I have an '03 JCW, swapped in a stage 2 sprintex twinscrew kit (i believe it has a 17% pulley, but I cannot recall if it's that or a 15% - emailed the vendor to see if he remembers, otherwise just gonna measure it since I will eventually need a new serpentine belt) in 2018. The car has a lot of suspension mods, but engine wise only has a factory JCW build/exhaust with resonator delete, CAI, and MSD ignition.

I blew a plug out of the #3 cylinder at 160k miles, dealership had to do the work since the car was too far from home to be towed by my insurance, leakdown test was solid so the machinist just put a thread insert in the head, along with a fresh head gasket and various other odds and ends, so only the bottom end hasn't been rebuilt on the car, everything else has been freshened within the last 20k miles. Oil consumption is minimal, about 1/2qt per 5k miles, blackstone reports are clean.

I didn't notice much difference in power going from the stock JCW with a 15% pulley on it. It feels peppy but not very fast. My old nissan 240sx with a bone stock (including the side mount intercooler) SR20DET making about 205BHP felt quicker.

I'm wondering if I want to really get the most out of what it currently has, if I should have it dyno tuned? The Sprintex kit is supposedly a bolt on, no modification/tune (other than a single wire for wiring the electric water pump) required setup. And am I potentially being held back by the injectors and possibly stock cam profile? With the fresh top end and a new head gasket, would I be safe to push the % underdrive even further?

If I get a new cam and stiffer valve springs, would it be worthwhile to raise the RPM redline (if the ECU is even able to do so without a standalone replacement) or should I keep that one on the backburner due to the stock bottom end?

 

It seems like with an entirely different supercharger, the ecu should need to be tuned.

If you can find someone that can tune the factory ecu, and preferably someone that has done a similar car before, I think you would see gains everywhere in the rpm band.

Without being able datalog the ecu and see how close you are to maxing out the stock injectors, it’s kinda hard to say if injectors would be necessary. A tuner experienced with coopers would probably be able to tell you before even putting it on the dyno.

Where are you located? One of the people I know of that may be able to help you is in FL.

 

Thanks for the input. Per sprintex's website, the stage 2 twinscrew is a "no tune required" upgrade, but it claims to put a regular cooper S to over 200WHP. With my ported head, MSD ignition, CAI and more freeflowing exhaust, I can't imagine I would be making less than 210 to the wheels with the kit set up properly.

I'm in the Seattle area, unfortunately. AFAIK there are no good mini specific tuners around here, but there are some good dyno shops I'd be willing to try.

 

You could try contacting GIAC. I know they've had ecu upgrades for the mini in the past. If you can somehow datalog your dyno runs with air/fuel ratio, then a tuner like GIAC should be able to tune a map specifically for your car.