Emilio700
Emilio700 New Reader
Sept. 15, 2014 9:17 p.m.

Some of you might know this car as the "95R". It spent most of its life at tracks around California with a stock NB2 engine + bolt-ons making ~145whp. Our Big Grip suspension package and few other bits round it out.

With the upcoming release of Jackson Racings CARB legal Rotrex supercharger kits, we wanted to take that blower hardware, pair it with a built race engine, E85, MS3pro engine management and see what it would do. Below are the results. We are quite pleased with it :)

The CARB kits are expected around January 2015 and already have their E.O. # D-700-4. Expect about a 50% increase over stock power. Intercooled using their DFC fuel box, 100% PnP. I think they are targeting around a $4000 price point.

oldeskewltoy SuperDork
Sept. 16, 2014 10:38 a.m.

More or less "stock" 1.6 liter 20V 4AGE outfitted with the same Rotrex... on gas

Emilio700
Emilio700 New Reader
Sept. 16, 2014 10:50 a.m.

Outstanding. "Silver top" right? That's what you get with a head that actually flows. What's that going in? Assuming ~30bhp in drivetrain losses, that' still 148hp/liter. On a Miata BP head that doesn't flow so well, we had to go deep to get this wheel horsepower. In this case, full CNC porting, +1 O/S stainless intake, +2 O/S Inconel exhaust valves, Tomei 10.8mm In and 10.0mm exhaust cams. That all gives us about a 20% increase in flow at .400 lift over a stock BP6D head.

4cylndrfury MegaDork
Sept. 16, 2014 11:10 a.m.

oldeskewltoy SuperDork
Sept. 17, 2014 5:41 p.m.
Emilio700 wrote: Outstanding. "Silver top" right? That's what you get with a head that actually flows. What's that going in?

yes silvertop... went in a Striker/Locust/Locost

Harvey Reader
Sept. 17, 2014 5:51 p.m.

The California people salivate while people who live in other states do a turbo kit instead.

Swank Force One MegaDork
Sept. 17, 2014 6:44 p.m.

Ehhhh... i'd consider a Rotrex over a turbo regardless.

fidelity101 SuperDork
Sept. 17, 2014 8:52 p.m.

I would love to rotrex my wankel one day.

edizzle89 Reader
Sept. 18, 2014 7:31 a.m.
fidelity101 wrote: I would love to rotrex my wankel one day.

sounds dirty

Swank Force One MegaDork
Sept. 18, 2014 7:33 a.m.

mndsm and i have talked about sticking a Rotrex on a rotary.

We're convinced that it has the potential to be the loudest thing ever.

I'd like to try it.

Harvey Reader
Sept. 18, 2014 8:30 a.m.
Swank Force One wrote: Ehhhh... i'd consider a Rotrex over a turbo regardless.

Max torque 230lb/ft with 300hp? Maybe I'm missing something, but that seems terrible to me relative to a decent turbo setup. Not trying to rain on the parade, but what's the advantage to the Rotrex setup?

Swank Force One MegaDork
Sept. 18, 2014 8:38 a.m.
Harvey wrote:
Swank Force One wrote: Ehhhh... i'd consider a Rotrex over a turbo regardless.

Max torque 230lb/ft with 300hp? Maybe I'm missing something, but that seems terrible to me relative to a decent turbo setup. Not trying to rain on the parade, but what's the advantage to the Rotrex setup?

Have you tried to keep a turbo miata together during long periods of extensive track work before?

Also, smooth power and power where you need it. Power at 2000rpms doesn't matter.

You could also call this a fun way to make power while saving your rods.

And the dyno posted doesn't represent a final result using that setup.

We've had/have/will have again a turbo miata or two. I still kick around the idea of ditching the turbo on our current one and sticking a Rotrex on it.

Harvey Reader
Sept. 18, 2014 8:45 a.m.
Swank Force One wrote:
Harvey wrote:
Swank Force One wrote: Ehhhh... i'd consider a Rotrex over a turbo regardless.

