ULTM8Z

I made a couple of mods that seemed to have a significant impact on my fuel mileage. Was getting ~27, now getting ~29. Not sure which one had the greatest impact...

I leaned out the highway fuel AFR to 16.5:1. Was running around 16 before (WB O2 is now oscillating between 16 and 16.5:1 as opposed to 15.5 to 16:1). I don't get any knock counts or surging and the plugs look good, so I'm taking that to mean it's doing ok. Considering how light I am on the throttle during steady state cruising, I'm not too surprised. I'm typically cruising on level ground at about ~8% throttle in OD with the converter locked up at 70 mph, at about 40-45 kPa MAP. Highway mode will disengage at 55 kPa, so it should be pretty safe IMO...

The other thing I was to also increased the delta-MAP enable threshold vs TPS to 5 kPa at 0-12.5% throttle (factory 8D is 3 kPa). Considering how much AE I run on the Miniram, this may have had the most impact. I'm thinking small imperceptible changes in throttle (imperceptible to my foot anyway) may have been inadvertently engaging AE during cruising, thereby throwing in more fuel than necessary. A small change in throttle position will have a fairly significant change in manifold pressure.

So increasing the delta-MAP threshold in the 0-12.5% TPS range seems like it may have helped a lot (I'm not sure 1/2 point on the AFR would have been worth a full 2 mpg).

Any rate, the Tunerpro readout (which I already tested to be accurate within about 1/2 mpg) was bouncing around between 28 and 30 mpg, so I'm taking the average of around 29 mpg. Crazy...

RJ IROC

QwkTrip

iTrader: (22)

That's some pretty dang good mileage! Especially considering you have a performance oriented engine, if I remember right?

I'm guessing your data logging can't monitor AE as its own channel?

I have Holley HP EFI but same concept where I had to blank out AE at low rate of change of TPS and MAP (speed density tune). I think you're on the right track!

That's a pretty lean "lean cruise". Might need to monitor that again next summer when temps get high.

ULTM8Z

the SAUJP does report when it goes into delta map AE. I didnt really look at that before I made the modification, so I'm kinda guessing here.

maybe I'll undo it and then see.

yeah its has a little bigger cam than the ZZ4, AFR 180cc heads and a Miniram intake.

as far as spark, I'll have to go look at my tune, but I think its about mid 40s at that rpm and map.

TTOP350

iTrader: (8)

Wow, very impressive. Need to send you a few cars of mine

QwkTrip

iTrader: (22)

Stout combo.

Fast355

iTrader: (2)

FWIW, I do not disengage highway mode until above 75 KPA when running a 7730 and in the EBL where the MAP table goes to 100KPA or my Express van with the 0411 that allows you to dial in at whatever load, I do not disengage it at all. I merely richen the fuel mixture slightly as the load increases. The aluminum head Vortec 350 in my Express van cruises 17:1 at 2,800 rpm and 50 kpa with 52* of timing while getting 18-19 mpg. 16.5:1 at 55 kpa and 16:0:1 at 60 KPA. I taper off .5:1 for each 5 KPA until I am down to 13:1. So 65 KPA at 15.5, 70 KPA at 15:0, 75 KPA at 14.5, 80 KPA at 14:0, 85 KPA at 13.5:1, 90 KPA at 13.0.

ULTM8Z

what gears and transmissions are you running?

I'm doing about 2300 rpm at 70.

skinny z

I like these stories about fuel efficiency as much as I like the ones about performance. It's always impressed that today's modern muscle car can squeeze out a decent MPG and have great performance too. It's even more impressive when that technology and result can be transferred to an older platform.
I too have tuned for a very lean highway cruise AFR. In and around 16-17:1 and even though this is old school with a carb and distributor, that AFR results in mid 20's for highway mileage. My manifold pressure (read in inches via a gauge) is about the same as that posted above. Ignition timing is around 50° at 2400 RPM. I definitely have some spark knock though.
Nice job on the tuning.

