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RPM TO MPH ratio

Discussion in 'ECU's, Electronics, and Tuning' started by khai_tuan_nguyen, Aug 4, 2003.

  1. khai_tuan_nguyen

    khai_tuan_nguyen Senior Member

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    I was just wondering the rpm to mph ratio on a B20 w/ b16 vtec head and LS tranny.

    On my setup for example it is about 70 mph on 5th gear at 4000 rpm. Is this about right?

    Thanks
     
  2. liquid00meth

    liquid00meth Senior Member

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    the motor and head make no difference, it is about the LS tranny. Look up the LS MPH chart, and there is your information
     
  3. khai_tuan_nguyen

    khai_tuan_nguyen Senior Member

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    The chart does not answer my question. It helps a little, but it says at 5th gear going 5000+ rpm i should be at like 180. I don't think with 1000 rpms more i would be going 110 mphs more. Right now i am at 70mph at 4000 rpms in 5th gear with 17 inch TSW revos.
     
  4. AllMotorMonster

    AllMotorMonster Senior Member

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    Your speedo is WAY off.....

    Top speed on the LS with the proper sized wheels @ 8000 RPM is around 160 REAL MPH
     
  5. NoJokE

    NoJokE Senior Member

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    171mph is top speed with a stock LS tranny and enough power to get it there
     
  6. Dman1100

    Dman1100 Senior Member

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    those 17's are throwing it way off
     
  7. khai_tuan_nguyen

    khai_tuan_nguyen Senior Member

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    is it possible to be throwing them that off though? IS there anything else that could be throwing them off?
     
  8. khai_tuan_nguyen

    khai_tuan_nguyen Senior Member

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    Also I just remembered i do not think (but not sure) that it is the tires, because when i bought the car it had the 17s on them and it had the stock hx engine (and tranny) and when i drove in 5th gear at about 3000 rpms it was like at 70-80 mph. Since then all i did was the B20b/ B16 engine and LS tranny swap... Any ideas?
     
  9. word

    word Senior Member

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    tire diameter and width definately throws the readings off, also, honda spedometers are about 5 mphs off especially at high revs, or as i've heard.

    there are tire size/width, final drive, gear ratio actual speed calculators online that you can find via google.com.
     
  10. khai_tuan_nguyen

    khai_tuan_nguyen Senior Member

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    thanks for the help guys, i understand that the tire size messes up the mph. Does it mess up the reading on the speedometer (i.e. if it says 65 mph am I really going 80) or does it just make the car slower (i.e. smaller tires = faster mph at specific rpm) or both. Also can anyone account for the other engine and trannies rpm to mph ratio compared to the new swap both with the same tires?

    thanks again
     
  11. liquid00meth

    liquid00meth Senior Member

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    Big rims only throw off your speedo if the tire diameter overall is changed. When done properly, your old fat tire will just be thinned down and filled in with more wheel. The overall diameter doesn't change. That is when it is done properly though, when done improperly, it throws things off. I have this handy image I just made to show it.

    on the left , you have your stock rim with fat ass tire. On the right, you have your new set up dubz with thin tires. Notice the overall diameter of the tire never changed, just how much rim is on the inside. Your car for all intents and purposes is perfectly calibrated in this situation.

    [​IMG]
     
  12. khai_tuan_nguyen

    khai_tuan_nguyen Senior Member

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    That is a phat picture. Ok so my tire and rims are calibrated fine. So any ideas why my mph to rpm is low.
     
  13. khai_tuan_nguyen

    khai_tuan_nguyen Senior Member

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  14. liquid00meth

    liquid00meth Senior Member

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    the thing is it would only be low if the vehicle speed or RPM sensors were messed, or your tires were actually SMALLER than the originals.
     
  15. khai_tuan_nguyen

    khai_tuan_nguyen Senior Member

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    I believe my rpms and mph is right, meaning when it says 70 mph it feels like i am going 70. What i mean by the problem is that the ratio of the rpms to the mph seems like it is wrong (70 mph at 4000 rpms in 5th) I think it could be something wrong with my setup or something. I think the sensors are reading right and all.
     
  16. liquid00meth

    liquid00meth Senior Member

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    I think the RPM reading is wrong.
     
  17. khai_tuan_nguyen

    khai_tuan_nguyen Senior Member

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    Nope because i have a timing light and they read the same, unless the timing light is based off of the rpm cluster
     
  18. Dman1100

    Dman1100 Senior Member

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  19. khai_tuan_nguyen

    khai_tuan_nguyen Senior Member

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    Thanks Dman but the rims + tires of the TSW 17s are the same as the rims + tires of the stock honda. I just have lower profile tires. So it should not make a difference. Could I have a different tranny and not know
     
  20. khai_tuan_nguyen

    khai_tuan_nguyen Senior Member

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    Could power be lost somewhere or slippign somewhere
     
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