Improving a Stage 1 supercharger setup

I have what is usually refered to as a stage 1 tune on my 1.8 NA. It’s based on BRP62 supercharger installed by P5. Phil also fitted a programmable ECU and lowered suspension. Other than that it’s standard. Is there anything I can do easily to improve throttle response torque? at lower revs e.g. when doing 30-50 in third? Above 4000 it’s great. Phil said the next level required intercooling, different pulley and much more particularly brake system. Will bigger throttle body, exhaust improve things?

What he says probably makes sense.intercooler or smaller pulley (increasing air density) or charge pressure at lower revs will make more than throttle body on a boosted setup

Phil at P5 is correct, as indeed he should be. Put your brakes at the top of the list.
Intercooler = an increase in (colder) forced oxygen burn. Good.
“Faster” pulley at the charger = higher volume of compressed atmos into the combustion chambers. Good.
All that is only applicable if your “old” piston rings & bearings are still up to the job.
Just because the mill seems to be OK just now, no G’tee additional compression stresses won’t tip it over…and our mills have a name for failing oil rings. I should know…with a standard mill.

But…get the brakes upgraded before anything else would be my advice.
No idea how competent your other chassis components are but I expect you realise that competent brakes are part of an Mx5’s performance even in standard engine specs…never mind ending up with more BHP & Torque than my 3ltr Monzas had.
Logically, little point in spending wads on additional grunt if you cannot safely & repeatedly reign it in.

Thanks. If anything my setup was cautious to avoid pre ignitiion.

Excellent advice. Thank you.

An intercooler alone won’t increase power as much as it does for a turbo. It’ll cool the compressed air and so reduce the boost pressure, which will in turn reduce the parasitic drag of the blower as it isn’t shoving air against such high pressure, but it will still pump almost the same mass flowrate of air (unlike a turbo which would respond by speeding up and flowing more air).

What it does do is reduce the risk of preignition so you can increase power with more of a safety margin. To do that you need to change the pulley ratio to spin it faster - either a bigger crank pulley or a smaller blower nose pulley.

The MP62 runs cooler than the equivalent M45 for the same power, but I’m not sure how far you can go without needing an intercooler or chargecooler. An over-the-radiator intercooler became popular for MP62s after Track Dog Racing came up with their design, but people started to notice poor throttle response and unstable idle (especially in Mk.2s if I recall correctly) because the extra pipework increases the post-throttle volume considerably, so there’s a time delay between throttle movements and pressure changes in the inlet tract. Phil at P5 came up with the twin throttle idea as a solution. Having a throttle at the stock position as well as pre-blower allows the idle pressure between the two throttles to be partway between the inlet manifold vacuum and atmospheric pressure. That stabilises everything and restores responsiveness though getting it all balanced can be a bit tricky and they’re inclined to be noisier.

For myself, I fitted a small water/air chargecooler barrel in the crossover pipe (though it’s a real squeeze) which doesn’t increase throttled volume at all.

Another option is to change the cams to optimise them for a supercharger. Skuzzle Motorsport offer a low-overlap cam regrind for supercharger use, though I haven’t read any independent reports on results.

Obviously any significant changes will need the ECU retuned.

Thank you. Stage 2 conversion that Phil offered ramped up the cost significantly because of the need to upgrade other components such as injectors fuel pump and not least brakes. Having had a test drive in Phil’s cold side M45 I decided stage 1 was good enough to put a smile on my face. And very successful it has proved. In any case looking at the Bofi racing website upgraded MX5s are available from them at reasonable cost.

As a user of a similar set up, I would agree with everything Martin says, although I find my air/air intercooler doesn’t have a noticeable effect on responsiveness. A low cost option that you could try is to fit adjustable cam sprockets. These can give some of the benefit of cams without the cost as they allow you to adjust the intake and exhaust timing to optimise it for forced induction. You can benefit from closing the exhaust valves earlier as you don’t need so much scavenging to fill the cylinder, and keep the intake open slightly longer. Small benefits but for little cost.

Thanks - an interesting possibility. Internet research suggests adjustable cam sprockets require careful setting up. Some have questioned gains. One thing I still have stock exhaust. Even if there are no power gains, a new cat back might help or sound better. Attracted to MX5parts or Bofi racing offerings. Any views?

Well, I may not be typical but I did try a Cobalt exhaust from Moss, which I gathered was reckoned to be a little quieter and better sounding than the MX5parts one, but I eventually concluded I just didn’t like anything louder than stock so I swapped back. I must say though that the fit and finish was excellent.