Diffs, boxes, combinations and such

[G]

At the moment I'm working on reawakening my 240 which has sat in the shed for a long time.

Prior to being laid up (the car, not me!), the car and and I enjoyed the experience of employing nearly every shonky tradesman in the biz to work on the car. Names that have been mentioned on this site ad nauseum and which I won't repeat yet again.

Anyway, this time, I hope to do a little better.

 

To date, since tentatively rejoining the z community I'm happy to say I've met some great people. Names that appear on this site again and again and who tirelessly seem to give of their time, energy and knowledge.

 

Anyway, I digress as I'm about to return to the knowledge well once again to ask more questions!!!

 

At the moment my car is running a 240k/240z box (I think) and what I assume is a 3.5 or 3.7 rear ratio. Whilst I search somewhat in vain for a P90 head for an engine rebuild, I'm going to try and focus on the driveline and suspension and getting that working properly.

 

Current plan is to replace the box with a 260 jobbie and the diff with a 4.1 or 4.3, then fixup the suspension. No point going fast in a straight line if you can enjoy the curves!!

 

For those who've done these mods, do you find a 4.3 too tall for a road car?

I have the opportunity to buy an R190 4.4 LSD, but wonder if it's just going to be too high for something which isn't going to hit the track.

I've also been reading about WRX rear end swaps, but I wonder if in the long run it's just easier to try and source a Nissan r180 rather than try to modify stuff to fit a z.

 

I'm also guessing there are good and bad ratio boxes for 260's. In combination with the 4.1 or 4.3, I'm wondering what makes a good 'fit'?

 

General thoughts or ramblings appreciated!

 

 

 

 

[d3c0y]

4.1 is the max you want to go in a road car. Even then the revs are up there at 110. I mean obviously its up to you at the end of the day and how much of a road going race car you want on the road.

 

R190? I would be checking this out carefully as the only R190s I know about are Nissan competition LSDs and very rare.

 

The subi diffs are a very cheap way to get an LSD and a relatively new diff in you car. Only mod required is the axels as these are the same albeit updated r180 the cars came with.

 

There is a sticky on gearboxes detailing ratios and which box is the one to get. Go read up there first.

 

If your car is a manual and an r180 it should be running a 3.9 open diff.

[Six_Shooter]

To start with I see this a lot, a higher numerically gear is a "short" or "low gear" ratio. A lower numerically gear is a "tall" or "high" gear.

 

The choice of ratio depends on a lot of factors, as mentioned where you want the engine revving to while at cruising speeds, the type of acceleration you want, and finally how much power you have.

 

I have found in a couple cars that once more power was added the diff ratio had a large factor in just how the car accelerated, as in how quickly I needed to shift, namely 1st gear. In my 240, I have a turbo L28 that is making around the 300 HP mark. I originally had a 3.54 R180, and the gear ratio was decent, 1st gear wasn't too short, highway revs (at 110 to 120 kph) were decent. Before the turbo the L28 was a stock N/A version, with Weber downdrafts.

 

I swapped to 3.90 R200, to be able to use Z31 CV axles, and while accel is great, I feel the gear is too short for me. !st gear when I'm at the drag strip is over too quickly to be a really good ratio for me, even though top end trap RPM is pretty good. I also feel that the shorter gear doesn't put enough load on the engine to get the turbo to spool in first gear, at least not as much as I'd like. Highway speeds I find I'm revving a bit higher than I'd like, even in 5th, but I'm just used to the steep overdrives and tall gears of more modern vehicles.

 

This is with a 4 speed 240 box when it was N/A, and a 5 speed ZX box, when it went to turbo, 1st 4 gear ratios being the same from what I've been able to determine through research.

 

There is an online Java script calculator that deals with the Z transmission gear ratios and plots them on a graph, to give you an idea of what changing the diff ratios will do for changing the RPM spread of each gear. I just don't recall what the URL is.

[luvemfast]

I have a 4.365 diff, at 100kph revs are around 3,500rpm. Too high for a road car IMHO.

 

Gear calculator can be found on the locost website.

 

    EDIT   

Heres the link to the download

http://locost7.info/gearcalc.php

[G]

Sounds like I should go with a 3.9 then. The car was originally auto, so I think it has currently has a 3.5 in it.

 

As for the R190 - it's real. It's a Nismo 4.44, which i suppose is only really useful if you're racing or REALLY want to build a replica 432R.

 

I'm tempted to go the Subi route. Maybe I need to do further searching on a "how to".

 

Cheers Guys.

[Luni260z]

I have a 4.365 diff, at 100kph revs are around 3,500rpm. Too high for a road car IMHO.

 

 

I'm putting in a 4.365 diff, at 100kph I'm hoping it revs around 3,500rpm. My engine really only gets going at 3000rpm, so I'm hoping it'll be perfect for a road car that's fun to drive.

 

The car was an AUTO, and the AUTO diff in it at present makes it pretty sluggish (well, at least compared to my previous 3.9 always manual zed).

 

I'd recommend a 4.111 if you want to be sensible.

[dat2kman]

R190 is a rare unit, parts for this are definately NLA!

It used H190 live axle centre with remachined hemisphere into aspecial cast housing.

Sort of left over bits from early Datsun Spirts 2000 live axle Comp parts for the early race and rally 240Z program.

 

The works rally cars used some, but swung over to R180 as tooling at Nissan was set up for mass production of R180, and LSD units became available.

 

I have four H190 LSD units, and a selection of new Nismo CW&P's for the race Spirts 2000 and the Fury 120Y

 

Have no interst in R version!

[G]

I'm now tempted to go the Subaru diff route with the outputs from the US.

 

Sounds like a workable solution to get an R180 LSD in a decent ratio.