Max torque 230lb/ft with 300hp? Maybe I'm missing something, but that seems terrible to me relative to a decent turbo setup. Not trying to rain on the parade, but what's the advantage to the Rotrex setup?

Have you tried to keep a turbo miata together during long periods of extensive track work before?

Also, smooth power and power where you need it. Power at 2000rpms doesn't matter.

You could also call this a fun way to make power while saving your rods.

And the dyno posted doesn't represent a final result using that setup.

We've had/have/will have again a turbo miata or two. I still kick around the idea of ditching the turbo on our current one and sticking a Rotrex on it.

Tis true, ze turbo she is a hot mess on the track, but you can't tell me with all the tuning options out there that you can't make smooth power out of some of the modern turbo setups.

Sure, if I had unlimited funds I'd have both a supercharged Miata and a turbocharged one. Just like I have my F40 Ferrari and my F50.

Swank Force One MegaDork
Sept. 18, 2014 8:56 a.m.
Harvey wrote:
Swank Force One wrote:
Harvey wrote:
Swank Force One wrote: Ehhhh... i'd consider a Rotrex over a turbo regardless.

Max torque 230lb/ft with 300hp? Maybe I'm missing something, but that seems terrible to me relative to a decent turbo setup. Not trying to rain on the parade, but what's the advantage to the Rotrex setup?

Have you tried to keep a turbo miata together during long periods of extensive track work before?

Also, smooth power and power where you need it. Power at 2000rpms doesn't matter.

You could also call this a fun way to make power while saving your rods.

And the dyno posted doesn't represent a final result using that setup.

We've had/have/will have again a turbo miata or two. I still kick around the idea of ditching the turbo on our current one and sticking a Rotrex on it.

Tis true, ze turbo she is a hot mess on the track, but you can't tell me with all the tuning options out there that you can't make smooth power out of some of the modern turbo setups.

Sure, if I had unlimited funds I'd have both a supercharged Miata and a turbocharged one. Just like I have my F40 Ferrari and my F50.

Oh you can absolutely make smooth power out of a turbo setup, but a square 300whp/300wtq turbo Miata is likely to hit like a hammer and be rough to drive.

Unless you intentionally tune to make less power somewhere, and who likes turning cars down from 11?

Harvey HalfDork
Sept. 18, 2014 8:58 a.m.
Swank Force One wrote:
Harvey wrote:
Swank Force One wrote:
Harvey wrote:
Swank Force One wrote: Ehhhh... i'd consider a Rotrex over a turbo regardless.

Max torque 230lb/ft with 300hp? Maybe I'm missing something, but that seems terrible to me relative to a decent turbo setup. Not trying to rain on the parade, but what's the advantage to the Rotrex setup?

Have you tried to keep a turbo miata together during long periods of extensive track work before?

Also, smooth power and power where you need it. Power at 2000rpms doesn't matter.

You could also call this a fun way to make power while saving your rods.

And the dyno posted doesn't represent a final result using that setup.

We've had/have/will have again a turbo miata or two. I still kick around the idea of ditching the turbo on our current one and sticking a Rotrex on it.

Tis true, ze turbo she is a hot mess on the track, but you can't tell me with all the tuning options out there that you can't make smooth power out of some of the modern turbo setups.

Sure, if I had unlimited funds I'd have both a supercharged Miata and a turbocharged one. Just like I have my F40 Ferrari and my F50.

Oh you can absolutely make smooth power out of a turbo setup, but a square 300whp/300wtq turbo Miata is likely to hit like a hammer and be rough to drive.

Unless you intentionally tune to make less power somewhere, and who likes turning cars down from 11?

I like a good hammering.

Wait, what did I just say?

Swank Force One MegaDork
Sept. 18, 2014 9:01 a.m.

Oh you know, just Miata things.

mazdeuce UberDork
Sept. 18, 2014 9:08 a.m.
Swank Force One wrote: mndsm and i have talked about sticking a Rotrex on a rotary. We're convinced that it has the potential to be the loudest thing ever. I'd like to try it.

