?Correlation between HP & economy?

[dacook]

I'm confused about HP & economy. Common sense would suggest they should have an inverse relationship, yet:

1) My '02 turbocharged SS routinely got 17-18 mpg around town, 22-23 mpg freeway. It dynoed at 436 RWHP. I'm sure the flywheel HP would have been ballpark 500.

2) The 5th gen. V8s are supposed to get 23 MPG at "only" 400-422 ENGINE HP. At the rear wheels they're probably going to come in at 330 or so. (exact # doesn't matter for this question, it will be less than 400)

This begs the question: why did I get better HP per MPG with my SS?

Another example:

The 5th gen. V6 is supposed to get 26 MPG with a 300 HP engine.

I just finished filling up my '05 Impala (3400 engine). I got 25 MPG mostly highway miles. I don't know what the HP is on that engine but I know it's WAY south of 300.

Can anyone give me a good explanation for these seemingly anomalous observations?

-How does the V6 5th gen. get better MPG AND have considerably more power than my Impala?

-Why did my turbocharged SS get as good MPG as the upcoming V8 5th gen. AND have considerably more power?

Hmmmm?????

(Another question I'm kicking around now is why in the heck did I sell that SS )

[Steve0]

Its a cominbation of things which lead to fuel economy. Engine efficiency and power curve, gearing, weight, rolling resistance and aerodynamics to name a few. Depending on the combination of variables you'll get different fuel economy.

Few other points:
- Your turbocharged engine uses fuel according to how much boost is being fed to the engine amongst other variables. Its not neccearily a direct comparison to compare a forced induction motor to a naturally aspirated one.

- The new SS is geared shorter than the 4th gens were which can have an adverse affect on fuel economy is some 400lbs heavier. If it gets the same highway fuel economy that the 4th gens got in real world conditions, I'd be super impressed.

- The EPA ratings are not going to be 100% what you see. Here's a decent article on the prodcedures.: http://www.epa.gov/fueleconomy/420f06069.htm

The important thing to know is that its just a standardized test used to compare vehicles. I'm sure people will exceed whats on the window sticker for the highway. City wise, its hard to say... with a driver youre talking 4000lbs of SS to push around.

[TrickStang37]

Originally Posted by Steve0

Its a cominbation of things which lead to fuel economy. Engine efficiency and power curve, gearing, weight, rolling resistance and aerodynamics to name a few. Depending on the combination of variables you'll get different fuel economy.

Few other points:
- Your turbocharged engine uses fuel according to how much boost is being fed to the engine amongst other variables. Its not neccearily a direct comparison to compare a forced induction motor to a naturally aspirated one.

- The new SS is geared shorter than the 4th gens were which can have an adverse affect on fuel economy is some 400lbs heavier. If it gets the same highway fuel economy that the 4th gens got in real world conditions, I'd be super impressed.

- The EPA ratings are not going to be 100% what you see. Here's a decent article on the prodcedures.: http://www.epa.gov/fueleconomy/420f06069.htm

The important thing to know is that its just a standardized test used to compare vehicles. I'm sure people will exceed whats on the window sticker for the highway. City wise, its hard to say... with a driver youre talking 4000lbs of SS to push around.

the GEARING
may be shorter, but coupled with the tire/wheel size, the gearing as a whole is pretty horrible for performance (better for fuel econ).

BTW, if the drivetrain losses for the new SS is the same as the corvette, then the camaro should be making ~350rwhp for the A6 and ~370-375rwhp for the M6.

[skorpion317]

Originally Posted by dacook

The 5th gen. V6 is supposed to get 26 MPG with a 300 HP engine.

I just finished filling up my '05 Impala (3400 engine). I got 25 MPG mostly highway miles. I don't know what the HP is on that engine but I know it's WAY south of 300.

Can anyone give me a good explanation for these seemingly anomalous observations?

-How does the V6 5th gen. get better MPG AND have considerably more power than my Impala?

Two words: direct injection. More power, better fuel economy.

[Snap50]

I've noticed that mileage is directly related to weight pushed and rpm.

Our C5 generally got 20 or better even though pushed hard most of the time, and the Tahoe with 25 less hp, variable displacement but 1500 more pounds is generally 16 or so driven lightly in the same places. Those differences are maily weight biased.