Need help to lower my diff ratio

[Homer]

I'm running a 54 plate rx8 with a turbo Diesel engine in it about 300bhp but the revs are to high

So I'm after getting a lower diff been told that the rx7 automatic crown wheel and pinion will fit ?? Then it be 3.909 I think

I'm running standard diff which is 40 teeth crown and 9 on the pinion think it's a 4.444

Hope this is a better add second time lucky

[GySgtFrank]

Your best bet is to swap the rear to a different diff completely. You will never be able to get the kind of ratios you will need in a Mazda diff, let alone the fact that the torque from a diesel will most likely shred any differential set up for a rotary. Depending on the diesel you will want your cruising rpm at 75 to be about 1600 - 1700 rpm. This will require around a 2:1 final drive ratio with a 25 inch tire. Depending upon the overdrive ratio in the transmission you use, it is still going to leave you looking for 2.73:1 or higher gears. You might look into the Ford 9 inch as there are standalone center sections made that can be adapted to work with your independent rear suspension and a lot of gear sets made for them. Any way you look at it, it will require a fair amount of money and fabrication to make it work. Other than that the auto tranny FD gears are probably the best you're going to get, but you aren't going to be happy with the results. They won't even get close to altering the rpms enough for a diesel engine.

[Homer]

I'm using the original rx8 gearbox

[RETed]

This is a warning.

You basically are running three concurrent threads asking the same thing two of them in this section + your intro thread.
Please stop starting new threads asking the same thing.
I will close the older thread and keep this one active for now.


-Ted

[Homer]

I stoped useing the other ones I was getting crap over nothing

[RETed]

If you're going to do this the next time, please alert the mods to shut the thread down first.
This is a legitimate reason to click the "alert" icon (white triangle with red border with the "!" in it) and state as such.
Also, as the OP, if you feel your threads are being dirtied, please feel free to do the same to alert the mods / admins to such problems.


-Ted

[chibikougan]

Originally Posted by Homer

I stopped using the other ones I was getting crap to see if i had a spine and could take a little razz and my lazy writing has everyone trying to help me pulling their hair out just to decipher the hoodie speak.

Can you count the errors? Anyway lovely job cleaning it up as well as you have!

[chibikougan]

Originally Posted by GySgtFrank

Your best bet is to swap the rear to a different diff completely. You will never be able to get the kind of ratios you will need in a Mazda diff, let alone the fact that the torque from a diesel will most likely shred any differential set up for a rotary. Depending on the diesel you will want your cruising rpm at 75 to be about 1600 - 1700 rpm. This will require around a 2:1 final drive ratio with a 25 inch tire. Depending upon the overdrive ratio in the transmission you use, it is still going to leave you looking for 2.73:1 or higher gears. You might look into the Ford 9 inch as there are standalone center sections made that can be adapted to work with your independent rear suspension and a lot of gear sets made for them. Any way you look at it, it will require a fair amount of money and fabrication to make it work. Other than that the auto tranny FD gears are probably the best you're going to get, but you aren't going to be happy with the results. They won't even get close to altering the rpms enough for a diesel engine.