JPrevost

So you want to save some buck well here are things I've implemented on some of my tunes over the years that have increased gas mileage.
First things first, running a leaner AFR during cruising and low load situations (not accelerating). Highway mode is in many of the masks for thirdgens and you should try it out. Running with an AFR between 15.7-16.5 has yielded the best for me. Running these AFRs at higher load (cruising above 55mph) will increase your oil temps so it's a balance you have to consider. I've noticed my oil temps stayed right at 215 and would drop to 205 when I pulled out some timing and ran stoich (closed loop). I've measured gains of 2mpg highway on my car and 2-4mpg on others. The more RPM you turn on the highway the more heat you're going to put into the oil from friction alone... so if you've got some gears out back don't expect much increase but if you've got 3.08-3.42's expect 3-4mpg.
Now if you really want to just plan save on gas and aren't in a hurry, SLOW DOWN. The faster you go the worse your mileage will be (if engine is in low part of it's BSFC curve). Aero drag is a direct factor of speed and it gets really bad above 55mph. Example; Friends GTP (eaton supercharged) was getting 30-32mpg highway when cruising at 75mph. One night he was curious what he would get if he slowed down and at 55mph he got around better than 40mpg!
Now comes the rather technical part, the engines BSFC curve. A BSFC curve of an engine starts offf pretty high, declines as the volumetric efficiency increases and then starts to rise again (usually before peak torque) because of friction. For this reason you will get good mileage if you keep the revs in the motor's "happy range". It changes for every motor combo but in general stock tight cam engines like the lower RPM and more cam/heads like higher RPM. Example; a stock 305 TPI might want 2000rpm, 350 TPI at 1900rpm, 305 TBI at 1800rpm, hot 350 at 2300rpm. It's usually below 3000rpm and above 1600rpm. You just have to experiment or get it dyno tested.
As for spark, that's a hard one. I don't like running much spark but that's because of my combustion chamber. It's a fastburn so it doesn't need much timing. I'll run 38-40 max on the highway be it in closed loop or highway mode. The non-fastburn's wanted 42-45 degrees at cruise. The one that wanted 45 degrees I was concerned about so we looked at the oil temps. I didn't like 250 degrees so I took out some timing and ran only a 15.2:1 afr. The loss was about 1.5mpg but the oil temps were down at 225, we left it at that.
So remember, add timing and the oil temps go up. As the oil temps go up the protetion goes down and you can end up spending more on frequenty oil changes than on gas EVEN with gas climbing like it is.
Now for some stuff I haven't been able to measure but from a couple people they say it's made a noticable difference.
Increased shift firmness of trans. The less heat you make from slipping the trans the more efficient the power transfer. Heat is BAD and with only about a third of the energy from burning gas going into the trans you don't want to loose even MORE so firm up those shifts. On the same note, run a tighter torque converter. Run a lock up torque converter and tune it properly to release during moderate to heavy acceleration but have it locked the rest of the time (decel, cruise, light acceleration).
Get a manual trans if you can. They are more efficient, you can't argue this one without looking stupid.
Have the trans shift points near stock on a stock motor and don't run a light govnr on your auto, with a good shift kit you should be able to hold a gear to redline so the govnr is only going to hurt your city mileage.
Use DFCO like it's your buisness. On the same note, do NOT take out a lot of timing in the decel area's of your SA tables. The more timing you take out the more the car will engine brake, even when in decel enlean AND DFCO. I'm very aggressive with DFCO because I can hardly notice the difference of transitioning in and out. Some don't like it but tuff you know what. If you want better mileage USE DFCO and decel enlean.
I gotta go get my hair cut but I think I covered most of it. Feel free to argue with me or post up idea's. Keep in mind there are always compromises but with how well these engines are being built and the relatively low specific output I believe 10-20 degrees increase in oil temps is worth it for the 2-4mpg.

MrDude_1

any tips on how to be more agressive with DFCO? im sure theres some gains to be had for me since i almost always downshift...

i guess it has to be general info.. since im not running the same ECM... but anyhelp would be cool.

TPIgirl

husband says tighter spark plug gaps cut down misfires when running leaner than stoich,
and that blocking the EGR will improve MPG.

