Which Diff For L28 Skyline?

[coupe72001]

I am going to pick my car up from the tuners this weekend. He says mechanically it came up a treat, but he doesn't like my 4.9:1 ratio R180 LSD at all, on the grounds that the car wants to spend all its time up at a really high rev range, and so it isn't making the most out of it's torque. I don't like the idea of losing acceleration, but he says the diff isn't making the most of the engine's potential anyway.

He's pushing me to convert a 3.9:1 diff to LSD, arguing that his Datsun 1600 ran out of legs on the Phillip Island straight using a 4.4 ratio. His diff builder does the conversion surprisingly cheaply.

The car is a Skyline C210 sedan, with L28, triples, (making maybe 150hp?) marginally lighter than the 1210kg standard. It has a SR20det 5 speed, with the following ratios (I think):

1st: 3.321

2nd: 1.902

3rd: 1.308

4th: 1.000

5th: 0.759

I would like it to remain a quick streeter, that can do the occasional track day with the NDSOC club without being totally put to shame.

Any ideas? 3.9, 4.1, 4.4, leave it alone...

[BensDR30]

4.9???

That sounds like a NISMO ratio or the front diff from a 720 4x4 (or were they 5.1's??)

L28 with triples - go for a 3.9 or maybe a 4.1 (3.7 would probably be a bit too tall - 3.54 was too tall for my old L28ET MR30, but man it had some legs!)

I'd expect that a 3.9 would be the standard ratio for the C210 anyway (it was on the MR30)

[coupe72001]

Pretty sure its a 720 truck diff with a WRX LSD centre.

So that's 2 votes for 3.9 (or 4.1)...

[blind_elk]

4.9 is more like the sort of ratio for a rally car - rapid acceleration out of corners, keep the engine up near peak torque.

I reckon something like the 4.1 ('74-on 180B SSS had this ratio) would be a good compromise between acceleration and top speed.

[passin ewe]

Yeah, go for the 3.9. You've got the same set up as me, and my 3.9 is spot on I reckon. I agree with blind elk, that being a rally diff. You'd have no problem selling it on Bridibella ( rall site). I dynoed my l28 the other day, made 142@ the wheels. The tune was average apparantley,running way to rich. I have 72 grind coming from POWER PLAY which should be in in a week, current grind 68. Then I'm getting it tuned on a dyno, rather than by ear.

[BensDR30]

4.9 is more like the sort of ratio for a rally car - rapid acceleration out of corners, keep the engine up near peak torque.

I reckon something like the 4.1 ('74-on 180B SSS had this ratio) would be a good compromise between acceleration and top speed.

Except the 180B used an R160...

[Ghostrider]

Well for what it's worth, I'm using a 4.11 in the DR30 with same gear ratios for the likes of Wakefield & Winton, but Eastern Creek I'm going to 3.7 and for the PNV with it's L28et and bags of torque I'm going to use a 3.9 R200 LSD with gear ratios of 1. 3.592, 2. 2.246, 3. 1.415, 4. 1.000, 5. 0.813:1

My theory is on cruise in 5th I will get better driveability with the 3.9/0.813 instead of 4.11/0.833

Cheers, D

[coupe72001]

Really, really useful. Cheers guys.

Anyone else got a fav R180?

[OUTATIME]

say if ya wanted to change the ratios in a r180 from 3.9 to say around 4.11. is there a easy swap from another diff or what else used the r180 in those ratios? just swappin the crown and pinion gear. easy to do it on the r31s bw78's. pinni was 4.11 and skylines were 3.7 and 3.9. then vls were 3.45 i think... wondering if something similar with the r30s etc

cheers..

[passin ewe]

Hey Drew ,I wanna no how you got a SR20DET box behind the L series. Did you buy a special housing and did you have to alter the tail shaft. What other changes were made ?

[coupe72001]

The SR20 box came with a smashed rally car that I bought complete a couple of years back. I swapped the box, diff, L26 and twin carbs, suspension, wheels and tyres into my fairly stock sedan, and all for the bargain price of $4000... most of which has long since been broken or upgraded anyway.

From memory, the box was a standard C210 five speed, split, with the guts of a second hand SR20 box crammed inside. Apparently the Sr20 internals fitted in "like lego."

'Cause the bell housing is still L-series, the tailshaft and cross-member remain stock C210 items. From memory my gear lever is Datsun, but a slightly different shape to the C210 stick (it's 260Z or something random - a slight L shape rather than straight). Even the gear knob is stock C210.

Ill provide more details ASAP, my receipt file is with the car at the tuners.

[works 510]

My vote is 4.1

SR20 box swap involves pulling the sr20 or ca18 bellhousing off the box, getting a L series bellhousing.

1 selector shaft hole in the L series bell needs to be drilled out larger.

You need to pull one of the bearings off the sr20/ca18 box and replace it with the one from a L series box as the L series bearing is slightly smaller in diameter (replace bearing while your there)

Minor metal needs to be taken out off the L series bell due to one of the gears JUST touching it.

For more info, theres a tutorial on ozdat.

I did the swap before the tutorial was made, easy as

[coupe72001]

I am going to experiment with a couple of diffs this weekend. If it feels good, Ill send it off to get the LSD conversion.

However, I cant find a page which mentions which ratio came standard with which car!

Skyline C210 3.9:1?

Datsun 240k 4.1:1?

Mr30 ???

Has anyone committed this stuff to memory?

Also found the receipt for the gearbox conversion. $1300 from Mammi Motors in Vic, including brass button clutch, flywheel machining, swapping the internals over. The Sr20 box was supplied by the previous owner.

[BensDR30]

MR30 - 3.9:1

[works 510]

IRS S12 is also 4.1 r180, but CV's.

[BensDR30]

So is the R30.

But you won't find many IRS S12's around in Aus.

Your best bet for non-CV is 240/260Z automatic - 3.9:1

I wonder if you can fit R30 axles to C210 arms? I would be very surprised if there was no compatibility there. Changing the arms would probably be easiest, if feasible.

[passin ewe]

I use this at times. Look under "D" for Datsun. They've got Skyline and 240k listed.

http://www.difflap.com.au/ratios/n-r.htm

[coupe72001]

Again, great info, cheers. Anyone know what ratio the 280zx is? i've got a better chance of getting my hands on a 280zx diff than 240-260z.

[passin ewe]

At a guess 3.7. If you want a R180 3.9 ( non LSD) I've got a spare you can have for the cost of frieght.In good nik

[coupe72001]

Cheers Ricky, that's a really nice offer. I'll see if I can't first find something a bit closer though - we both know that Vic-WA freight stings a bit! On the topic I've got some seat covers for you... If you're interested PM me your details again and we can ship them over.