SETTING up a full-house IRS drag car is a fairly foreign concept here is Australia, so we asked Michael for the idiotís guide.
ďEssentially you want to set the car up with the camber at zero as itís going down the track, so that youíre using the full contact patch of the tyre. The challenge is that as the car moves through its travel and squats, the camber changes.
ďYou put the car on the wheel aligner and pull it down to where you think itíll sit as itís going down the track and dial in the camber to suit, but as it rebounds youíll always lose some of the contact patch. Weíve ended up with three degrees of variance in camber from the top to the bottom of suspension travel, and weíve mucked around a lot with different arms to make it work.Ē
WHEN setting out to build a late-model Commodore as a dedicated straight-liner, most would stick with an LS-based powerplant up front and convert to a four-link in the rear. Michael Arnold chose the path less travelled. He ditched the LS from his VE ute in favour of an old-school Chevy small-block, and upgraded the factory independent rear end with weaponsgrade components.
Although itís still early in the carís development, itís already gone 7.85 over the quarter on radials, making it the quickest IRSequipped Commodore in the country.
ďIRS is big in the US but no one is really doing it here in Australia,Ē Michael says. ďI wanted to do something different and outside the square. Weíre getting there with it!Ē
Given that LS engines are all the rage at the moment, you probably wouldnít expect to find a dirty old small-block riding up front, but Michaelís mill delivers the goods.
ďItís a personal thing. I donít believe an LS will make the same power and retain the same level of reliability. There are plenty of them out there making good power but I prefer the earlier small-block.Ē
Michaelís fondness for Chevyís venerable small-block might have something to do with the success heís enjoyed with his other toy Ė a 23deg-headed, 400ci small block-powered HT Holden ute.
Over the years the HT has evolved from nitrous through blown to
Paint: Voodoo Blue
Brand: Chev 400ci small-block Induction: Custom Racer Pro EFI inlet manifold, ID2000 injectors ECU: Link Thunder Turbo: Twin Precision 68/70 Heads: Racer Pro 13-degree Camshaft: Comp Cams Conrods: Carrillo Pistons: JE Crank: Callies Oil pump: Barnes six-stage Fuel system: Enderle 110 pump Cooling: Custom alloy radiator Exhaust: Four-inch alloy system Ignition: MSD
Gearbox: TCI Pro X Powerglide Converter: Converter Shop 4200rpm Diff: Custom 9in IRS with Driveshaft Shop CVs
Springs: Afco (f & r) Shocks: Strange (f), Santhuff (r) Brakes: Strange (f & r) Master cylinder: Wilwood
Rims: Weld Wheels V-Series; 15x4 (f), 15x12 (r) Rubber: Mickey Thompson; 29x4 (f), 29.5x10.5 (r)
turbocharged, and itís gone quicker each time. Itís run 7.32@197mph, and frankly that was beginning to feel a little sketchy.
ďI wanted to go faster, but with the HT getting towards 200mph something newer and a little bit safer seemed like a good idea,Ē Michael says.
Thatís where the VE comes into the equation. A factory SS that Mick bought as a statutory write-off, he upgraded it with all the good bits from a Maloo that fell afoul of the 2013 Queensland floods. So for all intents and purposes the carís a Maloo. And considering it runs sevens, it manages to look surprisingly like a garden-variety street car.
Impressively, all the mechanical and fabrication work was done in-house at Michaelís business, MA Mechanical. He tackled the engine, gearbox and diff builds, the turbo system and fab work himself, with a lot of help from Dave on the welder and a dedicated bunch of mates.
He sent the car to Brett at Warwick Panel & Paint, while he got stuck into the engine build with assistance from Matt at Next Level Racing.
To a Dart Little M block, Mick and Matt added a Callies crank, Carrillo rods and JE slugs, along with a Comp Cams solid-roller, and a Barnes six-stage dry-sump oil pump to keep things slippery. The combo is topped with a set of CNC-ported Racer Pro 13-degree heads, and a matching EFI manifold carrying ID2000 squirters. Mark from Godzilla Motorsport prescribed a pair of Precision 68/70 turbos and a Link Thunder ECU, and he also handles tuning duties.
ďEleven-twenty horsepower on 15psi was the initial figure on the chassis dyno,Ē Michael says. ďWhen it ran 7.80 it was on 22psi, which should be roughly 1650hp at the crank. In the end itíll be on 40psi plus Ė whatever it needs to run a six, basically!Ē
The motor is backed by a TCI Pro X Powerglide with a Converter Shop 4200rpm converter, but itís the third member thatís really of interest. There wasnít a great deal of expertise within Australia on building an IRS diff sufficient for six-second passes in a 3300lb car, so Michael had to look to the States for a solution.
ďThe guys from the Driveshaft Shop in the US do the rear ends in
a lot of the quicker IRS cars over there,Ē he says. ďI sourced the custom Driveshaft Shop CV shafts and carbonfibre tailshaft through Western Suburbs Differentials, and it should be up to the task.Ē
Itís all mated to a custom nine-inch centre, residing in an OEM cradle that has been shortened by eight inches to accommodate 29.5x10.5in tyres. All the standard mounting points are retained as per Mod Street Blown rules, with a pair of adjustable coil-over shocks for tunability.
ďThereís no real advantage to using IRS; in fact, itís just one big disadvantage!Ē Michael laughs. ďItís heavy, and the biggest disadvantage is that the rear camber changes as it squats, and you lose your contact patch. I was looking for a challenge rather than a technical advantage, and I want to enjoy the process of developing the new car with the IRS.
ďThere are guys in the States running 6.80s, and thatís what I want to do. I want to run a six-something. I donít care if itís a 6.99!
ďGetting the car to work will be a slow process. The power is there, we just need to work on the delivery, and get the car to work as we go. Itís fairly heavy at 3300lb; Iíve taken a lot of weight out but Iíve also put a lot back in. If I canít get it to work and the IRS ends up being the limiting factor, I wonít rule out putting a four-link in it. Itís already the quickest IRS Commodore in Australia, and Iíve been told itís the quickest VE in Australia, too. Thatís not the reason I built the car, but itís nice to know. Still, itís nowhere near where I want it to be.Ē
Watch this space, readers, because a six-second, steel-bodied, radial-tyred IRS Maloo is no joke!
I need to thank my wife for her understanding of my passion for drag racing and for putting up with the long hours at the workshop, away from home and the kids. Iíd also like to thank Brett Benz at Warwick Panel & Paint; Matt McCarthy at Next Level Racing; Paul at Thermal Edge Coating; Mark Jacobson at Godzilla Motorsport; Ray at Western Suburbs Diffs; and all the other people who helped with the build