Calculating 60-130 with JB4 Log.

MasterWang · 07-15-2013, 03:41 PM

For those of us without VBOX, here is my way of measuring 60-130 with a JB4 Log. We will be finding the exact RPM of both 60mph and 130mph, then subtracting the timestamp values to figure out exact duration time.

We can calculate the exact engine rpm at any given speeds (60 and 130 in this case), using this formula.

rpm = (mph * gear * final * 88) / (circumference/12)

mph: We are using 60 and 130 here.
gear: gear ratio of your car (3rd and 4th)
final: final drive ratio of your car
(both Gear & Final numbers can be found here- http://www.bokchoys.com/differential/GearRatios.htm)
88: combines several conversion factors
circumference: tire circumference (Calculator - http://www.csgnetwork.com/tiresizescalc.html)
12: inches to feet conversion

Using my 335i automatic coupe for an example...

60mph
RPM = (60 x 1.52 x 3.46 x 88) / (78.628 / 12)
RPM = 4238 in 3rd gear

130mph
RPM = (130 x 1.14 x 3.46 x 88) / (78.628 / 12)
RPM = 6887 in 4th gear

Now locate these two RPMs in the Jb4 .csv log, then simply subtract the 4238rpm timestamp from the 6887rpm timestamp.

Timestamp values are in 1/10 of a second, so adding a decimal point would give you the time in seconds.
Example: 105 = 10.5 seconds

-This calculation can be used to measure the time between any two speeds, although some speeds are reached between gear shifts (100mph is one).
-I'm also aware that this isn't 100% accurate!

Gizm0 · 07-15-2013, 04:43 PM

I save myself the hassle of doing the complicated math and just floor it while staring at the speedo and counting in my head... 1, 2, 3, 4, 5 etc...

E90Company · 07-15-2013, 11:33 PM

I can see a few flaws with this method, but I'd say it's a decent way to get an idea without buying a vbox. Nice job OP.

e46m3to335i · 07-16-2013, 12:04 AM

lfelunden · 07-16-2013, 06:02 AM

Well you could also just go into the hidden obd menu and turn on v-eff (GPS speed)

then record it and time it.

MasterWang · 07-16-2013, 01:15 PM

Quote:

Originally Posted by lfelunden

Well you could also just go into the hidden obd menu and turn on v-eff (GPS speed)

then record it and time it.

Interesting. How exactly does one record the v-eff?

lfelunden · 07-16-2013, 01:55 PM

Quote:

Originally Posted by MasterWang

Interesting. How exactly does one record the v-eff?

Well, just use a camera and a video editing program to calculate it

MasterWang · 12-02-2013, 01:35 PM

Jb4 can now log road speed.
Set future use D to 4, speed will be logged under low fuel pressure.

Just make sure you have ISO 27.8 or later.

07-15-2013, 03:41 PM	#1
MasterWang Captain 138 Rep 926 Posts Drives: F06 M6 Join Date: Jan 2011 Location: Overland Park, KS iTrader: (2)	Calculating 60-130 with JB4 Log. For those of us without VBOX, here is my way of measuring 60-130 with a JB4 Log. We will be finding the exact RPM of both 60mph and 130mph, then subtracting the timestamp values to figure out exact duration time. We can calculate the exact engine rpm at any given speeds (60 and 130 in this case), using this formula. *rpm = (mph gear * final * 88) / (circumference/12) mph: We are using 60 and 130 here. gear: gear ratio of your car (3rd and 4th) final: final drive ratio of your car (both Gear & Final numbers can be found here- http://www.bokchoys.com/differential/GearRatios.htm) 88: combines several conversion factors circumference: tire circumference (Calculator - http://www.csgnetwork.com/tiresizescalc.html) 12: inches to feet conversion Using my 335i automatic coupe for an example... 60mph RPM = (60 x 1.52 x 3.46 x 88) / (78.628 / 12) RPM = 4238 in 3rd gear 130mph RPM = (130 x 1.14 x 3.46 x 88) / (78.628 / 12) RPM = 6887 in 4th gear Now locate these two RPMs in the Jb4 .csv log, then simply subtract the 4238rpm timestamp from the 6887rpm timestamp. Timestamp values are in 1/10 of a second, so adding a decimal point would give you the time in seconds. Example:** 105 = 10.5 seconds -This calculation can be used to measure the time between any two speeds, although some speeds are reached between gear shifts (100mph is one). -I'm also aware that this isn't 100% accurate!
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07-15-2013, 04:43 PM	#2
Gizm0 Colonel 439 Rep 2,136 Posts Drives: 08 e92 335i 6mt Join Date: Jan 2013 Location: Virginia iTrader: (1)	I save myself the hassle of doing the complicated math and just floor it while staring at the speedo and counting in my head... 1, 2, 3, 4, 5 etc... __________________ JB4 G5 w/ Backend flash - Walbro 450lpfp - VRSF DPs - VRSF 5" stepped IC - DCI - ER CP w/ Tial BOV - 335is clutch
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07-15-2013, 11:33 PM	#3
E90Company Major General 198 Rep 6,136 Posts Drives: Car Join Date: Mar 2012 Location: FL iTrader: (2)	I can see a few flaws with this method, but I'd say it's a decent way to get an idea without buying a vbox. Nice job OP.
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07-16-2013, 12:04 AM	#4
e46m3to335i Major 177 Rep 1,380 Posts Drives: 2015 F80 M3 Join Date: Feb 2010 Location: Fort Bragg, NC iTrader: (26)
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07-16-2013, 06:02 AM	#5
lfelunden Banned 61 Rep 643 Posts Drives: BMW M5 F10 Join Date: Aug 2011 Location: German Autobahn iTrader: (0) Garage List 2013 BMW M5 [0.00] 2011 Alpina B3S Bit ... [9.50] 2010 Alpina B3 Biturbo [10.00] 2009 Alpina B5S [10.00]	Well you could also just go into the hidden obd menu and turn on v-eff (GPS speed) then record it and time it.
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12-02-2013, 01:35 PM	#8
MasterWang Captain 138 Rep 926 Posts Drives: F06 M6 Join Date: Jan 2011 Location: Overland Park, KS iTrader: (2)	Jb4 can now log road speed. Set future use D to 4, speed will be logged under low fuel pressure. Just make sure you have ISO 27.8 or later.
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