From: Brian Goodwin (

As I write this the Miata is on the dyno and the first run--on an
otherwise BONE STOCK 1.8 Miata showed HP at the REAR WHEELS (not the
crank) in the range of 150 which is great!  That compares with about
140 to 150 for Aerodyne Miatas and 125 to 130 for Sebring Miatas
(remember we are talking at the REAR WHEELS as opposed to at the
crankshaft which are the figures most people are accustomed to
quoting, and what the factory quotes, for Miatas such as 1.6 liter is
116 hp at the crank --- It is far less than 116 at the rear wheels, 100
or less, because quite a bit is lost in the process of getting the
power to the ground.).  Anyway, I wanted to see what the system would
do on a dyno without any other performance mods--not even a free flow
exhaust which should be good for about 6 to 10 hp on a blown system (4
hp on non-blown miatas that don't suffer the same pumping losses that
charged systems do because of the significant increase in gas volume
caused by the blower, etc.).

Anyway, I will send the list a full report on the unit's performance
after a day or two of driving!

As for the age-old question of which is better supercharging or turbo
charging -- there are so many factors to consider in the abstract before
you even look at application to the Miata.  Without getting too deep
into it at the moment here are some of the things I have learned along
the way about Miata application before deciding on my Autorotor.

First, the 1.6 and 1.8 should be considered separately.  What might be
the best system on one car may be second best on the other.  These are
different engines -- not only because of different displacement--they
are different engines entirely and react differently to different
types of charging.  The AUTOROTOR, for example is supposed to make
significantly more noise in its 1.6 application than its 1.8
application.  That being said I have driven Aerodyne 1.6 Miatas,
Sebring 1.6 and 1.8 miatas and here is the sum of what I think:

If you have a 1.6 -- you are in luck because the choices are excellent.
The Sebring is sized very well for that engine and is reportedly easy
to install (the directions were much simpler, with far fewer parts,
than my Autorotor instructions).  You get good response with good
engine flexibility and quiet operation.  What you give up is power in
the stock kit (though stock can be just a starting point as the Miata
club's project car demonstrates).  On the 1.6 the AERODYNE will
definitely give you more power (the CARB'd stage II kit).  My seat of
the pants impression is that very low on the rpms the Sebring feels a
bit stronger--like the 1000 to 1800 range.  Beyond 2000 rpms however
it is all Aerodyne (I am talking stage two--the only one I have
driven).  If I had a 1.6 I probably would have bought the Aerodyne.  I
like turbos, have more experience with them and find further
modifications on turbo systems easy.  I have not driven the Autorotor
1.6 but even Corky Bell himself tells me he prefers the Aerodyne on
the 1.6 engine.

For the 1.8 engine the choices are thinner.  I don't think the Sebring
is good bang for the buck on the 1.8.  Sebring charges an extra 100
for the 1.8 kit and gives you less percentage increase in power.  The
extra displacement means the Sebring is running at least a full pound
of boost less than its 1.6 brethren using the same pulley size.
Sebring experimented with a smaller pulley for the 1.8 in an attempt
to get the same 6 or 6.5 pounds of boost that they get on the 1.6.
This experiment apparently didn't work out because they decided to
ship with the same pulley size as on the 1.6.  The reason was probably
that the smaller pulley, with its higher blower speed, meant too much
heat for the non-intercooled kit at 6 to 6.5 pounds of boost.  Anyway,
if you want easy to install and moderate power gain it is still a nice
very clean package.

The AERODYNE story is somewhat similar.  The same sized unit is used
on the 1.8 where it too might be considered a bit small.  The other
side of the coin, however, is excellent response from VERY low revs
and great power high up.  Corky prefers the Autorotor for the 1.8 for
its greater low end torque but the Aerodyne is still a great option.
I live in California and Corky is not going to CARB the Aerodyne but
is CARBing the Autorotor so my choices are simplified for me.

There is at least one other mainstream option I have not driven and
know next to nothing about -- The Greddy kit.  There are writeups on
this kit in Grassroots Motorsports and Turbo Magazine.  It seems a
heck of a bargain at UNDER $1500 for the complete kit.  Looking at a
picture of the complete kit it also looks extremely simple -- so
installation should be a snap.  I am told the first kits shipped had
some problem having to do with calibration to the Japanese market CPU
rather than the U.S. market CPU--a problem that was being corrected
when I last talked with Greddy people who also said CARB is pending.
Anyway if anyone out there has one of these working they should write
the list with the details because I have only read about results
(Turbo says 0-60 in just over 6 seconds).  Sounds great for the price.
Since it's a non-variable vane classic turbo I would expect a bit more
lag than the Sebring or Autorotor but who knows--so many variables
involved so we need to hear from an owner!


