Joined
·
5,254 Posts
153bp is about 120whp on an mx5 and seems very low to be getting from an M45. An M45 set up should see you reach 180whp. I'd just keep the M45 with a suitable reduction pulley if I were you. Going NA is really hard, you generally sacrifice low end and mid range for peak power and really need to know what you are doing with matching parts together or you'll likely see very minimal gains. There's a build on here where being 2mm off on the manifold primary diameters cost 20hp. You'll also need a lot of dyno time and a tuner who is very knowledgeable. To put it into perspective the aforementioned build made over 200hp NA but spent over £3000 on dyno tuning alone IIRC.
The M45 will add low down torque and be much more fun and usable on the road rather than a 5k rpm only screamer. It'll also idle much better and be easier to live with. I say just turn the M45 up. M62s are very similar, they make a touch more power but do so more efficiently which is the real benefit. Same for the rotrex, they are a lot of money and are more for those who want turbo levels of power but for what ever reason dont want a turbo. As you already have an M45 there's little reason to upgrade to either IMO, no when you've not got all you can out of it yet.
BTW, the coldside M62 kits use an MP62 which has an internal bypass, are a lot of money, and very hard to find in the UK. Before you consider one you're best off looking at the fitment and intake routing issues as they are very tight and not something I'd be happy to live with.
The M45 will add low down torque and be much more fun and usable on the road rather than a 5k rpm only screamer. It'll also idle much better and be easier to live with. I say just turn the M45 up. M62s are very similar, they make a touch more power but do so more efficiently which is the real benefit. Same for the rotrex, they are a lot of money and are more for those who want turbo levels of power but for what ever reason dont want a turbo. As you already have an M45 there's little reason to upgrade to either IMO, no when you've not got all you can out of it yet.
BTW, the coldside M62 kits use an MP62 which has an internal bypass, are a lot of money, and very hard to find in the UK. Before you consider one you're best off looking at the fitment and intake routing issues as they are very tight and not something I'd be happy to live with.