Fast355

iTrader: (2)

10.5" full floating 14-bolt with 5.13 gears and a 4L85E transmission. Tires are a little more than 31.5" tall. LT265/75R16s.

2,800 rpm I stated is right at 70 mph.

I use the same tune year round, even towing my 6,000 lbs travel trailer. When the house on wheels is behind me, the load keeps the PCM from leaning the air/fuel mixture out much.

Kingtal0n

<3 economy threads

now, take everything out of the car, (weight reduction)
put the lightest rotating parts you can find on it (wheels, ds, etc...)
get a good alignment all the way around and use the right tires,
decent aerodynamics work (nothing obviously terrible for wind resistance)
make sure the car rolls easy enough (all wheel bearings and turning parts are 'lubricated')
add cruise control if you dont have it yet (essential and overlooked)

and I bet you find another 1-3mpg (its mostly about weight) at the right speed

GeneralDisorder

iTrader: (1)

I'm getting my EBL dialed in right now. Doing VE learns. After about a 25 mile round trip mostly freeway I averaged 34.5 mpg being very light on the throttle. It seems to be pretty accurate. I'm quite sure it's correct also since I was getting mid-high 20's running a $6E MAF setup that I took about 800 miles last weekend. I'm quite sure that the EBL highway mode is much better.

And the EBL runs really good too. I'm really impressed with it. I used the included bin for 5.0 auto TPI port-mod and made changes for the injectors and my temp settings, etc. Fired right up no issues. Although the SA table is too aggressive in the mid range. Odd since it has about 10 degrees more advance in the mid range than the 5.7 L98 map. Maybe my exhaust and rocker modifications have made the heads more efficient.

I'm running the stock 86 LB9, with headers and full exhaust, 1.6 rockers, and Bosch III 24's. 3000 stall non-locking converter, 3.7 rear gears.

GD

Kingtal0n

You can't go by anything electronic. The way to calculate economy is fill the tank, drive with an accurate speedo X miles, then re-fill the tank and calculate mileage.

No way anyone is doing 35mpg with a 3800lb vehicle, with any reasonable (4-7L) engine on gasoline.
Economy is mostly about weight. Unless its 2200lb vehicle with a V8 it won't do near 35. I believe the newest vettes with manual transmissions do 32~mpg cruising @ 3000lbs with direct injection and a manual trans.
Automatics are lucky to hit 30, and if it's a 4l80e it will be near 22-23 for most 3000lb vehicles.
An unlocked converter is also terrible for economy, that is worth 2-3mpg right there. I suspect real mileage is closer to 25mpg with 3800lbs, any V8, and an unlocked auto.
4l80e is usually 3-4mpg worse than the 700r4/60e variants in experience

ULTM8Z

actually weight is not a factor when cruising at constant speed. it matters during acceleration.

on mine, I validated the electronic readout with the fill up method several years ago. had to make a late night run so as to avoid traffic in order to do it. drove about 100 miles on order to get a good distance from which to measure.

obviously in real world driving in SoCal, that's still just a theoretical maximum mpg as those kinds of trips exceedingly rare.

Kingtal0n

lol

Weight is the most important thing because power is directly associated with weight. Power tells us how far an object moves in a specific time based on its weight.

power is directly related to fuel consumption. more weight, same speed, more power, more fuel needed.
Inertial losses are during acceleration.

first random quote from google
" An additional 100 pounds in your car can reduce gas mileage by up to 2%. The reduction is relative to the vehicle's weight: Smaller vehicles are more affected by increased weight than larger ones. For every 100 pounds in extra weight, plan on spending up to 6 cents more per gallon. "

another

" The EPA says that for every 100 pounds taken out of the vehicle, the fuel economy is increased by 1-2 percent. ... The chart below shows that for a small car with a 1.6-liter engine, reducing weight by five percent led to an increase in fuel economy of 2.1 percent on the EPA combined rating. "

try google pls

ULTM8Z

dude, if you're cruising at constant speed, it doesnt matter how much the car weighs. I dont need to Google it.

it's simple physics.

weight comes into play if you're accelerating. of course your overall mileage will increase of you count city mileage too.

