DIY Si
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| posted on 20/5/14 at 09:06 PM |
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MX-5 Mk1 LSD any good?
Following a recent Ebay bargain purchase, I now have a spare MX-5 gearbox, a prop to be cut down and a usable 4.1 (I think) diff. To my surprise the
diff has an LSD. I've not opened it up yet to see if it's the viscous version I expect, or the later Torsen type. This has left me with an
unexpected choice to make.
I hadn't expected the diff to have an LSD, and I know next to nothing about how it might fair in a 750Kgs car or if there's anything I can
do to alter how it works should I want or need to. I know many use the Sierra LSDs with no issues, even though they are meant for much bigger cars
than kits. I also have a 3.3 Sierra open diff sat waiting.
I will very soon have to make a choice as to which diff my car will use, MX-5 or Sierra. At present I have maybe a week or two until I get to the
point where I need to make a definite decision one way or the other. The MX-5 gives me better gearing, but the unknown LSD and I'll have to
figure out a sensible way to mount t. The Sierra is a known entity and much easier to mount, but will leave me with an un-uasble 170MPH theoretical
top speed and no LSD. Both diffs will need custom drive shafts and a prop, so that has no effect on the choice.
I have my thoughts on which way to go, but what would you go for, and why?
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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pewe
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| posted on 20/5/14 at 10:00 PM |
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There's an open diff in my F27 and a Torsen in the Eunos.
Based on driving both my inclination would be to use an open diff in yours (interestingly my F27 weighs in at 650kg as well).
The fluid MX5 diffs have been known to cause problems and wear out whilst the Torsen is long lasting.
However the Torsen does lock quite suddenly and I've had a few over-steery moments especially in the wet.
Now given the Eunos weighs something like 980kg and has exceptionally good weight distribution my expectation of having a Torsen in the F27 would be
that it could be quite leery. Personally I think the open diff makes the rear end handling predictable so would always opt for that.
T'other thing is there's quite a good market for Torsens amongst 5/Eunos owners, partic. those going down the turbo or supercharged route
- you could expect c.£350 for a Torsen on a good day.
HTH.
Cheers, Pewe10 
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DIY Si
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| posted on 20/5/14 at 10:10 PM |
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The cost of what I could maybe sell the (probably) viscous LSD would be all profit, and is something I had thought about. I only paid £21 for the box,
diff and prop! 
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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thefreak
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| posted on 21/5/14 at 01:37 PM |
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The older viscous diffs do have a habit of wearing out. So make sure it will lock up well.
There's a useful guide here: http://www.miata.net/garage/diffguide/ as to which diff is which.
My Exocet only weighs around 650kg and the Torsen diff fitted works really well, but it is a race car 
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