If you reckon you’ve seen everything there is to
see when it comes to Gen 3 modification, take a look at this – the magnificent
eight-throttle Harrop Hurricane manifold. This puppy is guaranteed to
drop jaws when you pop the bonnet!
The Stock Gen 3 Manifold – Why Replace
it?
According to Mark of Brisbane’s PowerTorque
workshop, the stock Gen 3 intake manifold is pretty good for a factory part –
but it does cause some restriction when you’ve done major work to the
engine.
Mark says a standard Gen 3 has about 3.5 kPa of
restriction through the factory manifold/throttle body at full power while a
typical cam and heads type upgrade has just over 4 kPa. A stroked Gen 3 making
serious power might see around 5 kPa restriction through the intake at full
noise.
At these outputs (about 400 – 500kW at the
flywheel) you will find substantial gains from upgrading the manifold
set-up.
The Harrop Hurricane Manifold
The Harrop Hurricane manifold offers abundant
induction airflow thanks to its eight throttle bodies (one for each cylinder)
and free-flow intake runners. It is quite likely the free-est flowing Gen 3
manifold on the market.
The Hurricane comprises three main parts – the
manifold with attached fuel rails, throttle bodies and the installation kit.
The Hurricane manifold is cast in-house by Harrop
using high-grade aluminium and comes heat-treated to enhance durability. The
manifold employs a runner length of around 50cm – a design that was derived
using Computational Fluid Dynamics (CFD) analysis software and drawing from
Harrop’s experience developing manifolds for race cars.
The manifold is also supplied with extruded fuel
rails which can accommodate whatever size injectors are required for the job.
Simply supply injectors and pressure regulator and you’re away.
There are two throttle diameters available – 52mm
and 55mm (the latter reserved for all-out applications). Each of the eight
throttles is opened by an elegant linkage system that features individual
throttle angle adjustment. This provides greater tuning flexibility in
situations where certain cylinders are running richer or leaner than others
(this can be an issue depending on airflow distribution into the throttles). The
throttle linkages are designed for use with the original throttle cable and
there’s a second cable facility to accommodate cruise control.
Interestingly, Harrop offers an optional
electronic throttle control system to suit late-model Gen 3s. Using a Hitachi
electric motor to drive the manifold’s front actuator shaft, it is possible to
retain the late-model factory management system and its throttle control logic.
Each throttle draws air through an individual
aluminium trumpet. The bell-mouth entry of each trumpet increases airflow into
the throttles and, depending on your preference, you can leave the trumpets
exposed under the bonnet for maximum visual impact. Alternatively, the trumpets
can be concealed in airboxes and connected to air filters that come in the
Harrop installation kit.
The installation kit is available as an extra-cost
option and comprises an airbox for each row of throttles, an inlet tray and twin
air filters.
The airboxes (which are moulded in fibreglass) are
designed to distribute airflow evenly into each throttle. The airboxes also
taper toward the rearmost throttles - we are told this taper enables space for
fitment into the US-spec Pontiac (Harrop expects the majority of consumer demand
to come from the States). The fibreglass airboxes are sealed against pressed
aluminium end plates that fit around each trumpet.
The airboxes are fed by 3 inch diameter inlets
that connect directly to a pair of pod air filters. These filters are a generic
brand as Harrop’s testing showed hardly any power difference using different
filter brands.
Airflow into the filters is channelled by a
fibreglass inlet tray that feeds cool air from over the top of the radiator.
Under-bonnet heat is kept away thanks to the inlet tray’s close fit against the
underside of the bonnet. But be aware that the inlet tray will rub the bonnet on
certain Gen 3 powered vehicles – we suggest contacting Harrop for details.
Bernie Robnick of Harrop explains that the
Hurricane manifold is a direct bolt-on replacement for all versions of the
LS1/LS2. The OE throttle position sensor is retained, an extension loom is used
to relocate the intake air temperature sensor and you are supplied with all
necessary vacuum fittings and brackets.
Bernie says the manifold can be used with either a
MAP or airflow meter load sensor. A MAP system is generally the most popular
choice and the appropriate MAP signal is sourced from a manifold fitting that
combines the vacuum from all cylinders. Alternatively, it is possible to use
twin airflow meters – one for each row of throttles.
Engine management is up to you - you’re free to
run a remapped standard ECU or switch to an aftermarket programmable system.
Cost and Benefit
There are two off-the-shelf configurations of the
Hurricane kit.
The base kit gives you the manifold, throttle
bodies, trumpets, fuel rails and all necessary installation hardware and comes
with a retail price of AUD$3800. However, if you include the installation kit
(comprising airboxes, twin air filters and an inlet tray) you’re looking at
AUD$4950. Electronic throttle control adds a further AUD$650.
Mark from PowerTorque says it’s typically a full
day of work to install the manifold and it’s another half day to perform the
extensive ECU tuning that’s required. This labour amounts to a bill of AUD$2000
(AUD$1000 for manifold fitment and AUD$1000 for tuning).
So what improvement do you get for your
AUD$6000-odd?
Well, the magnitude of the power gain depends very
much on the rest of the engine’s mechanical configuration – like we said, the
Hurricane manifold works best on engines having extensive modification. As a
guide, Mark says he typically sees 25 – 30kW extra at the flywheel which works
out to just below ten percent of the engine’s total power output. One 7.8-litre
example with a C5R block is making around 540kW...
But perhaps equally as important as the top-end
power gain is the smoother torque curve and massively improved throttle
response. And, of course, it’s impossible to ignore the rorty induction sound
and the stunning under-bonnet aesthetics.
It’s not a cheap upgrade when you include the
price of fitment and tuning, but if you’re building the ultimate Gen 3, the
Harrop Hurricane must be high on your list.
Contacts:
PowerTorque +61 7 3881 2379
Harrop +61 3 9474 0900
http://www.harrop.com.au
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