Is it harmful to shift early?

Posted by RallyEclipse98, Jun 13, 2011
420A Drivetrain Tech - Transmission, clutch, flywheel, driveshaft, gears, differentials, transfer case, shifter, etc - specific to 2G N/T DSMs.

  1. RallyEclipse98

    RallyEclipse98 Proven Member

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    Lincoln, Nebraska
    I am driving for mileage since my commute is 60 miles. Is it bad if I shift very early to "sportshift"? I just want the best mileage out of the car and I have done everything I know possible except I want to make sure this isn't bad for the engine, drivetrain. Is it harming anything by shift early and pushing the throttle down far and slowing accelerating to the next short shift?
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  2. Kreez

    Kreez Supporting Member

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    Well you don't want to shift too early, that will bog the engine. That can be just as bad as overrevving it and will also negatively affect your gas mileage.
    Just shift at 2-3k. It's a high revving motor and is designed to be shifted around that range or a bit higher.

    And what is "sport shift"? Is this the latest term among the kids?
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  3. DSMnoobsause

    DSMnoobsause Supporting Member

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    You will use more gas shifting sooner and hitting the gas harder then just shifting regular. 3-4k range is normal. What is your milage right now?
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  4. dsm03

    dsm03 Proven Member

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    Brandon, MB_Canada
    Agreed with ^^

    Ever heard the the phrase, "to high of a gear"

    It will work your transmission harder shifting to early which indeed will consume more gas!

    If the commute is 60 miles a day, than idealy you would get best mileage staying around 55mph if its highway driving.
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  5. Shake_Zulla

    Shake_Zulla Proven Member

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    As said above it's hard on your motor, imagine taking a ten speed and shifting it into the fastest gear and then trying to move from a dead stop. You can imagine it is really hard to pedal right? Same thing applies.
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  6. RallyEclipse98

    RallyEclipse98 Proven Member

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    Lincoln, Nebraska
    http://www.dsmtuners.com/forums/newbie-forum/405488-how-do-you-get-good-mpg.html#post152617969

    Post 25 is where I saw the term "sportshift."

    http://www.dsmtuners.com/forums/articles-miscellaneous/254223-how-save-gas.html

    This thread was the one that sparked my interest in short shifting to save fuel.

    DSMnoobsauce...do you have any proof or credible sources to backup what you are saying regarding more fuel consumption with early shifts?
    #6
  7. Tyeler18

    Tyeler18 Proven Member

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    If you look into fuel maps for any car or just know how the engine operates you'll realize that you use more gas. The engine is trying to accelerate as fast as it can when you're at low rpm's with the pedal down, in order to accelerate at the same rate as say a lower gear at higher rpm's it needs to use more air/fuel to get going, thus using more gas.
    #7
  8. TunaTalon

    TunaTalon Proven Member

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    That was me on post 24 of that thread, and the term is short shifting not sport shifting.

    This thread has seriously conflicting information. I suggest the OP should Google ("short shifting" mileage) There are many references to using the technique to save fuel,both on the road and on the track.

    I stand by my prior post on the subject.
    #8
  9. ed1380

    ed1380 Proven Member

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    ATL, Georgia
    Not only does it bog the engine down. It also accelerates wear on rod bearings
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  10. TunaTalon

    TunaTalon Proven Member

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    How does the differential compression loading on the rod bearings between 3000 RPM and 6000 RPM compare to the differential inertial loading between 3000 RPM and 6000 RPM?

    Please provide references.
    #10
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  11. ed1380

    ed1380 Proven Member

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    ATL, Georgia
    I'm talking about bogging down under 2k rpm. you dont get full oil pressure therefore not full lubrication of the bearings
    #11
  12. TunaTalon

    TunaTalon Proven Member

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    Well Ok then. How does the differential oil pressure between 2K RPM and 4K RPM compare to the differential inertial load on the rod bearings between 2K RPM and 4K RPM?
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  13. ed1380

    ed1380 Proven Member

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    ATL, Georgia
    after 2k oil pressure doesnt change much. thats why I said under 2k. after 2k there is slightly more wear at lower rpm's but not a considerable amount

    I'm sure there's some scientific explanation, but the quickest way to explain it is by examples.

    IE: you have 10 bags of cement to carry. if you carry 5 at a time, you're going to hurt yourself. but get it done in 2 trips. at the end of the day you accomplished your task but hurt yourself
    or you carry it one bag at a time. you accomplish the same amount of work, but it takes you longer. at the end of the day you accomplished the same amount of work but didnt hurt yourself.

    the way it relates to rod bearings is by amount of fuel burned per combustion stroke. if you bog the motor down it will see a high load value and dump x amount of fuel per stroke. lots of fuel=big boom=lots of load on bearings. AND if you're under 2k rpm then you're also not getting full lubrication, which = very very bad day for your bearings.

    just look at a fuel map. at low rpm, high load x amount of fuel is injected. and at high rpm, low load same amount of fuel injected.


    TL:DR- low rpm and bogging down = bad.
    #13
  14. TunaTalon

    TunaTalon Proven Member

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    Well Ok then you have a scoop. I would have used references and math but cement stories work for other people.

