Project HQ: Diff mechanicals

Project HQ may have some 'old school' flair, but there's some tricky tech lurking underneath in the diff mechanicals. Harrop Engineering is one of the companies that creates it

Diff mechanicals: Harrop Engineering

On the face of it, our mighty HQ project is a blast from the past: it dates back to the early seventies, has a pushrod bent eight in the snout, and pretty much everything is manual. However, it would be a mistake to dismiss it as a technology-free lump.

The basics may hark back to a different era, but there is some serious development and refinement sitting behind many of the components – as good an example as any is the diff, made by Harrop.

That name should sound familiar. It’s been in the motoring and motorsport business for a very long time and has made a significant contribution over the years, particularly to the development of the Touring Car/V8 supercar series.

Heath Moore, the General Manager of the company, takes up the story: “This year is our 60th anniversary – a significant milestone.

“The business has evolved dramatically since its inception with Len Harrop. Now we’re more diverse than we’ve been, in terms of product mix, capabilities and customers.” There are broadly three customer segments: their traditional performance arm, industrial component work, and original equipment for car makers such as Ford.

Performance equipment remains prominent. “The business changed hands in 2008 – Tim, Len’s grnadson, is still our Operations Manager.

“We’re still very strong in that area and it’s our bread and butter. But we also have an industrial segment, which isn’t the sexy cars but business-to-business transactions where people are coming to us to get precision components made. It’s been very successful for us. Medical, defence, rail and rolling stock, aerospace.

“We’ve also got OE work. We developed the superchargers on the XR8 and previously the FPV GT. We also work with Lotus cars in the UK.

“That all helps smooth out the volatility in the market.

“It has driven growth we otherwise wouldn’t have achieved if we had just focused on domestic business with a little bit of export performance components, plus aftermarket and motorsport work.

“Motorsport, with the company’s involvement in Touring Cars over the years, made up a big percentage of the business. We now develop components for street cars owned by enthusiasts who go to the track, rather than just professional race teams.

“Back then (15-or-so years ago) it was probably more semi-professional teams where a company like Harrop would help develop brake packages, drivelines and chassis tuning. Modern motorsport now is a big business in itself and those teams are very self-sufficient.

“We’re probably doing less motorsport specifically now but the product is still very much related to making cars go faster. We’re appealing to the enthusiast who might do a club day, rather than Holden Racing Team competing for a championship.

Some folk may remember the company’s central role in the ambitious Hunwick-Hallam and then Hunwick-Harrop motorcycles, which is now widely seen as being years ahead of its time. “If that program was active now, given how unique and innovative it was, I think the market would be all over it,” says Moore.

“There was strong interest at the time, but when the GFC came along…”

So, let’s get back to the HQ diff. “For the HQ project there was a nine-inch third member that was cast in our foundry. That’s actually an evolution of our supercar motorsport driveline, designed at Harrop, cast in our foundry and machined in the shop. The ring and pinion is sourced – we’re not gear-cutters – when you’re talking about Ford nine-inch there is a plethora of options in the aftermarket.

“The Truetrac (used in the diff) is essentially Eaton technology, but we’re the only company outside Eaton that’s allowed to manufacture product using their technology. The nine-inch has got an Eaton product in it – supplied by them. However the company designs and manufactures a Truetrac variant for several other applications, covering Ford, GM, and a variety of four-wheel drives.

“It’s been incredibly successful for Harrop to have that collaboration. Eaton technology is well proven, both for OE and aftermarket, plus military, so adapting it for the Australian market made sense.

“Truetrac is a mechanical limited slip diff – it doesn’t use clutch packs and I believe the nine-inch has ten pinion gears, so it’s incredibly strong.

It’s a torque-biasing (senses slip and transfers torque to the wheel with grip) LSD, so it doesn’t fully lock up, but it’s perfect for a streetcar that sees the track. Supercars use a spool, while NASCARs use a Detroit Locker.

So it should be more civilised to drive? “Very much so, it’s a fantastic compromise and if you have a high horsepower combination, it’s not going to burn out the clutch packs like a traditional LSD would. And that explains the popularity of them. These guys that have supercharged Commodores and Falcons and engine swaps for HQs and EHs, they’ll run a Truetrac because they’re nice and compliant on the road, it’s predictable, gets the power down and doesn’t wear out.

“If its powertrain or driveline related, that’s where we originaly specialised and that’s where we continue to invest R&D budget. Supercharger systems for global vehicle platforms are an area where we’re seeing growth and making a significant investment. We’ve traditionally developed supercharger kits for Commodores, going back to VT.”

Superchargers have long been a high-profile part of the business and remain a very important part of the performance mix. Harrop makes OE units for Ford, you’ll see their equipment on Lotus, and there’s a hugely popular aftermarket range for LS engines.

“Now you’ll see them for BMW M3, the Toyota 86 or Audi – vehicles that are sold all over the world and are performance oriented. While some of those vehicles are very expensive here and not sold in big volumes, in the US market an M3 is almost like buying a Holden Commodore and, like the enthusiasts here in Australia, they’re fanatical and passionate about spending money on making them go faster.

“The four-wheel-drive market is probably the stand-out where Harrop traditionally doesn’t have that reference. Our product is the E-locker, a selectable locking diff – we are flat-out producing them and the demand for them is growing. The business will continue to focus on the 4WD segment as much as the performance segment.”

The company also has its own workshop, though it has no intention of expanding this area of the business. “We have a performance centre we established because we had a lot of customers asking, “can I come to Harrops to have it fitted?” For many years we just focused on the manufacturing and reselling to the trade – it’s not a big part of the business, but there is a group of enthusiasts who love coming in, seeing the product manufactured and being fitted at the factory.

“In Melbourne we have a lot of trade customers who we supply and support – it’s a boutique fitment centre. It has a state of the art dynocell, two hoists and one technician. It’s good for product development, as you learn more about the different model iterations – it’s aided the R&D process.”

Harrop’s current product list includes oil coolers, radiators, intake manifolds, a new LS-focused camshaft program, plus diffs and a limited run of axles.

Look out for some upcoming events to celebrate the company’s 60th birthday.

The HQ Talent Pool

The line-up of magicians who’ve assisted with Project HQ is pretty extensive and represents a very handy list of suppliers you should consider if tackling a project yourself in future.

BENDIGO RETRO MUSCLE CARS
Bodywork
www.bendigoretro.com.au

RARE SPARES
Classic car parts
www.rarespares.net.au

PRECISION INTERNATIONAL
Engine
www.precisionintl.com/

MAL WOOD AUTOMOTIVE
Transmission
www.malwoodauto.com.au

TOP TORQUE
Engine machining and assembly
www.toptorque.com.au

MCDONALD BROTHERS RACING
Diff
www.mcdonaldbrosracing.com.au

HARROP ENGINEERING
Diff mechanicals
www.harrop.com.au

HOPPERS STOPPERS
Brakes
Ph: 03-9748 6950

ICE IGNITION
Ignition system
www.iceignition.com

DI FILIPPO PERFORMANCE EXHAUSTS
Exhaust system
www.darrendifilippo.com.au

DAVIES CRAIG
Water pump
www.daviescraig.com.au

AUSSIE DESERT COOLER
Radiator
www.aussiedesertcooloer.com.au