Nismo GT Pro LSD configurations

[tidi0x]

My package came in early. I noticed that in the instructions (this is labeled a 2024 model) they no longer indicate that the diff can be "Adjusted" as I have seen in older post, however they now list specific part numbers for each version of the diff. Interestingly they also show a 1.7 way LSD which I never saw in the parts catalog, but it's a variant of the 1.5 way (of which I think this is just a pinion flip). 

 I am not going to upload all the pages of the manual as some are just disassembly and install by professional warnings. 

The first page is all the different part numbers associated with the kit. Note for the GT-Pro there is 3 LSD PN's 20 17 and 15. (see bottom for appendix of images)

 

The first photo is how it came assembled in the kit as 2 way. notice how the side flange ramps are actually different angles and the pinion ramp matches those angles. 

Now I have flipped the pinion, so the side ramps are still in 2 way, but the pinion ramps are miss matched giving the decal ramp a gap and a more aggressive position. I believe this is a 1.5 way configuration, but I am not sure which version the standard 1.5 or the 1.7 (45* ramp)

this is the default 1 way... you can see the solid back of the pinion engages the side flanges. the diffs spring loaded sides should mean this completely prevents any spreading to engage the decel gate.

My original suggested 1.5 way. this is with the pinion flipped from the original way, you can see the 1 way side ramp is resting on the pinion ramp. meaning on decel the differential will twist and lock up the side flanges.

 

 

Appendix images

[GTSBoy]

6 hours ago, tidi0x said:

My original suggested 1.5 way. this is with the pinion flipped from the original way, you can see the 1 way side ramp is resting on the pinion ramp. meaning on decel the differential will twist and lock up the side flanges.

 

This is the one that I don't think you could actually assemble. Look how far apart the side flanges are compared to the other configurations.

[Kinkstaah]

I'm assuming you ordered the 38420-RSS20-B5?

[Murray_Calavera]

I've got the same diff as you in the 2 way configuration.

9 hours ago, tidi0x said:

Now I have flipped the pinion, so the side ramps are still in 2 way, but the pinion ramps are miss matched giving the decal ramp a gap and a more aggressive position.

I didn't know this was a thing, thanks heaps for posting this up. 

[tidi0x]

3 hours ago, GTSBoy said:

This is the one that I don't think you could actually assemble. Look how far apart the side flanges are compared to the other configurations.

Valid point, I did not consider that. 

1 hour ago, Kinkstaah said:

I'm assuming you ordered the 38420-RSS20-B5?

Yes, this was the only one available in the states. Everything else I would have to import. 

27 minutes ago, Murray_Calavera said:

I've got the same diff as you in the 2 way configuration.

I didn't know this was a thing, thanks heaps for posting this up. 

I am not saying this is a correct config. thinking about my ramblings with this diff, those sharp edges or off angle ramps are probably bad for the health of the diff and should not be considered, so I would only run this diff in the intended 1.5 way or 2 way 

 

I have reviewed the catalog more, and realized it was always in front of my face... they consider a 1* ramp angle a 1.5 way... so what everyone considers visually a 1 way is their 1.5 way. Which is wild to me to think that a 1* ramp makes it a 1.5 way. However this is backed up by a few older instruction pictures, and the motoIQ stuff. 

page 113 https://www.nismo.co.jp/products/web_catalogue/pdf/catalogue_2023.pdf, 

or 

the product page https://www.nismo.co.jp/products/web_catalogue/special/gt_lsd/

 

I think I am going to stick with the diff in the 2way position; its probably not going to feel much different than my GT already does, but its fresher, plated better, and I can adjust the preload, 🤷‍♂️.  

 

 

[Dose Pipe Sutututu]

Best photos available on the internet, thank you and well done.

[Kinkstaah]

Wait, so the ACCELERATION ramp is 55 degree on both configs, and decel is 45 degree on the 2 way? (or the 1.5 because it's not the same blablablabla).

That would match my experience, insofar that the decel lockup is harder than the accel lockup. It was absolutely stupid to use on road configs, but I found out later my subframe was solide-r than most.

It is however great to know for sure what many had been suspecting, and ultimately the 1.5 and 2 way in GT Pro form are really the same part, it's just what state it's configured in when it comes to the customer.

[tidi0x]

11 minutes ago, Kinkstaah said:

Wait, so the ACCELERATION ramp is 55 degree on both configs, and decel is 45 degree on the 2 way? (or the 1.5 because it's not the same blablablabla).