He said theoretically that running EGR should improve mileage, but every test he's seen or done shows otherwise.

dimented24x7

iTrader: (2)

EGR is a good thing. Not only does it help reduce knock when your running lean (its primary purpose), but you also are reburning some of your exhaust, which allows you to extract a little more energy from your gas.

Grumpy

Except you generally have to add some timing, and fuel to run it, negating any benefits. Like TPIGirl's husband, I've never found any gains running it.

Plus with the elevated (cylinder) temps from running more timing, there's more of a chance for Tip-In Preignition.

dimented24x7

iTrader: (2)

Isnt the main purpose of the EGR to lower combustion temps to reduce NOx emmisions?

MrDude_1

bah. ignore the EGR issue...

any ideas on DFCO?

Z69

Yes- seen it on industrial apps using high dollar sensors with full control of EGR volume, fuel, & air.
Water works too. Messes with the CO though.

dimented24x7

iTrader: (2)

i wonder how much of a benifit is really had from having full control vs. the on/off sort of deal like what our cars have? The gm engines that use the linear egrs have PID loop control for the egrs position and everything, making it fully variable.

RBob

iTrader: (1)

For DFCO I try to set it up to be enabled as quickly and easily as possible. Then have it in affect until the last moment. The last moment defined by the upper MAP, lower RPM and lower MPH terms.

Shorten the delay(s) before going into DFCO, lower the coolant enable threshold. Then tweak the DFCO IAC steps to your liking. Smaller steps will have greater braking affect, larger steps will cause the vehicle to roll-on.

Another important area for fuel mileage is AE. At lower delta TPS & MAP, run as little AE as possible. Can then run a decent level of AE at higher deltas (if you are into those areas you aren't concerned about MPG).

An area that ties in with low AE settings is launch mode SA. I've found that it can crutch lean at takeoff and improve fuel mileage.

RBob.

3.8TransAM

If anyone would care to comment on highway mode and strategies for TPI cars.

I have not had luck engaging it on my next to stock 350 GTA or my modified 383 Formula.

Even adjusted it so the highway fuel and spark are tied directly together using the fuel qualifiers(thanks, u know who u r).

Havent managed an observable increase on highway trips were I went thru a full tank.

Just looking for comments and maybe figuring out a few answers.

Being unemployed sucks, being forced to drive the saturn almost 100% of the time cause of gas prices sucks worse :-(

later
Jeremy

TPIgirl

husband suggests you may not see measurable benefit from highway mode unless you are running a good open loop tune.
I don't know as I've never tried it.

Z69

With vortec heads and a 383 you may not need much more timing, and with that small cam and good chamber you might not need a lot of fuel either for good part throttle performance. Your combo may not respond to HW mode.
Are your sure your not disengaging it with your driving style.
With the timer you might not ever allow it to stay on for long.
Cruise control in the flat is great for that. Also if you have a lot of AE, it will negate HW mode beneifits to some extent.

JPrevost

Highway mode... I don't even run the highway SA, it's zeroed out. My 2mpg gains were stricktly leaning out the AFR. I tried running 2 degrees of highway SA and I couldn't get the engine to like it. It would work in the spring/fall but summer/winter (gas, weather) it would show knock. So I just took it out all together and didn't loose any mpg.
As for DFCO, lowering the enable temp is a first. GM doesn't do this ONLY because they are trying to get the engine up to temp as fast as possible for emissions. Hot intakes keep the mix in vapor, this is why cold engines need a LOT more AE.
Running the least amount of AE needed is always good and if you do a lot of on and off the throttle driving (city and stop lights) then try and use very little TPS AE and more MAP AE. The TPS AE can (with some masks like the 8746 TBI) load up the engine at warm restarts where choke is still on.
Honestly, I've not noticed anybody needing to advance the timing in "highway" mode because when I'm in that area of the SA map I know I'm cruising so I just set that area to exactly what the engine wants.
I haven't tested warm air induction, EGR, or water injection but I do know that high tire pressures WORK. Picked up 1mpg highway and 2mpg city by going from 34psi to 42psi on 245/50-16's.
A zero chamber zero toe alignment is also best. Some people have said running a lot of chamber has gotten them mileage because they're contact patch is smaller. I don't understand how they think it's better, maybe somebody can explain why it 'could' be.
Just wanted to note, like Grumpy, EGR hasn't done much of anything for mileage. I used to think it did but I don't think anybody has proven gains. EGR is for emissions, I think that's pretty much a given by now.
Is there anything else?
Oh, I almost forgot. Did you know that a golf ball that is smooth has a smaller boundry layer because of the size of the dimples. A smaller boundry layer is more aerodynamic (displaces less air against it's directional vector). For this reason, a dirty car or one that's banged up pretty bad like hail damage will be more aero dynamic . So if things get real bad, pull out the ball peen hammer and get to smacking . I'm actually serious about that to some extent. A dirty car should theoretically be more aerodynamic than a clean waxed version! Certain spoilers and less frontal surface area (no ground effects) also lower aero drag. Just some things to think about. In the end, we all should just get back to the pony wars of old... REAL old, and just start riding real horses.

