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big gear skeptic

Discussion in 'New Edge Cobras' started by bossracer, Dec 22, 2006.

  1. bossracer

    bossracer New Member Established Member

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    I've searched and read all through the posts about the advantages to switching to a bigger gear. IE- 4.30, 4.88 etc. I read all about the experts saying the lower gearing wouldn't really effect net MPG that much. And I was skeptical.

    So, I went over to one of the rpm/speed calculators and input some data. I wanted to find out what gear would equal my stone stock 3.27 if left in 4th. I was surprised to see that a 4.88 final drive ratio in 5th exactly matched my current 3.27 if left in 4th. Next I devised a test card, and set about gathering some data.

    I had originally planned to gather more data, but thought I would share what I found out today.

    Givens -- nice day here in SW Texas. Light winds, mid 60's temp. I drive a 3 hour cruise one way home every weekend from Del Rio to San Antonio. About 160 miles. Overall, it is slightly down hill, as Del Rio is about 1000 feet above sea level and San Antonio is about 500 feet. 99 Cobra stone stock, stock tire size, no mods. Has a bra on the front. Car was lightly loaded with just me and a few gifts in the trunk. I checked air pressures before I started and evened them all 4 out at 44 psi.

    I filled up and hit the highway. The first leg was 66 miles to the next big town. I set the cruise at 70 mph in 5th gear for a baseline and only had to slow down through one very small town and then come to a quick stop at the border patrol checkpoint. Then, once in the thriving metropolis of Uvalde, I stopped and filled up at 66 miles. The car burned 2.7 gallons for 24.4 mpg, and 2.4 gallons per hour fuel burn. RPM was right at 2000 RPM.

    Next, I got on the same highway and continued East for San Antonio. Again, I had to slow down through some small towns, but not for long. Driving through Hondo is about the same as driving through Uvalde, so I figure it is a wash. This time I kept it in 4th, exactly replicating what the car would be like in 5th with 4.88 gears. RPM was right at 3000 RPM. The noise was not bad at all. The Khumos make far more noise. I had the stereo blasting as well. Excessive engine noise was not a problem. I stopped and filled up again at 70 miles. This time, the car burned 2.9 gallons but I did drive a touch farther. MPG is 24.1 and essentially the same 2.4 gallons per hour fuel burn.

    I was expecting far worse mpg at the 3000 rpm steady cruise.

    So, all those guys with the big gears are right. It really doesn't make much difference with this motor. My guess is 4.30's would barely reduce the MPG.

    Of course I did not factor in a humming bird farting upwind and causing some bees to circle around and temporarily alter the magnetic field of the earth. I just tried my best to keep the car at the same 2 RPM's over a relatively flat stretch of road on the same day and see what the difference was.

    Let the daggers start flying.

    Dano
     
  2. 3B99SVT

    3B99SVT Top down makes me smile Established Member

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    The other day I tried the "drive in 4th" idea to check out what a lower gear does (higher ratio). I didn't do the mpg thing that you did (nice job, by the way) -- it was just to see what the sound was like. The freeway speeds around here are 70 mph w/most going a little faster. I have to say that cruising 85 mph in fourth wasn't my favorite thing to do. I kept thinking that I need to change gears. I'd like to drive in a car w/gears next to feel the benefit.
     
  3. ex-PJs snake

    ex-PJs snake That Others May Live Established Member

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    I believe the 99/01's were rated at 17 city and 24 highway.
    Looks to me that your "stone stock" Cobra is doing just what the car spec'd out to do regardless of gear selection being utilized. My understanding and belief was that gear selection made little difference in fuel mileage. If it did, it was never worthy of complaining about by me. My 99' has 3.73s and with my intercooled P1SC and moderate SCT tune, my Cobra does the same, if not better in most cases and instances, than what Ford spec'd the stock 99/01 Cobra's to do. I am happy and good analysis, bossracer.
     
    Last edited: Dec 22, 2006
  4. VirtualSVT

    VirtualSVT lolololololololololol Established Member

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    Don't fear the gear.
     
  5. Quadcammer

    Quadcammer 4cams aren't better then1 Established Member

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    damn ace, 44 psi cold?

    you gotta be getting near the max psi for those tires.
     
  6. SPXTrader

    SPXTrader Certified Loon Established Member

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    ...Then, once in the thriving metropolis of Uvalde...

    ...driving through Uvalde...

    Sounds like a body part, if I'm pronouncing it correctly!

    "Then, she let me drive through the thriving metropolis of her Uvalde!"

    j/k....nice job on the MPG thing...gears aren't that bad if you can take the noise...and Quad's right.....waaaayyy too much air!
     
  7. elyrain

    elyrain Member Established Member

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    The only thing that effected my MPG with gears is I want to mash the gas at every stoplight, lol. I try and shift at about 2200 or so if I'm in "gas saver" mode and I always get over 20mpg, you can't ask much more out of a sports car.

    BTW, I got the same MPG with 4.10's as I do with 4.56's.
     
  8. omj

    omj Well-Known Member Established Member

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    elyrain-was there much performance difference going from 4.10 to 4.56?
     
  9. Double"O"

    Double"O" N2S come get some Established Member

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    44psi!! damn dude! I'll get the ride was somewhat rough...not to mention your were most likely at the MAX PSI for those tires

    but nice comparo!
     
  10. viperbluelx

    viperbluelx Sexton's Performance Established Member

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    I swapped from 4.10 to 4.56 in my old mystic Cobra

    It was like adding a 50 shot from a dead stop when I was on sticky tires.
     
  11. elyrain

    elyrain Member Established Member

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    With the 4.10's and street tires you can still some what mash 1st and second gear and not spin to badly. With 4.56's forget about it. I had BFG DR's when I first switched and with DR's your street traction is really good, but I couldn't stand the weak sidewalls in the corners.

    I switched 4 years ago so I don't remember much else why I switched except that my 4.10's where shot and I don't think they were good for my MPH because I would trap in the low RPM range with the 4.10's and alot higher RPMS with the 4.56's.
     
  12. SnkBtn99

    SnkBtn99 Speeding bullet!! Established Member

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    Screw the gears .... We need more candy canes !!!! Merry Christmas!
     
  13. 99riocobra

    99riocobra i like ice cream Established Member

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    agreed. :thumbsup:
     
  14. 1999WhiteSVT

    1999WhiteSVT STLMustangs.com Established Member

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    yeah these modular motors have a really good MPG range (or whatever you want to call it)

    however, i think on an old 5.0 or any non-modular motor, you will probably see a big difference in MPG with gears
     
  15. brkntrxn

    brkntrxn Inappropriate Motorsports Established Member

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    I have gotten a best of 21.72mpg at 72mph average in my 99. That is with 509rwhp and 4.10s... shifting at 2k and babying it. I typically average much less due to the weight of my foot.
     
  16. omj

    omj Well-Known Member Established Member

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    Do 4.56+ gear require a notch in the crosspin when you have a 3/4 or 7/8 pin?
     
  17. Sonic Blue GT

    Sonic Blue GT Banned

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    It would seem to me that where you would see a loss in MPG is only in city driving. I'd think that from a stop and go standpoint the car would suck more gas being that the engine is revving higher in the low ends of the shift spectrum when using larger gears.
     
  18. 01yellercobra

    01yellercobra AKA slo984now Established Member

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    The motor would have an easier time getting the car moving. If the motor doesn't have to work as hard it uses less gas.
     
  19. Sonic Blue GT

    Sonic Blue GT Banned

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    OK...now i see it...
     

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