 stall, 350 TBI making 218/339 at the wheels.

 

Sorry I hadn't seen this before. IIRC you have L31 heads so you don't need as much timing. Too much ignition advance (when using fast burn, efficient combustion heads) means you prematurely make peak cylinder pressure which actually helps slow the engine down rather than in optimally turning the load on the drivetrain (the trans, and hence the road driving wheels).

You ought to try 32 degs max at part throttle cruise.

 

So you are saying even with lean cruise enabled to not have it add any timing if one is already at 32 degs?

Thanks.......DM

 

I have lowered them even more. The highlited is my caaruze zone.
I just did a 101 mile trip the other day (with in town driving) and topped the tank off near home it took 3.04 gallons to fill it back up.
I had filled the tank the night before. Do the math. And I have High-way Mode disabled at the moment.
I had been going the wrong way and the milage went down.

 

zipfast..............what speed are you running when at cruise? That's alot better than I have been getting in a lighter car and with a 305. It has gotten better now that I'm running CL and been tuning with the BLM's. This shot was today if indeed it is correct.

Also if you don't mind what cam are you running?

DM

 

I cruise at 60 (2 lane) and 65-70 (4 lane)
The cops here in Pa frown really hard on speeding, ask me how
I know $180.00 and 4 points later

As for the cam it's a COMP cam 12-388-12 (CS 252AH-12)
Lift .453 int .470 exh (w/1.6)
Lobe sep 112
Dur @ .050 206 int 212 exh

Not really that good of a cam but I had it on the shelf.

 

That's pretty much the same speeds as myself. I edged it up a bit this week after watching the EBL mpg display and it showed better mileage at 70-73ish than at 65. My timing is a little above yours at cruise but not too much.

Our final drive ratio is about the same if your OD ratio is .70 Same for the cam as mine is 203/210 476/480. IIRC

Have you tuned enough to try LEAN CRUISE yet?

 

Well that brings about a story of how the milage screen can be disleading.
I had (till last week) been using Highway Mode (Lean Cruise) and
was tuning acording to the numbers. AFR's in the 18-19 range. I thought
I was doing great then I filled it up and did the milage / gallons and found
out that I only got 18 MPG for that tank
So I disabled LC and poof the milage came back up. I had way to lean a mixture
and had to push the gas harder (higher PW like Grumpy said at the top of this thread).
That was back in May that this thread started and I got to watching the MPG
screen and not paying attenion to the PW.

 

When I tried LC the engine did not like it at all......just too lean. Next time I try it I will vary the AFR's. IE: richer than the 16.8ish in the EBL bin but leaner than 14.7. Watching the mpg display helps "learn" one at what rpm the engine is "happier" for mileage. Just going back to CL has helped a good bit. It sounds as though you are heading in the right direction.

 

(DM91RS)Do you ever check you IM's?
Also if you live in a Hilly area try down shifting to 4th at the start of a hill.
Don't just Gas it.

 

Sorry I did not see this. I think by now you know about my IM status.

I am not sure what size hills you are refering to here though. And at what speed are you talking of?


DM

 

Is your EGR disabled? I think LC is intended to work with EGR, and it probably helps to have high swirl heads (Vortec, LT1, or earlier TBI swirl-type 810, 191, 193, 187).

 

What if one has Vortec's and no egr?

 

My EGR is hooked up, the GM preformance intake (based off a truck intake) has the egr on the front passenger side and the input hole is on the driver side. Meaning I had to adapt it to work ( 1/2" copper tube worked perft-o-mondo).

 

Do not worry about EGR, it is not needed for lean cruise.

Try commanding 16:1 or less at cruseing speed. You may actaul get like 17.5:1 at times acording to the wideband with a commanded high 16 teens.

If you feel any lean missing go back until it is gone. It will not hurt your motor but your milage will not get any better.

 

After thinking about it Rbob did not have egr usable when the EBL was released and it came with Lean cruise.

I agree.......just back the afr's down until any missing is gone.