Yeah, we all know our cars don't get great mileage. But why? Does anyone actually know the technical reason? There are other, larger displacement engines that employ lesser technology, make more hp and get better mileage.

I've searched here and not found anything offering an explanation.

 

I think it's the gearing and the torque curve of the motor.

The more torque the engine makes at lower rpms, the more power it makes at that particular rpm, the more fuel (usually) it needs.

Plus the engine is turning about 3000 rpms in top gear at 80mph. Not exactly economic.

 

i think it has to do with the high lead-footage coefficient

 

yeah the transmission has a lot to do with it. We need a 6th gear or 7 gear to get RPMs down to 2k at 80 mph and we would probably get 30 mpg on the highway. I think that's how Lexus does it with the IS350 and it makes more power than the VQ.

 

I know on my X it is the gearing . When I am on the highway , most of the time I am cruising at a minimum of 3,000 RPM.
I can still squeeze 29 imperial MPG out of it on straight highway with no energetic passing. But it is soo hard to keep your foot out of it.

 

Like Chris mentioned, it has to do with your right foot. It only gets worse
once you do mods like intake and exhaust. The sound created by these mods
tells your brain to listen more often, and damit we do!

 

Having owned a 3-speed auto, 460cid F250 with short gears, I know what an effect gearing has, but in the G's case I'm not convinced that's all there is to it. i have no empirical evidence, but it seems if you loaf around town in, say, a 3.6 Caddy and a 3.5 G, the Cad will get better mpg. Seems like something about the engine design (or computer mapping?) uses a lot of fuel.

 

It's a V6 tuned for performance and the car is a fat pig.

 

^^ yeah I'm thinking that's probably most of it, along with the other responses e.g gearing. Guess I was looking for something more esoteric that just isn't there.

 

The VQ in the G is performance tuned.

Look at the Honda K20 for a good example.

There are two major variants, a 160hp and 200hp version.

the 160 hp is tuned for economy, and the 200 for performance.

The VQ35 also comes in multiple variants. The Altima/Maxima versions are more geared towards economy. The G/Z's is for performance.


FYI, RPM does have an impact, but as I've said over and over, it is not a large one; t he VQ is a big bore motor. Long stroke would cause more loss to RPM than big bore.

Also, the 'legendary honda civic mpg' is obtained when civics are doing close to 4k at 80mph.

 

Wait, are you saying that civics get better mileage at 80mph than 55-60 mph?

 

I think for the displacement/power, it's great.

I don't know which caddy motor you are rferring to but the new one might be direct injected. Which improves hp and mpg.

I think the new HR versions get better mpg due to it's constant varible valve tech. But I'm not sure if these are direct injected. I don't think the VQ series 3.5s are DI'd.

 

more or less your right and wrong on the k20 platform...the 160 hp version only has 'vtec' intake cams while the 200 hp version has 'vtec' on both side cames (intake and exhaust) intake side is only good for mileage IMO.

Now the difference between the bigger engines getting good mileage is Id say the biggest difference is gearing...and how the valve train is set up...

Pushrods tuned well enough will always get good mileage, considering a 5.7l corvette gets 32 mpg highway. And our modular motors (basically DOHC set up) are not that great for mileage...

 

is it true that driving 65 MPH on the highway will get you the highest mpg? what about specifically for the VQ in the G?

 

i dunno but more efficient engines with direct injection seems to get good mileage.