Modifying the M42 318iS Author:
This is a compilation of things that are necessary to get real performance out
of the M42 engine that you use in a street/auto-x/mild track use car. These are
items that will improve the cars performance and not sacrifice any low-end
torque, which you want for street driving. These are all pretty much "bolt-on"
mods, using the engines factory internals. If you want your 318iS to really fly
on the street, these are the things you need to do:
Computer chip - This is a very basic and inexpensive modification
for your car. Chips usually run about $200-$300 and are very easy to install. A
chip on a stock M42 will bump the horsepower to about 145 (from 135) at the
peak. The low-end torque is increased as well to improve everyday drivability.
Though the real improvement comes at the top end; the chip widely increases the
power band on the M42, from 4600-6000 to 4500-6700. I recommend Jim Conforti
chips, as they are unarguably the best on the market for this motor, at a good
price as well. On a side note, you will find the M42 makes a very distinctive
"howl" from 6700-7200 rpm that reminds you that youíre driving an honest-to-God
Flywheel - A major problem with the M42 was that it had BMWís
'dual-massí flywheel; yes, it weighs almost twice as much as a 325i flywheel (as
the name would suggest), at 28.5 pounds. This is a big problem and absolutely
kills 1st and 2nd gear acceleration. Ever wondered why your 318iSís 0-60 was so
slow? Well, the flywheel is one of the reasons. There are 3 options to fix this:
1) use a 325i flywheel/clutch or 2) buy an aluminum flywheel for your M42's
clutch, and 3) an aluminum flywheel for using the 325i clutch. Buying an
aluminum flywheel for the M42 runs about $500-700 but is very light, and
requires no modification to be fitted. M42 aluminum flywheels are about 12
pounds, and 325i aluminum fly's are about 8 pounds. The 325i flywheel requires a
few other modifications to be fitted in the 318iS. Hereís what you need: 325i
flywheel, 325i clutch, 325i pressure plate, 325i drive-pinion for the starter
motor, and a Ď78-í83 323 throw-out bearing. Replace all these with the 318iS
parts and it bolts right together. After all is said and done, your 318iS will
have a LOT better acceleration in the first few gears, and deceleration will
take place much quicker, which helps on the street and in the auto-x.
Rear end gear - The 318iS is equipped with a 4.10 limited slip
from the factory, but you can do better. The desired gears out there are the
4.27 and the 4.45. You will find the 4.27 in E30 318i convertible 5 speedís and
the 4.45 is in E36 318i automatics. The 4.45 is a wicked, wicked street gear but
will stick your RPM way up there on the highway. The 4.27 is a good compromise
of performance and everyday use. It should be known that to make a 4.45 work,
you have to swap the gearset into your E30ís differential, or find an automatic
318ti, which has a 4.45 and also has trailing arm rear suspension! So the E36
318ti 4.45 bolts right onto an E30, though finding an automatic 318ti with LSD
may be difficult.
Adjust the cam timing - You know how on the E30 M3 you have to buy
a $300 kit with adjustable cam sprockets to tune your cam timing? Not on the
318iS! The M42 is equipped with tunable cam sprockets from the factory. So pull
your Cosmoline covered valve cover off and with the proper tools you can tweak
your intake and exhaust cams up to 6 degrees +/- to provide more top end
horsepower or more low end torque. See, you donít have to blow a grand on a set
of Schrick cams to make your M42ís cams a little hotter. The best setup is to
adjust the intake cam to 5 degrees (advanced) and leave the exhaust cam alone. I
would recommend having a shop do this work.
Muffler - The 318iS is equipped with a very free flowing exhaust
manifold and center section with 2.25" stainless piping. The bottleneck in the
system is the muffler. Thee are a few options for this. The first is a cat-back
system, which replaces the piping and boxes behind the catalytic converter.
Supersprint makes an excellent cat-back system that runs about $400. You can
also simply replace the muffler. There are a variety of mufflers on the market
but there is one that is very inexpensive, sounds great (not too loud, but
throaty), and fits an E30 very well - it is made by Walker-Dynamax and is called
the "Super-Turbo" muffler. It is available from Summit Racing at the price of
about $40. We have had great success with these mufflers, and even use them in
3" size on our E30/S50 cars.
Intake system - The 318iS stock airbox works well, but a cone
filter setup works better, but only if you have a well-built heatshield! Get a
large K&N setup with the AFM adapter and all. Go to Home Depot, buy some
Reflectex and build a "cool-air" system by cutting and fitting a heatshield. It
is worth it in the end. While you are working on the intake, get the secondary
plate of your throttle-body bored out 3mm to 57mm. This will make a difference.
Summary: You will find that with a little time, a little cash, and a little
elbow grease, you can tune your 318iS to really perform. William Zubrick's 318is
with a properly built intake, Supersprint cat-back, and Jim Conforti chip puts
131hp to the wheels on a chassis dynomometer. Enjoy!