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RPM diff ratio

RATBOX

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just a general question i've just bought a VY berlina wagon 5.7 auto i'm curious about the diff ratio, having owned other 5.7 commodores utes and SSs this seems to be revving a little harder @115kmh revs are around 2200RPM from memory others i've had at this speed are around 1800RPM what do others say is normal just wondering if mine might have had a lower diff ratio fitted, speedo seems spot on based on a GPS speed app on my phone

thanks
 

markalan1two

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probably 3.46 manual rear gears
 

EYY

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2150 rpm is normal with 3.07 gears for that speed. Small variations in tyre size, tacho accuracy etc though.
 

RATBOX

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thanks for the replies, maybe just seems to be revving a bit harder being a wagon can hear the exhaust more
 

markalan1two

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http://www.apexgarage.com/tech/gear_ratios.shtml
here the link to work it out.
if you have 235/45/17 you Tyre diameter is 25.31
VY auto ratio's are
1=3.059-1
2=1.625-1
3=1-1
4=0.696-1
you can change your final drive and see the differences
 

RATBOX

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thanks, used the link dunno if i'm doing something wrong but get no results from it, when i hit calculate all i get in all the boxes is NaN
 

EYY

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That link figures out max rpm in each gear. You can’t do reverse calculations. All you need to know is that 1850 rpm at 100kmph is approximately correct for 3.07 geared commodores with tyres close to original rolling diameter (of course commercial variants are different due to larger tyres).

Base your comparison off this.

Eg.
In the case of 3.73 gears:
1850/3.07=602

602*3.73=2247rpm@100kmph
 
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