Engine - Intake System
The original intake system of the Geo Storm is a pretty good design. The 4XE1 DOHC manifold is a true work
of art, it's eight runner manifold incorporates secondary intake valves, which close four of the intake runners
at low engine speeds to improve low end torque, and then open at high engine speeds to provide additional flow
for to improve maximum power output. The inside of the 4XE1 DOHC, as well as the 4XE1 SOHC, and 4XF1 manifolds,
are all highly developed for maximum air flow. And the intake system uses ducts behind the fender to draw in
cooler air from outside the engine compartment.
But the manufacturer made several compromises for noise reduction and cost reduction, so there is improvement to
K&N Drop In Air Filter Element
The K&N reusable cotton air filter element is a good investment for those planning to retain the stock filter
canister/box and piping. It provides a little flow improvement, and the significant advantage of being reusable
and much more durable than the factory paper filter. The cotton element is enclosed in a metal screen, to protect
it from damage and prevent anything large and heavy from getting past the filter element and into the manifold
and/or engine. The cotton element can be washed, dried, and re-iled to renew its filtering ability, and then reused.
Hot Air Intake Systems – A Bad Idea
Many of these are described as “Short Ram”. They place the filter between the battery and the brake master
cylinder or strut tower. Others are misrepresented as cold-air-intakes, but actually place the filter element
below the battery, and behind the radiator (such as
and Robie the Robot intake systems),
where it is still within the engine compartment, and still brings in only hot air.
These hot air intake systems represent a power loss when compared to the OEM intake system, which starts out as
a cold-air-intake, that takes in air through that plastic ducting which extends behind the fender.
Cold Air Intake
A true cold air-intake-system is made up of pipe, connected by flexible “turbo hose” type connectors, exiting
the engine compartment, and locating the filter element behind the bumper or fender, where it will draw in cool
air that has not been heated by the engine, the exhaust, or the radiator. Cool air makes more power. And the
extended length of the smooth walled and consistent diameter (cross sectional area) encourages a laminar air
flow effect, which improves flow and power.
Look for 3 inch diameter pipe with mandrel bends for the best flow.
Look for pipe with flared ends (similar to heater hose and radiator hose fittings), which will not slip loose due
to engine vibration and movement.
Chrome plating will help reflect radiated heat away from the intake air as it travels down the pipe through the
engine compartment. Aluminum should be avoided because it absorbs heat from the engine compartment and heats
the air passing through the pipe.
Look for a high quality air filter element, such as K&N. The filter will need to be cleaned every 6-12 months.
Cheap filters won’t last long, won’t flow well, or won’t protect the engine.
If the air filter element is located in the wheel well, a splash guard will be needed to keep the tire from
slinging water and filth onto the filter.
The Isuzuperformance Cold Air Intake System is the only system available that provides all of these features.
Oil Separator / Catch Can
For racing and high cornering speeds, an oil separator should be placed in the in the crankcase breather vent
line. This is the steel pipe between the valve cover (transmission end or flywheel end) and the rubber intake
accordion hose before the throttle body. This steel pipe will need to be replaced with a hose routed through
an oil separator. If a cold air intake is being used, the rigid vent pipe will already have been replaced with
a hose. The oil separator is needed because the intake camshaft slings oil onto the inside ceiling of the valve
cover, which then puddles on top of the baffle plate within the valve cover.
When the vehicle is taken into a high speed right hand turn, the oil puddle will move to the end of the valve
cover, through the breather pipe/hose, and into the intake hose/pipe. Any vapor or foam will be pulled into
the intake manifold. Some will be pulled directly into the engine (causing a gray puff of smoke from the exhaust).
The rest will coat the throttlebody and manifold and attract a layer of dirt and filth. Liquid oil will also
run down the intake hose/pipe, into the air filter canister or cone filter, and run out on the ground beneath
the vehicle. This can cause disqualification from autocross or road racing event due to an apparent “oil leak”.
An oil separator, or catch can, plumbed into the crankcase breather vent line, will prevent engine oil from being
sucked into the engine, or running out of the air filter canister.
A secondary benefit is that this will keep the inside of the intake manifold, the intake ports in the cylinder
head, and the backs of the intake valves, from being coated with dirt and gunk. For turbocharged engines, this
will also prevent oil from fouling the impeller and intercooler, which causes various problems, not the least
of which is reduced intercooler efficiency.
The throttlebody is a valve that controls air flow into the engine. With fuel injection, the gas pedal controls
the throttlebody opening and everything else is controlled by the computer system. The more air put into the
engine, the more gasoline the computer will add to match, and engine speed is increased.
The throttlebody represents a bottleneck in airflow. The DOHC/GSi throttlebody is about 2 1/8 inch in diameter
(the Base 12 Valve is slightly smaller). The throttlebody can be ported out to 2 5/16 inch in diameter,
providing a noticeable increase in upper range power.
Isuzuperformance was the first to port throttlebodies for Isuzu engines, developing the modification with RC
Engineering in the late 1980’s.
Intake Manifold Porting
The original intake manifold designs for both the Base 12-Valve and the DOHC engines is very good, and one of
the primary reasons that these engines have such high power-per-unit-of-displacement compared to other engines.
But some additional power can be found by enlarging and smoothing the internal passages within the manifolds.
The difference between the standard manifolds and the factory racing team manifolds, and later the fabled
“Type-Competition” manifolds of the Type-C Geminis, was a thorough de-burring and smoothing during the final
stage of production. Taking that one step further, with Extrudehoning, makes these manifolds will really
Isuzuperformance was the first to Extrudehone manifolds for Isuzu engines in the late 1980’s.
Phenolic Spacers – A Waste of Money
These are plastic spacers cut to the shape and pattern of gaskets, to be used between the throttle body and the
intake manifold, the between the upper and lower intake manifold halves, and/or between the lower intake manifold
and the cylinder head. The claim is that these pieces of plastic form an termal insulation barrier and prevent
heat transfer to the intake manifold and/or throttlebody. The truth is that these spacers are completely and
totally worthless. The factory gaskets between the throttlebody, manifold, and head, are non-metal, and do not
conduct heat. The heat transfer to the intake manifold and the throttlebody is via the bolts, nuts, and studs
which secure these pieces to the engine and the two brackets bolted between the cylinder head and the upper half
of the intake manifold. Heat is conducted through the metal of the threaded fasteners (nine in the manifold,
four in the throttlebody), from one piece of aluminum to the next, and through the manifold support brackets
(steel on the accessory end, aluminum on the flywheel end) which conduct heat directly from the cylinder head
to the upper manifold. Plastic spacers do nothing to prevent this from happening.
This is another of the pseudo performance products championed by and sold by
Robie the Robot.
© 2010-2014 StormOwners.Com. All Rights Reserved.
Click here to return to the Geo Storm Owners Page Tuning Index.