GOING FASTER

[pkite4]

Hi Matt-
Can you tell me more about your flag? how much, where did you get it done, how
long did it take etc?

Cheers
Peter (DRGN-1)

[...]

[clive.granger]

It would be good if we can have a reasonable discussion about this. I didn't
contribute to the previous wind-up on this topic but will add my 2 cents worth
before this thread goes ballistic.

I drive a supercharged car but am not biased one way or the other (I think).

I have been driving my 1994 1800cc with a Jackson Racing (JR) supercharger (SC)
for a year now. It is running 6 psi boost. It does NOT boost all the time; it
has a bypass that 'free wheels' the unit until needed. Along with the
supercharger I also bought a high flow fuel pump and the JR timing box (which
piggybacks on the stock ECU).It boosts from very low revs all the way to
redline and it is VERY easy to redline the car in the lower gears.
I am pleased with the way the car drives. It does not feel very different from
a naturally aspirated MX-5, only more powerful. I have also uprated the
suspension (Konis and King springs),brakes (stock 1800 rotors with Hawk HP Plus
pads and high temp fluid), clutch (heavy duty and slightly larger diameter) and
fitted a torsen diff. I would recommend you do the same before boosting the
engine power. I also have a proper roll bar fitted.

All this has not been cheap. I am not a mechanic. The SC plus add-ons cost me
around $10,000 by the time they were fitted (International exchange rates,
cartage, GST, fitting by a professional mechanic). That does not include the
suspension and transmission upgrades. I gave up keeping account of the cost; it
was embarassing.

Why did I fit the JR SC?

I looked at the AVO turbo (Australian manufacture) option as well as the JR.
The Flying Miata options were just too expensive for me at the time. I think
all the options are great but the JR SC was a closer fit to what I wanted and
could afford. If you want outright top end power go for a turbo.
Superchargers will give you power lower down the rev range but lose out to a
turbo as the revs increase.

I think the turbo option MAY be more fiddly to install and set up correctly and
if you need something like a LINK ECU to get it running correctly it will cost
more as well. Mind you, the JR install is NOT as straight forward as the
advertising suggests. You can also get idling problems with the supercharger;
although JR seem to be improving. I have not had any significant problems with
my unit though I know a few people who have. It may be that mine is newer and
they are ironing out the problems. The JR timing box is not as sophisticated
as an after market ECU but to me that is an advantage; there are no parameters
to fiddle around with and the stock setting is fine.

If you go more than around 8 psi you are probably going to have to work the
engine as well. All the reading I have done indicates 6 psi (SC or turbo) will
have no impact on the life of the stock engine at all.

Depending on who you talk to the JR unit is not the best. Some say the
Autorotor supercharger is better; it certainly puts out higher boost. The
Autorotor is also more expensive. The JR unit does not come with an intercooler
(the Autorotor does). Personally I do not think an intercooler is that much use
on a supercharger, particularly running at only 6psi. Far more gains are to be
made getting cold air into the unit rather than cooling the air after it has
been boosted. The supercharger flows a specific amount of air based on the
engine revs. You don't get any more air by intercooling after a (JR)
supercharger though by lowering the temp you may help to stop pre detonation.
With a turbo there are definite gains to be had by intercooling. Turbos tend to
heat the air passing through them more than (JR) superchargers and as the air
condenses in the intercooler the turbo just pumps more in.

I have had next to no problems with the JR SC in the year I have had it
installed. As stated before, it is running at the 'stock' 6psi. It develops
around 95KW at the rear wheels. This is not huge but it is a whole heap of
fun to drive. It accelerates hard from 1000rpm to redline. If you want an MX-5
that is just like a normal one, that is not in constant need of adjustment and
does not need an engine re-build I would recommend the JR supercharger. A low
boost turbo would probably be just as good but would not give the same
acceleration pattern and may be harder to install and tune. If, however, you
want a bullet that will frighten the Subaru and Nissan brigades, and have an
unlimited budget, go for an AVO or Flying Miata turbo running 19psi boost with
completely reworked engine internals, transmission, suspension and brakes.
Good Luck.

Clive.


Quoting Matt Gunn <MattGunn@newstalkzb.co.nz>:

[...]

[my2cta]

I have a question for all you lucky people with go-faster MX5s. I've heard
lots of other turbos on the roads blowing off what is presumably too much
boost (e.g. driving round town) - very disconcerting. Do superchargers do
this as well? Does it only happen to turbos that are using higher boost
pressures, or just some brands of turbo? It's a quirk I'd rather be without
- a bit like truck air brakes.

Tim Dutton
MY2CTA

[Fletcher Blades]

Turbo's only...


A turbo isnt mechanically linked to the engine... it spins freely by
itself (driven by exhaust gas, but can free-wheel on its own) so if
you close the throttle... it keeps on spinning... and creates boost
when it isnt needed... A blow off valve releases this over-pressure
(to atmosphere, often with a trumpet to emphasise the noise!, or back
to the inlet- almost silent), so that the turbine keeps spinning, and
is "on boost" when you open the throttle again. The alternative is
that the turbine keeps spinning, trying to pump/compress air against
the closed throttle plate, and stalls the turbine... When the
throttle is closed, having no boost isnt a problem... but when you
open the throttle again, the turbo takes time to spin up to speed...
hence "turbo lag"

A supercharger is directly driven off the crank shaft... you close
the throttle plate, the engine slows down and so does the
super-charger... no un-required boost... you open the throttle back
up... the engine turns faster and so does the super-charger... no lag
either...

Please dont take this as a pro-super or anti-turbo post... I'm just
explaining why a super doesnt need a blow-off valve...

The "Pssshht pssshht" noise is usually there because the owner wants
it... blow-off valves that feed back into the intake are nearly
noise-less...

Fletch.