DIFFERENTIAL EQUATION

> AIDEN STEPS OUT OF HIS MX-5 AND INTO A REAL CAR – A VL COMMODORE HE’S LOOKING TO RUN IN DRAG CHALLENGE ’17. BUT FIRST HE NEEDS TO ENSURE THE DIFF WILL COP THE PUNISHMENT

TECH TORQUE STORY AIDEN TAYLOR PHOTOS CHRIS THOROGOOD, NATHAN JACOBS & AT

I’VE been working at Street Machine for almost two years now, and in that time I’ve become obsessed with drag racing. In my previous life, I was all about the corners, enjoying a few track days here and there in my girly Mazda MX-5 daily driver. But since clocking on at SM and taking a few trips to Calder Park, I’ve undergone a transformation from the magazine’s resident hairdresser to an avowed disciple of old-school, straight-line speed.

In 2015 I experienced my first Street Machine Drag Challenge – five tracks, five days, awesome racing and great camaraderie; it was one of the best weeks of the year. I soon decided that I needed to build a fast street car and do Drag Challenge myself. Having never had a project car – aka ‘money pit’ – before, I had no idea what I was in for.

I’ve always been a Holden man, and my first inclination was a HK/T/G sedan – until I realised I couldn’t afford one that wasn’t about to collapse under its own weight from the dreaded tin worm. An early Commodore was next on the list; something in decent condition with a 308 in it that I could stroke out to 355 cubes and have a bit of fun with.

After I’d perused Gumtree (as you do) for a few months with no luck, my old man came to me one day and said he’d found a car. Yeah right, Dad – what is it, a Nissan Cube? Nope, it ended up being a pretty straight red VL Commodore SL that an old bloke at his work was selling. He’d owned it since new and it had been his daily driver for 30 years. He just wanted to get rid of it, as he’d already got his new wheels – a brand-spankin’ Porsche SUV.

How’s that for an upgrade?

Long story short, I did some very ill-informed research and figured I could make a heap of power out of the standard RB30 six-cylinder by strapping on a turbo. Fifteen hundred dollars later, the car was mine, and with six months’ rego too – you beauty!

The plan initially was to do a very mild set-up for Drag Challenge 2016, with a Garrett GT35

STEP 01

First item on the agenda was removing the old 80s-style wheels. I wanted to shorten up the housing so I could fit some big-offset 15in drag-style wheels under the rear, though I was yet to buy the exact wheels I wanted. Luckily Geelong Diffs had a set of Convo Pros handy. Here, Matt slides them onto my standard rear end – clearly they hang out a bit, but this gives a good indication of how much to lop off either end of the diff

STEP 02

The rear end is then disassembled and the housing put into the bath for a clean-up to remove all the surface rust and oil sludge that had built up over my VL’s 30 years on the road

03 STEP

With the diff removed, the body is lowered on the hoist over the Convos. The gap between the wheels is measured so Matt knows exactly how much to trim off either end of the diff

turbo on the standard engine and R33 Skyline manual ’box. Shortly after I got the car, I started collecting parts and had the boys at Geelong Diffs work their magic on the rear end, as the 25-spline factory single-spinner diff wasn’t going to cut it for racing.

Next was the gearbox, and this was where things started to get out of control. A Skyline five-speed in good nick was harder to find than I thought, and for the price of a used God-knows-how-long-it’ll-last manual I could probably get an auto built for just a bit more coin and go even faster. So I toyed with that idea while I upgraded brakes and suspension at home in the shed.

Mind you, this was the first time I had even worked on a car of any kind. With the help of a few mates, a workshop manual and The Internet, we managed to upgrade the rear shocks, install an adjustable Panhard bar and bring the front brake discs and calipers up to VL Turbo-spec. There is still more to be done to bring the car up to snuff, but it was satisfying to tackle these jobs ourselves.

Drag Challenge 2016 was getting closer, but I still had no gearbox or turbo. It was pretty clear I wasn’t going to make it. No worries; surely I’ll be ready for DC 2017. This is a classic street machiner move, according to Scotty and Telfo.

So, filled with motivation after last year’s Drag Challenge, I stripped off the engine's external hardware, ready to take over to Adam Rogash at MPW Performance & Race Fab for some custom turbo piping and an E85-ready fuel system. I got the car there and explained that I’d decided to go auto and I wanted to put 20lb of boost through the standard engine and run 10s. This was met with silence.

Followed by laughter.

“There’s no way you’ll run 10s with a standard engine,” Adam chortled. Luke Foley then inspected my old nugget and said: “You might run a 10 – once.” But this guy on Instagram told me it would be okay!

