What recommended lsd diff/ratio for F20c in 510?

[78dattysun]

Looking to buy a diff for my 4 dr 510 with Honda s2000 f20c/6spd trans. Car is for street use. Not a big budget to spend but don't mind spending the money for the right option and don't mind changing to CV's. I'm not educated enough to decide what ratio and lsd to choose. I was just thinking subaru and started looking for one but you know how that goes. Can't find one lol. But I read about ppl using the R200 from the 260z, s30 Silvia etc.. But that looks giant. so just looking to be directed in the right path. Thanks

[ggzilla]

FJ20 is a high revving engine, so use a steep final drive ratio like 4.375 or 4.625

[78dattysun]

Ya its a f20c ap1 motor an they do rev high but what diff would that be? Thanks

[datzenmike]

You can get it in R-160 but probably after market. The same in R-180 is stronger and 4.375 is found in early 720 4x4s and the 4.625 in the first gen Pathfinder with Z24i motor.

[78dattysun]

OK nice. What one do you recommend?

[datzenmike]

How much does the FJ20 make

[78dattysun]

JDM 250 PS (183.88 kW) @ 9,200rpm & 22.2kgm (217.71 Nm) @ 7,500 rpm

USDM 240 HP @ 8,300 rpm; 153 ft lb, 207 Nm @ 7,500 rpm

Redline: 8900 rpm

VTEC: 6100 rpm

 

That's off wiki but I was told it's the jdm motor. Bought the car with motor swap done.

[78dattysun]

Oh and not the fj20 it's those damn honda engine lol the f20c.

[78dattysun]

The fj20e is about 148hp,at 6000 rpm

The fj20et is about 187hp, at 6400 rpm

[datzenmike]

Err on the high side. R-180.

 

'80-'82 720 4x4s had a nice 4.375 front diff in them. The beauty of a 4x4 is it spends very little time in gear. I doubt a truck with 100K on it was driven a 1,000 miles in low range 4x4. The 4.625 is available but I think too much for the street.

[78dattysun]

Awesome that's gives me more hope in finding a diff. Thank you! Do you know if it would fit right up where the old one went and the stock 510 half shafts too?

[RTB]

Man I just sold my 4.625 LSD. 

[78dattysun]

Damn! Lol that's ok

[ggzilla]

You'll rarely be able to get it to 9000 rpm with the wimpy gears. But if you dont mind using less than the peak power, go with the 4.375.

[78dattysun]

Ya that would suck tho. So you think the 4.625 would be a better choice?

[Sealik]

"Do you know if it would fit right up where the old one went and the stock 510 half shafts too?"

 

Yes....just swap the R160 stubs into a 720 diff.

Also.....the dust shields are different, so use the 720 shields on the R160 stubs

 

 

The shields are taller on the 160 and spot welded into place.

Shields on the 720 are just pressed on and can easily be pried off with a flat screwdriver etc.

 

[78dattysun]

Nice! Thanks for the detailed pics. That will deff help. Now just have to find it lol.

[78dattysun]

So I found a 85 720 on c list with front diff but he doesn't know the gear ratio. I'm guessing it's a 4.11, but would the 4.11 just be too big?

[Stupid_fast]

AP1 has a 1.160 primary gear reduction in the gearbox. 

 

Rear end is a 4.10.

 

 

510 weighs ~900lb less.  3.90's should be good. 

[ggzilla]

3.90 is good for fuel economy. For performance I'd go with 4.625. It'll limit you top speed to maybe 90 mph so depends on what your goal is.

[510T]

So I found a 85 720 on c list with front diff but he doesn't know the gear ratio. I'm guessing it's a 4.11, but would the 4.11 just be too big?

 

That would be a great choice.

[Farmer Joe]

what comes stock in the S2000 the f20 came from? this is an important detail. if you can get it as close to factory, youll prolly be set. 

 

another question, is the 6 speed double or single overdrive? if its a double, you could run 4.37/4.62, have great acceleration, and with the double OD still run the freeway without overevving. 

 

if its just a single overdrive, id go for a 3.90/4.11 for all around performance. while it might not have a boatload of torque, youll have 5 gears before OD to catch up.

 

id shoot for an R180 also.. a 160 would prolly hold up, if youre nice to it, but whos nice to their stuff? lol

 

good luck. 

[datzenmike]

Damn.

Have to agree.
 

So I found a 85 720 on c list with front diff but he doesn't know the gear ratio. I'm guessing it's a 4.11, but would the 4.11 just be too big?

All 720 4x4s used the R-180 front differential. Generally the L20B and Z22 4x4 had 4.625 on the long beds and 4.375 on the others. The Z24 4x4 had 4.11s. But best to look art the engine tag under the pass side hood hinge on the inner fender. This will say what was installed.
 

 

This isn't a 4x4 but look in the bottom right corner.38 is a 3889. 41 would be 4.11. 43 would be 4.375 and so on

.
 

[KlassicMotion]

For what it's worth, the R160 should hold up.  That's what the Subaru WRX (and Legacy) uses, the WRX puts out 250hp from the factory.  The STI uses an R180, and puts out closer to 300hp, obviously it's assumed it will get thrashed around more.   R180 is heavier, but maybe it would give you assurance that something won't break.

 

If going with the R160 I suggest using Subaru if you can't find the 720 diff.  The Subaru diffs are much more abundant in junk and usually pretty cheap.  (A Subie R180 still maybe easier to find over a 720 front R180).  Common ratios for the Subaru are 4.11, 4.44 (I have a 4.44 VLSD I'm not going to need).  You can drop the whole diff in, but I believe you have to convert to the CV's. The other option would be to pull the ring and pinion out of of the Subie diff, and put it in the Datsun R160.  It's not a direct bolt, I don't remember all the details off hand, but I think I remember you have to drill and tap the R160 to accept the larger mounting bolts that the Subie ring gear uses.  After researching it, this is the method I decided I would use if I needed to change out my gears.  I would pull up those links for you, but my computer is down, and I don't have any links on my wife's laptop... Not a big deal though, use the Ratsun search bar and look for "subie diff", or "subaru diff" and a lot of links pull up.

[Stupid_fast]

3.90 is good for fuel economy. For performance I'd go with 4.625. It'll limit you top speed to maybe 90 mph so depends on what your goal is.

I disagree.  

 

S2000 already has gear reduction in the transmission, effective final drive is already shorter than the diff gearing. 

 

My dad has an AP1 w/ AP2 2.2 liter stock 4.10 rear end that already revs quick through the gears.  Honestly I think shorter gearing would hurt acceleration in such a light car.  your going from a 2750lb car to a ~2150lb car. 

 

Already spins 3800rpm at 70 with stock diff with the 0.810 6th gear. 

Plus 510's usually using shorter sidewall tires. 

 

Depends on what OP is going to use it for too.  On a hillclimb car or short track car it may be beneficial to have shorter gearing, but I really don't see any practical or street situation where you'd ever want shorter than stock.  It'd just rev too quick.