That would match my experience, insofar that the decel lockup is harder than the accel lockup. It was absolutely stupid to use on road configs, but I found out later my subframe was solide-r than most.

It is however great to know for sure what many had been suspecting, and ultimately the 1.5 and 2 way in GT Pro form are really the same part, it's just what state it's configured in when it comes to the customer.

yes, the 2 way is 55* on accel, 45* on decel. where as the 1.5 way is 55* on accel, 1* on decel.

where as ATS lsd looks like it uses something more like 5-20* ramp for their 1.5 way 

[Kinkstaah]

The terms i've always heard have been 45deg (most 'force/lock') to 90 degree (no, force/lock)

So 45 degree is more locky than 55 degree. Which seems odd from the perspective of lock on decel versus accel. I suppose it IS a race part, so inciting rotation on corner entry is actually what it was, you know, designed for.

[GTSBoy]

Nah Nah Nah.

The drive side is on the right. You can tell, because the 1-way opening has its 1° angle, decel side on the left, and so the 2-way opening must be overrun on the left too. The overrun ramp on the 2-way opening is steeper (ie, closer to the ineffective 1-way's 1° ramp) than it is to the drive side's angle to the right. The drive ramp is 55° FROM THE VERTICAL. The decel side is 45° from the vertical.

What that amounts to is, the more laid down towards the horizontal the opening's ramp is, the more spreading effect that cam has on it as the cam rotates.

Compare that to the ATS graphic posted above, where you can clearly see the difference between the angles on a real 1-way, a real 1.5-way, and a real 2-way (where the ATS 2-way actually appears to have the same angle on both accel and overrun ramps).

[Kinkstaah]

I would think the left side of this is 45 degree and the right side of this is 55 degree. There'd be more pressure with this going left than going right....?

[MBS206]

2 minutes ago, Kinkstaah said:

I would think the left side of this is 45 degree and the right side of this is 55 degree. There'd be more pressure with this going left than going right....?

It's about how easily it can move it too. It needs more force to go left being at a steeper angle. So since it needs more force, it's going to mean it takes a lot more effort (slip) to get it to push out. As to the right is easier to spread, it's going to be easier for it to lock up.

[GTSBoy]

1 minute ago, Kinkstaah said:

I would think the left side of this is 45 degree and the right side of this is 55 degree.

Yes.

1 minute ago, Kinkstaah said:

There'd be more pressure with this going left than going right....?

Do  thought experiment. Make the left ramp, the 45° ramp, one degree steeper. It will then be 44° from the vertical. What happens to the forces? Too hard to tell? Well, add one more degree, and then keep doing that until it looks exactly like the near vertical wall of the 1-way opening. I would suggest that every degree less than 45° (from vertical) reduces the reaction force, if continually removing them from 45 gets you back to the 1-way profile.

[Kinkstaah]

I agree, thus 45 degree is the *max* force one could apply to it. This is similar to what I've seen in uh... simulations... which allow you to play with diff ramp angles.

Anything higher (or lower) than 45 degree would produce less force as 45 is the max... triangley. 

I would state the 1 way is 90 degree, at least this is how my brain and other ways of explaining it refer to it. 90 degree also effectively acted completely open. I realise Nismo refer to it not as 90 (or 89) but "1". So I'm not understanding the angle on which these angles are based.

[MBS206]

15 minutes ago, Kinkstaah said:

I agree, thus 45 degree is the *max* force one could apply to it. This is similar to what I've seen in uh... simulations... which allow you to play with diff ramp angles.

Anything higher (or lower) than 45 degree would produce less force as 45 is the max... triangley. 

I would state the 1 way is 90 degree, at least this is how my brain and other ways of explaining it refer to it. 90 degree also effectively acted completely open. I realise Nismo refer to it not as 90 (or 89) but "1". So I'm not understanding the angle on which these angles are based.

It's the angle of the ramp from the vertical.

You're measuring from the horizontal.

To convert, take 90* minus your angle reference = Nismo Angle.

[MBS206]

Also, it is just about triangularity. The less angle, the easier it physically is to do.

Think of the amount of slip you're getting, as how hard you need to push an object.

More slip, equals pushing way harder.

Then the ramp is how steep the hill is. The Accel is less slip, which means it takes less pushing (less slip) to get it to be able to push apart.

However, the steeper sides on the decell means it will take a lot more pushing (slip) to get it up the ramp.