A dynamometer, or "dyno" as they're called by you and I, is a device for measuring force, moment of force (torque), or power. In the automotive world, they're used to precisely calculate the power produced by a vehicle's engine at the wheels. A stand-alone dyno setup can cost more than $50,000. Here's how some guys decided to build their own redneck dyno for just $2,000.
What you'll need: A dual-wheel truck axle with a working differential. Four truck tires. Welding gear. Metal beams. Maybe an eddy-current brake. Concrete, gravel and some steel tubing. A farm. The help of two guys from Norway who've already done this. This guide.
Drift-car builders Hans Røthe (Driftfun) and Sindre Haga (Customshit.no) were frustrated by the lack of dyno in their lives. At the duo's outpost in the hinterlands northeast of Oslo, where they'd built two turbocharged LS1-powered Mazda RX7s, they had no way to properly — and safely — tune the cars before heading out on the road.
Buy a chassis dyno? Hell no. Those damn things cost money. Big money. Tens of thousands. But don't forget who we're talking about: Norwegians, the people who crushed Hitler's atomic-bomb program by staging commando raids on their own nuclear plant, which at the time was under Nazi occupation. Norwegians are the founding members of Team Live Badass.
Enter the "redneck dyno." Internet legend holds that somewhere in the US existed a makeshift, but serviceable chassis dyno built out of junkyard parts — specifically the rear-end assembly from a heavy truck. The links are dead now [actually, not all of them], but owing to Røthe and Haga's handiwork, the redneck dyno lives — 4,000 miles away.
The project sprang to life from a single post on LS1tech:
First of all, if anyone ever has come up with a stupid idea of how you could build a "cheap" and functional dynamometer/dynaoack/etc i want to know!
Inspired by another forum member, who quoted a version of "the legend," Røthe and Haga set out to find a usable truck axle. Read on as they take us through the sketchy, but ultimately successful build.
Step one: Find a proper axle.
Røthe and Haga located theirs — 1,800 pounds of Volvo bus rear-end — at a local truck parts yard for about $1,000.
Step two: Lock down the diff.
Balancing the wheel-braking effect to be equal on both sides is particularly important to Røthe and Haga, who know they must keep uneven forces from tearing their cars' drift-ready welded diffs apart. The solution? Weld the bus's differential. Not so easy, as they found:
We finally got the rear axle into our shop. Rigged the axle on a pair of jacks and had a discussion of how to lock the diff. We saw a hose sticking out of the diff. housing but didn't think any more about it. Only way to lock it was at that moment to weld it. We started cutting holes in the back of the housing so we could weld through them. Unfortunately the diff was sealed so we couldn't find the gears to weld. That meant we had to tear it apart. So we did. It was hell of a job and took three to four hours with rusted bolts, etc.
And that tube? Turns out it was for the Volvo's air-controlled lockup, and thus unnecessary for the task at hand.
Step three: Apply the brakes.
"A few people came to see the progress and discussed whether the truck brakes [were strong] enough or not," Haga said. "Some also [said] that we didn't need so much brake power to hold a 350kw (470 hp) LS1 on full power. You can turn this around, upside down as much as you want, but if you have 350kw you need to get rid of it."
They got the the original bus's air brakes up and running. But they later installed a second, electromagnetic brake on the input shaft, which cost another $1,000. It was a no-sweat install, however, since the bus had been fitted originally with a similar retarder brake. Together, the brakes provided plenty of force to draw down all that high-velocity, high-inertia spinning. Getting the brakes to work evenly on both sides, however, would be a longer-term project.
Step four: Build the support structure.
Framing out a place for the axle to rest was just a matter of re-purposing stuff they had lying around. "We dug out a old truck frame from the snow and hacked it in four pieces. The four pieces made the frame to hold the rear axle and the ramps." Problem solved. It works! Kind of!
Step five: Drag it outside and set it up.
Naturally, they needed two tiers of land — one on which to place the dyno, the other for the car. This, they had available, by way of Norway's considerable snowfall. You may need an excavator for this step.
Step six: Test it out on video!
Step seven: Revise for safety!
After a few incidents of the unit sinking into the aforementioned Norway snow, the guys set about bolting the entire redneck dyno assembly to a steel-reinforced concrete foundation. They mounted steel frames around the axle, both as safety walls and to support a new ramp.
For easier automotive ingress, they filled in the approach with 8" of gravel.
Step eight: Stand back and admire your handiwork. I mean it; STAND BACK.
Since these photos were taken, Røthe and Haga have further refined the dyno. Some additional tweaking to the brakes have yielded better balance of brake pressure between the right and left sides, and better control over resistance — a must for torque testing. They've also bootlegged a method to measure output, adding load cells — transducers that convert force into a measurable electrical output — to the ropes holding the car back. That, along with the speed of the wheels, they use to determine watts. Yes, it's a work in progress.
(Hat tip to LSXtv.com!)