I don't think the manner of how the valves are actuated make a diff. If anything the compromises that have to be made with pushrod actuation should make it less efficent. It's that the few pushrod motors in production today have large displacements and use very tall gearing to achieve that mileage. Or use displacement on demand. It's not really testament to it's engine design.

 

bump

 

Displacement times rpm is the bulk of it since the fuel is controlled by O2 to equal 14.7 A/F. Every rpm is 3 squiirts of fuel and the amount of fuel is precise to the airflow.

Engines are tuned to 55 mph for best economy since that was the speed that highway MPG tests were conducted for EPA.

 

can a tuner alter the instructions in the ECU to provide more optimal tuning at a higher/more realistic speed for highway driving?

 

my car gets great gas milage when im on the N gear

 

Don't the Altima and Maxima also achieve horrible fuel economy? I have heard many complaining about the same things we are.

I average 14 MPG with constant shifting at 1800-2200 RPM (I hate when manumatic won't let me pop into 5th gear at 40 km/h); these cars are horrible for gas.

I think the VQ is just not a terribly efficient engine since it is used for too many applications. Added they tried making a 3400lb car achieve sports car 0-60 results; they probably made the gearing too aggressive.

 

again, gearing is not the source of bad MPG.

Driving habits are.

Basic hypermiling techniques will get you a combined mid 20's no problem on a G35.

 

I can average 19 MPG on pure city, and just pulled 29.2 on a 300+ loop in the mountains.

Light foot off the line does wonders.

 

I honestly don't see how people claim to only get ridiculous numbers like 11-12 city and 20-22 highway in these cars, unless they are automatic and never use overdrive, AWD, and have a garbage truck chained to the bumper being dragged behind them.

I regularly get ~20 in 75% city / 25 % highway driving (beating the living **** out of the car on a constant basis), and also 27mpg on the highway at speeds 80+mph with the AC on. Around town I usually shift between 3000-4000 rpm too.

 

The vette has such a tall 6th gear though... It is like 1700 rpms at like 70mph....

 

New 08 EPA estimates show the Vette gets only 15/25 city/hwy... (Auto)....
On the G...I regularly get 19 mpg in city and 26 hwy with cruise set at 68... The issue with the VQ is that there is a lot of usable torque pretty much distributed in every gear...and the other issue is as many told already it need another tall gear for that highway cruising.....

 

As evidence that gearing is the more minor factor in the equation resulting in overall fuel economy I give you the example the 2007 Peugeot 207 I drove in Greece for three weeks in July.

That 2600 lb. car was equipped with the base 80bhp 1399 cc 4 cylinder engine. The engine has only 2 valves per cylinder and is only SOHC. There is no forced induction nor direct injection.

At 130 kph which is approximately 78 mph the small engine was turning at 4000 rpm. Yet I drove a distance of 150 km (90 miles) using only 2 gallons of unleaded fuel. That translates to fuel economy of 45 MPG.

The fact remains that 3500 cc is a large displacement for an automotive engine. DOHC an variable valve timing improve engine airflow intake and reduce emissions. According to Mercedes Benz literature a 7 speed automatic transmission can yield a 7% improvement in fuel efficiency over a 5 speed auto with a similar displacement engine.

In most large displacement engines a 7% improvement in fuel economy would equal at most 2 miles per gallon!!!

VW-Audi is proving the best way to increase fuel economy while yielding impressive power: Small displacement (1999 cc) engines with forced induction and direct injection. And the diesel option as in the Audi TT diesel which will deliver 170 bhp, 258 lb-ft of torque and 44 MPG!!!!!

 

+1.

I get great mileage in my G... I get anywhere from 18mpg when I'm having fun, to a combined average of 23-28 when I'm conserving fuel, and I average at least 30 on the freeways. 500 miles a tank is not a problem for me. And at most, I'm really not that conservative...

Whomever said they're shifting at 1800-2200 to save fuel... learn to drive.

 

BTW, no car is getting their best mileage at 80mph... it may seem like that because as your speeding through the turns, inclines, declines, and traffic, you aren't letting off the gas as much, so you don't have a need to stomp on the gas as much, so you aren't wasting more energy than you need to maintain that speed... but if you learn to drive correctly at lower speeds, you will find that you can get much better mileage.

 

Well, you got some of it right. The automatic and AWD parts.

I did expect a bit better than I'm getting, but maybe I shouldn't have. With my 6-speed Z, I used to get over 25 mpg with 65% highway and racing the heck out of it on a regular basis. With my 6-speed Accord, I'd get 28mpg (mind you, this is a car rated at 27 highway) with the same type of driving.

Now with the G35X I'm getting 20-21. Yeah, its like 400 lbs more than the Z, but its also detuned a bit, so I was hoping for 23-24, frankly. I think the automatic kills it more than anything else.