mx5cartalk.com

I am thinking about a NB MX5 for a rotary engine conversion.


I notice mention of a chassis strength increase from NB series 1 to NB series 2...
http://en.wikipedia.org/wiki/Mazda_MX-5

The body was strengthened, gaining 16% in bending rigidity and 22% in torsional rigidity. With the minimum of options, the 2001 model weighed 1,065 kg (2,350 lb).

Is this increase in chassis strength between the models achieved by bolt on braces, which could be applied easily to a NB series 1, or are there structural changes in the chassis panels, or structurally elsewhere, to achieve the increased chassis strength?


Other changes probably not so useful, or needed, for a rotor conversion...
- 6 speed box probably not up to the power/abuse
- brakes may need upgrading, even from larger series 2 brakes, to aftermarket MX5, or maybe FD RX7 brakes/hubs for better brakes and more choice of wheels
- projector headlights, better brake lights, can be fitted from series 2 to series 1
- seats will be replaced
- suspension will be upgraded, possibly Ohlins, need to research best options


Any other pros/cons for/against feature/spec changes between Aussie series 1/2 models to suit a rotary engine conversion?

One might be the larger wheels on the series 2 being a better starting point for larger brakes, and for larger aftermarket wheels to fit within rego dept maximum wheel size increase rules.

Though the simpler non-ABS brake system on the series 1 might be better suited to brake rotor/caliper upgrades/changes?


Thanks.

You cannot legally do a 13B -turbo- conversion within current rules.

With that in mind an upgrade to brakes is not likely required, and certaintly an NB2 brake setup would suffice, no worries.

The stiffening can be bolted on. Suggested would be an NB1 with flying miata butterfly brace and roll bar.

You wont make more power than the 6 speed can handle on an n/a 13B street engine.

Hub swap will make engineering difficult and the fastest MX5s in the world run stock hubs and 15'' wheels.

Dann

Thanks for the reply.

13B turbo does fit within stock car weight/replacement engine/rotary equivalence/etc. rego rules, at least here in the ACT, and I think also in NSW.

I called a local engineer a while ago to ask him about a 20B non-turbo into an MX5, he initially laughed and said no chance, and that you couldn't even put a 13B into one, but after I hassled him to actually check the rules against the MX5 weight specs, he agreed that a 20B non-turbo or 13B turbo are both within the rego rules, in terms of engine capacity at least.

Will be a high power 13B single turbo, with some sort of custom high mount manifold to fit the turbo in, as there doesn't seem to be enough room for the 13B-REW twin turbo setup in the MX5 engine bay, at least based on looking at a 13B turbo NA MX5 track car at Wakefield Park a couple of weeks ago...




Thought about 20B non-turbo, but the increased cost and hassle over a single turbo 13B, along with not making nearly as much power as a 13B turbo could, is making me lean towards a 13B turbo MX5 instead.

A 20B non-turbo MX5 would be sweet though, and unique. 20B normally aspirated response in an MX5 would be fun, I reckon.

The hub swap/engineering issue would probably mean aftermarket MX5 brakes would be the easiest choice. Though I would like to put Spirit R RX7 cross drilled rotors and red calipers on it, but engineering would be a hassle, or most probably not possible, with machined stubs to fit the RX7 hubs/brakes.

If the stiffening, as you say, can easily be achieved with chassis/strut/etc. braces, then the series 1 NB is a much more interesting possibility for base car than it would have been. Maybe having no ABS, would make it better for brake upgrades (beyond the performance of the series 2 brakes), and along with manual steering rack (I think?), make it a better/rawer drivers/performance track oriented street car than a series 2 NB, after the rotor conversion?

I was really leaning towards the series 2 as a more refined and better base for this build, but I suppose as most of the improved bits over series 1 would be replaced, and if the chassis strengthening in the series 2 is just braces, then I am not really sure which way to go now.

Larger wheels is just for looks, a personal choice really, not based on performance at all. Would like either 17s or 18s I think, but need to have a good look for some nice looking track oriented MX5s, to see what I like in MX5 body kits and styling.

NitroDann wrote:The stiffening can be bolted on. Suggested would be an NB1 with flying miata butterfly brace and roll bar.

That is handy, am looking at the V8 Roadsters bare front subrame that they use for LSx V8 conversions, just without the V8 engine mounts, as a starting point for the rotor conversion, so can order them at the same time...
http://www.flyinmiata.com/index.php?dep ... %201990-97

This is one of the V8 subframes...


And a V8 setup installed, maybe some of the other chassis stiffening braces would be useful for my build as well?...