If you two could get out of my head it would be great. I'm over here wondering if I could run a blow through carb setup, just because.

Keith Tanner MegaDork
Sept. 18, 2014 9:09 a.m.

I usually liken the power curve of a centrifugal supercharger to a highly tuned naturally aspirated engine. Since boost is directly related to engine speed, the faster you spin it the happier it is. They also tend to be fairly easy to tune as they don't add any backpressure and you're not running a lot of boost at torque peak, where you're most likely to detonate.

I can see the appeal for track work. I suspect cooling is easier than with a turbo due to the lack of backpressure and no turbo pumping heat into the coolant, but I've not spent much time on working with high power centrifugals on track. You're less likely to notice the lower torque level because you're keeping the revs up, the same way a highly strung naturally aspirated engine can be a PITA on the street but rewarding on the track. You won't get that low end punch that you do with positive displacement or a turbo (or lots and lots of cubic inches), that's the tradeoff.

If you're looking at area under the curve, you wouldn't be comparing this car to a 300/300 turbo. You'd be looking at something closer to a 250/250 setup, and you can get a pretty smooth powerband out of that. But that's more of a rally/street viewpoint, where you need that area. The 250/250 turbo would lose out to this thing on the straights. I'm looking forward to what Emilio can do with this tool when he really cuts loose. I think it'll suit him well.

oldeskewltoy SuperDork
Sept. 18, 2014 9:57 a.m.

The Rotrex isn't like most other centrifugal superchargers, it incorporates a planetary gear drive for quicker pressure build.

Just a brainfart... Since the Mazda 4 banger can't breath why not just get rid of it?????

I know... I know self promotion... but using a LEEN adapter on the 6 speed (99-05) you can slip in a well massaged Toyota "A" series...

Keith Tanner MegaDork
Sept. 18, 2014 10:28 a.m.

I thought the Rotrex planetary box was just a different way of dealing with the internal gearbox found on every centrifugal. Does it actually change gear ratios as the thing speeds up? It was my understanding that the only way to build boost faster on a centrifugal was to overspin it and then bleed off pressure at the high end.

Swank Force One MegaDork
Sept. 18, 2014 10:36 a.m.
Keith Tanner wrote: I thought the Rotrex planetary box was just a different way of dealing with the internal gearbox found on every centrifugal. Does it actually change gear ratios as the thing speeds up? It was my understanding that the only way to build boost faster on a centrifugal was to overspin it and then bleed off pressure at the high end.

You understand correctly.

Took me a minute to figure out what Emilio was doing when i first noticed the external wastegate on the INTAKE manifold.

Emilio700
Emilio700 New Reader
Sept. 18, 2014 12:39 p.m.
Harvey wrote: Max torque 230lb/ft with 300hp? Maybe I'm missing something, but that seems terrible to me relative to a decent turbo setup. Not trying to rain on the parade, but what's the advantage to the Rotrex setup?

Depends on what you value. The greater low RPM boost from a turbo does not come without a price. Instant low rpm boost in a turbo means a nearly open exhaust (loud), small to medium sized turbo, lots of octane and relatively high base compression. I had a setup like that about 10 years ago with an FM kit running a GT2554R and open exhaust. Instant boost that quit at about 230whp on our 91 pump gas. Most turbo guys want more peak power so a larger turbo is used with lower static compression, increasing boost lag at low rpm. Personally, I hate any lag in TPS vs torque. As a a race driver, I'm fine tuning slip angle on the way into, through and past the apex by modulating torque. With a Rotrex car, it's just like driving a big N/A engine. Deviate feels about like an E36 M3 engine. Seamless power everywhere that builds with RPM. A turbo OTOH, is much more difficult to get anywhere near that linear TPS vs Torque relationship. Usually involves TPS and RM based 4 port boost control that takes some level of expertise to get dialed in without spikes or creep. Not impossible, just not PnP easy like the Rotrex.

