so, as most of you know i got this shitty ass "j30" diff that locks when it wants to, yeah fine, i'll use it daily and a welded for drift events, as i can swap a diff out in under 30 minutes.

what I'm getting at, is i know a J30 is a lower ratio, like a 3:96 or whatever the fuck, i don't care, but on the highway, the RPMs tell a different story...

i know in most of my nissans, all the 240's, the GTR, KA or SR what the fuck ever, that my RPMs on the highway were pretty much right at 3,500rpm@80mph, almost like i could set a watch by it... even in the GTR with the taller 4:11 ring set (not much further off than the stock 4:08 in s buckets). and i noticed in my car, that doing 80, i'm just right about at 4,000rpm @ 80mph... as far as i know, a J30 SHOULD make it to where you're LESS than 3,500 @ 80mph...

so what the fuck is up? i don't have enough difference in tire/wheel to make an extra 500+rpm over what a J30 diff SHOULD be doing...

i'm going to weld up a S13 or 14 diff, and yank out this "unknown" J30 and count the teeth on the ring set, and was wondering if anyone here ran the 4:36 VLSD that came in what, the 180SX Type X, the R32 GTS4, and whatever else?

anyone run into anything like this?


also i noticed yesterday, pulling out of the shop, i went to do a sweet red neck yee haw burnout, and in 1st, it just one tire fired, then i hit second, heard a clunk from the back and both just roasted all the down like 100ft, into third it held lock, the chirp into 4th was only one tire... pile of shit... as far as i know, a VLSD shouldn't be clunking/locking like that...

possible that i have a 4:36 ring set in my diff? has anyone or is anyone running one and have similar RPMs highway? i noticed my car has a substantial low end acceleration, more so that my last SR, more than what it's 233whp (i have a dyno sheet) SHOULD be doing, it's almost more RAWR than my GTR was...

so yeah, what up?

 

Hey there BZ...hope this helps. I used it to confirm I had a 180sx diff without popping it open. Enjoy:

Gear Ratio Speed Calculator

...that might answer some of your questions.

-Royce

 

great little link man!


i'll check it out when i have more time, bout to head out now, but thanks!

 

Here is a link for the gear ratios of the typical 240sx trans KA/SR/CA...
Nissan 240SX Performance Modification/Transmission - Wikibooks, open books for an open world

Plug that info in with the diameter of you tires and you will have a good idea of what speed/rpm you will be turning with based on the ratio of your specific diff.

-Royce

 

its a 4:11

 

i was thinking the same, only car i know of that had the 4:11 is the R32 GTR, which would make it a mechanical LSD... could be wrong on it's origins...

 

The ratio doesn't imply anything about what type of LSD it is. People mix and match all the time.

Other aspects affect rpm in 5th. Tire size is one, and 5th gear ratio is the other. The NA boxes had .838 5th gear ratios, but were externally identical. The DET boxes were .759 5th.

If you want to know your ratio without opening the pumpkin, then just crawl under the car with the rear wheels off the ground. Mark the position of one of the output shafts and the input shaft. Now count how many rotations on the input shaft it takes to rotate the output shaft once. It will be easy to see the difference in 3.92, 4.08, and 4.36 rotations. Make sure both output shafts spin in unison, by the way.

 

awesome, as far as i know, the box is the S14 SR20DET box that came on the engine... people do mix and match, i know that, but who would want to put a taller ring set on a VLSD? it's like pissing into the wind, after a night of binge drinking, so it'd be all yellow/brown and smell like popcorn in yo face!


while i'm fucking with the car, i'll go ahead and do that ep, thanks!

(EDIT: not the stale piss part, but jacking it up and spinning it)

 

chris, so i marked and rotated, both marks ended up perfectly matched up after 4 full rotations on the output shafts, with a little bit of error spinning the tires, still confused, close to the 3:92, but also close to the 4:08, so i'm still kind of confused... even double and tripple checked, it was all pretty much 4 solid rotations...

 

pretty much or a little over 4 spins... if you wanted to be baller drop the diff and see what the number of teeth are.. or you prob dont give a fuck lol