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-   -   Tested: speed vs. MPG, 2008 Corvette Z06 (505 hp) (https://ecomodder.com/forum/showthread.php/tested-speed-vs-mpg-2008-corvette-z06-505-a-9841.html)

MetroMPG 08-26-2009 09:33 AM

Tested: speed vs. MPG, 2008 Corvette Z06 (505 hp)
 
http://ecomodder.com/imgs/2008-corvette-z06.jpg

One of the guys I sail against regularly in our local sailing races (24 foot Shark fleet) has a 2008 Corvette Z06 with the 6-speed manual transmission.

After last night's race (we won! :)), I brought up the subject of fuel economy, and he gave me his version of the occasionally heard story that Corvettes get surprisingly good fuel economy - given their power - when driven reasonably.

We know that the car's "secret" is its massive torque paired with very tall gearing and relatively good aerodynamics (Cd of 0.28, CdA of 6.27 for a '92 Vette - source), which allow it to loaf down the blacktop in top gear even at fairly low speeds. Sometimes they even win mileage competitions: http://ecomodder.com/forum/showthrea...thon-5508.html

Just for kicks, we're going to go out and get data to do a "speed vs. MPG" graph in the next few days.

Watch this thread!

[EDIT, Sept 11: added EPA ratings...]

For reference, the car's EPA fuel economy ratings are: 15 mpg (US) city / 24 mpg (US) highway / 18 mpg (US) combined

Source: Model 1 Vehicle Characteristics

[EDIT, August 28: added graph below, plus methodology ...]

http://ecomodder.com/imgs/graph-speed-mpg-corvette.gif

Weather conditions:

August 27, 2009
Sunny, 18C
Wind E 7 km/h
Pressure 102.2 kpa
Humidity 48%

Raw numbers:
Speed km/h ... E (mpg US) ... W (mpg US) ... Avg mpg

50 ... 28.4 ... 29.0 ... 28.7
60 ... 35.9 ... 37.0 ... 36.5
70 ... 35.6 ... 35.6 ... 35.6
80 ... 33.4 ... 33.4 ... 33.4
90 ... 31.8 ... 32.1 ... 32.0
100 ... 30.6 ... 29.3 ... 30.0
110 ... 28.1 ... 27.5 ... 27.8
120 ... 25.9 ... 25.6 ... 25.8
Methodology:
Air conditioning was off, windows were up, and fresh air was on fan setting 2.

Speed was set once per pair of bi-directional runs with cruise control, cancelled with the brake between runs. Car was brought up to speed & leveled off before passing a "start" marker (road sign) where the ScanGauge was reset. (Note: other than entering engine size, ScanGauge was not calibrated to this car, speed & fuel use offsets were left at zero). Reading was taken after passing a "finish" marker and cruise was cancelled.
Route:
2 lane highway, straight, dry & level (follows river edge). The road runs SSW/NNE and can be found here: 1000 Islands Parkway - Google Maps
Traffic conditions:
There was rarely traffic ahead in my lane, and no closer than 5 seconds when present. Some traffic was present in the oncoming lane.
---

See also:

Daox 08-26-2009 09:41 AM

So... that car has roughly 10x the horsepower of the Flea and 20x more than the ForkenSwift ... This should be interesting.

MetroMPG 08-26-2009 09:46 AM

True! I'm just going to guess, but I think despite having ~10x the Flea's peak power, it may post numbers that are in the range of 50% of the Flea's original speed vs. mpg graph, at least at lower speeds.

Daox 08-26-2009 10:04 AM

Does this engine have cylinder deactivation?

NiHaoMike 08-26-2009 10:11 AM

Looks like Pulse & Glide will work great at just about all "normal" speeds...

MetroMPG 08-26-2009 10:13 AM

Good question - I'm not sure. I'll find out of course.

---

NiHaoMike - we'll see about Pulse & Glide...

Dieselman 08-26-2009 10:41 AM

Quote:

Originally Posted by MetroMPG (Post 123912)
Sometimes they even win mileage competitions: http://ecomodder.com/forum/showthrea...thon-5508.html

It's easy to make a high consumption car win in economy trials where the % better than official figures wins, in fact the less economical the car is normally, the easier it is to win, just drive economically and switch off at every opportunity. It's the switching off that really pays the dividend.

Note the overall economy is only 30mpg (imp)
averaging 30.96 mpg over the trip's two-day, 411-mile route. That mark represents an improvement of 61.26-percent over the Z06's official European combined mileage figures and is a new record for the MPG Marathon

MetroMPG 08-26-2009 10:45 AM

Point taken, dieselman. Scoring method is a regular bone of contention in mileage competitions.

micondie 08-26-2009 10:51 AM

I have a 93 Trans Am with 6-speed that also gets very good highway mileage (high 20's). It's not how much power you have, it's how much you USE!!!

jamesqf 08-26-2009 02:24 PM

Quote:

Originally Posted by micondie (Post 123935)
I have a 93 Trans Am with 6-speed that also gets very good highway mileage (high 20's).

