For the 2006 Impala

3.9L V6 = 19/27
5.3L V8 = 18/28

What the deal with GMs 3.9L, it isn't living up to GM's previous pushrod V6s and the 3.9L has VVT. Does the enigne just need better gearing? Or is it a gas pig compared to the old 3.4L and 3.8L?

THe LS4 on the other hand is just an amazing engine

 

I noticed that too. I imagine a good bit of it is gearing. Perhaps they want the 240 hp 3.9L version to have some real snap over the 211 hp 3.5L. I've driven a 3.5L (it was in a Grand Prix at the time, serving as mule duty for the new Impy). The 3.5L is geared to get that 31 or 32 mpg rating (first and second gear take you to pretty high speeds when wound out).

Evidently even a relatively minor change in axle ratio can make a significant difference, at least in the number that shows up on the window sticker. If you look at the G6 website, the base car with the 200 hp V6 option has a different axle ratio than the G6 GT with the same engine. I was actually surprised, pleasantly, by that. The GT gets a more aggressive axle ratio. Not like 3.42 vs. 4.10, but there is a difference. It also costs the GT a couple of mpg on the highway rating. Which may not turn out to be such a significant difference in real world, interstate cruising.

From the G6 specs:

Base w/ 3.5 V6, auto: 3.05 axle 19/32 mpg
GT w/ 3.5 V6, auto: 3.29 axle 18/29 mpg (3 mpg epa cycle drop for 3.29 vs. 3.05!)
GTP w/ 3.9 V6, auto: 3.69 axle 18/26 mpg (kinda low, less than the heavier Imp)
GTP w/ 3.9 V6, six speed: 3.55 axle No figures given

I imagine the six speed 3.9L should be close to 30 mpg highway (the two extra gears should help. 6th gear is pretty relaxed in that car; I've driven several).

Checking the Impala specs...

3.5L gets a 2.86 (fuel saver!)
3.9L gets a 3.29 (same as G6 GTP, yet the Impala shows a mpg better number... Perhaps the G6 number is not final, but an estimate...)
5.3L gets a 2.93 (all that torque lets it get away with a taller axle and still be quick, with DoD helping it get a 28 mpg rating.)

The new fwd six speed autos are going to be sweet. They better be out soon...

 

Yeah, yeah. What we want to know is how good do they feel to the driver, have any imput?

 

GM needs all those new 6 speeds badly, GTO is a perfect exmple of how much better a 6 vs. 4 speed would be. I expect it to help the High displacement FWD cars too.


note Impala 3.9 is the same as the G6 GT (that is why it beats the GTP)

 

Unfortunately, no. I've driven an XLR-V with the six speed, and it was pretty sweet. But I haven't driven a fwd six speed yet. I even typed them out by hand, and I still missed that. Too many axle ratios and fuel economy numbers rattling around my head. Or I'm just an idiot.

 

why should GM stop at 6, make it a 7 speed heck with it... give it some gears to choose from...

make it lead the industry not catch up...

Ohh yea the differential makes a big difference on the sticker... like the trucks with the same engine will range because of differentials, 4x4 or whatver...

but on a side note... are those VVT engines Pushrods? they arent right?

they are OHC engines, so a bit heavier?

 

My wifes AVG. MPG is 13.0-13.4 in our GXP on the street.

 

I keep trying to tell people that my 97z28 gets better gas mileage than my 00 Grand Prix GTP, but nobody believes me

 

The 3.5L and 3.9L are pushrod, 60 degree V6 engines. Not OHC. The single cam has a phaser on it, so the valve timing can be advanced/retarded. But overlap (between exhaust and intake) cannot be changed, as it can be when the intake and exhaust valves have their own dedicated camshafts.

 

cant be... a sports car with a v8.... cant be, no way, not gonna happen, not possible...

 

My friends '00 GTP gets 23 MPG in town...I've never seen an LT1 do that.

 

my mistake they are ohv... not ohc...

 

My L98 got 19/28 with an auto and 3.23 gears. At least it did until I spun the engine too high.

 

When I went to Florida for spring break, I averaged 30-31 mpg. I have an LT1 with crappy 2.73's

 

When I made my trip to Des Moines I got 30 mpg on the highway. Crappy 4.11's here