Some folks don't mind that lag. I know a few friends that actually like that Vtec like hit of torque that comes whenever it's darn good and ready. To them, that "feels fast". The seamless, instant torque delivery of a good Rotrex build is fast, just doesn't feel as violent. That said, Deviate fairly leaps if you jump on the throttle at anything above 4500rpm.

Having been down the road of building a turbo setup that will survive sustained track use with a fast driver in summer heat, I know it isn't cheap or simple. A Rotrex build OTOH, is pretty much bolt on out of the box. Easy to tune, bombproof. No custom V-band manifolds, heat shielding, boost controls, water lines, high pressure oil lines. A good friend after driving Deviate said "5 bolts and you're a hero". Not quite that simple but you get the idea. His daily is a 300whp NB with a GT28 sized turbo BTW.

In any case, the 100lb increase in torque at the stock torque peak of 4800rpm, available instantaneously is "enough" for most drivers to put a smile on their face. Peak OEM torque is matched at 1500rpm. Look at the plot again. If I didn't state "supercharged" there most would assume a 3.0L high revving N/A motor.

There will always be the internet readers who are deeply disappointed if any Miata power adder doesn't exceed the power to weight ratio of a ZR1. I'm OK with that.

Keith Tanner wrote: I thought the Rotrex planetary box was just a different way of dealing with the internal gearbox found on every centrifugal. Does it actually change gear ratios as the thing speeds up? It was my understanding that the only way to build boost faster on a centrifugal was to overspin it and then bleed off pressure at the high end.

Correct. Most folks are familiar with the Vortech centrifugal. Basically a big, low rpm belt driven turbo. They usually operated at a 2:1 drive ratio using helical gear, thus the noise. Being so slow, the compressor had to be huge to push any air. These types of compressor don't really become efficient until the tips of the blades are moving fast. This is why Vortech are know for having a bit of a dual personality, nothing at all down low then whoosh. The Rotrex using a gearless planetary arrangement (traction drive), driven at 9.49:1 (I'm not making that up) in the case of the C30 series. Being spun at 120k rpm, the compressor wheel can be tiny, about the size of a Garret 2560 give or take. It's also equally efficient. Almost no noise from it because there are no teeth meshing. So it is still technically a centrifugal but without the stereotypical inefficiency of a slow turning Vortech style blower. I think of the Rotrex as a belt driven turbo. You trade boost down low for instant response, greater thermodynamic efficiency, simpler and more reliable hardware. Not everyone's cup of tea but for some people, it's spot on perfect. Now if we can just figure out a way to drive one with electric motors at whatever speed we want..

Spinout007 UltraDork
Sept. 19, 2014 3:55 p.m.

Whelp I was going to build SWMBO a turbo miata next year. This JUST might need a closer look. She short shifts every gear anyway.

ProDarwin UltraDork
Sept. 19, 2014 4:10 p.m.

Awesome. I like the simplicity of this setup. Not so sold on the pricepoint though :(

What kind of power can be made reliably on stock internals with one of these?

Emilio700 wrote: Now if we can just figure out a way to drive one with electric motors at whatever speed we want..

Not sure which gears are spinning/fixed in the Rotrex setup... but whichever one is fixed needs an electric motor added to it so you can change the ratio on the fly (like the Prius transmission).

Emilio700
Emilio700 New Reader
Sept. 19, 2014 4:47 p.m.
ProDarwin wrote: What kind of power can be made reliably on stock internals with one of these?

For how long? One pull dyno queen, I'd say 350whp with a C30-94. Wouldn't last very long on stock rods, bearings and valve springs though. Long block is the limiter, not the blower.

On a stock NB engine with an oil cooler, reroute and good radiator, I think 240whp is a good range to detune to in order to keep it alive for frequent track use. Above that forged internals, billet oil pump gears and/or billet damper are needed. Again, if its a car that never sees autocross or track use, just the occasional burst on the highway or onramp, you could tune a bit higher, just watch those gauges.

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