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Discussion Starter #1 (Edited)
I've debated posting this in the normal tech or performance section, I've decided to go with the performance section since it involves some of the performance aspects of these cars engines.

As you all know I drive a Solstice and not a Sky, but for this informative bit that matters not at all since this was a test of the engine and not the exterior of the car.

For a while the 20/28 MPG values were a highly debated value especially compared to some V6/V8 engines that get nearly comparable fuel economy values (on non-roadsters of course though). Why should these more powerful large displacement engines get better fuel economy values then this brand new tech smaller displacement i4 engine get? Well some of that can be chalked up to this being a Roadster (other cars using this engine do get much better fuel economy values) but it doesn't explain it all.

I decided to do a little experiment to test an idea I had. So ok the city/highway values are best case scenarios for someone driving economicaly. How many Mustang GT/GTO/Corvette owners do you know who can get the real rated values on their cars without driving like a grandma all the time (what's the point of owning a car like that then)? Reading a lot of info on various boards for the other cars once you get your foot on the go pedal with a car like that your fuel economy greatly dips down well into the mid to low 10's range. There's a price to pay for high displacement engines under full load of course.

What about our car, what happens when you drive it under load all the time? Well I decided to find out and drove everywhere at 4000 RPM or higher (very few times I was at 3500 for more then a minute due to gearing and traffic flow) which is where most of the cars power is really coming on. I was usually in the RPM range of 4000~5500 during this experiment. I was only under WOT during initial acceleration from stoplights or when passing on the highway. I jack-rabbited every start and drove like a crazyman everywhere I went during this timeframe. To work, to the store, on the highway, etc. I filled up with a new tank of 93 octane, reset the fuel eocnomy in the DIC and zoomed off from the gas station.

As some of you know I also auto-x my Solstice. I've reset my fuel economy DIC several times and recorded values from 6mpg to 9mpg depending on track design. This is usually WOT most of the time with high RPMs also. I was personally expecting to see values at or under 15 mpg for this experiment.

All said and done I drove 212.9 miles on 11.5 gallons of 93 octane fuel.
212.9 / 11.5 == 18.5 MPG :eek:
The DIC read 18.3 MPG and was amasingly close to my calculated values. I was very shocked that after driving that hard for that long I maintained a value only 1.5 MPG off the estimated city "economy" driving estimate.

Like a good engineer I decided to double check my values by doing this experiment again. Suffice to say I got 18.4 MPG the second time around.

Our engines might not have the best top end economy numbers for our car types, but I'm defintely glad to say I can get good fuel economy values while still driving like a mad man. :thumbs:
 

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Thanks for the good info. We appreciate it. Skyfan
 

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On an 80 mile drive I reset the fuel economy to see what I would get cruising on a flat road at 55mph with 93 octane. The indicator said 30.2 mpg average fuel economy. Normally I don't go 55 and get closer to 26 mpg highway and 24 city... but I was impressed with breaking the 30!
 

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yup this is exactly the difference between a 4 banger and a big v8. The vette gets that gas mileage either by babying or because of the ridiculous final gear ratio.. You trounce on the v8 and ride it hard, it'll suck that gas RIGHT through . Even if you trounce on a 4 banger you're not going ot be getting that low.

And as for the difference in gas mileage between on the road and track. Track you're staying more in the RL right? There is a major difference between sticking above 6000 rpm, and 4000 rpm :D. Especially when it's almost always WOT.

WOT is what will kill your mileage as well ;)
 

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Thanks for your "hard work" :lol: Very interesting results indeed... :thumbs:

When I get my RedLine I'm going to HAVE to do this experiment. It should be fun!!!

Regards,

:willy: BA :willy:
 

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Discussion Starter #6
Freakazoid said:
And as for the difference in gas mileage between on the road and track. Track you're staying more in the RL right? There is a major difference between sticking above 6000 rpm, and 4000 rpm :D. Especially when it's almost always WOT.

WOT is what will kill your mileage as well ;)
Since it's auto-x I'm not in the RL very often, it's the WOT (Wide Open Throttle for those who don't know) that really gets you like you said.
 

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brentil said:
I decided to do a little experiment to test an idea I had. So ok the city/highway values are best case scenarios for someone driving economicaly. How many Mustang GT/GTO/Corvette owners do you know who can get the real rated values on their cars without driving like a grandma all the time (what's the point of owning a car like that then)?
Actually I have spoken with new Vette owners who get the advertized 28 mpg with doing 70 to 75 and one guy even told me he got that at 80. An amazing vehicle. I hope the Sky will also get close to or over the advertise mpg at real highway speed.:thumbs:
 

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brentil said:
Our engines might not have the best top end economy numbers for our car types, but I'm defintely glad to say I can get good fuel economy values while still driving like a mad man. :thumbs:
Come on man you know you just like to hotdog it all day long.....Drive like you stole it. Skip......hehehe:cheers:
 

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Brentil the sly might be a bit lower due to it's excess weight compared to the solstice...SKY tips in at over 3k solstice at 2900...(Or less without A/C)
BUt Areo Drag might be different from car to car too! so not sure....
 

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Discussion Starter #11
TexSon said:
Actually I have spoken with new Vette owners who get the advertized 28 mpg with doing 70 to 75 and one guy even told me he got that at 80. An amazing vehicle. I hope the Sky will also get close to or over the advertise mpg at real highway speed.:thumbs:
Yeah, in 6th gear tooling around at like 1500 RPM of course you're going to get good fuel economy. Corvette also has a much better aero drag then us. If they drove around at 4000+ RPM doing 75 mph their fuel ecnomy would drop to the very low teens.
 

