Miata Mailing List: January 1997, Message #53
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   From: (none)

Subject: Supercharger and Turbos-long term considerations

   Date: (none)



Hey all:



As probably one of the newest retailers, I've been learned a lot concerning

the wear and tear on stock engines by the hand of supercharged units and

turbos.



There are many things to consider (yes on the negative side) when getting

ready to plunk down the $1500-$4000 for forced induction systems.



1. You got to remember the car won't last forever or as long as a normally

aspirated unit (common sense I think)



Not that the engine will blow up or something, but you 're looking at some

increased maintenance costs for clutches, seals, gaskets, etc which will

tend to die off much sooner in a modified engine.



Robert Baca (Banzai racing and development) races a 1994 Turbo Eclipse runs

21 psi in his car. BUT in order to do this, he has added an oil cooler,

turbo timing devices and auxiliary computers as well as new rods, pistons,

etc. The car sees a daily commute, but even he concedes that it will not

run as long as it would have under its normal configuration at 10 psi.





2. Running higher than the factory settings in boost (i.e. +5 to 10 psi)

may give some outrageous horsepower gains (and be a helluva lot funner of

course) but you're talking about eating up the longevity of the engine.



Mind you, it's only a four cyclinder unit built to originally take a

non-induction system (of course the pre '93 Miata tend to be a bit more

durable). I disagree with some manufacturer/dealer claims about hitting

high hp with small displacement engines as being "normal" or "not hurting"

the motor and then siting for instance INDY cars displacing what 2.0 liters

or so and putting out 500+ hp. True that it works, BUT most HIGH, HIGH

performance race cars get engine rebuilds how often?



But even in the event of running higher boost, it is best to consider a

good rebuild replacing pistons, rods, bigger injectors, etc.





3. Buy a system tailored to your driving needs!



If your car is a daily driver, buy a good sc unit. It's relativly cheaper

than turbos and easier to maintain. For drivers who's Miata is the#3 car in

the garage, a turbo set-up is good for the all out speed crowd. Turbos take

a bit more attention (as in letting it sit for a bit too "cool off") and

oil changes tend to be a bit more frequent.





[us]

Currently, I'm running a Eaton based Sebring unit with 118k miles on our

1991 A pkg. A Borla exhaust system is about the only other mod on the car

aside from suspension work and a wheel upgrade (15 x 7 with 205/50 tires).

It runs 6.5 psi of boost with an MSD unit at 10 degrees (CA gas mind you).

A Bell Cartech auxiliary fuel pump assists in fuel delivery.



As sort of an experiemnt, our Eaton s/c went in at 108k and has seen

moderately heavy street racing against Honda VTECS, Mustangs, etc.

(Obviously I don't advocate this but we wind up doing it anyway huh?). At

115k miles, pretty much all the main seals went, crank front and rear,

sprockets, etc.....at 118k....the head gasket went. (not cheap! to replace

these!) I was prepared for the seals to go but the head gasket was a bit of

a surprise. (My pals at Banzai grinned and mumbled something about s/c's

having a tendency to stress head gaskets....)





The stock 1.6L clutch is still holding up great (we drop it at 4500rpm

almost every Friday night so.....).





My next project will be a turbo/intercooler set-up using the GReddy kit

(Mitsubishi TD04) and a borrowed RX-7 intercooler. But I also plan on

yanking the block out of the 1993 we're looking at and doing a good rebuild

(rods, pistons, larger oil passages, port/polish, etc.) My goal is 18 psi

for what almost 300hp.



I will be doing a more in depth editorial on this subject on our January

Newsletter.



-Percy

M. Roadster Performance