Close

Page 6 of 9 FirstFirst ... 45678 ... LastLast
Results 126 to 150 of 218
  1. #126
    Join Date
    Jun 2010
    Location
    Boynton Beach, FL
    Posts
    1,209
    Rep Points
    1,449.2
    Mentioned
    61 Post(s)
    Rep Power
    0


    3 out of 3 members liked this post. Yes Reputation No
    Food for thought


  2. #127
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    118,817
    Rep Points
    31,802.7
    Mentioned
    2085 Post(s)
    Rep Power
    319


    Yes Reputation No
    Click here to enlarge Originally Posted by BoostAddict Click here to enlarge
    Good post! http://www.bimmerboost.com/content.p...ls-on-the-dyno

  3. #128
    Join Date
    Jun 2012
    Posts
    1,177
    Rep Points
    801.6
    Mentioned
    14 Post(s)
    Rep Power
    9


    1 out of 1 members liked this post. Yes Reputation No
    I mean, they lost 20hp... that makes sense simply from the inertia alone. Those rear tires and wheels are so much heavier and have so much wider of a contact patch. The graphs are offset because they are scaling in mph and not rpm. No clue why they would scale in MPH since the dynojet doesn't require ratios as an input...

    This may be of some use:

    http://forums.corvetteforum.com/c5-t...o-numbers.html

  4. #129
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    118,817
    Rep Points
    31,802.7
    Mentioned
    2085 Post(s)
    Rep Power
    319


    Yes Reputation No
    This seems to be a very good explanation:

    Higher ratio gears will give you lower chassis dyno numbers for a strange, but logical reason. In essence, the DynoJet calculates hp based on the time it takes to spin up the 2800lb roller assembly. It's basically work divided by time and rpm. Think about this: If you car is at idle in neutral and you stab the throttle, it will take time to accelerate to redline...let's say 1.1 seconds. Now let's say it takes 8.2 seconds for your car to accelerate the DynoJet from low speed to top speed with 3.23 gears and 7.3 seconds with 3.73 gears. Dyno printout says 355 rwhp with 3.23 gears and 346 rwhp with 3.73 gears...why?

    Think aabout this: In the 8.2 seconds it takes to spin the rollers with 3.23 gears, it would still take the motor about 1.1 seconds to overcome its own inertia (idle to redline). There's about 13.4% of the work used just to accelerate the motor itself. With 3.73 gears, the time to reach redline decreases to 7.3 seconds. Divide the 1.1 seconds into the 7.3 seconds and you will see that overcoming the internal engine inertia costs 15.1% of the work with 3.73 gears. There is less hp available during this time period to spin the rollers so the DynoJet will read a slightly lower hp figure. Make sense, or did I lose you?"

  5. #130
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    118,817
    Rep Points
    31,802.7
    Mentioned
    2085 Post(s)
    Rep Power
    319


    Yes Reputation No
    Click here to enlarge Originally Posted by rudypoochris Click here to enlarge
    I mean, they lost 20hp... that makes sense simply from the inertia alone. Those rear tires and wheels are so much heavier and have so much wider of a contact patch. The graphs are offset because they are scaling in mph and not rpm. No clue why they would scale in MPH since the dynojet doesn't require ratios as an input...

    This may be of some use:

    http://forums.corvetteforum.com/c5-t...o-numbers.html
    Very nice post, reading it, learning. Good stuff.

  6. #131
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    118,817
    Rep Points
    31,802.7
    Mentioned
    2085 Post(s)
    Rep Power
    319


    Yes Reputation No
    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    This seems to be a very good explanation:

    [/I]
    What I'm trying to understand here is how does he calculate the 1.1 seconds to overcome its own inertia?

  7. #132
    Join Date
    Jul 2012
    Posts
    112
    Rep Points
    181.3
    Mentioned
    4 Post(s)
    Rep Power
    2


    Yes Reputation No
    Its not calculated. The 1.1 sec figure was just made up for the sake of making the example.

  8. #133
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    118,817
    Rep Points
    31,802.7
    Mentioned
    2085 Post(s)
    Rep Power
    319


    Yes Reputation No
    Click here to enlarge Originally Posted by JC335xi Click here to enlarge
    Its not calculated. The 1.1 sec figure was just made up for the sake of making the example.
    Well how do you calculate it?

  9. #134
    Join Date
    Jul 2012
    Posts
    112
    Rep Points
    181.3
    Mentioned
    4 Post(s)
    Rep Power
    2


    Yes Reputation No
    Think about this: If you car is at idle in neutral and you stab the throttle, it will take time to accelerate to redline...let's say 1.1 seconds.
    From this it appears to be a measurement you would take for your engine not a calculated value.

