Diff ratio's and fuel economy. big/small case
Posted: Fri Feb 09, 2007 4:34 pm
right i've been driving my 325i auto for about 6months now and notice that the auto with the 3.64lsd only turns 2600rpm at 70mph. this leads to a little bit of a strange phenomenon being that if i run the car closer to 80mph the fuel consumption is better then at 70 as the engine is turning 2900rpm and running high VE efficiency %.
as it stands this is what the gearing gives out.
Gearbox:-
Tyre:- Michelin all patterns 205/55 x 15
-------------------------------------------------------------------------------------------
Top Gear gives 25.953 MPH/1000 RPM and a top speed of 168.698 MPH at 6500 RPM
Engine speeds in top gear:-
30 MPH = 1156 RPM 40 MPH = 1541 RPM 50 MPH = 1927 RPM 60 MPH = 2312 RPM
70 MPH = 2697 RPM 80 MPH = 3082 RPM 90 MPH = 3468 RPM 100 MPH = 3853 RPM
Top Speed in 1 gear = 49.657 MPH
And changes into 2 gear at 3879 RPM dropping 2621 RPM
Top Speed in 2 gear = 83.209 MPH
And changes into 3 gear at 4392 RPM dropping 2108 RPM
Top Speed in 3 gear = 123.149 MPH
And changes into 4 gear at 4745 RPM dropping 1755 RPM
Top Speed in 4 gear = 168.698 MPH
a 3.91 diff would give this, meaning at 70 it would be nearer peak torque and actually able to work easier due to the easier ratio to push as well. should give a nice boost in acceleration too.
Gearbox:-
Tyre:- Michelin all patterns 205/55 x 15
-------------------------------------------------------------------------------------------
Top Gear gives 24.161 MPH/1000 RPM and a top speed of 157.049 MPH at 6500 RPM
Engine speeds in top gear:-
30 MPH = 1242 RPM 40 MPH = 1656 RPM 50 MPH = 2069 RPM 60 MPH = 2483 RPM
70 MPH = 2897 RPM 80 MPH = 3311 RPM 90 MPH = 3725 RPM 100 MPH = 4139 RPM
Top Speed in 1 gear = 46.228 MPH
And changes into 2 gear at 3879 RPM dropping 2621 RPM
Top Speed in 2 gear = 77.463 MPH
And changes into 3 gear at 4392 RPM dropping 2108 RPM
Top Speed in 3 gear = 114.645 MPH
And changes into 4 gear at 4745 RPM dropping 1755 RPM
Top Speed in 4 gear = 157.049 MPH
4.1 might be a bit short but still useable. but again much harder to find in big case
as it stands this is what the gearing gives out.
Gearbox:-
Tyre:- Michelin all patterns 205/55 x 15
-------------------------------------------------------------------------------------------
Top Gear gives 25.953 MPH/1000 RPM and a top speed of 168.698 MPH at 6500 RPM
Engine speeds in top gear:-
30 MPH = 1156 RPM 40 MPH = 1541 RPM 50 MPH = 1927 RPM 60 MPH = 2312 RPM
70 MPH = 2697 RPM 80 MPH = 3082 RPM 90 MPH = 3468 RPM 100 MPH = 3853 RPM
Top Speed in 1 gear = 49.657 MPH
And changes into 2 gear at 3879 RPM dropping 2621 RPM
Top Speed in 2 gear = 83.209 MPH
And changes into 3 gear at 4392 RPM dropping 2108 RPM
Top Speed in 3 gear = 123.149 MPH
And changes into 4 gear at 4745 RPM dropping 1755 RPM
Top Speed in 4 gear = 168.698 MPH
a 3.91 diff would give this, meaning at 70 it would be nearer peak torque and actually able to work easier due to the easier ratio to push as well. should give a nice boost in acceleration too.
Gearbox:-
Tyre:- Michelin all patterns 205/55 x 15
-------------------------------------------------------------------------------------------
Top Gear gives 24.161 MPH/1000 RPM and a top speed of 157.049 MPH at 6500 RPM
Engine speeds in top gear:-
30 MPH = 1242 RPM 40 MPH = 1656 RPM 50 MPH = 2069 RPM 60 MPH = 2483 RPM
70 MPH = 2897 RPM 80 MPH = 3311 RPM 90 MPH = 3725 RPM 100 MPH = 4139 RPM
Top Speed in 1 gear = 46.228 MPH
And changes into 2 gear at 3879 RPM dropping 2621 RPM
Top Speed in 2 gear = 77.463 MPH
And changes into 3 gear at 4392 RPM dropping 2108 RPM
Top Speed in 3 gear = 114.645 MPH
And changes into 4 gear at 4745 RPM dropping 1755 RPM
Top Speed in 4 gear = 157.049 MPH
4.1 might be a bit short but still useable. but again much harder to find in big case