dimented24x7

iTrader: (2)

I guess if your car is a little 2" dia. sphere it may help get better fuel economy I think the dimples bit only applies to small spheres. IIRC, the laminar flow that wouldve been present would have made for a larger low pressure region behind the ball.

Wasnt there a luxo car that had a textured surface to on its underside not too long ago? I think the idea was to help reduce noise. Maybe the extra turbulence prevents vortex shedding from forming after protrusions on the undercarrage.

One thing I still want to try is full closed loop WB control without any cats. Bet with a small cam you could save a pile of money running leaner when cruising and not having to drown the motor in fuel to shut down the cat at WOT.

3.8TransAM

Government whackjobs actually did testing on clean vs. dirty cars.

Their findings were that with a clean car, you could see a .25-.50mpg improvement. So it would be depending on the car and rolling mud pile vs waxed and shiny. Not much to go on lol

All my highway mode testing is done with cruise on and 100-200 mile distances, ie fill when i leave and fill the tank when i get there.

I also havent tried highway mode with zero timing added during HI and just a little bit on the lean side. Least on the 383.

Oh well, just one more thing to experiment with and life goes on

later
Jeremy

Black 91 Z28

As per the golf ball, the dimples cause the boundary layer to go turbulent earlier which delays seperation to further back on the ball which drops the drag on the ball.

As per the post, keep it coming gas is expensive and hard to find down here in MS at the moment.

TPIgirl

I run a paper fuel filter on my PCV line and it seems to help a little with mileage. I also think the car runs better if I use the 87 octane that doesn't have the 10% ethanol.
I'm talking about my Hyundai Elantra here.

Grumpy

ANYTHING that you can do to lessen the amount of oil going thur the combustion chambers is a good thing, a *proper* oil vapor/ air seperator would be even better.

By the same token, my truck likes the alky brews.

Captain C

If you have a loose converter, you can put the lockup setpoints back to stock. That will increase your mileage as well.

I don't know how much of the above articles are going to apply to my $6e code but I do believe the DFCO is in there and I should be able to do some mods there. I can also change the AFR's.

I have to fix the speedo first and eliminate the VSS code before I can finalize my tuning on the stuff I already have going. I have a PROMinator so I will be able to switch from performance to street to mileage with the turn of a dial.....

JPrevost

-Raise your TPS requirement before going into PE Mode. This hasn't been tested fully yet but 2 Lt1's (both EE mask and manuals) have shown improvements in mileage. 2mpg average by doing this but 1 of them I had lowered the TPS BEFORE going the other way with the table so his results aren't pure, the other is. Take that for what it's worth. I know the SUV's have a PE mode delay and if you don't enable PE until a higher TPS that 'should' save you some gas. You might need to take out a little bit of timing if you have older combustion chamber designs. The fastburns didn't need any trimming.

SB406

Anybody care to elaborate on decel enlean? I see it in the hack, but not in tunerpro. How do I use it and what does it do?

Also, getting more aggressive with DFCO means lowering both the upper and lower DFCO threshhold values, right?

I'm running a 7747.

One more thing...7747 has an option for the TCC to be locked or unlocked during DFCO. Stock, it's unlocked. Do I want to change this?