  10. #135
    Join Date
    May 2011
    Location
    Houston, Texas
    Posts
    1,641
    Rep Points
    2,149.9
    Mentioned
    71 Post(s)
    Rep Power
    22


    Yes Reputation No
    Do mustang dynos calculate differently? Most AT cars put out more TQ than 6MT on any given dyno. When I swapped my rear diff from 3.08 to 3.46 my TQ increased.

    I thought it was common knowledge that higher gear ratio (3.46) increases TQ?
    2010 e92 M3 Jet Black | DCT | ESS Tuned | Akrapovic Slip-on | Challenge X-pipe | AFE Intake | 18" Volk TE37SL | KW V3 Coilovers | RPI Scoops | Under Drive Pulley

    2007 e92 Mont. Blue 335i | 6MT | COBB Tuned | Quaife 3.46 LSD | Helix FMIC | AA DPs | HKS Exhaust | DCI | Stett CP w/ Forged DVs | KWv2 Coilovers | UUC Sway Bars & SSK | HPF Stg 2 Clutch | HFS-4 | M3 Suspension Bits | DEFIVfab Diff Lockdown Kit | Stoptech Trophy BBK

  11. #136
    Join Date
    Sep 2012
    Location
    Brisbane, Australia
    Posts
    3,293
    Rep Points
    1,435.7
    Mentioned
    53 Post(s)
    Rep Power
    15


    Yes Reputation No
    Shorter gears read lower horsepower due to some magic mumbo? Thats not how it actually works though!

    it just proves again that dyno horsepower figures are total bs for comparing anything other than your car pre-mod to your car post-mod... Assuming your mod isn't changing your gewr ratios

    and if i'm to understand this correctly, dzennos car gets free dynojet horsepower from simply having longer gearing?

    ed: and it's pretty common knowledge that bigger+heavier wheels and tires reduces power seen at said wheels.. Want to go for max hp numbers? Fit skinny 17's lol

  12. #137
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    118,817
    Rep Points
    31,802.7
    Mentioned
    2085 Post(s)
    Rep Power
    319


    Yes Reputation No
    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
    and if i'm to understand this correctly, dzennos car gets free dynojet horsepower from simply having longer gearing?
    That would be correct on an inertia based dyno it seems.

  13. #138
    Join Date
    Sep 2012
    Location
    Brisbane, Australia
    Posts
    3,293
    Rep Points
    1,435.7
    Mentioned
    53 Post(s)
    Rep Power
    15


    Yes Reputation No
    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    That would be correct on an inertia based dyno it seems.
    Wow.. Well i guess that's why dyno dynamics/ mustang (same type correct? We only really get DD over here) are considered 'more accurate' ?

    ed: ok dynojet are more consistent between dynos, but dyno dynamics are easier to compare when used on the same dyno

  14. #139
    Join Date
    Jun 2012
    Posts
    1,177
    Rep Points
    801.6
    Mentioned
    14 Post(s)
    Rep Power
    9


    Yes Reputation No
    Shorter gearing costs you power. Greater changes in ratio require more effort to turn. Additionally larger ratios means one shaft is turning faster than the other, friction increases with V^2. This is a big reason why you can dyno a car like an S2000 and end up with less HP than a 225hp Mustang 5.0. The drive train consumes much more energy due to the higher ratios. Some of this is mitigated by weaker input components if they are used.

  15. #140
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    118,817
    Rep Points
    31,802.7
    Mentioned
    2085 Post(s)
    Rep Power
    319


    Yes Reputation No
    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
    Wow.. Well i guess that's why dyno dynamics/ mustang (same type correct? We only really get DD over here) are considered 'more accurate' ?
    They aren't more accurate as much as for tuning load based dynos are preferred.

  16. #141
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    118,817
    Rep Points
    31,802.7
    Mentioned
    2085 Post(s)
    Rep Power
    319


    Yes Reputation No
    Click here to enlarge Originally Posted by rudypoochris Click here to enlarge
    Shorter gearing costs you power. Greater changes in ratio require more effort to turn. Additionally larger ratios means one shaft is turning faster than the other, friction increases with V^2. This is a big reason why you can dyno a car like an S2000 and end up with less HP than a 225hp Mustang 5.0. The drive train consumes much more energy due to the higher ratios. Some of this is mitigated by weaker input components if they are used.
    There's truth to this but you do get a mathematical torque increase which has to translate.

