Hyper-Gas Hemi

This article was first published in October 1998.

T04-equipped and running straight LP-gas, this six-pack Val's ready to unleash its tyre power of 280kW (375hp) down your street! But you'd never tell by just looking at it......

Colin Townsend is the man responsible for one of the most awarded modified vehicles in Australia - his immaculate black quad-Weber'd FJ Holden. So it's no great shock to see his family's second car is something also quite out of the ordinary. That wasn't the original idea though; Colin's a Holden man through-and-through and he thought that big gold Val in the driveway would never catch his creative attention. Oh well, we all make mistakes...

The 1970 VG Valiant you're seeing here was actually the first model to come to Australia factory-fitted with the famous Hemi engine. It is also the last of that body shape, which often fools people into thinking it's got the old 'slant' engine under the long bonnet. For our American audience, the car is based on the Dodge Dart of the same era with only minor differences dividing the two.

Recognising the Hemi six as a hugely underrated mill, Colin set off on a mechanical path completely different to the one he adopted for his famous Holden. Even so, the boosted LP-gas fed Hemi churns out an easy (very easy) 280kW (375hp) at the wheels! Looking at the dyno graph, his comments about a sticky wastegate are obvious; look at that spike! Despite this, the car is very progressive on the road - it's damn strong from around 2000rpm right up to the conservative 5000rpm limit. There's massive grunt absolutely everywhere!

Colin kicked it all off by purchasing a 265ci (4.3litre) engine someone else had built to 'turbo specifications'. This sheltered forged Venolia forged pistons that provide a static CR of 7.5:1, a linished/peened and cleaned up crankshaft, and a collection of 6-Pack conrods. ARP rod bolts, full-floating tapered gudgeon pins and a 6 Pack harmonic balancer were also fitted for increased engine longevity.

An early-model 245ci (4 litre) Hemi cylinder head was fitted to the block to bump the CR up a bit, since the high-octane LP gas would help cure any detonation problems. Then a Crow 'turbo' cam was inserted along with 360ci (5.9 litre) V8 valves and Crane HD valve springs. The head was also cleaned up and fastened to the block with the standard Chrysler head studs. Colin tested these prior to fitting the head and says they can be torqued-up quite a lot before waving the white flag. Copper cylinder head and intake manifold gaskets have been fabricated and fitted to endure boosted turbo conditions.

A single stage belt-driven oil pump drinks from a wet sump that contains three 'gates'- these are effectively baffles to prevent surge. A Mazda RX7 oil cooler is also mounted low at the front of the car, while extra water cooling capacity came in the form of an ex-360ci Chrysler radiator.

Capitalising on the strength of the Valiant's cast engine parts, Colin has left the standard exhaust manifold bolted to the head but has given it some minor modification to suit. This meant removing the factory 'hot box' and adding a flexible section of pipe to cope with temperature induced expansion. The result works just as well as any fabricated system but is much simpler in design (and is cheaper!).

In keeping with the car's street-driven theme, a relatively small T04 (P-Trim we think) turbo size has been chosen, enabling maximum boost to be reached by 2500rpm. However, its efficiency drops off at around 5500rpm. A clever boost switch on the gear stick enables boost to be increased from 14psi to a substantial 20psi as required. Colin stresses that 'low boost' is always selected for street use to help comply with local laws.

A 42mm Garrett external wastegate bypasses the turbo and merges into a 2½ inch collector pipe. The exhaust then branches out into twin 2¼ inch pipes with dual straight-though mufflers. Once again the car is perfectly suited to daily driving with its relative quietness. All of the turbo system and exhaust pipes have been HPC ceramic coated and while Colin admits the $A1,000 isn't cheap, he says that it's worth every cent. He swears there are dramatically reduced under bonnet temps and a definite power improvement.

The warm, compressed air from the turbo passes through mandrel plumbing into an ex-Mitsubishi air-to-air intercooler sitting in front of the radiator. It's here we saw a gadget that had us totally floored. The trick system uses a wastegate actuator, an arrangement of levers and some simple pneumatic components. The assembly is bolted to the front numberplate. Whenever the engine's on boost, the plate slides down about 8cm allowing air to pass freely through the intercooler core! But we were intrigued with the notion of making the plate disappear whenever the car came on boost......

Colin also took a different route when it comes to blow-off valves; he hasn't got one. Instead, there's a large diameter butterfly at the mouth of the compressor inlet that opens and closes as the engine throttle butterfly moves. Careful adjustment has enabled boost to rise instantly after gear changes.

Wanting something different, Colin installed a gas induction system that is ideally suited to the turbo application. Here in Oz, our fuel ratings are quite poor when compared to some countries, so he opted for LP gas which has a minimum octane rating of around 100RON no matter what the source.

Using a standard Holley 4-barrel flange pattern, an Impco 425 gas carb was fitted to the standard intake manifold - which required minor mods to convert it to 4-barrel configuration. Relatively minor alteration to some of the plumbing and passages inside the carb was performed to enable boost pressure to be tolerated. The Impco combines with a Model E converter. Because the car runs on LP gas 100% of the time, all the original fuel lines, filler and tank have been discarded to shed some weight.

Spark is delivered using a re-graphed dizzy which has 10 degrees centrifugal advance and 14 degrees initial advance (plus vacuum). The otherwise standard ignition also uses a Mallory high-energy coil for a guaranteed spark.

Ford's built-tuff Top Loader gearbox handles the elephant-like torque from the engine's steel flywheel and gets prodded by a quick-shifting Hurst shifter. A strong 1727kg (3800lb) clamping pressure plate nails the 5-paddle Kevlar clutch plate hard against the flywheel to prevent slip. A "nice and thick" 3½ inch diameter Chrysler by Chrysler ('C by C' is easier!) tailshaft now runs below the car after being shortened to suit.

The 'Unbelievable Reliability' award must go to the poor C by C diff out the back that has endured 20,000kays (12,430miles) of hard turbo driving. Sporting the standard 2.77:1 ratio, the car can still pull cleanly off the line with the engine's massive torque combining with the tall gears to really run rampant in the top-end. At present the diff centre is open but Colin's dead keen on getting an LSD soon.

Very similar in style to Chrysler-released optional wheels, the 14 inch polished Magnum rims wear Toyo tyres all 'round; 215/60s at the front and 235/60s at the rear.

Colin has added extra bracing to the front end as well as quite heavy gauge bracing from the front through to the rear suspension, effectively making a full chassis. Colin jokes that the rule that a stiff chassis improves handling probably doesn't apply to the Val; she's a bit old in the suspension area! Pacer front torsion-bar suspension is bolted under the nose with a tailored-to-fit CM model Chrysler swaybar also in place. The rear 'sproings' have had an extra leaf added and an aftermarket swaybar stops the rear from leaning over.

The vague original re-circulating-ball steering has been banished in favour of an early Commodore rack-and-pinion setup. While this conversion sounds like an impossible dream, Colin suggested it was fairly easy since the rack was about the right length. The steering mod is just another superb detail so easily overlooked in this car.

Slowing the 1560kg (3432lb) car are vented discs (about 11 inches in diameter) with matched single-pot calipers at the front and finned Pacer drums at the back. This system is good for about 2 heavy stops; after that, be careful.

The elderly body was respayed in what was supposed to be a match of the original colour, but no matter, the new shade actually looks better.... It was just before the respray that Colin noticed some fatigue lines (ie cracks!) appearing on the A-pillars - a result of the Hemi's stupendous torque!

Ahh, like we said before - there's just so much grunt...

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