rear end gear ratios and a few other questions rpm vs. mph...blah blah!

[b-rett]

hello all,i have just recently purchased an r32 GTS 5 bolt rear diff for a 1jz_240 project. i am running a 5-speed r154 trans from the 7m chassis (toyota) - if anyone is familiar with it.

first, i am wondering what kind of rpm vs. mph you all are seeing with your rear ends? i know the transmission gearing will differ a bit, but just trying to get a rough idea of what i can expect.

second, i'm seeing a few threads where ppl are stating that the gear ratio on the 300zx turbo diffs (3.69) is a higher gear ratio than say the non turbo diffs (4.10). what is the logic behind the numbers nissan has published/what exactly do they mean?

for instance with the 3.69 gearing, are we at 2500rpm going 70mph? and with the 4.10 are we at 3500rpm going 70mph? this information would be helpful. thanks a million!

[ELEMENT692121]

the ratios of the trans will make the rpms differ also .. you have to have the total ratio of the selected gear and also the rear ratio to get an rpm to speed calcuation .. for eaxample 3.69 ratio the drive shaft has to turn 3.69 turns to get the wheels to turn one rotation 4.10 same thing driveshaft has to rotate 4.10 times to get the rear to turn one full rotation .. then what u need to know is the ratio of the top gear if your looking for an rpm to speed ratio .. also tire size is a factor ..

[b-rett]

oh yeah i understand that. i guess i am trying to understand more or less how nissan has setup their ratio.

all things constant besides the rear end....so, am i at a higher rpm with the 4.36 ratio diff oppossed to the 3.69? so higher rpm but still the same speed with the 4.36 ratio diff, correct?

thank you,

[ELEMENT692121]

yeah a 3.69 diff would be tacking lower at 60 than a 4.69 diff because a 3.69 means that the drive shaft has to turn 3.69 times to turn the ring gear once and a 4.69 drive shaft would have to turn 4.69 times to turn the ring gear once ..

[Imissmyturbo]

My rear has a 4:11 ratio and with the R-154 transmission I can hit around 125 mph in 4th gear. With your 1jz you should be able to go a bit faster since you can rev higher. I am looking to get a taller rear for my setup since I am almost hitting the rev limiter in 4th in the 1/4 and I am still running low boost.

[b-rett]

so i think i will end up getting there quicker...i believe the R32 rears have a 4.36...not 100% on that.

is yours an r32 rear end as well? thanks man,

brett

[ELEMENT692121]

4.36 is a good rear for acceleration .. will deff pull harder

[b-rett]

very well then...i think i will end up needing a lower ratio rear end (NA 300zx i guess) which will keep me out of 5th gear at the strip. we'll see. should be fun though...

can anyone verify the ratio in the r32 GTS or any other skyline rears? thanks,