StudioVRM

Racing Secrets Revealed

How to Build a Honda Prelude Racecar Part 8 - Moving Up a Class

by Roger

How to Build a Honda Prelude Racecar Part 8 - Moving Up a Class

Much in the same way that cars in Formula 1, NASCAR, and pro touring car series have evolved over the years, club racing classes also evolve to stay current with popular trends in the automotive industry.

In the past few years in particular, club racers have steadily migrated away from traditional racing classes that specified lists of makes, models, and modifications, towards one of two types of classes:

  1. Spec or Factory-prepared classes composed of a single make and model of car that are all modified to a pre-defined spec. Examples include:
    • Spec Miata
    • Spec E46
    • Spec Racer Ford 3
  2. Performance-balanced classes which group cars into classes based on lap times or statistics such as power to weight ratio:
    • AER / Champcar / WRL
    • Super Touring
    • Bracket Sprint Racing

The allure of these types of classes is that the promise of closer competition as the rules minimize the potential for someone to dominate their class with a "ringer" car.

What does all this mean for the StudioVRM Prelude, a car that was originally built for the traditional and regional-centric Improved Touring and Honda Challenge classes? It was time to change with the times and find a new class to run in. So I employed the same method that I described in Part 1 of this series and chose two current and relevant classes: SCCA Super Touring Under and the US Touring Car Championship, sanctioned by NASA.

What are SCCA Super Touring and  USTCC?

 
Interestingly, both SCCA Super Touring and the US Touring Car Championship were created to achieve the same goal: To give club racers a place to race previous-generation Pirelli World Challenge touring cars.

For those of you who may not be familiar with the name, Pirelli World Challenge is a North American pro racing series based around production cars that anyone can buy new in the US and Canada. A huge list of manufacturers (Acura, BMW, Chevrolet, Chrysler, Ford, Kia, Mazda, Porsche, Subaru, and Volkswagen just to name a few) have used it as a platform to showcase the performance potential of their street cars. When the manufacturers bring out the latest and greatest models, World Challenge teams often sell their old cars to club racers at a very reasonable price. Hence both Super Touring Under and USTCC were born.


Super Touring Under

Photo: Wikipedia Commons

Super Touring Under has since evolved into a highly-accessible class for modified cars under 3.2 liters. Unusually, the class uses a displacement to weight ratio to balance the performance of their cars, with modifiers for factors like drivetrain layout (FWD vs RWD vs AWD) and suspension layout (Macpherson strut vs Double A-Arm suspension). A 2 liter Subaru BRZ, for example, can compete at a feather weight 2200 lbs with its naturally aspirated FA20 motor. An E36 chassis BMW M3 meanwhile is handicapped at 3200 lbs to offset the power advantage of its 3.2 liter S50.

This means that cars come in all shapes and sizes, mixing turbocharged, supercharged, and naturally aspirated cars, with and without aftermarket aero. The grid from last year's runoffs saw a brand-new Honda Civic Si line up on the grid alongside a Dodge SRT4 and a Subaru Impreza 2.5RS. 

Encouragingly for us, the winner of the 2017 SCCA Runoffs drove a K-swapped 4th gen Honda Prelude Si to the checkered flag.


US Touring Car Championship

Photo: US Touring Car Championship

USTCC meanwhile caters to drivers of current and late model touring cars who prefer the feeling of a pro racing environment. The series retains sponsor support from prominent names in the automotive industry, which equates to generous prizes and contingencies for participants.

The rules are an interesting variant of the classic power to weight formula that takes gear ratio into account. The modification-friendly nature of the USTCC rulebook make it seem a bit daunting at first, but when you look at the cars that are competing, you quickly realize that they are similar to what you might see in NASA GTS or SCCA Touring. There four sub classes to accommodate everything from heavily modified tube-frame cars to older cars with fewer modifications. That said, even the entry-level Sportsman class cars are far from slow - All USTCC classes use Hankook F200 race slicks, allowing these cars to corner faster and harder than their DOT R Compound-shod brethren.

Due to the similarities it's very easy to build a car that is legal and competitive in both series. So that's exactly what we are going to do.

What are we Upgrading?

As you can imagine, there's a lot to be done to bring the car up to spec for these mod-friendly classes:

Engine

Both classes allow for a moderate level of internal engine modifications, including upgraded cams, high compression pistons, and porting of the head. With this in mind, we've already taken the first step by having Racer Brown Camshafts grind a custom cam for us, which powertrain wizard Robert Oliver installed with Crower valve springs and AEM cam gears.

The car is still tuned to a conservative 7000 rpm rev limiter, but initial dyno tuning shows gains of around 18 hp over our previous configuration with stock cams and valvetrain. The plan for the off season is to raise the rev limiter and fine tune this engine to see if we can get as close as possible to 200whp on a Dynojet.

Aero

Both classes allow for popular bolt-on aero modifications. For us, that means a splitter, air dam, side skirts, and a rear wing. Super Touring Under specifies a minimum ride height of 4 inches (except for the air dam and splitter, which can be low as 3 inches off the ground), while USTCC has no minimum ride height.

Over the off season we plan to build a splitter to give us some front downforce, add a set of PCI side skirts to seal off the underbody, and balance it all with a Nine Lives rear wing.

Chassis

Last but not least, the rules allow for extensive weight reduction and roll cage construction which were previously not available to us under Improved Touring rules. The USTCC Sportsman rules give our < 200hp Prelude a minimum weight of just 2400 lbs, while in STU trim our 2.3 liter Honda is allowed a scant 2351 lb min weight. That's including driver and fuel.

As it sits today, the StudioVRM Prelude weighs a stout 2590 lbs, including driver and a gallon of gas. A carbon fiber hood, lexan rear windows, and lighter gusseting for the roll cage will help us get closer to the minimum weight. The car will also receive 17" wheels to take advantage of the slightly wider slicks available for that diameter.

Of course, it's a long list of items, so we're taking it one step at a time. In a few days we will be at NJ Motorsports Park, testing out some setup changes in preparation for these upgrades. Either way, it's going to be a fun winter.

See you at the track.

~R