What We Tell People
 

I accidently came across a copy of the local paper where I had been interviewed about how to improve MPG. This was from May 2008 when gas prices were near their peak. Like most people who get asked such things, I gave them the old clichés about air up, slow down, tune-up, yadda, yadda, yadda. As Kevin Kostner in “Bull Durham” told the rookie: “Cliches are your friend.”

Fast forward to this spring. I buy a 1996 Impala SS (I always wanted one of those) as a driver while I get more aggressive on the pickup. A bit of work tracking down the usual used-car gremlins and trying to baseline the car in case I get the urge to ecomod it. It is a great driving car.

But the critter seems immune to the old chestnuts. I can hypermile my brains out or drive it like Tony Stewart (a very aggressive NASCAR driver for you non-US guys) and regardless I can throw about 1.5 MPG over the whole range. I’m running 60 psi in the tires (20% over the sidewall max). No joy. The car coasts well. But regardless, it gets 20 MPG plus or minus 0.75 MPG. The car is 35% lighter than the pickup but gets 30% LESS MPG.

If this were a truck, I’d say it is overgeared. MPG insensitivity to other measures is a classic symptom of overgeared trucks, but this car has 3.08 gears – pretty long-legged by today’s standards.

I think the big factors are the gas engine and the automatic transmission. The LT-1 runs nearly completely throttled and inefficiently and the torque converter is built for a high-powered engine and feels “loose” to me.

But, when you think about it, this is the vast majority configuration – gas engine and automatic transmission. Like it or not, this configuration is very resistant to the old chestnuts. So when we spouted the clichés, people tried them and got no results and they figure we are full of the brown & smelly stuff.

So, when (not if) the price of gas & diesel goes up again I am gonna change my tune. I’ll tell them:

1. No clichés. I presume you are smart enough to properly maintain your car.
2. If you drive less than 7,000 miles a year, don’t worry about it. Any meaningful action will cost more than it is worth.
3. If you drive enough that it hurts, trade in your Sequoia (euphemism for any SUV)for a Prius (euphemism for any high-MPG car). Take the trade-in beating and enjoy the good MPG.
4. If the price of fuel hurts enough but you really need a Sequoia or Tundra, you’ll have to become a form of hot-rodder to live with it. You’ll come to see the basjoos-mobile or Phil’s T-100 as beautiful, you’ll do an engine and transmission change to a diesel with a stick and you’ll change you gearing and put those Goodrich Long Trail TA’s (low RR 16 tires) on the vehicle.
5. Don’t waste your money on snake-oil solutions like acetone, two-stroke oil, or Brown’s gas.
6. Small modifications general get small results.

The clichés have been tried, tested and proven effective on most of the vehicles. An AT by default makes hypermiling harder because you have to fight it most of the time. I tell people with a MT not to fear rolling heavily into the throttle and shift early, but I can't tell people stuck with an AT to punch it, because they have mostly no control over the shifting. There are so many variables that affect fuel mileage that the best advice to give people would be to head over here. But since very few people will do that, my generic advice is to take is easy, slow down and use your brakes as little as possible.

I am not all that familiar with that particular vehicle but it may be either a converter with a high stall speed and lots of slip at normal road speeds or possible a totally shot converter / trans ass'y.

I would find someone who knows these cars backwards and get it them. They should be able to tell you fairly quickly.
Try a local "old school" car club or an internet search.

Pete.

Car clubs think MPG is craziness. They all act they are wanting to win the Indy 500.

The car is basically a Caprice cop car with a lower stance and Corvette engine.

The old chestnuts are tried and proven but just not all that effective for gas engine/automatic transmission cars (the vast majority).

They do all we tell them and drive wildly out of their comfort zone and get 1-2 MPG improvement. They want more. They think we are nuts and go back to texting while they drive.

Put a diesel in it and improve by at least 40%.

Put in a stick and gain another 20%.

Gas/automatic versions of my Super Duty struggle to get 10 MPG. Straight from the factory I got 18 MPG.

