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Yeah I had all the original receipts with that car and it cost a lot. The guy didn’t do things by halves, which is why I bought it!
The M45 is the go to kit, it’s cheap (relative) and there’s lots of options available.
Other options are there but it kind of depends on what you want from the car and how much you want to spend.
A rotrex will be more compact, and better performance by far, being a modern centrifugal supercharger, but it’s expensive.
The other option is an M62, I know of only one person who’s fitted this supercharger that was active on MX5Nutz, it’s a pain to install because it’s a bigger supercharger, but the result is more volume so more power.
The problem with the M45 is the same as all roots superchargers, you can spin them faster but they make a tonne more heat and you eventually over spin them so if you want to make lots of power then there’s no replacement for displacement and that counts even for forced induction!
Saying that, if you want a decent bump in power, and aren’t keen to constantly be upping it, then an M45 supercharger install is perfect. There’s a reason it’s so common, because it just works.
I would say that don’t do the 2 stages separately, mine was never on a standalone ECU and while there was nothing really “wrong” with it, and it ran pretty well, I’ve been in M45 supercharged MX5s on proper standalone ECUs and the difference was a lot more than I thought it would be. Mine drove like a standard car but sometimes it would stutter, it wasn’t a perfect map, and basically it drove like a tuner car rather than OEM. Whereas the M45s on Megasquirt 2 or 3 I’ve been in with a proper map by a pro tuner, drove like OEM cars. I’ve not been in an ME221 car but it’s my understanding it’s even better.
I’d say from speaking with other people who went from piggybacks or Bipes & RRFPR to Megasquirt, they picked up 10-15bhp after a proper mapping session with a tuner, so my 180-185 could have been more like 200 on a decent ECU.
An M45 kit with an ME221, maybe a slightly smaller pulley, RX8 injectors, and an inter cooler is all you need for reliable smiles per miles.
Your other option is turbo, which is “easier” to upgrade, start with lower boost, raise it as you feel you need it, until eventually you go for a bigger turbo but then you end up needing forged rods, and suddenly you’re spending the best part of 5k.
A turbo MX5 is a properly fast car on a track, and a supercharged MX5 is still very quick, the difference is how you like your acceleration delivered. My supercharged car always felt like an NA car but the big numbers just arrived there quicker. I remember the day I picked it up I thought, doesn’t really feel that quick, then looked at the speedo and I was triple digits and still piling on the speed.
The turbo car can be faster but it will always feel faster because you get that shove into the back of the seat when the boost kicks in. Because of that you have to drive it like a fast car, you have to be wary of that boost, but supercharged can be a little more forgiving. On the flip side again, a good tuner such as Skuzzle can map boost by gear with the ME221 ECU and ensure that you don’t have those hairy moment so often.
A lot of this is probably easier discussed over a drink so give me a shout if you want to talk about it further.
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NurseHolliday
Had me worried there, glad you've still got yours. Thanks for all the info, the JR kit must have been pretty expensive back then. From what I've read the Eaton M45 seems the go-to supercharger, but I would like to know if there's a better choice nowadays as some info online is over 10 years old now. Probably got this horrifically wrong but do like the idea of
Stage 1: Eaton M45, Salon kit, crossover pipe
Stage 2: Me221 ECU, RX8 injectors, front mounted intercooler, sensors and dyno tune
After all that with yours good to know it didn't put you off the cars, and famous last words I know but 180bhp, plus the torque would make me very happy. Do want to visit a dyno soon to see what the baseline power (or lack of it) is, but can't help thinking that £80 could go towards something shiny or the blower eventually.