STEP 04

You can take as much as you want off the housing, but you can’t put it back on! Matt chops off about 85mm from each side of the diff so the Convos will fit. Without relocating the lower control arms and their associated bracketry inwards, this is about as much as you can take off a Borgy diff

STEP 05

The bushings in the lower control arms were absolutely buggered. So we grabbed a set of shiny new control arms with bushes (as they were only slightly more expensive than buying the bushes alone) and cut them up

STEP 06

In order to fit the big wheels and tyres, the outer edge of the control arm has to be trimmed down, but some lip is kept to maintain the strength of the part. I can now squeeze a 255/60 ET Street under the rear with minimal rubbing. The temptation to tub the rear and get the car sitting down hard over bigger rubber will no doubt prove too much for me, though

STEP 07

The shortened BorgWarner housing goes in the jig and new billet ends are slotted in and welded up

STEP 08

My new 31-spline Geelong Differentials axles are drilled with an HQ/Chev bolt pattern and the wheel studs screwed in. The axles are then test-fitted to the shortened differential and the boys take a few mil off the spline ends to ensure they match the shortened housing

STEP 09

BorgWarner diffs have a collapsible pinion spacer, which sets the preload between the large and small pinion bearings. We ditch that for a solid pinion spacer so the boys can set the preload on the pinion bearings and we know it’s not going to change no matter how many times I launch off the transbrake

STEP 10

No more single-pegger burnouts for me! Here’s the limited-slip centre we’re using – if one wheel loses traction, it will seamlessly shift power across to the wheel with the most grip. It should be perfect for the street-and-strip use I’m planning for the car

STEP 11

The new bearings and limited-slip gearset goes into the diff housing and Matt sets it up with between 6 and 8thou of backlash. We make sure there is a good contact pattern between the gearsets and we’re ready to rock ’n’ roll. We’ve kept our standard VL 3.45:1 diff gears for now; we might swap them for something else once we get to the track and see how times are

STEP 12

Matt gives the diff a fresh lick of paint, so now it looks brand new!

STEP 13

The diff goes back in the car with the new control arms.

With the shortened housing, my original wheels would no longer fit so I ended up buying the set of Convos – I reckon they look great, but I think a set of Weld V-Series rims are in the VL’s future. When I get home I’ll need to swap out the 30-year-old Pedders shocks and upgrade to an adjustable rear Panhard bar so I can get the diff centralised to minimise rubbing and maximise performance

STEP 14

New brake lines are installed for the rear drums.

All that’s left to do is bleed the system, put some oil in the diff and hit the road!

15 STEP

This is the finished product with 255/60 Mickey Thompson ET Street tyres, as opposed to the 245s I left Geelong Diffs on. I reckon it needs to sit a bit lower in the rear, but with standard wheel tubs that’ll cause all kinds of rubbing issues

T H A N K S

BIG thanks to Matt and Andrew at Geelong Differentials for their help on this one. They’ve worked on some of the toughest cars in the scene and are the experts when it comes to setting up diffs for tough streetand- strip machines. Give ’em a call on (03) 5278 1132.

Eek. By this time I had decided the VL had to be the fastest car I’d ever driven and scare the pants off me, so there was no point umming and ahhing – I had to build a new forged low-comp motor. I put a call into John Pilla at Powerhouse Engines and it was on. Original $10K budget well and truly blown, I ordered fancy pistons and rods along with a new Turbonetics 64mm turbo.

So from originally setting out to build a 300hp hack with a Skyline manual and a baby turbo, the project has snowballed into a 600hp, nineor 10-second street weapon with a transbraked Trimatic and a brand-new Turbonetics turbo, Haltech system and flex-fuel capability. Crikey!

You probably regularly read in this magazine of how cars go into the shop for a stone-chip fix-up and leave years later as Summernats Top 60 Elite show-stoppers, and wondered how on earth that could happen. Well, it’s very easy to get carried away with this sport – as my bank account and I are finding out first-hand.

Next time you read about my project VL we’ll break down the process of building the engine with the help of John Pilla and the Powerhouse Engines boys, but in this issue we’ll concentrate on the diff build.

It all started in September last year with a trip to Geelong Differentials. In the interests of saving cashola, and because my plans at the time didn’t include a forged motor, we decided to spruce up the existing BorgWarner set-up rather than stuffing a nine-inch under the car.

I think it’ll work really well though, because these these Borgy units are pretty tough and will easily handle the sort of power I'm looking at. There are guys running nines on them no problem, and Matt at Geelong Diffs is confident she’ll cop 700rwhp with no dramas.

At the time I was also going to have a manual gearbox, so we put a limited-slip centre in it with a set of 31-spline axles. I also wanted to drive it on the street a lot, so we decided against using a spool for now. With the LSD done up tight we’re confident it will still leave clean and straight off the transbrake. We kept the standard 3.45 diff gears for now – once we hit the track and see where we’re at with times we might swap them out for a different ratio. s