-Mike

JPrevost

Decel enlean commands an open loop AFR leaner than stoich when you first lift off the throttle. If you continue to be off the throttle DFCO should come on. Different masks take different modifications but in general it's safe to use DFCO down to 1000rpm or about 200rpm above idle. That gives the ecm time to fire the injectors and keep the motor from stalling.
I keep the TCC locked on decel on my f-body but not on the trucks I tune. The engine braking on a 3500lb vehicle isn't as bad on the clutch as a 5000lb vehicle with a tighter cam (more engine brake power). You don't want to overpower the tcc, it's not ment to handle a lot of power so use it sparingly. I've never had an issue with my f-body but some others with gn's and trucks have, so just be careful and don't stress it.

Grumpy

Ugh, only if you're absolutely sure about your AE covering the gap. Raising the TPS PE enable, is a great way to induce *tip-in* preignition.

JPrevost

Okay, I should have said, "you must drive like you're trying to save gas for any of the above to help." There, is that better?
Yeah, I know the AE can be tricky but taking out a couple degrees of timing in your high MAP/load and mid RPM should be enough to prevent pre-ig no? I've never had it happen when pulling timing. The only time I tune using PE SA is when I raise the TPS required PE values. I DID have pre-ig when we didn't take out any timing. Looking at truck calibrations you can see how much timing they've removed for a) having heavy vehicles and b) staying at stoich for as long as they possibly can without pissing off the driver.
I think our suburban was 16 deg max and then 2-4 was added for when in PE. Running with a lower TPS threshold you don't really need to bother with the PE SA table. Zero it out because it's highly unlikely you'll be at 90-100kpa at any RPM without triggering the richer AFR that PE brings. I hope I didn't loose too many people, if I did I can explain it better. Just speak up.

Fast355

iTrader: (2)

On my heavy G-van I run 12* Initial(never below this in the table), 20* centrifical starting at 1,200 and fully in by 2,800 rpm. Then I am running 10* vacuum advance on top of that. PE is set for 4* (did this to clean up the NOx emissions). I also have 4* added timing for the EGR. If you look the BPWC decreases in a 7747 when the EGR opens, that means less fuel. My van likes droping about 10# when the EGR opens just fine. I have the inital set at 6* in both the PROM and the distributer. I have the max spark advance now set at the distributer limited 48*. 42*+6*.

I also like to run A/F ratios in the 15.4:1 area at cruise speeds. I typically run at 50-70 map and 1,700-1,800 rpm going down flat highway.

I have always used the TCC locked during Decel, but use alot of IAC opening in decel. I don't get much compression braking that way. If I were to tow very heavy loads all the time, I have another chip that keeps the TCC unlocked during decel and has much less IAC opening, 30 counts for maximum engine braking. Right now I can coast forever before I slow down. Then when I tip back into it around town, the converter is already locked and the engine pulls. Don't have to wait for the converter to lock again. I am running a 2,000 rpm stall though. Keeping it unlocked around town sucks gas. I also have the minimum TCC load threshold set at 10% TPS throughout the whole table. I also keep the converter locked to 85% throttle, where I also kick in the PE, the transmission also downshifts 4-3 at about 85% throttle doing 80 too. Mandatory TCC lockup takes place at 75 mph. Works fine for driveability.

Grumpy

No need to get testy, remember this is an open board, with more then just a few novices. If you want to ignore them in your posts, fine, but, when you're corrected, a thanks would work alot better then coping an attitude.

Like you said, *I should have said*.

TPIgirl

Has anyone ever added an IAT vs SA-offset table to try and maximize mileage?
It seems like that would make sense especially if you are feeding the engine preheated air to cut down on the fuel need.

Oh and here's one more thing. If you could have the code trigger an interrupt relay to the A/C compressor whenever the TPS is increased a certain amount, wouldn't that save gas in the summer when you use the A/C a lot?
My Elantra has such little power it helps if I turn the A/C off when I'm leaving from a stop or speeding up. Once I get up to speed I turn it back on, but if the code could do it that would save the work of turning the switch on and off so much.
It seems to take much less pedal when the A/C compressor isn't running.

edit: same for climbing up hills. Turning the compressor off helps a lot. I thought about using a gravity tip-switch to cut the compressor off when climbing hills but I never tried it.

