I’ve just bought a nearly-new MX5 mainly for longer touring abroad and fun at home, and while the car does exactly what it says on the can, I would like just a little more grunt without compromising the basic car. So far, I’ve changed the exhaust to the bigger Mazda Sports unit, fitted a Pipercross panel air filter and had the ECU “optimised”. I wonder if changing the exhaust manifold for a 4:2:1 without-cat would take me any further, so has anyone experience of this change?
There’s some good gains to be had from changing the manifold.
BBR do one as do a couple of others like Racing beat.
BBR do a few packages now depending on what you would like to acheive.
Not sure what “optimised” means , but you would also benefit from a remap after the manifold change.
Most of the manifold gains come from a 4-1 de cat . The BBR design may eek out a little more than the Racing Beat. My only advice is to plan carefully as to add bits at a time may increase the overall cost plus run the risk of incompatibilities. A 4-1 manifold decat plus remap will give you around 20bhp and the recently released cams from BBR a further 20bhp on top of that.
The downside of a de cat manifold is an increase in noise, not an issue with the OE back box but there are freer flowing exhausts available some of which will be loud with the de cat manifold.
Ultimately it depends how far you want to go. In terms of £ per bhp FI is competitive but you get the added bonus of much higher torque gains than NA modification.
Not to mention a big grin every time you put your foot down 
The turbo’d cars are very civilized and drive quite normally if you press the throttle lightly.
Thanks all, but just what is F1?
Forced induction, either supercharger or turbocharger.
eddie
Aah! Eff-Eye not F-one
Mea Culpa
and not really the solution I want
Without going all-the-way to Turbo, what best can be done to a conventional engine?
Engines make power by getting the fuel in and out as quickly as they can and being efficient with it.
Your engine capacity is fixed, the only way you are going to get more is better breathing, there are ways, but not cheap. Unless you are going to start down a throttle body route and super duper exhaust then you have what you have. You can also increase the rev limit, you need to mess with the chip on the ECU and ideally you would want hotter cams to take advantage. There is of course forced induction which is relatively cheap these days and not the black art it used to be.
There is no “cheap” mod to get 15% more power. A decent air filter change and use of the full rev range is one of the best ways to get more performance.
Thank you; that sounds entirely sensible and I look forward to exploring the full rev range. After a lazy 3.5 V8 Morgan I need to learna new style of driving and so far, I’m enjoying every minute