The Mitsubishi driver dropped to fourth place as Jason White extended his lead in the modern section despite his Lamborghini Gallardo catching fire on the final stage before Strahan.

Tony Quinn's McLaren continued to lead the showroom class over the Renault of TV star Grant Denyer, while South Australian Craig Haysman has driven his 1981 Triumph TR7 V8 into a commanding lead in classic outright.

After leaving Launceston on Thursday morning, Targa crews headed to the West Coast and an overnight stop in Strahan. The day was the longest of the event, with more than 140 kilometres of stages, including the infamous Cethana, Riana and Hellyer Gorge.

Although he was nearly a minute behind heading into the fourth day, Maguire was eager to push his Mitsubishi hard in an attempt to catch White's flying Lamborghini. And while he had maintained his second place over the opening two stages of the day, a blown head gasket on the 30km Riana stage put paid to his victory chances.

Despite a small engine fire near the end of the final stage, White's lead continued to grow. 2008 winner Steve Glenney set about climbing the leaderboard and finished the day in second place, two minutes and 27 seconds behind White. Had it not be for mechanical problems in his Nissan GT-R on day one, Glenney may well be leading.

Third place is held by last year's winner Jamie Vandenberg in another Nissan GT-R.

"We had a few dramas, such as smashing the battery on a big dip in Gunns Plains, but we changed that," White said.

With a lead of more than a minute, Quinn didn't feel the need to go flat out in his 2014 McLaren 650S, and drove within himself to end the day a minute and 23 seconds in front of Denyer.

Although Denyer's car costs around $450,000 less than Quinn's, the TV host drove superbly, winning stages and maintaining a 33-second gap over third-placed Craig Dean in a Ford Mustang.

Dean won four of the day's stages and is nearly three minutes ahead of the second Renault of Mike Sinclair, with eight-time Targa Tasmania winner Jim Richards in fifth place in a Porsche Cayman S.

"We were fourth fastest outright in Hellyer Gorge, which came as a surprise because we thought it suited the more powerful cars," Denyer said.

"I'm just getting used to pedalling this car harder and harder. We're not quick enough to win, so all we can hope to do is pressure Quinny and hope for the best."

Craig Haysman has had it pretty much all his own way in classic outright, and with his Triumph running well, his lead has blown out to over 3½ minutes.

"We haven't been pushing the car too hard and have been enjoying the stages we love," Haysman said.

WA's Stewart Liddle had been leading the 4WD showroom class, but dropped to fifth on the final stage after losing nearly five minutes. This gave the lead to the Subaru WRX of Angus Kennard.

Tim Hendy (Nissan Skyline) is a clear leader in early modern, Wayne Clarke is out in front in vintage in his 1938 Dodge Speedster Special, Jeff Beable (Nissan) leads Budget Sports, and Mark Laucke (Porsche) is well ahead in Thoroughbred Trophy. Alan Gluyas leads the technical TSD class in a Toyota 86 GTS.

The handicap classes are led by the 1948 Holden 215 of Paul Freestone (early classic), and the 1982 Porsche 944 of Leigh Achterberg (late classic).

The penultimate day of Targa has six stages and 122.42 competitive kilometres between Strahan and Hobart.