And if you think high 20s is good mileage, you're living in a different world :-) On an open highway with nothing much in the way of mountains to climb (say Hwy 50 from Carson City to the Toiyabes), I'll do 80+ mpg round trips - and that's including maybe 20-30 miles of dirt to get to the trailhead.

micondie 08-26-2009 02:37 PM

Quote:

Originally Posted by jamesqf (Post 123970)
And if you think high 20s is good mileage, you're living in a different world :-) On an open highway with nothing much in the way of mountains to climb (say Hwy 50 from Carson City to the Toiyabes), I'll do 80+ mpg round trips - and that's including maybe 20-30 miles of dirt to get to the trailhead.

I haven't driven the Trans Am enough lately to get an accurate mpg when driving for mpg. The high 20's were several years ago on the hilly New England interstates going 75-80MPH before I cared about mileage. What are you driving?

MetroMPG 08-26-2009 03:18 PM

I suppose "very good highway mileage" is a relative thing, eh?

Depends where you're coming from.

micondie 08-26-2009 03:29 PM

Quote:

Originally Posted by MetroMPG (Post 123982)
"Very good highway mileage" is a relative thing as well, eh?

Depends where you're coming from.

You are so right. I used to think my 66 vette got excellent mileage with the Rochester FI I put on it back in the 60"s, and it was lucky to get into the 20's.:D Of course back then gas was in the 20's too.

aerohead 08-26-2009 05:46 PM

coming up
 
Cool! Looking forward to it.Thanks!

ALS 08-27-2009 01:35 PM

Quote:

Originally Posted by jamesqf (Post 123970)
And if you think high 20s is good mileage, you're living in a different world :-)

High twenties was great in the mid to the late eighties.
I just got rid of my 87 Volvo 740 Turbo wagon .40 Cd. On a good day with no AC 26.5-27.0 mpg at 65 mph. You drove it at 70 mph with the AC on 23-24 mpg was normal.

After lowering, removing the roof rack, swapping out the automatic for a manual transmission and bumping up the rear gears to 3.31 for better gas mileage I could pull 29 mpg at 65 mph. I could pull 30-31 mpg at 55 mph.

It was Clunkered on Aug 3rd for a 2010 Prius. I'm sorry 40 mpg city today is the 30 mpg highway of 15 years ago.

jamesqf 08-27-2009 01:41 PM

Quote:

Originally Posted by ALS (Post 124192)
High twenties was great in the mid to the late eighties.

Humm... 1985 CRX, roughly 45 mpg?

MetroMPG 08-27-2009 02:07 PM

Heading out now to get the data...

ALS 08-27-2009 03:34 PM

Quote:

Originally Posted by jamesqf (Post 124198)
Humm... 1985 CRX, roughly 45 mpg?

exception to the rule. What did a four cylinder Regal, Celebrity, Taurus, K-Car or even a Plymouth Horizon get?

MetroMPG 08-27-2009 04:54 PM

http://ecomodder.com/imgs/2008-corvette-geo.jpg

Nothing super surprising to report. I'll post the full details & chart later, but here are the highlights:

  • Man, that was fun! :)
  • Best fuel economy is pretty much where we would expect to find it: at the lowest speed you can drive in top gear (contrary to some comments I've seen from high-performance vehicle owners who insist the MPG "peak" is found at higher speeds)
  • Best was 36.5 mpg (US) at 60 km/h (37 mph) - or 44 mpg (Imp.) / 6.4 L/100 km
  • Worst was 25.8 mpg (US) at 120 km/h (75 mph) - or 31 mpg (Imp.) / 9.1 L/100 km

More to come...

ALS 08-27-2009 06:32 PM

I've heard at 55 mph some owners (no AC) are getting in the low thirties.
Which just shows what really can be accomplished when the car companies are really trying. Imagine telling a Corvette engineer in 1970 that a 2009 Corvette would pull high twenties low thirties in fuel mileage, 0 to 60 mph in only 3.6 seconds, hit 100 in 7.9 seconds, and 150 in 17.5 seconds and still be able to hit 200 mph. :)

NiHaoMike 08-27-2009 10:18 PM

Did P&G help, hurt, or have no effect?

jamesqf 08-28-2009 12:00 AM

Quote:

Originally Posted by ALS (Post 124217)
exception to the rule. What did a four cylinder Regal, Celebrity, Taurus, K-Car or even a Plymouth Horizon get?