HaulnA$$

while not necessarily third gen related, the later PCM's have all of these functions in one form or another. Spark advance/retard vs. IAT. A/C off/on vs. RPM and TPS (some PCM's do not actually control A/C clutch, others do). The latest PCM's also incorporate other potentially fuel saving calibrations such as spark advance/retard vs. commanded AFR. Just FYI.

JPrevost

I wasn't testy. You're reading too much into the post. Just read it as it was written and not how you think I would say it. It was more friendly joke than anything, but if you want to read testy into it then there's nothing I can do except pity you.
Do you seriously think you're entitlement is always a "thanks"?
As proof that it wasn't a testy attitude, look at how long the quote was. I never quote that long and yes, as you pointed out, I did say "I should have said." making your reply about as useless as this one.

TPIGirl- Ultimately your A/C compressor would work mainly in decel only conditions where you're trying to slow down. Then it would operate ONLY when it has to during accel and cruising to keep the caben temps at desired levels.
As for the IAT vs SA table. Yes having a IAT vs SA table could be benifitial.

Fast355- what is the most timing you're running at high map (100kpa) without PE? Is it 32 and then 36 with PE? Just a side note, running more timing isn't going to reduce NOx. It'll raise them by creating more "compression" and heat in the cc. Retarding the timing lowers the BMEP and will lower the NOx, this I have proven on 3 different vehicles (Fiero, Suburban, F-body).

Z69

Doesn't that raise the HC?

IAT SA- I believe Bruce has something like that in his
personal code.

Fast355

iTrader: (2)

JPrevost--I should have specified, but my timing is just as you say 32* @ 2,800 not in PE and 36* in PE. In the emissions test they never hit PE, that lets me stay a little more retarded on the timing for smog and then still have good power when I mash it.

The highest timing advance number I see is 44*+4* for the egr. 48* is perfectly acceptable on mine, in 3rd gear at 70 with the tach at 2,400 and the map around 45-50. My typical cruise is about 1,750 RPM(75 MPH TCC locked) and 50-70 map.

At 50 map I get 38* timing 34*+4* EGR.
At 55 map I get 38*
At 60 map I get 38*
At 65 map I get 36*timing 32*+4* EGR
At 70 map I get 34*timing 30*+4* EGR
From there it decreases 2* for every 5 KPA.
At 95 map I get 20*(no EGR) @ 1,750.

TPIgirl- I currently have a vacuum switch to cut out my A/C compressor anytime my vacuum is lower than 6 in/hg. The vacuum switch was the stock TCC switch from my G20. I am now handling the TCC with the ECM so it was not needed. I can tell the difference in the pedal it takes to climb a large hill or accelerate up to speed on a ramp. The compressor on my G20 easily takes 20 hp off the crank. When it drops it almost feels like a mini passing gear. Combined with a few other things it has freed up maybe 1 mpg around town. Tough to quantify though as I don't have many miles on this change. Highway mileage is unchanged.

Captain C

Another thing to try is to raise your fuel pressure as much as the injectors can handle. The higher fuel pressure will give a finer mist and a cleaner, more efficient burn. You will obviously have to recalculate the injector size and may even need to change your pulse width if your code doesn't already recalculate it for you.

The F bodies were set at 39# for the 85 models and 43.5# (IIRC) for the 86-92 models. The new cars are running 60#, but they have a newer style injector. I don't know what F bodies are rated for pressure wise but I do recall people mentioning that after 50# the injectors might stick open. I don't know if that was just the factory injectors or F-body "style" injectors.

I have Accel 30# injectors that are currently set at 50# and they seem to work ok with the few miles I have put on them since installing the new fuel pump. I am going to have to cut the adjusting screw on my AFPR so I can remove it and put a shorter one in. I can't lower my fuel pressure since the screw is hitting the bottom of the plenum. But hey, if it works fine at 50# I'll probably just leave it there....

Another thought is that you might be able to increse the length of time you stay in highway mode before it disengages. In 6E I believe it is set at 30 seconds max before kicking out. I don't have my stuff on this computer so I can't verify until tonight when I get home......

Keep up the good work guys and gals as I am saving this stuff and filtering it out for what I can do to 6E

91Z28-350

I don't think that matters. If you're driving like you're trying to save gas, then you won't ever hit the PE point unless you lower the TPS requirement for it. Stock is what, 50% at low RPMS. If you're at high enough RPMs to get PE entry with low throttle, then you aren't driving to save gas. I don't break 30% when I drive it to save gas and I don't go over 85Kpa MAP.

