I'm in the early stages of the build and have all the major components from a miata (115bhp) ready to install. However, I'm starting to think I'd like more power and less weight so considering a few other engine options. I was thinking maybe bec but want something easy to live with with so maybe a 200bhp duratec mated to a mk3 mx5 box mat be the best option. So my question is will the miata diff be up to the task? I've designed my own rear end to house the diff but not so far gone that I couldn't change it if needed. It would be nice to save a few bob and use the bits I have where possible also.

Thanks, Paul

PS. If I opt to change I'll have complete Miata running gear (engine/box/prop/diff/etc) available. If I remember rightly it had done under 70k so should be sweet.

Diffs are quite strong, there are a lot of turbo'd and supercharged 5s about running 200hp with no problems, 250 -270 seems ok and some nutters are over 300 on standard diffs, I don't know if they have any problems though

Thank you!

Given the choice at this early stage use the larger and stronger diff from the late model 1.6 and 1.8's which had a 7" diameter crownwheel as opposed to the smaller 6.5" diff used in the crica 1989-94 1.6 mk1. The larger diff can be identifed by the rubber doughnut on the prop flange and will typically have push in rather than bolt on shafts (although there are a few with bolt on shafts).

Personal prefference if looking for an LSD would be ideally look for a type2 torsen or the type 1. At that power it's best to steer clear of the fuji diff. The VSLD was only used with the 6.5" CW so assuming you go for the larger diff you'll safely avoid buying one of these

Even if you lunch the diff, which is extremely unlikely, they're so cheap/plentiful I wouldn't worry.
Cheers, Pewe10

Most people seem to quote 300bhp (and the resulting amount of torque) to be the maximum to put through a 1800 diff. This is higher than what the conrods are said to take before bending, which is 250bhp. I've read the driveshafts can take about 400bhp.

The rubber flange (or lack of it) does not define if it's a 1800 diff or not. My open 1800 diff doesn't have one, but my type 1 Torsen does.

The driveshafts are interchangable between push-in and bolt-on (obviously you need the diff input stubs for the bolt on shafts as well!).

There are plenty of stories of early 1600 diffs failing on stock engines and I've seen it happen myself (although that was a welded 1600 diff on a standard engined autotest car).

I've never heard of a 1800 diff failing unless it was abused e.g. low oil levels.

[Edited on 26/4/14 by PorkChop]