According to epinions.com the 2003 Viper gets 13mpg on the highway. This is absurd!? Why such bad mileage? Corvette Z06’s get 28mpg highway because they are aerodynamic and have big gears… same with the Viper. What’s different about the Viper? Is it the big engine? Is it the extra soft tires? What is it using at 70mph, like 40 HP (at the most) @ <1500RPM’s ? Weird, right?
What mph do they test hwy mileage at? Does the Viper get better gas mileage going faster than this said mph? At what mph does the Viper get it’s best mileage? What coasts farther, in neutral @ 70 mph, vette or Viper (i know the viper weighs 200 lbs. more, but just for my own info)?
I can’t answer all your questions, but I’ll try my best. According to the EPA, the 2002 Viper gets 21mpg on the highway. I don’t know what they could have done to make the 2003 get mileage that is so much worse. Does the 2003 have a new engine? Maybe that was a typo and they got highway mileage confused with city mileage.
The funny thing is that the EPA highway test is based on an average speed of 48 mph and a top speed of 60 mph. Considering a lot of people drive 75 or 80 mph on the highways where I live, these figures aren’t very accurate. That might change though.
I think Nametag is on to something here. A 5.7L V8 and an 8.3L V10 are not going to have even close to the same consumption. Also, I know the 'Vette has a really, really high (the engine is at way low RPMs) gear for 6th, and it wouldn’t surprise me if the Viper’s 6th gear was lower, for more even gear spread, as the Viper is more performance oriented.
Not necessarily true. If they are geared properly, they should only be using the same HP to maintain the same speed (the cars have about same road load i presume). So, while the larger displacement engine will indeed drink more gas because the idle is so thirsty, it’s still going to be a fairly close one, and you said it wasn’t gonna be close. Last year the corvette and the Viper had 28 and 21mpg, respectively. And that’s with the Viper having more than 50% more displacement. That’s pretty close.
What happened to the Viper since 2002 is the real question here, and as for the gearing…
If the cite that aeropl posted is correct, then the Viper was tested on the highway at 48-60mph, and if i’m not mistaken, the Viper would be toggling between 5th & 6th gear. So, it’s not a matter of having a big 6th gear because the car will be at the same RPM’s pretty much. (I’m a little skeptical about that cite’s testing mph claim)
So, again i ask, what’s the real reason why the Vipers’ mileage is suffering so much as of late? By the way, I noticed the peak HP and torque have moved up a little for the Viper since 2002. This, coupled with a different gearing could eat up some more gas, right?
The EPA fuel efficiency testing is done on a dynamometer. Each car is run through an exercise regimen that was designed to approximate real life driving. It tops out at 55mph. The city driving cycle also is programmed to obey speed limits. :rolleyes: Many cars are designed to please this robot test drive. In other words, gear ratios, torque curves, etc. are arranged to deliver their best efficiency at legal speeds. The Viper’s engineers probably didn’t do that, and in real life it may get mileage quite different from what the EPA robot got. A fire breather like that is grumbling along at 55.
About the city driving EPA dyno test: Do they accelerate every car at the same rate, or do they use a certain percentage of the cars’ power, or something else? Do they account for wind resistance? I’ll go search for a cite.
No doubt, the Viper will get crappy mileage at 48-55mph. That things’ best mph is probably 65-70mph, i would guess. This would make the Viper get 20mpg in [i[real* hwy driving, probably. Slap some hard, non’sticky economy radials on there and it would probably run 25mpg.
So many people rag on big engines and how they drink so much gas. It’s not necessarily true! If you are not using very much HP, you will not be drinking that much more gas, period. It’s all about the road load, not the engine.
I’m willing to bet why the EPA still uses that outdated test: Big American SUV’s and trucks would look absolutely terrible if rated at 75mph. Their rolling & wind resistance would destroy any hope of having respectable numbers at that speed. And cars like the Viper with outstanding coefficients of drag get short-changed.
That settles it. Thanks. Serves me right for trusting epinions, Live and Learn.
Still would like to know if they acclerate the cars the same rate for testing city mileage and if they factor in wind resistance… probably do, i would just like to know for sure. Google doesn’t seem to want to supply this info…
I would like to share something that may or may not be pertinent any longer:
In the late '90s, Corvettes were equipped with equipment to specially tune their shifting alorithim so as to “beat” the EPA tests. When run through the official cycle, the transmission would alter its shift points to maximize fuel economy. GM even went so far as to force the driver of a manual transmission car to shift straight from 1st to 4th if their driving lined up with that of the official test cycle.
Perhaps part of the answer is that GM rigs their vehicles, whereas Chrysler is less concerned with the EPA mileage of their high-end sports car?
Current Vipers have that system as well, IIRC. If they were used to beat the tests, then you might be able to find out what the test uses by looking at the conditions in which that system is activated.
GM has a corporate rule that no car they sold would be hit by the EPA gas guzzler tax. The skip-shift on the 6-speed managed to bump mileage up just enough so the the Camaro/Firebird/Vette avoided the tax. So the “rigging” as you call it actually saved consumers money.