Words: Gareth Charlton Photos: Jamie Lipman

 

 

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! – what does it take to make a 304 bhp naturally-aspirated Duratec?

 

This is the main area where massive gains are made. "The size and shape of the throttle body is key," says Steve, without wanting to give 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 in take 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.  

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. 

 

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 components 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 manufacturers 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 spinning 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.

 

 

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 always 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.

 

Reproduced with permission from Classic Ford Magazine