Simon McBeath

 

SB Developments built its reputation producing potent, reliable GM (Vauxhall/Opel) XE engines upgrades, especially in 2.0-litre guise. But latterly, demand and market shifts have seen the company take on the new clubmans' favourites, the Ford Duratec and the Suzuki Hayabusa. And SBD has been adding the benefits of some new technologies to its existing tuning expertise to tackle the task. The results are a new lease of life for the venerable GM units, and tractability and power from the Duratec and Hayabusa. Those latest engine developments began when some of SBD's GM XE rally customers in Northern Ireland wanted to know why the Duratec appeared to be so strong. 

 

So company principal Steve Broughton decided to start two parallel development programmes, one to see what more could be done with the XE, the other essentially to square up to the inevitable shift to the Duratec in club rallying, sprinting, hillclimbing and short oval racing. 'I wasn't to keen on the Duratec initially,' remarked Broughton, 'although in the mild state of tune we first tested it I couldn't believe how smooth and strong it was throughout the rev range. It was very tractable. We then did another upgrade, but this time with a little bit of cylinder head work and we easily produced 250bhp [all this work was one on the 2.0-litre variant], again with very smooth performance. We figured then that torque delivery was the key…'

 

 

STEVE BROUGHTON 

Former British Aerospace engineer Steve Broughton established SBD Motorsport in 1992. A club rally driver himself, he initially supplied parts but then moved into engine building and, after a fraught first six months, hasn't looked back. His early engines proved durable and strong, attracting attention outside rallying and, when a rally engine he built beat the works' Vauxhall Astras, business took off. Work for various UK teams was followed by a contract with Opel in Turkey involving rally and Touring Car engines, as well as developing the FIA-homologated 'Kit Car' kit for the Astra Mk3. However , the time spent arranging these works deals convinced him his heart lay with club motorsport, and the business now focuses on developing engine parts rather than engine building. A key aspect of this is proving products in its own competition cars, so Broughton's hillclimbing OMS is being used for Hayabusa development, while long time friend Dick Hulbert's SBD Westfield runs the development 2.0-litre Duratec. SBD also develops software for MBE engine management systems, for whom it is the main UK agent and engine mapping services occupy much of Broughton's time.  

 

THE GM XE 

So what to do with the old GM XE then? 'The engine was getting on a bit, so people were going to more extreme measures on parts. But with demand for more performance we had to see what was possible. The first thing was a two-ring slipper piston, which Omega helped us with. This had a raised crown enabling a higher compression ratio, although up to 1mm could be machined off if required. And the pin was higher up in the piston, too. The pistons alone released an extra 10bhp, partly due to reduced friction but also through reduced side thrust loads [which also gives very good wear characteristics].'

 

Around this time an ex-Formula 1 cylinder head design engineer approached SBD with some work he had done on an XE head. This had yielded an extra 25cfm of airflow across the valve lift range. Using old SBD 'hydraulic' camshaft profiles and standard valves this head developed 268bhp on an engine configuration whose previous best was 252bhp. Steve Broughton: 'So we started more work with this chap. Going up 2mm on valve size but using a stock valve with a standard diameter stem [so that other stock valvetrain parts could be used] he was achieving 155-156cfm at 12mm valve lift, where the standard XE head gave 120cfm. I'd never really gone much on flow bench work, and even now it doesn't seem to necessarily correlate with more power. But it this case certain areas such as the valve seats were being carefully relieved. and with the cams as they were we were getting more flow at high lift.

 

So we decided to develop new cams with 10 degrees shorter duration to flow better at lower rpm. To keep things affordable we decided to limit lift so exotic valve springs weren't needed. We then went to long time supplier and partner Kent Cams (see sidebar). In the past we have tried high lift, long duration cams but that's no good. And in this case we decided that mid-range was key so we came up with new profiles combining shorter duration with reasonable lift. As it happens we did have to obtain new, improved springs but they're not too costly. 

 

'We then went to Track N Road's rolling road in Essex, where a number of well know engine developers do their testing because it's an amazing, highly repeatable facility. We had also fitted some new fuel injectors, 'disc valve' – types from Siemans, which produce a very good fan pattern from two to 7bar. We'd have been happy with anything over 270bhp. As it turned out we got very impressive torque. I'd never seen anything like the torque plot before (see figure 1, Vauxhall TP290+bhp kit ). The engine pulled on full throttle from idle and we saw peak power at 292bhp. 

 

SBD was understandably very pleased with this result, which almost certainly surpassed what had been achieved in earlier years by the works GM Touring and rally cars. But as well as the new cams profiles and CNC head and inlet manifold work, the engine also utilised 35mm inlet and 31mm exhaust valves, with slim 7mm valve stems, steel conrods, slipper pistons, a lightweight steel crankshaft, dry sump lubrication and all the requisite high quality studs, bolts and bearings to keep it all safe. 

 

The company subsequently supplied a number of these kits to rallying customers in Northern Ireland. 'But we then started getting calls from Duratec owners who had spotted these fast XE-powered cars!'

 

 

CAMSHAFT DEVELOPMENT

SBD's chosen camshaft manufacturer is Kent Cams (www.kentcams.com). Steve Broughton, company principal at SBD, explained why: 'In the past there were limitations on how a profile could be shaped. Kent uses a Lotus Engineering licensed software package called Lotus Concept Valve Train (www.lesoft.co.uk) to assist with cam profile design. This tells you about velocity peaks and so on, and allows you to keep clear of high stress areas to avoid valve bounce, running off the buckets, stress that causes wear and so on. 'Coupled to that, Kent has invested heavily in the latest CNC equipment, much improved grindstones and so on. This offers fantastic repeatability (plus or minus two or three microns), and this really helps, especially where there is little adjustment available. And it saves cost.'

