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
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