hi,

the diff centre in my aussie s1 RX7(1980) is shot and needs a replacing.

it curently runs the std 3.9:1 ratio but im thinking of going to a 4.1:1 or a 4.4:1 as the engines powerband isent coming on quick enough. (its only a rebuilt s2('82) 12a non ported)
the engine pulls at about 6000rpm up to 9000rpm ish.. (tacho only goes to 8k ) but it takes forever to get there

has any one here used a 4.1:1 or a 4.4:1 on a std style engine?
and if so was it worth it??(acceleration v fuel economy?)
what rpm was the engine when crusing at 100kph?? (60mph ish)in 5th or 4th gear??

im not expecting a mircle from from fitting one of these, but i want some result seeing as these diff centers are getting a little pricey (upto $300AUS for a 4.4:1 as against $100AUS for a 3.9:1)
also does anyone know about the speedo drive gear???
can you get one that works with the 4.4???

because there's only one thing worse than wasting fuel, thats wasting fuel then getting a ticket 'cause you were going 15kph faster than what the speedo said

input guys i need input..... am i wasting my time or not?

 

I swapped mine for a 4.4:1 ratio a while ago and I'm pretty happy with the results. Obviously there was a slight increase in fuel consumption but the improvement in performance is very noticeable. I wouldn't worry too much about getting a ticket since the speedo will be showing faster than you are actually going but you can correct it by installing a ratio box. That's what I did. It's just a little gearbox that goes in between the speedo cable and speedo drive. You just work out how much error your odometer has over a given distance and get the ratio box made to suit. As for highway cruising mine pulls about 3500rpm at 100kph in 5th gear. Hope this helps.

 

Rev Head, where did you get a 'ratio box' made?

 

By a shop that specializes in auto instrumentation and speedometers.