What will throt­tle bod­ies give your Porsche? Well, if it’s an air-cooled 911, 964 or 993, then about an ex­tra 25bhp of pure bolt on power, more when com­bined with other mods. We get the low­down from AT Power Throt­tles and its in­ge­nious ‘shaft­less throt­tle

911 Porsche World - - Practical Porsche -

They’re a mod­est bunch over at AT Power Throt­tles in Wy­mond­ham, Nor­folk. Not prone to blow­ing their own trum­pets, de­spite man­u­fac­tur­ing quite a few of them. But the team at AT does have some good tales to tell: you just have to work long and hard to prise them free.

One such tale re­lates back to when the cur­rent own­ers bought the com­pany from the ad­min­is­tra­tors five years ago. There had been ‘is­sues’ con­cern­ing some of the prod­ucts sold by AT in its pre­vi­ous guise, but rather than just draw­ing a dis­creet veil over prob­lems that weren’t in any way their re­spon­si­bil­ity, the new AT team con­tacted all dis­grun­tled cus­tomers. Of­fered to fix and im­prove the af­fected com­po­nents. For free. ‘It cost us a six-fig­ure sum,’ ad­mits AT’S Busi­ness De­vel­op­ment Man­ager, Paul Knapp, ‘but it meant that we could get on with turn­ing around the com­pany with­out a back­ground of ill-feel­ing. We could ring cus­tomers up and they would be happy to hear from us, be­cause they knew we were han­dling their is­sues.’

As a con­se­quence of the team’s ret­i­cence to self-pro­mote, many of us will never have heard of AT Power. ‘In the sim­plest pos­si­ble terms,’ ex­plains Ben Clifton, tech­ni­cal sales man­ager, ‘what we do is to make peo­ple’s cars go faster.’ More specif­i­cally, though, the firm de­signs, tests and man­u­fac­tures throt­tle bod­ies and other throt­tle as­sem­blies and all their an­cil­lary com­po­nents, oil pumps and dry sumps, pri­mar­ily for mo­tor­sport ap­pli­ca­tions but also for the per­for­mance tun­ing mar­ket. And while AT Power is Uk-based, it sells its prod­ucts to a global au­di­ence.

The piece of tech­nol­ogy of which AT is proud­est – and has won awards for – is its ‘shaft­less throt­tle’ in­side its throt­tle bod­ies, claimed to achieve an ex­tra 25bhp when used on air-cooled 911, 964 and 993 flat-six mo­tors. Throt­tle body set­ups use a but­ter­fly valve in­side the trum­pet to vary the amount of air en­ter­ing the cylin­ders; typ­i­cally, this but­ter­fly is mounted on a shaft or spin­dle, and is held in place by a cou­ple of screws. When the but­ter­fly is fully open, at full throt­tle, the shaft and screws pro­trude from the sur­face of the but­ter­fly, ob­struct­ing and dis­rupt­ing the flow of air past it.

AT’S but­ter­fly isn’t mounted to a shaft and so doesn’t need screws. In­stead it piv­ots around lobes that slot di­rectly into the walls of the trum­pet’s bore, leav­ing the sur­face of the but­ter­fly free of im­ped­i­ments to clean air­flow. In the full throt­tle po­si­tion – that is, when the but­ter­fly is sit­ting ver­ti­cally in­side the bore for max­i­mum in­take of air – the

but­ter­fly presents a sharp, aero­dy­nam­i­cally shaped edge to the in­com­ing gale, fur­ther pro­mot­ing speed of air­flow. AT claims that in tests its shaft­less but­ter­fly al­lows 99.5% as much air­flow as hav­ing no but­ter­fly at all, and that com­pared with tra­di­tional set­ups its sys­tem im­proves air­flow by up to 15% on com­mon throt­tle body sizes. And, of course, the higher the air­flow’s ve­loc­ity, the greater the vol­u­met­ric ef­fi­ciency, lead­ing to more power and torque.

AT Power de­signs and man­u­fac­tures most of its com­po­nents and as­sem­blies on­site, much of them from bil­let alu­minium, in­clud­ing its fuel rails. As Ben ex­plains, it’s all about keep­ing a tight rein on qual­ity, and dot­ted around the work sta­tions are posters re­in­forc­ing the mes­sage to keep stan­dards high and to con­stantly check that the job’s be­ing done prop­erly. Ad­mit­tedly it’s only a sub­jec­tive mea­sure, but if you pick up any in­di­vid­ual com­po­nent or ac­ti­vate, say, a throt­tle link­age, then you can feel the pre­ci­sion and crafts­man­ship that has gone into them.

Part of the qual­ity process in­volves test­ing in­di­vid­ual as­sem­blies, which is done in-house. Oil pumps, for in­stance, are run for many hours at a time in­side a spe­cial­ly­de­signed test booth, to en­sure they func­tion as they should un­der load. And ev­ery cus­tomer is pro­vided with a Test Flow Data Sheet so they can see ex­actly how their oil pump per­formed. AT is big on that kind of trans­parency, and dur­ing throt­tle body builds, for in­stance, will pho­to­graph ev­ery stage of the con­struc­tion pro­ce­dure. One highly re­spected rally en­gine builder even in­sists on Gopro footage of its throt­tle bod­ies in build, which AT is more than happy to sup­ply.