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brentil said:
Yeah, in 6th gear tooling around at like 1500 RPM of course you're going to get good fuel economy. Corvette also has a much better aero drag then us. If they drove around at 4000+ RPM doing 75 mph their fuel ecnomy would drop to the very low teens.
Guys - I routinely cruised 80-85mph in my 99 Hardtop vette, throw in some city driving...and I consistently got 26-28mpg...And that was with the occasional (at least once or twice a day) romp on the throttle, enough to get the rear end sideways. The 6spd vettes (all Hardtops are 6spds) have 3.42 final gear ratios, so even 5th or 6th gear they can still accelerate, but continue to get great gas mileage. The big difference is at 2k rpms, I would be doing 90mph, and still the engine was barely turning...

Not trying to bash anyone here by any means, but vettes and sky's are different animals...different trannys, different motors...
 

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WHY GM engineering wins out in the end!

I think that the Sky gets it's mileage due to it's weight and wide front end which requires X amount of energy to move and push through the air. For example if you put a four cylinder in a motor home you'll probably still get 8 MPG. Even with your aggressive driving Brentil you still had the same amount of weight/cd to push around. You still had to drive close to the speed limit and your throttle usage was probably similar at cruising whether you were in 4th or 5th.
A Corvette weighs about the same as the Sky and has a bit lower cd; the X amount of weight/cd is probably similar to the Sky and thus similar mileage.
I think this would be true for GM motors, similar vehicle size, good tuning and good technology.

Now talking about horsepower versus mileage:
The above is not true with forced induction or a ridiculous motor like a Lamborghini’s V10 or a BMW's straight 6. The M3 gets terrible mileage with their straight 6s (3.2L/333HP getting 16 MPG around town vs. Corvette's 6.0L/400Hp 18MPG). But the 3.2L has a compression ratio of 11.5 (exponentially more fuel is required for a higher compression ratio to keep a safe air/fuel ratio) AND it requires 7900 RPMS to make 333 horses. A 3.2L motor pumping air at 7900 RPMs is moving X amount of air which requires X amount of fuel.

The Lambo is even worse with 9 MPG around town! She has a 6.2 L V10 that redlines at 7500 with a compression ratio of 10.7, which pumps/ignites the amount of air/fuel to create 580 horses.

No compare the Lambo/ZO6/Viper (a bar graph would be very useful)
Lambo 6.2 Liters, 580 Horses, 10.7 Compression ratio, 7500 Redline, 8 MPG
ZO6 7.0 Liters, 505 Horses, 11.0 Compression ratio, 6300 Redline, 16 MPG
Viper 8.3 Liters, 510 Horses, 9.6 Compression ratio, 5600 Redline, 12 MPG

Other vehicles with Mileage x Horsepower
ZO6= 8080
Prius=6600
Viper= 6060
M3= 5280
S2000= 4740
Lambo= 4640
Yaris= 3604
Sky= 3363

Remember GM rocks! The 505HP Z06 is 19% more efficient then the Prius!
 

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For mileage+efficiency the best numbers would be:
(weight/cd)/horsepower)/final drive ratio).MPG= X
 

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I am a mad man driving and average between 16.9-19 MPG depending on any HWY driving but this is with an extended run on the DIC I dont reset it (Haven't in like 2k miles) Most of my driving is stop and GO GO GO
 

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Discussion Starter #17
automag928 said:
Guys - I routinely cruised 80-85mph in my 99 Hardtop vette, throw in some city driving...and I consistently got 26-28mpg...And that was with the occasional (at least once or twice a day) romp on the throttle, enough to get the rear end sideways. The 6spd vettes (all Hardtops are 6spds) have 3.42 final gear ratios, so even 5th or 6th gear they can still accelerate, but continue to get great gas mileage. The big difference is at 2k rpms, I would be doing 90mph, and still the engine was barely turning...

Not trying to bash anyone here by any means, but vettes and sky's are different animals...different trannys, different motors...
What I'm trying to point out is under constant load situations. Put your vette in a gear that would at any situation make the car run at 4000RPM and drive everywhere at 4000 RPM. This means never using 5th or 6th gear on the highway. I'm pretty sure you'd see a very significant drop in fuel economy.
 

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What I'm trying to point out is under constant load situations. Put your vette in a gear that would at any situation make the car run at 4000RPM and drive everywhere at 4000 RPM. This means never using 5th or 6th gear on the highway. I'm pretty sure you'd see a very significant drop in fuel economy.
Vettes are geared to a certain extent to make acceptable MPG ratings and
are set up to turn the engine at cruise as low as possible - the auto runs about 1200 RPM at 65 MPH, as I recall. I also seem to remember that the Vette requires around 12 HP to maintain 65 MPH on level road, with no headwind and dry pavement. I forget how much power was required for each component - air resistence, tire rolling resistence, and mechanical friction, but I believe that air resistence and rolling resistence were by far the most significant forces impeding
forward motion.
 

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I chalk this up to better car design. Especially in areo drag and in the gearing of cars. My un-aerodynamic tank of a sedan (the '04 Malibu) gets up into the 30's when used extensively on the highway. A car like that 10 years ago got way less MPG (my old '97 GA got about 22 MPG on the highway and it was of similar hp/lb ratio). So we've come a long way!!

I can't wait to see the real world Sky RL numbers for MPG.
 

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Mileage, like engine wear largely comes from load, not rpm. I get 22-23mpg in my TA w/ h&c, driving like a normal person. It dips if I always try to accelerate faster than needed and still stay in a normal rpm range. My friend has an audi something or other that runs 3800rpm on the highway and tags 30+ mpg. Not to say rpm doesn't matter at all, but pedal postion kills mpg many times over rpm.
 
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