That's my advice to people, as well. Some heed it. Most don't. :p That's their problem.:D
Following your (and my) advice, my 4 liter Mustang isn't too far behind your 2 liter Elantra.:)

Big Dave -

Yeah, but you don't have to ask an MPG question. Just say you want to control the shifting and/or think you have a sick tranny. If it's an SS I would think that someone had tried to "manumaticize" the tranny. For fun I blinged "+4L60E manumatic" and found these :

Manumatic Technology : TwistMachine.com, CNC Innovations for Hot Rods
I am assuming you have the 4L60E tranny because of this :

Chevrolet Impala - Wikipedia, the free encyclopedia
Ooooooh, methinks you could convert it to a stick and have fun again.

CarloSW2

If I keep it, it will get a T-56 or maybe a Tremec 6060.

Another thing you could work on is the whole manumatic idea, since it's a #x##E version.

I bet you if you shift the selector into the lowest gear, take off like a moron, foot to the floor, you won't hit redline. The TCU will automatically shift without your input (via the selector lever). That means you can manually control when the TCU sets shift points with switches, and you can probably manually control TC lockup as well.

If you're worried about the transmission dying, doing the mods will just kill it faster (in your mind) so you can swap to a manual sooner. :)

With a 350 ya need to practically be idling down the freeway to end up in a decent part of your BSFC map. In order to get near 30mpg ya need to drop from ~1500rpm@55mph to ~1000rpm@55mph, and even then, you'll still only be at ~400g/kWh instead of the optimum around ~300g/kWh.

I had basically the same engine in... a '94 Corvette. I had a huge range in mileage depending on how I drove it: 10-29mpg. If I was being good, it wasn't hard to stay in the 25-29 range though. Mine was a manual.

Besides the tranny, the big differences are:

• Weight. Maybe you can try to remove some mass.
• Aerodynamics. Some of the aero tricks may help here, but that fact is, it's a big car.
• Gearing. 0.5:1 overdrive in the manual... But the auto was still geared higher than your car with 2.73:1 differentials. It may be worth switching over.

Switching to a manual shift probably won't help enough to matter. The big problem with the auto is the inefficiency of the tranny design. You need to use power to operate the pump and you'll always have the torque converter to deal with.

-Mike

The big problem with the auto is having to push fluid around. That's the largest inefficiency with automagic transmissions. They're still directly connected from input to output by gears and clutches, just like a manual. The fluid movement is the demon there, and for obvious reasons, you can't overcome it. The difference isn't THAT dramatic in efficiencies between manuals and automatics of this time period, though. It's only a couple percent torque loss, mostly due to the locking torque convertor, which locks at a 1:1 ratio input to output. From that point on, there are small frictional losses, some fluid pumping, and then the output.

The torque convertor losses are able to be eliminated once you've left 1st gear, since you can manually lock the TC. If you're not using alot of torque to accelerate, you can safely accelerate under TC lock without causing it to let loose.

Yes ATs are harder but not completely impossible, my 98 buick I am stuck with for a while should be proof well enough of that.

Also Big Dave, I could get approx. 24mpg with the 93 350 gas suburban we use for crafts on the highway, you need to probably drive a little harder than you are used to and vary your speed quite a bit. Since that weighs about 2k more and is as aerodynamic as a brick you should be able to tweak your SS better than a Suburban.

(I assume Big Dave has a scamguage so he can see what the car does under different throttle and situations.)

One thing on highway driving I have noticed on all my AT's is that the MPGs will drop after a while sometimes while going DOWNHILL under light throttle, you instinctively push in a little to hold speed above downshift and the FE drops and speed continues to drop. Then I notice my flat road steady state MPGs are severely dropped after one of these type of incidents.

