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HMROID, a Plum Crazy blown-Hemi Challenger that’s out of this world

28 August 2015


Some things need no introduction, and when you can combine them all in one short and sweet statement, you know you’re onto a winner — so come and drool over this Plum Crazy blown Hemi Challenger with us


Walking into Rob Penman Motorsport is like walking into an automotive candy store — absolute wall-to-wall V8 heaven. And one of the first bits of V8 nirvana you see is the big, purple arse of HMROID poking out the door. And what an arse it is — those huge ET Streets are barely contained under the car’s bodywork. You have to wonder when you see tyres this big on a street car just what the hell it’s powered by. In this case, it’s a supercharged 498ci Hemi. Yeah, that’ll do it.

Mike had just put a fresh set of ETs on the back because the last set got down to the canvas — was that after one trip to the dairy or two? Tyre frying is something HMROID does without too much coaxing. We jumped into the car to go for a burst down the street. After all, Mike had to bed those new tyres in sometime.

Now, I’ve had a few hold on tight moments in cars, and I’ve even had some holy shit moments, but when Mike started this monster up, I had a holy shit, what can I hold onto? moment. When Mike hits the start button, all conversation ceases. ‘Loud’ doesn’t even begin to describe the sound erupting from underneath this beast — 498ci of supercharged Hemi exiting through dump pipes right under my butt. My teeth were chattering, my vision got fuzzy and all I could do was laugh. I look across the car and Mike has this huge grin on his face. Somebody said, “Take it easy on him Mike” as we got in, so that grin on Mike’s face had me worried.

We got out onto a private road, cruised forward to a certain point, paused, then nailed it. The tail steps out, those new tyres start laying down a rubber carpet on the road, and we launch forward — producing an engine noise that would have rivalled that of a Boeing 747 on take-off. We got down to the end of the street and Mike turned the monster around. As I look up the street in front of us, I see people hauling their kids out of their houses and lining up on the side of the road. There was a guy who had stopped his car, had got out to watch, he was giving Mike the wheel spin gesture. This car has that kind of presence, it makes people stop dead in their tracks to watch it go by. Not one to disappoint a crowd, Mike nailed it again, and all I could do was laugh.

Barry Keach is the reason HMROID exists. Barry, Grant May, and Alan Stacy built it back in the ’90s. Barry wanted a hardcore Pro Street car that would see plenty of drag strip action. Back when Barry owned it, it was peach-coloured with a massive scoop on the bonnet. It had very little in the way of an interior, all stripped out and ready to race.

When Mike bought HMROID back in 2003, his vision was clear, he could see through the peach paint job and bonnet scoop to realise that here lurked a wicked Pro Street car. The first thing to happen was the removal of the Harwood fibreglass scoop from the bonnet, flicked off at a swap meet for $20. The car then went to the colour doctors. In the first week of ownership, HMROID went to see Paul Taylor at Accurate Panelbeaters for a respray. Mike got Paul to paint it with an original ’70s colour called ‘Plum Crazy’, so the car remains a fruit, though it’s now a plum, not a peach. HMROID had seen some hard years of drag racing when Mike got hold of it — that engine has seen some money poured into it. When Barry owned the vehicle, it was estimated that the engine was worth twice as much as the car. I’d hate to think what it owes Mike now.

The block started out as a 426ci Hemi, with a 60-thou overbore and a stroker crank. But now it’s a solid-mounted 498ci Hemi. When Mike got it, a Scat crank was ordered from the USA, which took four months to arrive and cost moonbeams. But when it eventually arrived, it turned out to be the wrong one, so he ordered another one — cue another four month wait. To bring it up to weight for the massive rods and pistons, it had to have a whole lot of Mallory metal added to it, work that was undertaken by Peter Farrant of Auckland Balance in Glenfield. It’s kept its Nascar rods and Arias pistons and rings. The pistons come in at one kilo each, as do the Nascar rods — heavy bastards.

The domes were cut off the top of the pistons to lower the compression for the blower. Making sure there is plenty of lubricant pouring through the engine is a Milodon external oil pump. The top end of the motor is similarly laced with beastly internals. There is a Crower cam pushing Isky pushrods up to Crower roller rockers. The cam is kept spinning thanks to a Keith Black gear drive. It took three days to set the gear drive up correctly, but it hasn’t given a jot of trouble since. Manley monster duty stainless steel valves are kept in place and bouncing up and down by a set of Crower double valve springs. The whole lot is kept together with a Milodon stud kit. All of that lovely valve gear is housed in a set of Mopar cast iron performance heads. So, as you can see, this engine doesn’t pretend to be high tech — no, its just super heavy duty. Old-fashioned power the hard and heavy way.

On top of the engine you will find an Al’s Blower Drive scoop sitting on top of a couple of 1150cfm Dominators, which have been fitted with Mark Segedin metering plates. And that’s a 6-71 Mooneyham blower driven by an Al’s Blower Drive drive kit. Mike has just replaced the top drive cog to increase the blower from 15 per cent over-driven to 25 per cent over-driven. Fuel is provided to this thirsty set up by a Barry Grant fuel pump and distribution system package. One full pump on the accelerator pedal in this honey delivers 200ml of fuel to the carbs.