As I said earlier, different worlds. Did anyone actually buy American cars back then? The CRX was probably the mpg champ, or close, but the Honda Civics & similar of that era got in the 30s. Heck, I get over 25 mpg from my '88 Toyota pickup, which is 4WD, and usually driven on roads where 4WD is needed, and/or hauling loads of firewood &c.

SentraSE-R 08-28-2009 01:39 AM

I have a pretty good recollection of road trip mileage on my cars. All thrashed to 7 mph above the speed limit before I hypermiled.

1959 Buick Electra (364 cu in) - 12 mpg
1963 Rambler American 220 - 25 mpg
1970 Datsun pickup - 25 mpg
1977 IH Scout II 4X4 (302 cu in) - 11 mpg
1976 Datsun B210 - 36 mpg
1983 Nissan Sentra wagon - 35-45 mpg
1987 AMC GTA - 36 mpg
1987 Chevy Astro (4.3 L) - 15-17 mpg (22 mpg @ 55 mph)
1996 Nissan Sentra SE-R - 36 mpg
2002 Nissan Sentra SE-R - 26 mpg (43 mpg hypermiling)
2006 Scion xB - 32 mpg (45-59 mpg hypermiling)

MetroMPG 08-28-2009 08:25 AM

Quote:

Originally Posted by NiHaoMike (Post 124268)
Did P&G help, hurt, or have no effect?

Unfortunately, we didn't do any P&G comparison runs - spent nearly 2 hours just getting the steady state data.

MetroMPG 08-28-2009 04:00 PM

I've updated Post 1 at the top of this thread with this graph of the results, plus methodology & raw numbers.

http://ecomodder.com/imgs/graph-speed-mpg-corvette.gif

MetroMPG 08-28-2009 04:40 PM

Interesting: I just looked up the Corvette Z06's fuel EPA economy rating:

Model 1 Vehicle Characteristics

It's 15 mpg (US) city / 24 mpg (US) highway / 18 mpg (US) combined

No wonder the British guy was able to win his competition on % over the government rating.

Extend the graph, and this car "meets" its EPA highway rating at 130+ km/h / 80+ mph! (Steady state, level road, etc.)

That's astounding. In stock form, my car's "EPA highway" speed was below 100 km/h / 60 mph.

jcp123 08-28-2009 08:36 PM

Quote:

Originally Posted by MetroMPG (Post 123982)
I suppose "very good highway mileage" is a relative thing, eh?

Depends where you're coming from.

I got one tank that was approaching 21mpg in my Mustang and I was elated :D

Mustang Dave 08-28-2009 08:46 PM

Thanks for posting this, MetroMPG. :thumbup:
That speed vs. MPG graph pretty much mirrors my experience with my Mustang. Most performance car enthusiasts ass-u-me performance cars have a "sweet spot" around 75 MPH. That just ain't so with modern (efficient) fuel injection systems. In my experience, the best FE is at the lowest speed in your top gear. In my case, about 35-40 MPH.
And it's interesting that most people can't believe that a performance car can get fuel "economy".
According to EPA's 2008 estimates, I should be getting 17 City/ 25 Highway/ 20 Combined with my Mustang.
The worst I've ever gotten was .02 MPG under EPA Highway. (24.98) And that was because I ran it in the garage to charge the battery (at ZERO MPG) during the Winter.
According to ecomodder.com's criteria, I've never not been a hypermiler with my Mustang. :)
I'm getting better fuel economy with my Mustang than a lot of people get with their 4-cylinder Camrys and Altimas. :thumbup:
A major part of it is the "nut behind the wheel" and route planning.
As they say, YMMV. :)

MetroMPG 08-29-2009 01:55 PM

Quote:

Originally Posted by Mustang Dave (Post 124454)
Most performance car enthusiasts ass-u-me performance cars have a "sweet spot" around 75 MPH.

I've seen statements to that effect so many times I was beginning to wonder if maybe it was true.

My relative lack of experience with big displacement, high torque engines (with the single exception of my first car - in which I never paid attention to fuel consumption) had me doubting common sense.

Not any more!

(PS - my Firefly is a "performance car" of a different kind - high efficiency is high performance! I don't like that "fast" = the only kind of "performance".)

instarx 08-31-2009 10:04 AM

But wait. You said the ScanGauge wasn't calibrated to the corvette. Doesn't that mean that those MPG figures you posted don't mean anything? Without calibration don't the scanguauge readings simply show the relationship between mileage and speed, and not actual MPG? I don't have or use a scanguage so maybe I just don't understand how it interacts with the car.