Fast355

iTrader: (2)

My TPS to enable PE is 85% at lower engine speeds and 50% at RPMs over about 2,400. My feeling is that if I am running the engine to 2,400 or above, I need the power. The other thing is that while towing it runs about that(3rd gear), I want it to dump more fuel in, quicker while the engine is heavily loaded, to keep the pistons in one piece.

With a 5,000+ lbs truck, 3.08 gears, and only 312 CID, I frequently see MAP readings of near 100 kPA. Mainly at low-rpm, in OD, while accelerating or hill climbing. It takes all the bottem end torque this engine can muster to accelerate up a hill while in OD with the converter locked. I usually try to stay out of passing gear though, for fuel economy. With 3.73s or 4.10s this would not be near the problem it is. I bet I wouldn't get anywhere near the fuel mileage or engine life though.

91Z28-350

A 5,000+ lb truck doesn't really follow the same load patterns as an f-body.

Why are you loading to 100KPa in OD up a hill (presumably at low RPMs)? It'll probably be more efficient to downshift it instead of bogging the engine. I can hit 100Kpa in 6th going up a hill at 1000rpm, but I don't see the point when I can be about 500-700rpm higher in 4th at 60Kpa.

I have 3.23 gears. I never quite got around to putting in 4.11s.

Grumpy

The TCC is not meant for high load useage, unless you have a multi disc, or kevlar version, and then those even have limits.

You need to also consider the bearing loads. You can put alot of *scuffing* load into a bearing, by too much load at too low of rpm.
I run alot higher GVWs with alot more engine/ rear gear, and unload the converter, and downshift to avoid the above.

I do 5K mile oil changes (usually with a fair amount of towing), and with the tune I have, the oil comes out looking almost new. The tranny fluid never shows any signs of smelling bad, and the last pan drop in the tranny had NO clutch material.

Just some points to consider.

Fast355

iTrader: (2)

I don't really have a choice. My transmission (700r4) is hydraulically controlled. Being from a van, it has a 85% TV valve in it from GM. If I want power, I mash it harder. Just cruising along, it doesn't need it. The thermal efficiency of the engine is better when it is loaded more heavily.

Grumpy-I am not turning down your advice as they are very valid points, but my last 355 didn't have any scruff marks on the bearings and they were nice and evenly colored as well. That was stock style bearings, cast crank, no balancing, 70 psi oil pressure and running to 6,000 all the time. With the coated bearings, balanced parts, 70 psi oil pressure, proper bearing clearances, and a forged crank I am not too worried about it. Just the old 355s crank broke the rear flange off, due to machining/casting flaws. My oil looks the same at 3,000 miles as it does when it goes in. I do alot of city driving in a hot climate and change it more often. The original tranny did not have any clutch material in the pan either (even with 250,000 on it). The sun shell broke on my original high mile 1983 700r4 when I put the 355 in front of it. The original TCC clutch was on a vacuum switch in 3rd gear and was always locked in 4th. The wiring dictated this. I would worry more, IF if felt the converter shuddering alot. My fluid is clean and still smells like new, and the transmission already has 10,000 miles on it.

My 305 is somewhat torque limited at part throttle when not in PE anyway. Early Buick 3.8 FWDs used to use a slight timing reduction in 1st and 2nd gear to keep from tearing up the TH125C, they pulled the timing like 8* and made a 30% torque reduction.

dimented24x7

iTrader: (2)

They even have derivative spark control routines to stablize the engine, which I thought was cool. Sort of a double edged sword on an old, tired motor, though.

Another possible savings measure is fly by wire throttle. Id love to have that. Being able to modulate the throttle would reduce alot of the need for transient fueling.

Grumpy

One project setting on the self is using a FBW, using it in series with the stock mechanical one. Then just run it open with a TPS vs RPM vs Buffer. I'd like to get away from having any form of AE, and then be able to use a really large TB I have one the self beside the FBW one.

JPrevost

FBW is a lot of fun for drag racing, not so much fun in OEM programmed form!

dimented24x7

iTrader: (2)

Im sure its a pain. The code to control it is probably PID loop heaven...