How QA1 MOD Shocks Power 4,000 HP Drag Radial Machines
Radial-tire drag racing at the sport’s highest levels puts unique demands on a chassis and suspension system — a result of the thousands of horsepower being delicately balanced with the inherent nature of how a radial tire functions.
Patrick Miller calls the tuning shots on his father Jeff’s Camaro that is campaigned in drag radial racing’s premier class, Radial versus The World, as well as the 1967 Camaro of Bill Lutz that’s raced in the N/T (No-Time) 275 radial class. Both cars feature horsepower from all-aluminum, purpose-built Hemi engines that sport screw-type superchargers, producing some 4,000-plus horsepower. Each car is outfitted with 9-inch-stroke QA1 MOD Series four-way-adjustable shocks on the rear, and given the horsepower, weight, and the very nature of how the suspension operates, represents the greatest level of abuse you’ll find doled out on a pair of shocks anywhere in the sport of drag racing. But for Miller, the MOD Series shocks have delivered in every way.
“These can absolutely go out there and run with the $15,000 shocks that everyone thinks you’ve got to have," Miller says. "They don’t leak air, so I don’t ever have to worry about checking the canisters, and they don’t leak oil. We put hundreds of run on them, fully topping them out every time down the track."
A traditional bias-ply slick drag racing tire that many people may be familiar with has a very forgiving sidewall that squats upon acceleration; with carefully controlled wheel speed and balanced transfer of weight, the tire will gradually snap back into shape and continue accelerating the car forward. A radial tire, however, is very unforgiving and requires consistent traction — if it breaks loose and spins, there’s no recovering it.
To do this, racers utilize the sheer horsepower of the engine and the shock and spring package to separate the rear suspension to put “bite” into the tire so that it hooks and goes. A very sticky racing surface helps support this action. With the rearend hiked up — often above the crankshaft centerline — weight is being transferred forward to keep the nose on the ground so that the horsepower can quickly be applied. It’s not uncommon for crew chiefs to be applying maximum boost, nitrous oxide pressure, and ignition timing within the first few tenths of a second of a run. The car at this point is acting in effect like a cantilever: the rear shocks and the vehicle’s weight trying to force the nose down while the engine’s power is trying to turn it over backward.
Racers will sometimes — but not always — run a longer rear shock than a slick-tire counterpart, and will valve the shocks appropriately to fully separate the shocks right off the starting line, with adequate rebound to help control the action but not to inhibit it. Where slick-tire cars keep their shocks in the fluid range, radial cars extend the shock to a “dead stop” with considerable momentum behind the piston as it separates.
Crew chiefs will dial the compression in much tighter than a street car enthusiast would consider proper, to keep the shock separated and control its ability to return to ride height until the driver steps off of the throttle at the finish line. As the race car is accelerating downtrack, the downforce generated by the 200-plus-miles-per-hour speeds over the body is trying to force the shock back to ride height, all the while the car is still trying to wheelstand and launch itself into lower earth orbit.
On a less prime racing surface, crew chiefs like Miller will allow their front struts some degree of extension to get the center of gravity (the crankshaft centerline) up higher to transfer the weight to the rear tires to keep them planted. Conversely, however, they then must dial back the introduction of horsepower to keep the front end of the car on the ground. It is, again, a very delicate balance that has resulted equally in world records and highlight reels over the years.
"We try to reach maximum extension of the shock at about 1 to 1.2 seconds into the run, so we’re controlling how quick it can extend, via horsepower application and rebound valving,” Miller explains.
From there, it’s about managing the shock’s action as the car gains speed — an area where he puts the MOD Series’ low-speed bleed to work.
“It’s really fun working with the MOD Series with the low speed bleed, because it actually affects it a lot," Miller says. "A small adjustment will change how the car settles downtrack, without upsetting it. I can keep it where it will stay fully extended, but as the speed increases I like to get it where it levels out some, just to improve aerodynamics. So we’ll loosen up the low speed bleed to get it to come back in a very controlled fashion.”
The MOD Series feature unique modular, interchangeable valve packs that can be quickly removed and replaced with the shocks on the vehicle — a major benefit to racers like the Miller’s and Lutz who need to develop and tweak the suspension combination from track to track. Patrick, through testing and refinement, has found a set of packs for drag radial and the big slick-tire applications, and along with some spring rate changes, simply swaps out the valve packs and he’s ready to go. “Every once in a while I might try something a little different and make a valving adjustment, but typically that’s only if I’m trying something new with the 4-link," Miller explains.
“I’ve had cars that we’ve put MOD Series on, and what I would normally run for a valve pack doesn’t necessarily work on everything — but you throw them on, make a run, and with all of the shock dyno graphs for the different valve packs at our disposal, it makes it really easy to swap the packs and get the shocks where I want them on the very next run," Miller says.
"As much as we abuse our shocks, it’s been really impressive that after all of the runs that we put on them, we can take them apart and the fluid still looks new and clean. Usually it’s red or metallic...it looks like it’s been run — but the MOD Series doesn’t hurt the oil at all," he adds.
The QA1 MOD Series Shock At A Glance
QA1’s MOD Series shocks feature 4-way adjustability, providing independent control of high-speed and low-speed compression and rebound with 24 clicks of adjustment. This allows precise suspension tuning based on shaft speed, not vehicle speed. Low-speed adjustment affects body roll, squat, and pitch, while high-speed adjustment controls impacts from bumps, potholes, and track irregularities.
Compression controls how the shock resists suspension compression under braking or cornering, while rebound manages how the suspension extends after compression, influencing tire contact. Low-speed compression adjustment affects chassis control during weight transfer, while high-speed compression stiffens resistance to rapid impacts. High-speed rebound adjustment prevents excessive suspension separation, critical for maintaining traction during launches in drag racing or over bumps on a road course. Low-speed rebound helps control how the chassis return to its settled position, keeping weight properly distributed under acceleration.
MOD Series shocks feature modular QuickTune valve packs, allowing users to swap valve stacks without removing the shock. These dry valve packs offer adjustability without internal disassembly, allowing fast changes for street, autocross, road course, or drag racing setups. Valve packs range from soft to extra firm, with tuning potential up to 1,300 lbs. of force.
In drag racing, high-speed rebound tuning prevents excessive rear suspension separation in applications where that is desired, improving traction, while low-speed compression and rebound manage weight transfer, controlling front-end lift for a consistent launch. In road course and autocross, low-speed rebound keeps tires planted during transitions, while high-speed compression adjustments help absorb curbing and track imperfections. Street driving benefits from the MOD Series’ ability to be dialed down for comfort without sacrificing performance.
A floating piston in the remote canister prevents cavitation, ensuring consistent damping at extreme loads. The indexable shock base provides flexible mounting options, allowing easy access to adjustments. The nitrogen-charged external canister, set at 60 psi, improves valving consistency and responsiveness.
The MOD Series’ precision adjustability, durability, and modular tuning make it the premier solution for high-performance suspension applications, delivering optimized control for every driving condition.