MetroMPG 08-31-2009 11:04 AM

The ScanGauge readings weren't verified against filling the gas tank of the Vette - that's what I mean by uncalibrated. So yes, there's the possibility the MPG figures aren't exact... but it's unlikely they're out by more than a few percent.

My experience with the SG (comparing with "zero offsets" to filling the tank in several vehicles) is that it's not usually far off for "normal" driving, like the kind done for this test.

Quote:

I don't have or use a scanguage so maybe I just don't understand how it interacts with the car.
The ScanGauge calculates fuel use indirectly: it determines it based on air consumption, assuming a stoichiometric air/fuel ratio for a warmed up vehicle in closed loop operation (such as for this test).

PaleMelanesian 08-31-2009 11:20 AM

In my experience, the Scangauge tends to be slightly optimistic, but only by a small margin, like 3%. Whatever the offset is, it's a percentage and not a constant value. The curve on the chart will not change with calibration, just the scale on the Y axis would change. The most efficient speed will still be 30 kph / 37 mph, it just might be 36 instead of 36.5 mpg.

MadisonMPG 08-31-2009 05:54 PM

Someone asked did it have cylinder de-activation earlier, I don't think it does. Are the Vett's still fiberglass?

PaleMelanesian 09-01-2009 09:12 AM

I believe the standard ones are, but the Z06 is carbon fiber.

gone-ot 09-01-2009 11:01 AM

Quote:

Originally Posted by Mustang Dave (Post 124454)
In my experience, the best FE is at the lowest speed in your top gear.

...exactly! That's the condition where you get SLOWEST engine speed for the MOST throttle opening (without being WOT), ie: least amount of "pumping" loss for the hp generated.

...anybody remember the Oldsmoble "Turnpike" cruisers?

gone-ot 09-01-2009 02:20 PM

Quote:

Originally Posted by MetroMPG (Post 124399)
I've updated Post 1 at the top of this thread with this graph of the results, plus methodology & raw numbers.

http://ecomodder.com/imgs/graph-speed-mpg-corvette.gif

...if my number-crunching is correct (6th=0.57:1), the missing rpms would be 1,093 rpm at 50 mph and 1,230 rpm at 56 mph...sound about right?

PaleMelanesian 09-01-2009 02:26 PM

I get 1080 and 1215, but it's close.

MetroMPG 09-02-2009 12:10 AM

Quote:

Originally Posted by MadisonMPG (Post 124985)
Someone asked did it have cylinder de-activation earlier, I don't think it does.

You're right - it does not.

Quote:

Are the Vett's still fiberglass?
Yes. The Z06 has some carbon fiber (the owner mentioned the liners inside the wheel wells as an example, and a balsa wood/carbon fiber composite floor). Also the frame is aluminum, vs. steel in the regular model.

Big Dave 09-02-2009 09:48 PM

I think this data vindicates my approach of low RPM = max MPG, even for gasoline engines. The Z06 with its LS7 engine has such mammoth torque as to allow operation at vividly low RPMs. The same principle works for a high-revving Honda engine, just the cutoff for lugging occurs at a higher RPM.

As you can see from this, the Tremec 6060 transmission used in the Z06 has a 0.63:1 top overdrive ratio, but a 0.5:1 ratio could be had if MPG were to be emphasized.

Tremec TR-6060 transmission - Wikipedia, the free encyclopedia

BTW, I am seriously looking at getting the Challenger version to replace the ZF6-650 in my truck. That with a couple of aero tweaks might get me over 30 MPG in my mixed-driving circuit. It has an optimal ratio spread and its 600 ft-lb rating is A-OK for my Powerstroke which has been dyno-tested to deliver 560 ft-lb max torque. Having a 1.54:1 overall reduction should give spectacular results.

Too bad the GM 4.5 liter diesel is dead. Given the LS7 in this test is operating way below its peak volumetric efficiency, it is incurring huge pumping losses for not much power. The diesel suffers no such loss. It would be interesting to see what a 4.5 could have done if fed the 70 cetane Fischer-Tropsch fuel the Audi & Peugeot prototype racers use.

PaleMelanesian 09-03-2009 09:55 AM

Quote:

Originally Posted by Big Dave (Post 125543)
I think this data vindicates my approach of low RPM = max MPG, even for gasoline engines. The Z06 with its LS7 engine has such mammoth torque as to allow operation at vividly low RPMs. The same principle works for a high-revving Honda engine, just the cutoff for lugging occurs at a higher RPM.

I concur. I have no tachometer, so I finally paid more attention to my rpm on the Scangauge this morning. I can gain speed from about 800 rpm with my little Honda. I typically run P&G cycles in the 1000-1500 rpm range. That's lower than I thought I was doing. ;)


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