Hi everyone.        

Got a ton of e-mail with questions about the autorotor.  Because I
have to get a project out at work today I will not get a chance to
answer everybody's questions until this weekend--But I promise I WILL
answer everyone's questions as best I can by next week.

What are my first impressions?

In brief here they are.  This unit changes the whole character of the
car.  If you decide on this one be prepared for it to feel and sound
totally different.  The unit itself makes more noise than either the
Sebring or the Aerodyne turbo cars I have driven.  That said the sound
is not necessarily objectionable.  The car is not really louder, just
different sounding.  It is a bit disconcerting at first but I found
myself quickly getting used to the new sounds - and liking them.

At just off idle rolling speed it just sounds like you have a custom
exhaust on -- a low tone rumble-like sound to about 2500rpm.  If you
drive with a very light throttle the car sounds almost stock from
about 2500 all the way to redline (no, the boost is not always on like
the silly Sebring negative advertising suggests and a few people have
asked me about.).  If you hit it so the supercharger engages you hear
a superchager whine and the total sound impression is not unlike a
Mazda rotary. (And if you don't like the sound you can just add a
dynomat hoodliner from any good stereo store then hear just your
exhaust burbble.)  Unfortunately yesterday it was raining hard so I
can't say too much about performance yet -- everytime I hit it I broke
both tires loose on the wet ground.

The only time I was able to really lock up was a couple of times this
morning on the way to work.  I even surprised my first Mustang.  He
pulled up on my right a block before the left turn onto the freeway
obviously intending to beat me to the ramp.  The ground was half-dry
because of a break in the rain and I heard his tires chirp when the
light went green so I hit it after a rolling start from about 2000rpm.
Luckily the tires held this time and away I went shooting right passed
him (got a feeling more tire and a new clutch will be sooner rather
than later).  He got off the same exit when I got to work and asked me
at a light if I had a mustang motor in it (guess he knows what a
monster miata is).  Sure was fun.

Early impressions are that it feels much like the Sebring from 2000 to
4000.  When you get to 4000, however, it definately outruns my seat of
the pants impression of the sebring.  (If you hit the gas before you
disengage the clutch you get boost instantly but I have not been able
to lock it up this way yet.)  Regarding 4000 rpms -- once you get to
about 3800 you better know where the car is pointed because you will
be there in a hurry.  I have only had it above 4000 three times but
enough to know it just rockets from there on.  It is nice having real
torque down low.  The dyno showed an AVERAGE rear wheel torque (as
opposed to the higher at-the-crank numbers) of well over 140 measuring
from 2000 to redline with a VERY FLAT TORQUE CURVE.  I already notice
I drive it lower in rpms now because I can.  It feels stronger at 2000
to 4000 than it did stock at 4000 to 6000.

While it undoubtedly makes more power than the other kits out there,
it is not without tradeoffs.  The installation of the Sebring is
definately a cleaner looking setup that runs quieter and can be
installed easily by the do-it-yourselfer.  On the dyno the Sebring
only shows 125 to 130hp at the rear wheels while our final dyno
numbers yesterday for this otherwise bone stock miata were 156.3 hp at
the rear wheels (not at the crank like the factory quotes -- 116 for 1.6
liter, 128 for 1.8 liter etc. but at the wheels where a stock 1.6
makes about 98hp and stock 1.8 liter makes about 108.). So you have to
decide what you want more -- ease of installation and quiet result -- or
tough installation and a more dramatic result.

I will give a much more detailed report later after I have had more
opportunities to drive it on dry ground.

ps. I did NOT install it myself.  I have done this kind of work before
(installed a sprintex lyschom screw unit which is very similar on a
Mustang) but my work keeps me too busy right now and frankly I found
the instructions to this kit daunting.  I started the work anyway but
after the car was on jack stands for two weeks because I was at work I
got tired of waiting for my schedule to clear up and decided it was
just better to pay to have it done anyway.  I put all the stock stuff
back on and drove it to Mechtech in Escondido California

Mine was the fifth Miata they have done (they also do the Aerodyne
kit).  They have a first class dyno and far more experience than I.
Corky recommended Mechtech and I found they gave great service -- with
the dyno tuning an added super plus!  I would recommend them to
anyone.  You want to talk with Jim.  If you go tell em I sent YA!