The fuel cell is nestled between the huge tubs in the boot. Avgas is the only fuel that ever goes in the tank, and with this much fuel being fed into the engine, it needs a bloody huge spark to get it firing. All of the ignition is handled by an MSD setup that delivers enough spark to send you straight to heaven. An MSD dizzy feeds 12mm Mallory leads that send the spark to NGK Race spark plugs. There is no room in the engine bay for the battery, so that has been relocated to the boot. Exhaust is shoved out through a set of Hooker two-inch Super Comp headers. A huge thanks go to Rob and his crew at Rob Penman Motorsport for all of the hours that have been spent getting this engine to where it is.

When Mike bought the car, it had already had a custom half chassis made up from two-inch box section that tied into the eight-point roll cage. When Mike axed the Harwood scoop off the lid, he also took a spoiler off the boot — he wanted HMROID to look as close to street as possible. An original T/A Challenger spoiler adorns the boot, with a T/A air dam bookending the Challenger at the front. Logan Rooke of Logan Signs made up the graphics down the sides of the beast. Take a good hard look at the curve of the guard over the rear tyres. Notice that flat spot at the top — the wheel arch had to be lengthened by four inches just to fit those massive tyres.

Those rear tyres are a pair of enormous Mickey Thompson ET Streets measuring 33×18.5×15 inches, and they’re wrapped around a set of equally large 15×15-inch Centreline rims. HMROID still manages to light them up as though they’re just skinny little bits of rubber. Of course, for such a monstrous motor to make such serious rubber the weak link in the torque’s journey from crankshaft to road, a suitable heavy-duty drivetrain is required — and naturally HMROID’s got that too. The transmission is a TorqueFlite 727 fitted with a Fairbanks reverse shifter, with the stick on the shifter made from solid billet, designed to look just like the four-speed original.

The trans is running an A1 converter at a 2800 stall with an A1 manual valve body. Out the back, handling the huge torque and power set through from the trans, is a narrowed factory Dana 60 PosiTraction diff running a 4.11:1 ratio with Strange axles. This mountain of an engine is pumping out 726hp at the rear wheels, and it hasn’t even been tuned properly yet! Stopping this show are the standard factory brakes with a proportioning valve for burnout time. Mike assures me they are more than up to the job, but I reckon Mike’s just got nerves of steel. The front suspension is standard, with a factory heavy-duty roll bar and Koni adjustable shocks, and the rear features a custom made four-link set up, again with Koni adjustable shocks.

On the inside, HMROID has received lots of attention. Mike made up all of the carpets, fitted the door panels back in, and put the centre console back around the shifter. The dashboard was custom-made and is full of Auto Meter Sport Comp gauges, with that huge Auto Meter Pro Comp tacho mounted on the dash. But there’s no stereo — Mike prefers the blown Hemi soundtrack, and at full throttle this mad child would drown out most stereos anyway.

Does it end here for HMROID? Not bloody likely. While Mike is still breathing, there will always be plans afoot. It hasn’t received its tune up yet, but still develops 726hp at the rear wheels.

So what has it given back to Mike? His best quarter so far is a 10.0 flat, and that was with a tired motor. With another 100hp and more on the way after tuning, God only knows how far down into the nines it’ll be, and I’ll be watching closely to see how it turns out.

Words: Lachlan Chambers
Photos: Sean Craig

1971 Dodge Challenger

  • Engine: 498ci Hemi, 426 Hemi block, 0.060-inch overbore, solid mounts, Kellogg steel crankshaft, Nascar rods, Arias forged pistons, Crower Cam, Isky pushrods, Crower roller rockers, Manley stainless steel valves, Crower double valve springs, Mopar ported cast iron heads, Keith Black gear drive, Milodon oil pump, Milodon stud kit, Al’s Blower Drives scoop, twin 1150cfm Holley Dominator carbs, Mooneyham 6-71 supercharger, Cragar intake manifold, Barry Grant fuel pump, Barry Grant fuel system, Hooker Super Comp two-inch headers, MSD ignition, MSD distributor, Mallory 12mm leads, NGK Race spark plugs
  • Drivetrain: TorqueFlite 727, A1 manual valve body, A1 2800rpm stall converter, Fairbanks reverse shifter, Dana 60 diff, shortened housing, 4.11:1 final drive ratio, PosiTraction LSD head, Strange axles
  • Suspension: Factory front suspension, Koni adjustable shocks, heavy-duty sway bar, custom rear four-link
  • Wheels/tyres: 15×7- and 15×15-inch Centreline Convo Pros, 205/65R15 Yokohama front tyres, 33×18.5×15 Mickey Thompson ET Streets
  • Performance: 726hp (at the wheels, awaiting tune)