Skip Shift Explanation, Please

BigsViper

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I've spent the last hour doing a search so sorry if I'm wasting everyones time but I tried to find out on my own.

I know all about the skip shift on my car and how to get around it. What I don't know is the theory behind how that makes for effective emissions control. Common sense tells me that the car runs richer and burns fuel less effeciently when it's in 4th at 15mph. What were they thinking? How does this help pass the Kalifornia emissions tests? Thanks in advance....
 

CAS

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Bigs - I think it's there to keep revs down - the EPA figures that if you start out in first at a low RPM, chances are you're not going to need a lot of throttle and when you shift into fourth, your revs are still down and will be for awhile, using less fuel and therefore, cleaner/less exhaust.
 

Dyno Dave

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It is for the EPA driving cycle. The faster that big V-10 spins the more air and fuel get pumped through it causing a hit on the hydrocarbons. It's got more than enough torque so it can handle the driving cycle in 4th and turn more slowly and pump out less HC.
 

genXgts

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Hey Bigs, I thought it was unrelated to emissions and concerned with EPA MPG averages. By bringing up the Vipers mileage during the EPA loop by forcing the first to fourth shift under the precise conditions the EPA test dicticts, the Vipers mileage shot up. This then brought up the CAFE (corporate average) numbers and saved DC $$$$$$.

any sense to my ramblings?
 

GR8_ASP

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More likely saved us dollars on on reduced fuel guzzler tax. With the Viper annual volume it would be hard pressed to make any impact on corporate numbers. But even with it the guzzler penaly has been in the $3k range. Just another way to help support our country. Between sales tax, gas guzzler, value based registration fees and the recently canceled luxury tax, Viper owners have been very good supporters of the US government.
 

joe117

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I think the 1st to 4th shift is an attempt to increase fuel economy in order to improve the "Corporate Average Fuel Economy". I believe there was some federal mandate that forced auto makers to have some specified CAFE value.
 

Marv S

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I don't think CAGS is a federal mandate but is a financial choice that auto makers decide on and with the low end torque of American Muscle they try to avoid the tax as much as they can.
http://www.fueleconomy.gov/feg/info.shtml#guzzler


The 6 speed M5, Lambos, etc. don't have skip shift or CAGS. I think the lambo was rated about the lowest mpg car.
 

ViperRay

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The CAFE rules that Joe117 is referring to is definitely a federal mandate. An auto company must produce cars with a fuel efficiency ON AVERAGE of at least 27.5 mpg and trucks (SUV escape clause) of 20.7 mpg. This law (congress) was enacted in 1975 after the Arab oil embargo allegedly to encourage fuel efficiency (and less dependence on foreign oil) and decrease emissions (neither of which it has done). What it has done is jeopardize the American companies who have been selling alot of SUV's. Because companies like Honda and Toyota produce many fuel efficient cars, they can sell us the gas guzzlers and still meet the CAFE rules easily.
I have to think that the skip shift helps them meet these fuel efficiency standards although I don't know if that's why it was initiated. I suspect that companies that sell us very few cars like Lambo are exempted.
 

Marv S

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Ok, it's a "mandate", but a mandate that can be broken provided the penalty is paid. Porsche doesn't have a vehicle that meets the average requirement but the customers pay extra for the fun.

What is the penalty for not meeting CAFE requirements for any given model year (MY)?
The penalty for failing to meet CAFE standards recently increased from $5.00 to $5.50 per tenth of a mile per gallon for each tenth under the target value times the total volume of those vehicles manufactured for a given model year.

Since 1983, manufacturers have paid more than $500 million in civil penalties. Most European manufacturers regularly pay CAFE civil penalties ranging from less than $1 million to more than $20 million annually. Asian and domestic manufacturers have never paid a civil penalty.


For MY 2002, five passenger car fleets including BMW, DaimlerChrysler import, Fiat, Lotus, and Porsche are projected to fail to meet 27.5 mpg passenger car CAFE standard. In addition, two light truck fleets including BMW and Volkswagen will likely fail to meet the light truck CAFE standard of 20.7 mpg. Final Reports for MY 2002 provided by the EPA to NHTSA in mid-calendar year of 2003 may adjust these projections favorably

http://www.nhtsa.dot.gov/cars/rules/cafe/overview.htm


http://www.cars.com/carsapp/national/?szc=85004&srv=parser&act=display&tf=/advice/bestworst/mileage/2003/makes/porsche.tmpl
 

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