Oddly enough letting off the gas while coasting downhill and allowing the GPH to drop to idle levels seems to "reset" my fe after the above happens so when I push the throttle back in my FE stays hi, my power is improved and I can once again maintain speed without suffering reduced FE. Trouble is when I let off the gas it doesn't just drop, it drops down then pops back up to .75gph then sslllooowwwly drops to my idle fuel rate around .4gph so I need a long gentle downslope to maintain speed.

Some have said its because of my lockup, some have said its a case of detroit fever where the motor has been running leaner than normal and than the computer corrects, whatever the case I am slowly figuring out the AT vehicle's "quirks" at least on the Buick.

Something else I have noticed, my Dodge crewcab drops fuel consumption instantly to idle levels when you put it in neutral which makes a huge FE difference than leaving it in D and suffering double the fuel consumption. My Buick is the opposite using less fuel when left in gear, odd. My Dodge also uses about the same amount of fuel under heavy accerlation (GPH) as when you accelerate more moderately, wheras my buick is also reverse, your better off with moderate on the buick than heavy.

Another odd quirk is that my buick once the motor is warm drops fuel consumption linear with the throttle when its in open loop after a restart at a stopsign or light, so when I take off and then coast to the next light my consumption rates drops instantly to .52gph instead of hovering at .75gph for about 5 seconds. So I am actually better in open loop with a hot engine in town than with it left in closed loop.

Also you need to take care coasting your auto since there is a point where your FE drops below an acceptable level since you are forced to leave the
motor on. I try to end up somewhere around 15-18mph when I have to then come to a complete stop, below that ruins my FE except if I know the light is about to change then conserving momentum helps.

Good Luck Big Dave, a little more patience and you will find that hypermiling an auto can be fruitfull as well but the techniques you use on a manual DO NOT directly translate, you need to figure out the quirks and drive strangely to get better MPGs on an auto. You need to feather and play with the throttle much more than you are probably accustomed to. You will also need to plan your routes more carefully to avoid stopping at all costs. In stop and go in town driving can easily be half the MPGs as highway driving on a typical auto, so you can drive up to double the distance to get around those situations in an auto and still burn the same amount of fuel.

Agreed, autotragic transmissions are FE killers in town.

To reduce fluid pumping losses, you can switch to Dexron-VI or Amsoil's new ATL. Also, see if there's a cheap shift kit that reduces shift times. I'm trying both the Dex-VI and shift kit in a few weeks on my Buick. The results should be interesting.

And playing with the throttle is a must. Shifting into N to prolong glides downhill also works wonders.

This is one thing I love about my wife's new Saturn - I can EOC safely, and it's an automagic.

The only PITA about it is that you have to anticipate the engine's restart cycle, because as soon as you touch the key, it's started, and you have to have it back into gear from neutral within about a second, or the engine is revving 3k RPM. Stupid Saturn ECM programming.

That car will coast for miles, too.

I can tell you, Couch, that using Dexron VI is expensive, but you should never need to change it again, once you're done. I bought it from Wally World, and haven't had a problem with it yet, but if I have to change her fluid again, it's probably going back to DexIII... I can usually get that stuff free from friends.

Yeah, I was going to do the Wally-World Dex-VI.

Congrats on the SS, I always liked those cars, especially being an LT1 guy myself.

As far as the converter in your car goes, I would guess that it probably uses the same converter as my Formula, which has a stall speed of 1800 rpm. Mine does feel a little bit loose sometimes at low speeds, like in parking lots for example. Obviously this is done for performance reasons.

Does this car have a solid axle or IRS? I'm wondering if it uses the same 10 bolt rear end as the F Bodies. If it does you should be able to get some 2.73 gears from an F Body, that would help. But I think the biggest gain would be swapping to a T-56. As waffle said the only way to load this engine effectively is to get the RPMs very low, and the 4L60E just isn't going to let you do that. This is even more true of your car, since the iron head B Body LT1s use a different cam than the F/Y Body LT1s which is geared more towards low end torque.

Phase 1: T-56 Manual Easy project

Phase 2: LH6 DOD engine PCM Mission: Impossible