JRSC M45 on '99 Miata...what's my HP ceiling?

I'm about to close the deal on a low-mile '99 Miata equipped with an M45 blower and custom (split/dual) exhaust. Car comes equipped with a 6-speed and Torsen diff. I plan to use it as a wife-friendy weekend cruiser and (very) occasional track car. The SC was installed professionally by a speed shop 30K miles ago but I do not have any specific details beyond that.

My original goal was a newer Rotrex system but that changed when I found a very good deal on this minty, already FI car. I am, given price, essentially getting the blower for free. I've done quite a bit of research so I know that...

- there are many SC and turbo systems that create far more power
- some folks (including many posters on an infamous turbo-focused forum) openly mock the M45s relatively low hp output...perhaps rightfully so
- most folks running M45s seem to be seeing numbers around the 140/150 whp mark and describe the result as "fun" rather than "impressive"
- the guys at Track Dog Racing make several complementary parts (intercooler, pulley, card, etc) that they claim can push the M45 to within a cat's whisker of 200whp -- which would be a game-changing bump
- there is a camp of M45 defenders who maintain that the older system is underrated, provides dependable power and better-than-advertised low-to-midrange torque (a good street-car formula)

To be clear, I'm not looking to go above 200whp in an older Miata and I'm going to heed the advice I've been given that power beyond 220hp or so can start to eat stock internals. That said, I want to squeeze as much dependable power as I can out of the existing SC setup. So...can anyone out there give me real-world examples of M45 units that have been pushed past the 150/160 mark while retaining some semblance of dependability? And if you can, can you share your magic formula?

This humble noob thanks everyone in advance for helpful replies.

It's simple physics. That little blower was originally sized - 30 years ago - to be used as a 6 psi system on a 1.6, making about 140 rwhp. It was pretty well suited to that.

Push it harder and you'll generate heat a lot faster than you'll generate power. They quickly get to the point where you're getting more boost but not getting any more power due to crazy intake temps. They also start to generate more driveability problems, especially if you install an air/air intercooler. Basically, it's at the point of diminishing returns right out of the box on a 1.8.

My recommendation is always to just enjoy it as-is. You'll tear your hair out trying to push it much further.

Stock internals are good for 250 rwhp for decades. But that's not going to be a concern here :)

In reply to Keith Tanner :

Thanks, Keith. Been so long since I had a "fun" car that I'd have been happy taking corners and rowing gears in a naturally aspirated car...so the extra oomph from the M45 will probably be gravy...until I chase bigger power. Then again, a C5Z will eventually grace my garage so the Miata may just remain "as is" (after requisite wheel, tire, suspension upgrades).

Recently bought your book, btw. Had a number of folks tell me it's the de facto bible for Miata modification. 

Keith Tanner said:

It's simple physics. That little blower was originally sized - 30 years ago - to be used as a 6 psi system on a 1.6, making about 140 rwhp. It was pretty well suited to that.

Exactly. It must be noted that that power number is achievable on a NA setup. OP I think you should pass up on that deal, and save your money for a modern supercharger or an NA setup.

The only thing you need to do to keep that type of setup dependable is keep the charge temps in check. The problems with air to air intercoolers and throttled volume, idle stuff etc can be avoided by using a 'bullet style' water to air intercooler in the piping that goes across the front of the motor. A little more complicated but if you have a good enough intercooler system to keep the temps down then you can max it out and have a fast miata. I personally dont think you should pass on the deal if the price is right and you've got your expectations in the right place.  

I will add that checking the tune is great insurance. A bad tune, even at 150whp, can blow up an engine. If it doesn't have a wideband already, it might be a good idea to take it to a dyno and just make sure the bandaid fuel adder /timing retarder cards those things typically came with are doing their job. Header and EUDM/JDM "flat top" manifold are good for some ponies as well, and won't cause the supercharger to work any harder, but you'll need a proper ECU to take advantage of them. 

my miata needs no more power.  I am super slow as it is..

However, I WANT more power.

the MCM Turbo vs. supercharger series in an MX5 is a good use of your time.

Turbo vs super is always laid out as a fundamental thing. In reality, it's all about the implementation. The turbo can be the bottom end torque monster that gets winded up top. The super can be weak down low but really wake up near redline (see: ND Miatas). 

For example, here's an M45 supercharger with a "big boost kit" on a 1.6 laid out against a GT2554 turbo. Same car, same engine management (Voodoo box and a Sebring timing retard), same little 2.25" exhaust. This was done at altitude where the turbo spools slower and the "big boost kit" on the supercharger basically makes it equivalent to a sea level version. Not shown is the change in driveability - the supercharger was a little funky.

https://www.flyinmiata.com/tech/dyno_runs/M45_vs_VoodooII_1.6.pdf 

Again, this isn't turbo vs super. It's about implementation of the system. You can't generalize.

In reply to Keith Tanner :

Just ordered your book.