Diff change

[bozie]

I am currently running a 1600 cross flow that revs to about 6200 with a type e 4speed and a 4.1 diff I have just done my first race and struggled on the straights I have a 3.54 diff in the garage so was going to change them over. What sort of difference would I see from a 4.1 to a 3.54. I know I will lose acceleration and gain top end but how much will it be 2mph or 20mph

cheers all

[puddy]

Need to know the tyre size or rolling radius . I have the same with 175 50 13's and at 4k on the motorway its around 60 to 70mph.

 

Puddy

[bozie]

They are 185'60R13 my speedo is at 110mph at 6250rpm but not sure how accurate the speedo is with different engine, box and diff.

Cheers

[katana]

Other thing to consider is you may not have the power to pull the taller diff ratio? Suck eggs time - speed is irrelevant as you need the engine to be max'd out approaching or at the fastest point on the track so unless the engine has the power to pull that ratio it'll never be optimal. You may find that a 3.9 may be better?

[RWL81P]

my rs2000 did 90 in 3rd and about 115 in 4th. with the rocket box and 3.54 diff. on closed roads of course.

[khanlad]

Ford quote 18.4 mph per 1000 rpm in top with a 3.54 but with 175/70 tyres

[puddy]

According to this with your info put in at 6250 rpm ,  1.1 in 4th gear , http://www.boosttown.com/gearbox_differential/speed_calculator.php

 

4.1 = 98.33 mph

 

3.54 = 113.88 mph

 

puddy