Hi, day three with the autorotor and the clutch is already slipping.
Finally got a chance to drive this thing on dry ground last night.  I
drove around and around on some of the less populated roads in the
area.  The power is REAL.  Hit the gas at 20 or 30 and suddenly you
notice yourself passing the 100 mark on roads marked 35 before you
know it.  I had planned the necessity of a clutch but did not think it
would wear out as soon as it is.  I have done NO HARD launches from a
standing start and the clutch is already slipping.  I notice it now
only in third gear in the high RPM's but obviously it won't last
long -- just too much power for the poor thing.  I would appreciate
hearing from those with performance clutches and charged engines on
their thoughts regarding clutch selection and performance.  I am
thinking I will go with a Centerforce Dual Friction model.  Comments?

On Noise -- Had many questions on this and I have to change what I
reported earlier.  Why?  Because my earlier reports were with the top
and windows up because of rain.  The noise question had a different
answer with the top down.  With the top down there are two distinctly
different sounds.  You hear the supercharger whine that you expect.
You also hear much belt sound--just the belts running.  Some of this
may be because I have yet to replace the plastic pan--more sound is
getting out or reflecting off the ground?  Neither sound is loud
enough to annoy me but I may put a Scosche or Dynomat hood sound
blanket on someday.  Then again, I have driven it much of the time
with the radio off focused on listening to it.  When I turn the radio
on I don't hear anything from the supercharger--and I don't play my
music especially loud.  Hope that helps everyone who asked about this
guage the level of sound.



1. This is a serious modification to the car.

The look of your engine bay is very different.  Tubes and wires, etc.,
have significantly grown in number.  No doubt the Sebring/Aerodyne
I/Greddy systems are cleaner more stock looking setups.  I am not
saying the Autorotor looks sloppy or anything.  Just that all in all
it is not near as simple as some of the more basic kits.  Along with
greater complexity come some greater compromises in the "stockness" of
the car.  What do I mean by this?  For example--the Autorotor does not
easily allow replacement of the plastic undertray.  I have been
meaning to get it back on but doing so will require some trimming and
the task has so far eluded me.  The Autorotor fit issue is caused by
the intercooler tubes.  They run from the unit down under the base of
the radiator and up to the intercooler which is mounted in front of
the radiator (in the Miata's "mouth").  From the intercooler the tubes
then run back under the base of the radiator and back up to the
intake.  Where the tubes pass under the car they interfere with the
underside tray and prevent its easy re-installation.  From getting
under there with the tray it is apparent to me that with trimming it
could all fit (if anyone has an Aerodyne II, which I remember as
having a similar intercooler setup, and you have replaced this tray
successfully I would like to hear about it.).  All that said I am not
sure if I care anymore about the tray being on.  My understanding is
that modern cars have these mainly for a slight improvement in
underbody aerodynamics.  My Fiat 124 had no such tray and I never knew
I was missing something until I bought the Miata.  I certainly make up
in horsepower what I lose in slipperiness.  However, I thought
everyone should be aware of this before buying.  The simpler kits like
the Greddy/Aerodyne stage I/Sebring etc., don't require removal of the

I notice the additional load on the engine at cold startups.  It is
not bad.  It is as if you were starting your car with the
air-conditioning already running--you notice it but it doesn't cause
problems.  The car will sometimes go into its cold weather start mode
(higher starting idle) as a result of this initial load.  Starting the
car when warm does not cause this.  As far as load while driving I
don't notice it at all now.  In the first couple of days I was driving
the car very very gingerly.  If you drive it with a very very light
throttle you will feel the load of the belt as you leave idle in first
gear.  I now drive it just like I did before the supercharger was put
on and I don't notice the load.  You can drive it around town with
light throttle so you stay out of boost and beyond that first gear
start it feels very stock (note my stock clutch is slipping so this is
part of the first gear start issue).

2. Tunning issues

The fit of the intercooler tubes could be better on my kit.  Most of
the tubes line up fine.  The connection between first tube and the
second however has a gap of about an inch.  The rubber joints are
about three inches long and cover the gap.  However, the installation
directions say that the tubes should be setup so they are touching
because otherwise the constant stresses of on/off boost will cause
failure of the joint over time.  This joint is also close to the
supercharger belt.  I have already discovered what happens when these
bad boys get together--they have a screaming bad time.  The tubes were
secured out of the charger's path by a nylon cinch that was installed
by Mechtech.  While I was very happy with Mechtech's work generally, I
think one strap was leaving an accident waiting to happen.  Driving
down the road the other day, under boost, the strap broke and the
tubes got close enough for contact and the belt was gone in a heart