    2K RPM in second gear is about 20 MPH in my Talon. Maybe I should.... Nah.
    #14
  15. ed1380

    ed1380 Proven Member

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    ATL, Georgia
    I'm not an engineer, so I dont know the exact values or theorums, but I can show real life illustrations proving my point.


    To the OP- here's the stock fuel map. higher number=less fuel=better mpg

    Attached Files:

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    #15
  16. VelocitàPaola

    VelocitàPaola DSM N/T Moderator

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    You realize you're in a 420A forum, right?
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  17. ed1380

    ed1380 Proven Member

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    ATL, Georgia
    That's the only fuel map I had, and I showed where the NA map ends :coy:
    #17
  18. VelocitàPaola

    VelocitàPaola DSM N/T Moderator

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    Okay, I just thought it was worth asking since you called it "the" stock fuel map with a certain measure of authority.
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  19. ed1380

    ed1380 Proven Member

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    ATL, Georgia
    I get what you're saying. My mistake of wording it wrong.
    #19
  20. TunaTalon

    TunaTalon Proven Member

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    Fuel per pulse is relevant for tuning, but shifting changes the load and the RPM.

    Less fuel per injector pulse would be a good thing if efficiency was measured in fuel /revolution. However; on the road or track distance/fuel is more important. Like for example, miles/gal.

    Up shifting my Talon to second gear allows me to use only 57% as many fuel injector pulses/mile as in first gear. As long as fuel/pulse doesn't go up more than 57% the mileage will be improved.

    Short shifting for fuel economy is an old well known technique to save gas. Like any rule of thumb it works best when staying on the ranch of reasonable. Don't shift from first to fourth at 10 MPH. If your car bucks and stalls you're overdoing it.
    Last edited by a moderator: Jul 10, 2014
    #20
  21. Shake_Zulla

    Shake_Zulla Proven Member

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    Just thought I would throw my hat in the ring here. After this debate took off, I decided to do some research on the matter and what I found was interesting. As far as mileage goes I'm with Paul on this one and this debate needs to be in the proper forum. Stock 4g63 fuel maps are of little help here and the OP might get confused. But really everything is relative. Depending on mods, altitude and even tire pressure the MPG will change and it would take a considerable amount of calculation to figure what the best rpm range would be. Now as far as addressing the adverse effects on the motor this is where I needed some correction. I think a lot of us grew up being told that if you lug a motor it damages it and wastes gas. This might have been the case in the days before fuel injection and knock sensors but is not the case anymore. Now there is some weight to what ed1380 says when oil pressure is to low. When load is greater than the lubrication then damages occur but what RMP range, gear and speed is that at? TunaTalon has a very good point that without technical data you can't put a blanket number out there. Hell the lubrication efficiency will change with the weight of oil used, age of oil and temp of oil so its really too hard to say. General rule of thumb from what I have found on newer fuel injected cars with knock sensors is that if you are stalling the motor it is possible that you are damaging the motor however if the rpms are climbing then you are ok no matter the initial rpm's. I hope this helps a little. My advice to the OP is drive it one way for a tank and write down your MPG and then drive it a different way and see which one is better. Pretty technical hu?

    @ OP: You are asking a question that hinges a lot of personal opinion. Research is probably needed on your part so you can form your own opinion... or you could decided not to care about saving an extra 4 bucks a month.
    #21
  22. Th3DooM

    Th3DooM Proven Member

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    That is how I shift:

    1st to 2nd: 2.5 - 3k
    2nd to 3rd: 2.5 - 3k
    3rd to 4th: 2 - 2.5k
    4th to 5th: 2k

    Cruising at 1.5k to 2k rpm, Autobahn with 3k-3.5k (70 to 80mph with cruise control)

    After 25k miles of driving my car I always get about 28-30mpg including some high speed sessions on highways. The best I ever got were 37mpg with nearly a complete tank emptied on the highway (over 400miles of driving) :thumb: I bet there is more potential for saving gas, but that are some solid numbers and I am happy with that.
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  23. MJcanada

    MJcanada Proven Member

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    campabello, South_Carolina
    Depending on road i can shift below2k everytime. If its a pretty flat road I can shift at 1.5 k each gear. Just feathering it to accel slowly. Just depends on the situation. I can shift 2k all gears most cases without bogging.

    But i just say you can generally i shift btwn 1.8k-2.5k when trying to save.
    Last edited: Jan 1, 2013
    #23
  24. turboglenn

    turboglenn Proven Member

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    Lugging an engine has been known to be bad for a long time. And suppposedly is more apt to cause blowby in a N/a engine at that point. Every car manual i've read from cars i've owned states taking off too slowly and luging the engine will use gas as bad as taking off too fast, the 1982 datsu 280i had put it simply as calling them jack rabbit starts and turle starts, and swayiong that you should accelerate at a id throttle rate to the speed limit and then cruise, beause lugging and going too slow you've burner more fuel to get to the speed limit because you took more timeand were in a higher load for a given RPM, as compared to just applying mid throttle and getting there.
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  25. RallyEclipse98

    RallyEclipse98 Proven Member

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    I remember now I stopped shifting too early because my transmission gave me a whirring sound when I shifted really early (<2k).

    Man, in the future I may get an ultra-gauge because I'm nerdy like that.
    #25

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