  17. #142
    Join Date
    Sep 2012
    Location
    Brisbane, Australia
    Posts
    3,293
    Rep Points
    1,435.7
    Mentioned
    53 Post(s)
    Rep Power
    15


    1 out of 1 members liked this post. Yes Reputation No
    Click here to enlarge Originally Posted by rudypoochris Click here to enlarge
    Shorter gearing costs you power. Greater changes in ratio require more effort to turn. Additionally larger ratios means one shaft is turning faster than the other, friction increases with V^2. This is a big reason why you can dyno a car like an S2000 and end up with less HP than a 225hp Mustang 5.0. The drive train consumes much more energy due to the higher ratios. Some of this is mitigated by weaker input components if they are used.
    Well, it's actually longer gears take more effort (torque) to turn, hence they read out a lower torque o the wheels figure

    Torque is effort (a moment) at a specific time, power is torque over time
    ... I think i explained that wrong, but it's kinda the idea :/

    heat through friction isn't as big a deal as you seem to be saying, assuming all components are healthy and high quality. Yes heat will massively increase at much much higher rpm, but these are relatively snall rpm changes, and relatively low heat.

  18. #143
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    118,817
    Rep Points
    31,802.7
    Mentioned
    2085 Post(s)
    Rep Power
    319


    Yes Reputation No
    Gearing can make your head hurt.

  19. #144
    Join Date
    Sep 2012
    Location
    Brisbane, Australia
    Posts
    3,293
    Rep Points
    1,435.7
    Mentioned
    53 Post(s)
    Rep Power
    15


    Yes Reputation No
    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Gearing can make your head hurt.
    It's such a complicated topic, everything discussed here is.

    did you know that one horsepower is 550 pound feet per second?

    not entirely relevant, but interesting lol (i was trying to see what measurements i could convert to o understand things a bit simpler)

  20. #145
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    118,817
    Rep Points
    31,802.7
    Mentioned
    2085 Post(s)
    Rep Power
    319


    Yes Reputation No
    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
    did you know that one horsepower is 550 pound feet per second?
    Of course I knew that. How else do you measure getting 300 pounds of coal up a mine shaft?

    The real question is do you know how many watts are in 1 horse?

  21. #146
    Join Date
    Jun 2012
    Posts
    1,177
    Rep Points
    801.6
    Mentioned
    14 Post(s)
    Rep Power
    9


    Yes Reputation No
    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
    Well, it's actually longer gears take more effort (torque) to turn, hence they read out a lower torque o the wheels figure

    Torque is effort (a moment) at a specific time, power is torque over time
    ... I think i explained that wrong, but it's kinda the idea :/

    heat through friction isn't as big a deal as you seem to be saying, assuming all components are healthy and high quality. Yes heat will massively increase at much much higher rpm, but these are relatively snall rpm changes, and relatively low heat.
    No, shorter gears (higher ratios) consume more power. The heat is real... touch the transmission after doing a few 150mph pulls. Most of the power is lost in the rear end though since the 90 degree and hypoid gear sucks power.

    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    There's truth to this but you do get a mathematical torque increase which has to translate.
    Eh not really. You measure the RPMs via tach signal and the drum speed. Knowing the mass of the drum, the power is calculated although obviously torque is measured. That is why I didn't understand why they bothered to input gear ratios to get a MPH reading. It just serves to confuse here.

  22. #147
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    118,817
    Rep Points
    31,802.7
    Mentioned
    2085 Post(s)
    Rep Power
    319


    Yes Reputation No
    Click here to enlarge Originally Posted by rudypoochris Click here to enlarge
    Eh not really. You measure the RPMs via tach signal and the drum speed. Knowing the mass of the drum, the power is calculated although obviously torque is measured. That is why I didn't understand why they bothered to input gear ratios to get a MPH reading. It just serves to confuse here.
    I'm not really sure what you are saying, the torque multiplication changes with a shorter ratio.

  23. #148
    Join Date
    Jun 2012
    Posts
    1,177
    Rep Points
    801.6
    Mentioned
    14 Post(s)
    Rep Power
    9


    Yes Reputation No
    This may be worth reading. I wrote it a long time ago (18 years old) and unfortunately I had to compress it to make it fit in the attachments of this forum. I never got around to writing the drivetrain loss portion.
    Attached Files Attached Files

  24. #149
    Join Date
    Jun 2012
    Posts
    1,177
    Rep Points
    801.6
    Mentioned
    14 Post(s)
    Rep Power
    9


    Yes Reputation No
    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    I'm not really sure what you are saying, the torque multiplication changes with a shorter ratio.
    The torque at the wheels, but not at the motor. The dyno will give you torque at the motor although it is calculated back from torque at the wheels. That is why gearing can consume power and skew the results.

  25. #150
    Join Date
    Jan 2010
    Location
    SoCal
    Posts
    118,817
    Rep Points
    31,802.7
    Mentioned
    2085 Post(s)
    Rep Power
    319


    Yes Reputation No
    Click here to enlarge Originally Posted by rudypoochris Click here to enlarge
    The torque at the wheels, but not at the motor. The dyno will give you torque at the motor although it is calculated back from torque at the wheels. That is why gearing can consume power and skew the results.
    Yes, that is what I was saying.

Page 6 of 9 FirstFirst ... 45678 ... LastLast

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
  •