3.8L V6 Automatic, any tips? - Fuel Economy, Hypermiling, EcoModding News and Forum

ktaylor · 03-22-2011, 11:10 PM

I know I know, its like the demigod to hypermiling but it's not too terrible on gas... Buick did a decent job, 200HP and 21mpg rating. I've been getting consistent 28 mpg tanks. My commute is a lot of hwy driving. I've started leaving a bit earlier to dodge traffic (leaving at 6 am as compared to 6:30) but still regularly drive home in rush hour traffic.

My commute times are pretty much set, and I'm on the road for an hour and a half each way, so I have a lot of time to try new techniques. I'm more looking for help with efficient acceleration and best cruising speed info. I know that max gear/lowest speed is usually best but is this always true? If I let the AT shift and then ease off the gas, letting stay in gear and let the speed drop below the shift point does it help FE significantly?

I've heard accelerating with load at 2000 rpm is ideal. The AT stays around 2000 through first and second, then I can let off the gas around 45km/h to let it go into third where the rpm's drop to around 1250 (then the TC locks up). Should I push the pedal to where its on the verge of shifting down so I can get into 4th quicker?

I'm not into putting wings or tails or anything on my car...just adjusting the nut behind the wheel.

Thanks in advance

Kode

SentraSE-R · 03-23-2011, 12:02 AM

Get and install an Ultragauge or Scangauge, and you won't have to guess: you'll know what works best with your engine/transmission combination. Different engines have different BSFC charts, and what works for my 1NZ-FE engine in terms of acceleration doesn't necessarily apply to your 3.8 L engine.

ktaylor · 03-23-2011, 12:09 AM

Yeah I've been seriously considering one of those. I could probably see a good increase in FE with instant feedback. I haven't been able to find the BSFC for my car yet. Money's tight so I just need something in the meantime...

bandit86 · 03-23-2011, 12:22 AM

I just got one in my jeep. My 4.0L is happier at 65 than 60, must be a better spot for the torqu curve

Anyways I love my sg2, spent a lot of time playing wih it

99LeCouch · 03-23-2011, 07:13 PM

With the 3800 a SG is a must for best FE. These engines/PCM's will guzzle fuel given a chance. Be very gentle with the throttle application once you're at speed, as the TCC unlocks with quick throttle application.

I accelerate at 2000 RPM for most things since that's a good compromise between getting speed quickly and FE. Any slower wastes fuel by producing much less acceleration.

4th gear with a 3800/4T65 combination won't come until 48 mph or so. So it's either putting around at 28 mph with the TCC locked in 3rd or blasting up to 48 mph to get the TCC locked in 4th.

28 mpg highway is pretty good. I'm averaging 26 mpg doing a lot of rural 2-lane driving.

ktaylor · 03-24-2011, 08:37 PM

The speed limits are around 70-90 km/h for 70% of my commute. I can keep it locked at 70km/h. Keeping it on the highway should I stay close to 70km/h or like 90-95?

99LeCouch · 03-24-2011, 09:14 PM

85-95 km/h keeps the engine more in its torque peak and better able to handle any variations in terrain. The 3800 Series II has loads of torque at 1400-1600 RPM. At 58 mph or 95 km/h my Buick is running ~1550 RPM. It's happiest between 90 and 100 km/h, in my experience. Much lower and you're dropping into 3rd and much higher fuel consumption a lot more with any acceleration, and unable to force a shift to 4th until hitting ~75 km/h again.

rmay635703 · 03-24-2011, 09:34 PM

Yes 70km/hr will give the best FE IFF you don't have a lot of hills, I was able to average over 30mpg with my buick most of its life (and this included in town driving). With several 35-38mpg tanks on the car (very slow and very challenging)

Trouble is you have very little cushion if there are hills and the car will downshift if you are riding the edge of gear change, this isn't a game ending consequence but if it happens OFTEN it will ruin any gains you get from the low speed.

Generally if you can VERY VERY gently and slowly move the throttle in as you go down hills (accelerating) and very slowly and gently move the throttle out decellerating up hills when you can get away with it will give the best overal FE. A close 2nd is to hold the throttle in ONE position and never move it regardless of speed with the exception of when you are nearing the downshift point.

With mixed hills and whatnot 45-50mph (approx80kmh) (US) gives the best FE as long as you don't punch the gas going up the hill and let the car bleed and gain speed with hills.

95kmh will reduce FE on flat ground in most cases, its fine if you are going downhill though.

MUCH MUCH easier with some sort of guage to look at and you will see what I mean. I could easily exceed 32mpg (US) using these techniques, I always wanted 40mpg but its downrite impossible without some sort of mod like a manual transmission swap or ECM tuning or a block/air dam.

Another helpfull hint is that most people give too much gas on flat ground and don't realize it. A very small excess amount of throttle will not make the car move notably faster but it will make you loose 2-5mpg.

The way I've gotten around that for over 15years is to move the throttle all the way out then push it back in until I just maintain speed. Don't worry if you loose a little speed, just make sure you are a bit over the speed you need to go so you can settle into a safe slow HI FE speed without downshifting.

Good Luck
Ryan

SentraSE-R · 03-25-2011, 12:37 AM

^^^ What rmay says. Regardless of the torque curve, doubling your speed roughly quadruples your power requirements, and wastes much more fuel. If your TC locks at 65 kph, you're better off driving 65 kph in your 70 kph speed limit areas.

ktaylor · 03-25-2011, 03:04 AM

rmay, thanks for your detailed response.

I know exactly what you're talking about. I've had it a lot lately where I'm hugging too close to the shift point and from not realizing, slowly drop passed it, then I have to accelerate without the TCC locked up and cringe every time. I know the route really well and I'm going to start gaining a bit more speed before the big hills. There's one in particular thats really long and I need to be doing 90km/h and have the throttle pushed right down to where its on the verge or shifting and it still bleeds speed to 70km/h but doesn't down shift. If I'm lucky the light thats halfway up the hill stays green and I don't have to start from a dead stop on the long hill. Is it better to keep it locked in 4th on this hill or let it bleed down to like 50 km/h (3rd gear) or so and wait until I crest before picking it back up? Also, starting from a stop going uphill should I still accelerate at 2000 rpm? It obviously takes a lot longer to get into 3rd.

Thanks again everyone for all the tips. I'm glad to hear another Buick out there is getting over 30 mpg.