ISF differential - essential or not?

[Fanciee]

Hi all, apologies as I'm sure this has been discussed before but I couldnt find the answer I was after by searching the forum. If you can point me to a thread then please do!

I am in the market to buy an ISF after my RX7 gets a good enough offer on it. I have been examining the available choice and there is quite a stark difference in price between a facelift and the non-facelift variants, usually about 5k for similar miles. There are obviously more changes between pre and post facelift than just the diff, but most of them can be easily rectified with a mod or two (headlights, Bluetooth etc).

Is the torsen differential an essential purchase for those who give it a hoon every now and again? How effective is the e-diff in the pre-facelift model, is it very noticable in lower gears and launches, or does it behave roughly the same? I have no intent on taking it to the track, but those moments you give it some beans at a light I wouldnt want to be shown up by something purely because I couldnt put the power down with no proper diff. So how good is the e-diff? Or should I just bite the bullet and find a post-facelift. Another option would be swapping in a torsen diff further down the line, but I understand this can cost a lot on the second-hand market, if I can find one at all.

Thanks

[4969_LXS]

Hi @Fanciee, I have an 08 with the e-diff. It's not as good as modern solutions but is close, a friend's M140i e-diff reacted quicker and more effectively than the one in the ISF but a lot has changed in computing from 2008 to modern day.

Personally for general road use and the odd bit of fun, I haven't been lusting after the LSD. Only time it's caught me out is in manual mode mid corner upshifts on full throttle in the wet, but that'll unsettle any car, and one time trying to pull away from a junction at a really weird inclined angle.

When I've launched it off the line I've never had 1 wheel peel. I'll be going to 275 rear tyres when they need changing, they do fit the standard rims for that extra grip.

[RichGS11]

You'll need the opinion of someone who has had both ideally. I have a 2010 with a proper LSD and it is certainly fun, but even in the States guys upgrade them to uprated diffs. I haven't driven an 08 to feel the difference. I can't see there being much in the two, but interested to hear someone chime in with experience of the two.

[Fanciee]

13 hours ago, 4969_LXS said:

Personally for general road use and the odd bit of fun, I haven't been lusting after the LSD. Only time it's caught me out is in manual mode mid corner upshifts on full throttle in the wet, but that'll unsettle any car, and one time trying to pull away from a junction at a really weird inclined angle.

When I've launched it off the line I've never had 1 wheel peel. I'll be going to 275 rear tyres when they need changing, they do fit the standard rims for that extra grip.

Ok so it seems like it works well enough to be livable then, if I can still do a proper launch without leaving one black line 🙂

 

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You'll need the opinion of someone who has had both ideally. I have a 2010 with a proper LSD and it is certainly fun, but even in the States guys upgrade them to uprated diffs

Yeah I was hoping someone would be able to tell me the exact difference. And people will always upgrade them, there is always a better option 🙂 Do the aftermarket diffs fit in the open diff casing? Is there any difference at all in the differential housing that would prevent an open diff being internally upgraded?

[RichGS11]

1 hour ago, Fanciee said:

Ok so it seems like it works well enough to be livable then, if I can still do a proper launch without leaving one black line 🙂

 

Yeah I was hoping someone would be able to tell me the exact difference. And people will always upgrade them, there is always a better option 🙂 Do the aftermarket diffs fit in the open diff casing? Is there any difference at all in the differential housing that would prevent an open diff being internally upgraded?

No differencein housing, there are companies that make direct replacements. Obviously as it's a rare machine, they come at a cost, around $1800 but prices fluctuate and there are options. The diff certainly has saved me on a couple of occasions and helps put the power down more. I read somewhere about track times being quicker because of it, I'll have to try and dig it out.

The one thing that I think to remember is that diff or E-diff, there's no night and day difference and I haven't seen any posts that say otherwise. I'm into modifying cars and I'm constantly making my ISF lighter and quicker, and as a result, I read a lot of what happens Stateside and get ideas from there. An uprated diff is on the cards for me, but I'm upgrading my pulleys to lighter options first and replacing the front seats for a lighter option. I will eventually be tracking the car, hence the direction I've gone.

 

[C.B]

I have a eLSD and find it gets off the line really well, it helps the torque curve is well suited to launching, you wont have any complaints in that department.

[Fanciee]

Thanks for the info lads. I think I'll be more than happy saving a bit of cash and going with the pre-facelift from the sounds of it.

[Supacool1]

Useful thread. Thanks for posting and the replies. 😀