Prepping the car requires...
Prepping the car requires removing everything from the rear for working room. We'll get into the finer points of removing the stock rear suspension in the next F73 installment that covers the DSE rear suspension package, but for now we're just going to start with a clean slate for the mini-tub installation.
It's been said on many occasions, often by the losing drivers, that an autocross or open track event essentially becomes a tire race when a certain size and compound aren't mandated. The sentiment is that even if all else is equal, the tire can be the deciding factor. And to a certain extent that is true; just like a good driver can improve a car's ability to perform, good tire choice can make the playing field surprisingly level between mildly and wildly modified cars.
However, just as important as what type of tire being used is how much tire. Just like drag racers that tub the rear of their cars to install wider slicks for forward traction, installing wider tires on a track car yields greater lateral adhesion to the road through curves. Think about it; traction is the final tenuous point of contact between car and road that defines how the car will perform. No matter how effective a particular suspension design is in theory, it can be compromised by a lack of ability to implement it.
While there are quite a few limiting factors and resulting equations used in engineering for determining the true coefficient of traction for a vehicle on any given surface, the one we're chiefly concerned with pertains to F73's performance on a dry asphalt surface. Let's boil it down to the essentials; when all else is equal, more tire means more grip.
Even taking into account our...
Even taking into account our planned narrowed rearend and Rushforth wheels that were made specifically for F73, fitting 12-inch-wide wheels and Viper-sized rubber encounters a few logistical problems.
Stock second-gen F-bodies can easily accommodate 275 or 285-wide tires depending on wheel offset, but Detroit Speed's Deep Tub kit pushes the inner wheelwell 2.75 inches further inward, creating enough clearance for a much wider 335 tires. That's an increase that should make a significant difference in our lap times.
The bad news is, don't count on this being a weekend project if you're not an experienced fabricator and welder with the right tools. DSE's well-designed kit is definitely a labor saver and takes all the guesswork out of the process, but it is a fairly complicated endeavor that requires a seasoned eye and excellent welding skills. Though it should go without saying, those afraid taking a cutoff wheel, sawzall, or plasma cutter to their F-body also need not apply.
It's decision making time for the rear suspension too, as there are actually two ways to install the Deep Tubs, but both require some changes. To maintain the stock-style leaf spring setup DSE has assembled a full kit that includes the necessary hard parts including new spring pockets, offset shackles, framerail fill panels (for the required notch), and a revised upper shock crossmember to name a few. Our plan, however, consists of upgrading to DSE's Quadra Link kit down the road, so for now we're just installing the Deep Tubs by themselves.
Dropping the body down on...
Dropping the body down on the wheels accentuates the problem; even with the tire pressed against the inside of the wheelwell, the quarter-panel is actually sitting on top of the tread. There's no way to get these bad boys under stock sheetmetal.
Like most of Detroit Speed's parts, the Deep Tubs are designed to be a do-it-yourself garage project, but unfortunately we're still not quite confident enough in our welding abilities to tackle this one on our own, so we once again called on the professionals at A&E Motorsports in Santa Fe Springs, California. Even with decades of professional experience like A&E's lead fabricator Joe Walden has under his belt, count on a few solid days of work to complete the swap. Of course your time may vary, but this is one project that's better to take slow and steady and measure everything multiple times-this is definitely not something you want to do over.
What We Did
Cut out the narrow factory wheel tubs and grafted in Detroit Speed's Deep Tubs
We can now fit 12-inch-wide wheels with 335mm-wide tires
$440 per pair
The second issue is this bulge...
The second issue is this bulge at the front of the wheelwell. While it's difficult to discern in photos, the protrusion extends roughly 2 inches inward, further restricting tire size.
Standard oil-barrel-style tubs like the big-tire boys in drag racing use were overkill for our needs, plus we like the idea of keeping the modification subtle. DSE's 18-gauge stamped steel mini-tubs were designed with stealth in mind and nicely mimic the stock shape.
F73's interior was still gutted...
F73's interior was still gutted from the subframe install, so our first step was to make a cut line at the top of the bracket that ties the seat support to the wheelwell. Five spots welds were drilled out, then a cutoff wheel took care of the rest.
DSE supplies useful templates...
DSE supplies useful templates with detailed instructions with the kit that take the second-guessing out of the cut.
Since F73 is a '73 Camaro,...
Since F73 is a '73 Camaro, once the front template was positioned and secured with magnets, we used a punch to mark the center of the new location for the seat bolthole. 1975 and later F-bodies will skip this step. After making the punch, the seatbelt tab of the template was removed and the remaining paper revealed the cut line.
With the rear template positioned,...
With the rear template positioned, a strip of 2-inch wide tape was laid front to rear to complete the cut line.