GeneralDisorder

iTrader: (1)

Sure. It may not be completely accurate. I'll check with actual fueling data of course.

But the EBL knows exactly how much fuel is being delivered through the injectors. And the speedometer has been calibrated via GPS because I'm running a Dakota Digital box on the Firebird's electronic sending unit.

I don't see it being all that far off. The car is 3200 lbs. Also very aerodynamic. Very little throttle is required to maintain 60 MPH. And I was checking with fueling last weekend getting high 20's doing 75+ MPH for 800 miles.

I agree the locking converter should help. But I am near it's stall at cruise if I'm doing 75 or so.

Time will tell how accurate it's estimates are.

GD

skinny z

It can be seen that you're talking about two different types of mileage. Steady state or "Highway" vs "City".

Kingtal0n

You are trying to say if cruise at a constant speed, it doesn't matter whether I have a 32,000lb truck, a 250,000lb tank or a 3,000lb car the economy will be the same? LOL

cmon get serious. I am guessing nobody here has a degree in mechanical engineering yet or someone would have corrected this besides me.
Well lets examine and get help with a few concepts. I won't name call or make fun of you for not knowing; just don't get mad and I won't turn to internet cat for cheese.
I am 100% sure. not 99% sure but 100% sure that vehicle weight is a, if not the, most important aspect of a steady state cruise. Both from 15 years of experience and having several degrees on the subject(s).

The power equation gives us how far, how much weight, in how much time.
1 'coal miner pony' moves 33,000lbs 1 foot in 1 minute.

You can think of that as a steady state cruise of 33,000lbs vehicle that 1 pony has moved 1 foot in 1 minute.
So if we cut the weight in half, now the pony can move it twice as far in the same amount of time. The pony has doubled its velocity for the same amount of work input.
If we then dial back the work input so the distance is the same as before- we've doubled our fuel economy for a steady state cruise.

If that isn't simple enough based on weight we can rip the equation apart further.

I don't want to get into inductance, inertia, damping, viscous friction, momentum terms, capacitance, etc... and how they related to dynamical systems, electric/mechanical rotating motors and forces, until we establish this one simple fact that weight directly affects fuel economy. I mean is it really that hard to see that huge trucks using gasoline get terrible economy on the highway, and lightweight cars do not? And that lightweight corvettes with the same size engines as those trucks get the same economy as lightweight 4-cylinder cars of the same weight? Open ur eyes guys....

Kingtal0n

I've designed and written software to keep track of fueling so I am familiar with the methods employed here. The computer does NOT know how much fuel is being supplied to the injectors unless it has a device in the fuel line to measure the flow, or a scale to weigh the gasoline used from the fuel tank, or something like that. More likely, what you really have is an estimating software that "knows" injector size, fuel pressure, and manifold pressure. Then using maths it can get a rough idea. The problem is the injectors are not all the same size, and there is a delay between manifold pressure changes and fuel pressure compensation changes, and those small differences add up to major differences in the long term, which are further compounded by small errors in given constants (such as the mass density of the fuel which changes based on temp) (and the dakota digital box is not perfect). Basically its worthless for computing actual economy unless you have one of those devices I mentioned first which can actually weigh or tell a flow/mass rate of the fuel in the lines accurately.

ULTM8Z

actually I'm a mechanical engineer.

lol...but unfortunately not only is this way off topic from the point of my thread, it isn't an argument I give enough of a $h!t about winning (with someone I dont even know) such that I'm inclined to keep perpetuating it.

Kingtal0n

shame on you for saying 55,000lb trucks take the same amount of energy to push as a 3,000lb car at constant speed then. carry on move along etc