‘We’re also very con­scious of the fact that while we can test for many things in­side our work­shop, we don’t have the fa­cil­ity here to de­ter­mine long-term dura­bil­ity,’ says Ben. ‘So, for a cer­tain sys­tem we’re de­vel­op­ing for high per­for­mance Honda en­gines, we se­lected 25 of the coun­try’s top Honda racing and tun­ing out­fits, pro­vided the kit at cost, and let them use it in real world con­di­tions for a spe­cific pe­riod of time. We then re­trieved the kit, an­a­lysed it, im­proved it, and re­turned it. We re­peated that process three times, and while it’s time con­sum­ing and ex­pen­sive, from our per­spec­tive it’s a very worth­while in­vest­ment.’

On-site AT Power has both five-axis and three-axis milling ma­chines: it’s mes­meris­ing to watch the process of a block of alu­minium be­ing ac­cu­rately drilled and carved and shaved, amidst a cloud of

AT Power de­signs and man­u­fac­tures most of its com­po­nents on site

lu­bri­cant and shiny swarf, and then a com­plex com­po­nent emerges when the doors on the ma­chine open at the end of the process. Amongst myr­iad other op­er­a­tions that can be un­der­taken in­side AT’S in­dus­trial unit, there’s gal­vanis­ing equip­ment, a spray booth, and a ma­chine for mak­ing small in­jec­tion moulded plas­tic parts. An­o­dis­ing, how­ever, is out­sourced.

‘I think we tried just about ev­ery an­o­dis­ing com­pany in Bri­tain,’ re­veals Ben, and the out­fit we’ve ended up with is first­class. Ob­vi­ously an­o­dis­ing is purely for cos­met­ics, but we had to en­sure that it matches the high stan­dards of our hard­ware. Be­cause we work on a com­par­a­tively mod­est scale, we can be very flex­i­ble to­wards a cus­tomer’s spe­cial re­quire­ments – they can or­der sin­gle-colour an­o­dis­ing, multi-colours, or just an­odise par­tic­u­lar parts of the throt­tle body assem­bly.’

It’s not only with colours that AT Power can per­son­alise its of­fer­ings. ‘We work closely with en­gine tuners, mo­tor­sport out­fits and pri­vate in­di­vid­u­als to pro­vide ex­actly what it is that they need: we can de­sign sys­tems from scratch to achieve very spe­cific out­comes,’ says Ben. ‘That can mean, for ex­am­ple, pick­ing an in­let pipe length ap­pro­pri­ate to the type of driv­ing you do in your Porsche 911 – you might spend most of your time on the race track and want plenty of top end power, or maybe you want more mid-range torque for com­fort­able long-dis­tance tour­ing – through to cal­i­brat­ing a drive-by-wire throt­tle ac­tu­a­tor to com­ple­ment the af­ter­mar­ket ECU that’s fit­ted to your tur­bocharged Ja­panese mon­ster. Even our oil pumps fea­ture an in­te­grated ad­justable pres­sure re­lief valve that the cus­tomer can use to suit their spe­cific pres­sure and flow re­quire­ments.’

And there’s a va­ri­ety of throt­tle types to choose from, too. AT’S di­rect-to-head throt­tle bod­ies are not only port matched to suit in­di­vid­ual en­gines, they can also be spec­i­fied with in­di­vid­u­ally sized but­ter­flies for each in­let port, as well as a num­ber of

We can de­sign sys­tems from scratch to achieve very spe­cific out­comes

link­age op­tions and a choice of throt­tle po­si­tion sen­sors (TPSS). The com­pany’s range of univer­sal throt­tles can be sup­plied in di­rect-to-head con­fig­u­ra­tion, but can also be di­rectly mounted to a cus­tomer’s ex­ist­ing in­take man­i­fold. Both types of throt­tle body can be con­trolled us­ing AT’S drive-by-wire elec­tronic throt­tle ac­tu­a­tor.

There are also di­rect re­place­ment shaft­less big bore throt­tle kits that are a rel­a­tively sim­ple plug-and-play DIY in­stal­la­tion job, and drive-by-wire sin­gle throt­tles to com­ple­ment af­ter­mar­ket ECUS. And – again fea­tur­ing a shaft­less but­ter­fly – there are com­pact sin­gle throt­tle bod­ies pri­mar­ily aimed at su­per­charged and tur­bocharged ap­pli­ca­tions, but which work equally well on nat­u­rally as­pi­rated en­gines.

Parked to one side in AT’S work­shop is a wind­screen-less buggy, the only whole ve­hi­cle on the premises. ‘That be­longs to Chris Gold­spink, one of the com­pany’s di­rec­tors,’ re­marks Ben with a smile. ‘He’s been build­ing it as an af­ter-hours project, and as a sort of a chal­lenge. It was orig­i­nally pow­ered by a su­per­bike en­gine, but he swapped that for a 1 KRFE three­cylin­der unit from a Toy­ota Aygo, fit­ted with one of our throt­tle bod­ies and dry sump kits, that helps it pro­duce about 87bhp.

‘When Chris dis­cov­ered that there were no off-the-shelf brake caliper so­lu­tions to fit the buggy he went away to re­search how calipers are constructed, and then de­signed and man­u­fac­tured his own. It’s in­dica­tive of the way we ap­proach ev­ery­thing around here – when con­fronted with an ob­sta­cle, we find the very best so­lu­tion to over­come it.

‘Be­cause while we all ob­vi­ously want AT Power to be a com­mer­cial suc­cess, what re­ally mo­ti­vates us is a pas­sion for high qual­ity engi­neer­ing for high­per­for­mance ve­hi­cles – and that in­cludes drag bikes, bike en­gines for kit cars, sin­gle­seater race cars and even jet skis. We’re at our hap­pi­est when our cus­tomers are go­ing faster.’ PW

Di­rect to head throt­tle bod­ies can be matched to port size

A work of engi­neer­ing art and de­sign. Imag­ine a set of these perched on top of your air-cooled, flat­six mo­tor

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