PLENTY of us have memories of the Chrysler Sigma, one of Australia’s most popular family cars of the 1980s. But it’s not often you read ‘Sigma’ and ‘performance’ in the one sentence.

That’s not to say you can’t bulk them up though, as Jason Waye’s LS1-powered ’81 GH shows. The blue four-door packs a cammed 350rwhp LS1 and ran a PB of 11.8 at Drag Challenge 2019, yet it has also been through all the engineering hoops to be street-legal in Jason’s hometown of Adelaide!

The car turned out so well because Jason runs Tuff Mounts, a company specialising in fitting the right engines into the wrong cars. After his Barra-powered Fox-body Mustang wasn’t going to be ready for the Haltech Radial Blown class at DC19, he built the Sigma to tackle the new 235 Aspirated class that Tuff Mounts sponsors.

“It was dying to be done!” chuckles Jason. “I saw a Sigma when I attended Drag Challenge Weekend in Queensland and I thought, what a great idea!”

The build began in late June, after Jason found his Sigma in Victoria with the Astron four-pot already swapped for a carby Holden V8 and Trimatic. Jason disassembled the ex-Statesman LS1 to have the heads cleaned and serviced with new springs and stem seals, while a VCM 710 cam and oil pump kit were also installed. He then made it all fit in the Mitsubishi engine bay and tuned up the unlocked PCM to make 350rwhp.

The 4L60E four-speed autos aren’t known for strength under pressure, so Jason rebuilt his with upgraded clutches, bearings and valvebody. “Done properly, these are a reasonable trans,” Jason reckons. “I wanted one because it needed to be a road car for Drag Challenge – not just for down the strip.”

The JRM Transmissions-built ’box runs an AK 3600rpm converter, while the rear axle is a narrowed ex-Commodore BorgWarner that was already there.

“It already had a lot of the stuff we needed,” says Jason of his bargain buy. “Buying it like that [with a V8 swap] didn’t make the engine transplant any easier, but it saved us time and some money, as it already had a tougher transplanted diff in it and bigger V8-spec VR Commodore brakes.”

Once the Sigma had been through its shakedown process, Jason got it passed through engineering to be street-legal in South Australia, then hitched up the trailer and hit the road to Melbourne. Jason and co-driver Perry Martin opened their week with a 12.8 on Day One as they learned the car, knocked out a best of 7.73@87mph over the Mildura eighth-mile on Day Three, and set a PB of 11.84@113mph on Day Five back at Calder.

Jason and Perry hung around in Melbourne for a couple of extra days after Drag Challenge to run the Sig in the first Aussie Optima Search For The Ultimate Street Car event, which involved two types of motorkhana challenges, a run up the Calder strip and a couple of laps of the circuit.

“I’ve followed the Optima challenge since they kicked off in 2008 [in the USA],” Jason explains. “When I heard it was coming to Australia and it was going to be held at Calder the day after Drag Challenge wrapped up, I had to extend my trip a couple of days.”

Despite the Sigma not being optimally set up for hard cornering, Jason managed to finish third in the Vintage class behind far more circuit-oriented cars.

Now that DC19 is over, Jason is keen to move the Sigma on so he can get back into some of the other projects queuing quietly in the corner of the Tuff Mounts shop.

“The whole goal of the project was to show you can build something interesting and cool without spending a million dollars,” he says. “We took the time to make the car legal, and the guys at Regency [Park Vehicle Inspections] couldn’t believe how well the V8 fitted into the Sigma bay – they reckoned it looked like it was a factory installation. It drove so nicely on the road that we just spent the transit legs cruising without a problem.”

If you’re keen to add an 11-second Sigma to your fleet, get in touch with Jason through the Tuff Mounts website.

Jason’s is not the first Sigma to front up at DC – Sydney’s Dominic Pelle debuted his turbo LS-powered Sigma at DC last year and was joined by Brett Lowing with his nine-second turbo LS Sig in 2019. However, Jason’s car has been a development mule for his Muscle Garage/Tuff Mounts bolt-in engine swap kit, so it’s certainly not going to be the last V8 one we see!

Big-engined, smaller-body sleepers have been a part of street machine society for decades. The Sigma makes sense: the engine bay has plenty of clearance and the stout body can be torqued up with big power without popping the door latches. The beefy body, along with parts interchangeability (such as brakes) with other Aussie cars, make it a relatively simple engineering exercise and a great home for a V8

This Sigma was repainted when the carby Holden V8 was dropped in. That was around 20 years ago, so it’s not perfect, but it’s certainly nothing to be ashamed of. For DC, Jason fitted a reverse-cowl bonnet. Inside it has its grandma-comfy quilted-and-buttoned headlining, but Jason ran DC with a Kirkey drag-spec alloy seat so he had some headroom with his helmet on!

With the Sigma set up for drag racing and street cruising, Jason wasn’t expecting to set the timecards on fire at the Optima challenge, so he was surprised the car was competitive. “These tyres don’t have a lot of grip and the suspension isn’t really set up to do this kind of track work, but we’re not doing too badly,” he said. “The car is so comfortable on the road I don’t want to put race suspension in it, so we’ll have to come back with something much wilder for the next Optima challenge”

JASON WAYE
1981 MITSUBISHI GH SIGMA

Class: Tuff Mounts 235 Radial Aspirated

SPECS
Engine: 5.7L LS1
Cam: VCM #710
ECU: LSI PCM
Trans: GM 4L60E four-speed auto
Converter: AK 3600rpm
Diff: BTR, 4.1:1 gears
Previous PB: N/A
Best DC 2019 Pass: 11.84@113mph

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