 

THE DURATEC

Steve Broughton's in it al reservations about the Duratec engine centred on the lubrication system and the hydraulic cam chain tensioner: 'The oil return has been a bit of a problem, so we did some modifications to overcome that. And we also developed a new cam tensioner, too. Subsequently, we have seen no oil pressure fluctuations and minimal wear.'

 

But the Duratec's well-known strengths include significantly lower weight than the XE (95kg compared to over 110kg), a fundamentally good head design and a larger bore size (87.5mm compared to 86mm). This, together with its pent roof combustion chamber design, allows decent size valves, the standard sizes being 35.5mm inlet and 29.9mm exhaust. So for 2007 SBD started out developing a strong, reliable Duratec, initially using the standard crankshaft but with steel conrods, 'pot type' pistons and bigger throttle bodies fitted with eight injectors, four upper and four lower for improved fuel dispersion. With what Steve Broughton called 'a sensible camshaft and just a little CNC head and port work' this produced 283bhp and 192lb.ft.

 

'Then,' continued Broughton, 'Ford produced a new head in the USA that allowed 10 per cent greater flow. We put in 1mm bigger valves and fitted this. And with no other changes at all, the engine produced 304bhp and 195lb.ft (see figure 2,Duratec TP300+bhp kit ). It pulled from 1000rpm on full throttle, it was smooth and there were no bottom end losses.' and this was still mild cams. Running with just four lower injectors only dropped the power by 10bhp, which was still impressive and ahead of the XE.

 

Given the efficacy of SBD's cam profiles on the GM unit, the logical next step was to apply this principle to the Duratec. So new cams were designed based on the shorter duration, high-lift ones that worked so well in the XE. To considerable consternation through, the result was 4bhp less and 10lb.ft less torque. Broughton: 'The engine peaked 300rpm later, made less torque from 4000rpm, and only made the power it did because it revved more. It shouldn't have suffered a loss with the increased lift though, suggesting the duration is just too short for this engine. The fact that it peaked later is odd too. And that's where we are now [in April 2008]. The next step is some slipper pistons with smaller valve pockets and cam profiles that will combine the original duration with the lift of the cam that didn't quite work.'

 

Having already produced a 2.0-litre engine generating over 300bhp is no mean achievement, and to publicly admit a backward step in development emphasizes Broughton's determination (and confidence) that yet more performance is still to be obtained from the Duratec.

 

THE HAYABUSA

'The thing with bike engines,' muses Broughton, 'is that they're highly tuned already. The standard 1300cc Suzuki Hayabusa produces 155-175bhp, depending on the year of manufacture. So it has taken a while to make good improvements, but a lot of what we have done carried over the work we did on the GM XE. The standard head is a better design than the XE – it has 33mm inlet valves and flows about 136cfm. However, we're now up to 155cfm at 1mm less valve lift than the XE uses. But it took us (ourselves initially, then our ex-F1 chap) two years to achieve all the improvements. We're using rather high valve lift, about 2mm more than most tuners.'

 

So, as well as applying the new-found techniques on headwork and cam profile design, what other modifications have these engines received? Broughton replies: 'I realised most bike engine tuners were doing similar things to each other, perhaps being somewhat conservative in areas such as cam lift, so I decided to develop it in my own way. With these engines it's about low weight, responsiveness and the way the power is delivered. And making power here means high rpm. So we've developed new, lighter con rods and again moved the gudgeon pin higher up to reduce side thrust, friction and wear. We've also had some special 'bridge' pistons made. Many tuners here buy pistons in from the USA, which are very cheap at £250 per set because of the current exchange rate, but they are actually heavier than the standard pistons. Ours are £850 a set, partly because the relatively low number we currently make means they are CNC machined from billet. However, they are made on the same machine as Moto GP race pistons, and they are lighter than the production pistons!' he exclaims.

 

This programme perhaps exemplifies SBD's attention to detail, and the effort has produced a remarkable 251bhp from the 1396cc version (see figure 3, Hayabusa 1396cc kit), representing 180bhp per litre. 'But,' say Broughton with his usual honesty, 'we haven't yet proved this for longer than hillclimbs so far.'

 

 

BEST SELLERS 

SBD carries a broad range of products for the GM XE, Ford Duratec and Suzuki Hayabusa engines, but company principal Steve Broughton reckons its best seller is ready-to-run fuel injection systems that come with pre-mapped MBE ECUs. Individuals, trade customers and racing schools have all bought such systems and, if required, Broughton will visit to carry out mapping refinements. Con rod and pistons kits are the number two best seller, and many go direct to the trade, especially when it involves product that others can't obtain reasonably quickly. Engine kits are available from throttle body upgrades to full race specification.

 

An impressive 292bhp and 197lb.ft of torque have now been coaxed out of the 2.0-litre GM XE…leading to its continued use in a wide variety of clubman disciplines, from sprinting to hillclimbing.  

As well as the works' Westfield, SBD Duratecs are also proving popular in singer-seater applications…as are the company's Hayabusa engines. Here a 1.6-litre version installed in an OMS hillclimb single seater.

 

Reproduced with permission of Racecar Engineering Magazine