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Unless
you looked at last month's issue of Classic Ford with your eyes shut,
you'll have heard that SBD Motorsport has been doing rather special
things with the 2-litre Duratec motor, culminating in its latest 304bhp
creation. Not bad for 152 bhp-per-litre of naturally aspirated glory.
Since
initially taking a Duratec to the Autosport show two years ago, SBD
has been busy ploughing a lot of time, money and expertise into ensuring
it's the next generation of XE-beater. "We initially thought we'd
look into Duratecs about two years ago," says SBD gaffer Steve
Broughton. "I spoke to a guy in Holland who was making 280bhp,
albeit with reliability issues over the oil system and drivetrain. We
fixed or worked around all the problems until we'd developed something
suitable to replace them."
So,
with Steve understandably cagey about some of the finer details and
specifics - so would you if you'd put so much into developing a new
product to such a level! - whatdoes it take to make a 304 bhp naturally-aspirated
Duratec?
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Fuelling
This
is the main area where massive gains are made. "The size
and shape of the throttle body is key," says Steve, without
wanting togive away too many dark secrets. "Lots of people
use roller throttle bodies, but the problem with any barrel design
is that it has the tendency to stick if no filter is used (and
the questionable problem of reduced air intale if a filter is
used), and the barrels we tested also weren't as good on progression."
In
SBD's original design it encountered a few problems that it figured
out were down to the size of the throttle body. The throttle bodies
used by SBD are butterfly types, which give better progression
in this case and , as an added bonus, the air and fuel mix combines
even better as it tumbles off the butterfly.
The
Duratec requires an eight-injector set-up to make the headline
304bhp, with the same specification engine making 294bhp with
four injectors. As Steve say though, it's not about doubling the
amount of fuel going in to increase power: "the advantage
of a second set of injectors is to get the fuel to mix as soon
as possible," he explains, which is why the first set of
injectors are on the engine side of the butterfly, while the second
set are added above.
"Injectors
are used below the butterfly, as otherwise the fuel is just hitting
the butterfly when you crack the throttle open." Whereas
in this case the second set are only being called upon when it's
actually going to benefit the engine's fuelling.
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Strictly
speaking, the eight-injectors set-up's not an essential for a road car,
although if it's the 304 bhp you're after then it's the only way to
go!"Our eight-injector set-up was designed for Honda Touring Cars
in the '90s, and it tends to fade in and out of our systems - if we
can get away without using the second set altogether then even better,"
says Steve.
SBD
uses MBE management for all of its throttle body set-ups, with Steve
having worked on all manner of weird and wonderful creations, from Ferrari
F40s to Cossie Escorts.
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Head
Obviously,
headwork is vital to wringing every available horsepower out of
any engine, but it's also one of the standard Duratec's main strengths,
especially over the 2-litre Vauxhall XE. On a standard crank and
'pot' pistons, the Duratec can flow far more air than the XE,
with Steve claiming an achievable 283bhp on the standard valve
sizes.
While
the XE packs a 33mm inlet valve as standard, the Duratec boasts
35mm on the the inlet side, with room for expansion, too. Steve
reckons that once all componenets have been developed and taken
as far as they have with the XE, there'll be plenty more power
to come. All cams are developed in conjunction with Kent Cams,
with its new mega-bucks CNC machinery making advances easier and
ever more precise.
XE
cams are pretty much developed to their full potential, but Steve
believes there's more to come from the Duratec, which leads on
to one of SBD's next areas of development: the cam chain. While
a cam belt provides its own set of problems (snapping!), a chain
behaves differently under extreme loads. "From the work we've
done on the Hayabusa engine we've found all manufactureres use
high valve chain, which is fine if there's no massive valve lift,"
says Steve.
This
basically means that if you've got an extremely lairy set of cams
spnning at massive speeds, then they have the effect of trying
to push the chain off the pulley's teeth - not what you want when
dealing with extremes and minute adjustments in race conditions.
SBD has already made a manual cam chain tensioner as the hydraulic
ones were causing problems, but it's not stopping there; "We're
developing a roller chain for the next level of cams," says
Steve, which hopefully won't try and hop off the pulleys at extreme
revs.
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Block,
Pistons and Conrods
While
the stock Duratec crank is strong and good for big, reliable power,
SBD adds a keyway groove for durability and also provides steel cranks
for the optimum in race-bred reliability.
All
Duratec pistons SBD uses are lightweight 87.5mm Omega high-compression
pistons, although it's currently trying to develop this one step further,
giving a higher compression ratio but maintaining good valve-to-piston
clearance. "We alway try to maintain decent valve clearance, although
we're sticking to our stock piston for now," says Steve. "We
will then develop a slipper for the customer with a higher budget"
The
304 bhp Duratec's obviously dry-sumped too, with the standard engine's
oil circulation well and truly combated through developed galleries
and uprated pumps.
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SBD
Motorsport Ltd, Unit 15, Red Lion Business Park, Red Lion Road, Surbiton,
Surrey. KT6 7QD. Tel: 0208 391 0121.
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