Making it’s competition debut at the 2015 King of the Hammers, the Australian built OPW Ultra 10.4 was unveiled to the field as the first Ultra4 with fully independent suspension. While owner/driver Peter Antunac and navi Mal Van Ysseldyk got off to a good start at KOH in 2015, qualifying 26th, the teams efforts were hamstrung due to massive shipping delays impacting pre-race preparation, which forced their retirement after two laps.
Since then the OPW Ultra 10.4 returned to Australia and has gone on to dominate the King of the Hunter, the first official Ultra4 race in Australia and followed that up with victory at the Mad Max stage of the Outback Challenge. With twelve months of racing and development under their belt, Pete, Mal are the OPW team are now back on the Johnson Valley lakebed prepared for their 2016 KOH campaign.
We featured the OPW Ultra 10.4 in Edition 44 of Dirtcomp. Here’s a glimpse of the innovative design and engineering crafted in OPW’s Sydney workshop that lies beneath of the yellow and black panel work.
The chassis and cage is made from 2″ chromoly all precisely notched and tig welded together. The suspension arms are all hand fabricated from a combination of 3mm, 4mm and 6mm thick chromoly plate. Fox 10” coilovers hold the weight of the rig, while 12” travel Fox 5 tube bypass shocks soak up the bumps. Their mounting location allowing the rig to have 20” of wheel travel at each corner!
Clearance comes from the Hummer H1 portal boxes at the wheel end of the suspension arms. The portals allow for a gear reduction of 1.92 :1 in addition to the 3:1 ratios in the 9” diff centres. The locked centres are housed in a Dutchman IFS/IRS diff housing originally intended for Hot Rods and Drag cars.
While independent front suspension has been around for a few years in Ultra4 circles. The Independant rear design is what really sets the OPW Ultra10.4 apart from the rest. ‘With the live axle rear end Ultra 4 buggys, as soon as you bump something with the rear left, it will kick the whole car one way or the other, when they land again the suspension has to react, then settle again. With our car the IRS just seems to settle everything. Our car just doesn’t get kicked around at all. I love how you can just smash something in the back end, that wheel just pops up and the car keeps going straight, it’s smooth! ‘ said Pete
Suspension duties are left up to the 10” long FOX 2.5” coil overs and 12” travel FOX 3.5” – 5 tube bypass shocks. This equates to a massive 20 inches of travel at the wheels. Fox 2.0 hydraulic bump stops are the final safeguard against the desert whoops. Making a huge difference in the rocks is the rear steer, which allows Antunac to draw upon his Rock Crawling and Tuff Truck winning skill set to select lines that are not an option for other teams.
The engine itself is a 632 cubic inch V8 crate motor from the States, mated up to a seriously hardcore built Reid case Turbo 400 transmission and 4 speed Atlas transfer case. In high range the vehicle’s top speed is around the 180km/h mark. For the rocks, the low range ratios of 2:1, 2.72:1 and 5.44:1 give a huge amount of versatility. A Fast EFI Injection system is controlled by a Haltech ECU ensuring smooth delivery of power and an almost endless number of tuning and diagnostic options.
The Hummer portals allow for a central tyre inflation system, CTIS, to be used. This allows in cab control of the tyre pressures while on the go. The system in the OPW Ultra 10.4 is controlled by an electric solenoid air bag setup and allows individual tyre pressure control between 0 and 35psi, while Autometer Boost gauges monitor the pressure.
Hidden just under the front of the bonnet is the Gigglepin GP80 MK5 Series high mount winch. Built with 2 x Bow2 6.8HP motors, these winches are capable of pulling a 3 tonne truck at over 400ft per minute.
Internally, the vehicle is fitted with PRP suspension seats and 5 point harnesses, a PCI fresh air blower for helmet ventilation, a 10” Lowrance Rally GPS, radios, fire extinguishers, a first aid kit and harness cutters. Amongst all this there are a huge number of switches, buttons, levers and the rear steer joystick, making it busy behind the wheel.
Further developments since the shoot for the 2016 campaign include the addition of a front sway bar, Ultra Vision Lighting and a switch in rubber to 42″ BFGoodrich KR2 Tyres on 20″ Raceline Wheels.
With thousands of kilometres of testing under their belt and victories on the track back in Australia, Team OPW is back and ready to race. We at Dirtcomp wish Team OPW the best of luck in their 2016 King of Hammers campaign. Go hard!
Story by Chris Clark / Randall Kilner – Images by Randall Kilner