Anyway, I was suddenly driving a stock miata.  No problems driving it
with the belt off--it is just stock-like.  Nothing to be damaged by
driving it with the belt off.  Went by the local auto parts store and
picked up a new belt--this belt is a standard six rib 46.5 inch belt
that you can buy at most auto part stores.  Takes a couple of minutes
to put a new belt in and away you go.  Also bought a handful of the
same nylon straps and made sure that contact would not happen again.
I caution other buyers to learn from my experience and make sure this
can't happen.  I know my kit was one of the very first 1.8 kits--I
will tell Corky to take a look at the fit of this first to second pipe

Another "fit" issue was where the first intercooler pipe clears the
power steering pump reservoir.  Initially, on hard right turns I was
getting a vibration caused by contact of the tube and reservoir.  I
have fixed this by moving the reservoir further out of the way.
Everybody else can avoid this problem by making sure you allow about
an inch clearance between these two objects.  In fact, because of the
tube coming out of the side of the reservoir I would recommend the
reservoir be mounted full forward and at a slight tilt toward the
engine so that the tube coming out the side of the reservoir will be
tilted further below the nearby intercooler tube (You will understand
what I mean when you get there.).

That is about it on drawbacks and tuning so far except for a few
tidbits.  I have noticed a decline in gas mileage but have not gone
through enough tanks to really give an accurate figure of how
much--just that I do notice it.  I have gotten pretty accustomed to
the sound as well.  I have now had some other people in the car and
three people gave the same impression--sounds like a jet engine--not
in volume--but in tone etc., when you are on the boost.  Not my first
thought but, okay, I understand what they are saying.  My girlfriend
is one of these riders and I asked her if she found the sound
objectionable.  She does not.  The other two people in the car were
guys and they both--with big silly grins on their faces--thought it
sounded "like a jet--very cool."  You don't really hear this sound
unless you are under boost in mid to high rpms.  Driving the car
around town at moderate to light throttle it makes more sound than
stock but not much.  If I use the radio instead of listening to the
thing I don't notice the sound unless I am hard on the boost.

One more thing, plan on the clutch.  In fact, do the clutch just
before you add the Autorotor if you have a 1.8.  I still have not had
a chance to do the clutch.  It only slips once it gets hot but once
hot it really slips.  It just doesn't have the clamping pressure to
hold up.  I wish I had done it before the Autorotor installation cause
now I got to be without it for a day while the clutch is done.


1. This is a serious modification to the car (yes same thing as I said

The power is great.  The response is great.  Once accustomed to
driving it I find that I just love it.  I have to admit that I had
some moments the first week of ownership when I said to myself: "my
god what have I done!"  After owning the car for a while I really do
love it.  This car always handled great (especially with Jackson
Racing Sway bars, etc.) and now it has the grunt to go with the

The boost response is the best part.  The boost really is just
instantly there.  You hit the throttle and the gauge jumps to five psi
instantly then climbs smoothly from there.  By this I mean that if I
hit it while cruising along in second at 2000 rpm I see 5psi instantly
and about 6-7psi by 3000 and 8psi before 4000 rpms.  The seat of the
pants (and the dyno) show a very flat torque curve which slopes up
gently to its high point midway between 4000 and 5000 rpms, and it is
almost totally flat between 4000 and 5000, then slowly eases back down
again.  The power is also fluid, very controlable, yet very REAL.
When the belt was off and it was stock-like again I could not believe
I had put up with stock for as long as I did.  I was very surprised by
how accustomed I already was to the power.  I missed it so much I felt
driven to get the belt immediately back on so I could have my
power-miata back. To really understand how quick it is you have to
match speeds with another car, on the freeway for example, and then,
after matching their speed, punch it.  Suddenly the other car is in
the rearview mirror and disappearing fast.  Great fun.

Would I do it again?

Yes.  Before I drove it without the belt the other day I had some
moments when I was unsure--like when the first belt got destroyed.
However, I have moments of buyer's remorse about EVERYTHING I buy.  It
is just the way I am.  Driving it is really great fun.  Other drivers
are quite surprised when your miata just picks up and shows them its
taillights in a heartbeat or two.  Despite the complexity drawbacks
the results are a ton of fun, the power very serious, and it all so
far works very well.  This weekend I plan to take it on its first real
trip--a nice long drive into the local mountains.  The following
weekend I will try it for the first time at the track and report back
on results.

Comparisons with other things kits I have driven--impressions are
pretty much the same as when I last reported so see last report (and
if anyone knows anyone with the very inexpensive new Greddy unit get
them on the list so we have the benefit of their experience too).