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440 Posts
Discussion Starter · #1 · (Edited)
With 40 % interstate highway, 40% rural road/ Highway and 20% city driving in my attempt to get decent gas mileage, I got 293 till the low fuel light and at least 20.8 mpg. I really forced that last .15 gallon, so my mileage might have been higher.

I kept in under 105 mph on the interstate, and accelerated gently, only a few times getting it up to 5-6 psi boost. Coasted and short shifted where possible, and kept it under 3500 rpm or so.

All this indicates a Cobra with pulley and chip can do as well as stock for fuel economy and driveability. If I had really babied it, bet I could have gotten 23 Mpg.

Anybody try a few hundred miles on rural interstate @ 70-75?


Mods to get 450 HP , 467 Ft-lbs torque (SAE) out of my 2003 Sonic Blue coupe:

170 Deg Thermostat.

MM full length subs

QMP 3" 304 S/S exhaust With Cats

Amazon Diablo 2 program race/street Chip with switch

Amazon/ Razor 3.10 upper pulley

Royal Purple Lubes Everywhere
Water Wetter in Intercooler

BilletFlow Throttle Body with port matched inlet.
Metco #2 lb & 4 lb lower pulley kit ( 4 lb installed currently )

Metco 100MM upper idler with lightened modified bracket.

Billet Flow 100MM Idlers (2), Billet Flow 92 MM Idler (1),

Metco 3.2" Alternator pulley

Reinforced the Rear Seat delete kit with added trunk bulkhead for a kind of
sweet big Rotie/lab mix.

Amazon Stage 1 Filter kit
Denso Iridium plugs IT-20's

Gatorback belt # 4080797

· can be done
3,140 Posts
Two fuel pumps, 42# injectors. Boost gauge up, gas gauge down.

2,357 Posts
Because Ford made our cars pig rich from the factory and the government has to make there money also.

45 Posts
Keep it under 70 and watch that mileage fly up! When I'm being trying to get better mileage (ie, commuting), I've gotten up to 27 by completely babying it. Kinda offsets the 12 I get when I'm being an ass, right? 5th gear from 35mph to 50 then 6th gear. 5th still has reasonable accelleration for highway onramps if you aren't trying to break land speed records.

So, with that in mind I was wondering the same thing. The best I EVER got in my 2000 GT was 24mpg and I routinely get 23 in the cobra. In city traffic I get better than I got my GT (about 17, compared to 15 in the GT). Even our ratings are only off by 1mpg... does 1mpg really equate to gas guzzler?

I wonder if swapping in the GM 6th gear would increase the highway efficiency? I know my father's 'vette gets way better gas mileage on the highway than my cobra (around 32 or so... he got 50 once bu that was because one of his fuel pumps stopped working... ultra lean condition!)

516 Posts
I got 66 miles out of a tank of fuel til the low fuel light went on. 4.75 bout' that shit?? Now that was when I took it to the open track (road course) event.

I think they put it on...because they can. It's just the goverments way of saying.....if you want power to weight ratio in a car your gonna' pay. They don't have a gas guzzler tax on a V-10 truck that gets 12 freakin' mpg...WTF!!:shootbird

hehehe!! I always wanted to use that shoot the bird for something and what better than the gas guzzler tax.:shootbird :shootbird :shootbird

85 Posts
Can you believe that Ford couldn't find .5, yes POINT FIVE, mpg combined (using the formula below) to help us avoid that damn $1000??? Maybe, just maybe, if Ford would have given us the 0.50 6th gear ratio that the CamBirds have, then we could have avoided the damn fee! Bastages!

What is the Gas Guzzler Tax?

The Energy Tax Act of 1978 established a Gas Guzzler Tax on the sale of new model year vehicles whose fuel economy fails to meet certain statutory levels. The gas guzzler tax applies only to cars (not trucks) and is collected by the IRS. The fuel economy figures used to determine the Gas Guzzler Tax are different from the fuel economy values provided on this web site and the Fuel Economy Guide. The tax does not depend on your actual on-the-road mpg, which may be more or less than the EPA published value. The purpose of the Gas Guzzler Tax is to discourage the production and purchase of fuel inefficient vehicles. The amount of any applicable Gas Guzzler Tax paid by the manufacturer will be disclosed on the automobile's fuel economy label (the window sticker on new cars).

Unadjusted MPG(combined)* Tax
at least 22.5 No tax
at least 21.5, but less than 22.5 $1000
at least 20.5, but less than 21.5 $1300
at least 19.5, but less than 20.5 $1700
at least 18.5, but less than 19.5 $2100
at least 17.5, but less than 18.5 $2600
at least 16.5, but less than 17.5 $3000
at least 15.5, but less than 16.5 $3700
at least 14.5, but less than 15.5 $4500
at least 13.5, but less than 14.5 $5400
at least 12.5, but less than 13.5 $6400
less than 12.5 $7700

* The combined fuel economy MPG value (55 % city, 45 % highway) is used to determine tax liability. The MPG value is also adjusted slightly to account for differences in test procedures made since the base year. The MPG value is not adjusted for in-use short fall. The unadjusted combined MPG of a vehicle can be approximated from the city and highway values provided in the Fuel Economy Guide and on this website by the following equation:

(1/(.495/city MPG + .351/highway MPG))+.15

Since this is an approximate calculation, the actual gas guzzler tax may be off by one tax bracket.
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