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1995 Chevrolet Corvette ZR-1- Boosting The Beast

Newly Armed With A Supercharger, The Original "King Of The Hill" Accedes To The Throne Once Again

Randall Woods Dec 1, 2009

My story begins with a trip I made with my father, Ron, back in 2000. He was on his way to purchase his first ZR-1 (one of three he currently owns-two '95s and one '94 Lingenfelter 385) from H&H Corvette in Orlando, Florida. During the trip I caught the bug and purchased my own first Corvette, a Competition Yellow automatic LT1. This was to be the "gentlemen's hot rod" replacement for my '90 351ci supercharged and nitrous-injected Mustang. After a year of modifying the LT1 with readily available bolt-on parts, it was still very underpowered compared with a stock ZR-1, so the search began to upgrade to "The King of the Hill."

The decision to step up wasn't solely horsepower based; it also had much to do with the mystique, the engineering, and the history behind these vehicles. Prior to making the decision, I had read The Heart of the Beast: History of the LT5 V-8 and ZR-1 Corvette, by Anthony Young. Having spent my career as an engineering manager overseeing new-product design and manufacturing, both the mechanical and political elements behind the ZR-1 hit home, and I knew the car was something I wanted to own. In addition, I credit my father for giving me my passion for cars (I grew up not at little-league games, but at the dragstrip) and instilling in me a technical appreciation for advanced performance vehicles like the ZR-1.


SRP selected a supercharger head unit from Danish firm Rotrex. While dyno tests are still pending, the system should inflate rear-wheel output by 80-100 hp.

In March 2002, while attending a yearly Chevy and Corvette show in Chicago, I stumbled upon a low-mile 1995 Chevrolet Corvette ZR-1 for sale. The owner was taking down names and bids with the plan of letting the car go to the highest bidder. After some lengthy discussions with both him and his wife, he agreed to end his unofficial biding early and sell me the car for a very reasonable sum (about $10K under the typical dealer asking price at the time). The car had already gone through three owners before I made the purchase. But even though it was only seven years old, it only had 4,800 miles on the odometer.

After I got the car home and started inspecting it in detail, I noticed that the underside of the chassis was signed and dated "12/23/94." Wanting to know more, I contacted the original owner to get the story. As it turns out, he was an avid car collector, and this particular ZR-1 was the sixth and final one he had added to his collection. The story, as conveyed to me, was that he and his wife attended a Bowling Green plant tour on the last day of production for '94 models, when his car was scheduled to be built. Thanks to some high-profile connections, he was able to select the seats, assist in the wheel installation, sign and date the underside in a yellow marker, and be the first to turn the key and start the car.

He went on to say that this particular car was also used in a "ZR-1s by the Years" photo shoot during a National Corvette Museum event celebrating the production of the last ZR-1. At the end of our conversation, he offered to trade me for a new '02 Pontiac Trans Am Convertible, but I knew I had a great find, so I declined.


The intercooler and supercharger tubing are custom pieces designed specifically for the SRP kit.

Because of the rare nature of this ZR-1, the complexity of the LT5 engine, and the scarcity of replacement parts, my original plan was to leave the car alone and enjoy it in stock form. My resolve lasted only a few months, however, before I caught the bug to modify my new beast. It wasn't long before I realized that-aside from a few exhaust systems, air intakes, and clutches-aftermarket parts for the ZR-1 were essentially nonexistent. The low-volume nature of the vehicle meant that most manufacturers simply didn't see a viable market for such products.

Since I had experience in the engineering/product-design field, and was able to hand fabricate and machine parts, I took it upon myself to set up shop and see what I could offer myself. The plan was to design and manufacture true bolt-on performance products that I wanted for my own vehicle, and then, after testing and confirming the results on my "mobile R&D lab," offer the same products to the rest of the ZR-1 community.


In 2005 I formed Specialized Racing Products, LLC (SRP). Beginning the business with a simple offering-custom-fabricated low-temperature thermostats. I then broadened the product line to include underdrive pulleys, insulator plates, installation kits, chassis products, and more.

But the real challenge lay ahead. If I wanted to achieve substantial bolt-on horsepower, a supercharger seemed to be the logical answer. But how to design a supercharger system that would fit within the confines of the tight LT5 engine bay? I had entertained this idea since the day I purchased the car, but while blower installations had long been discussed on the various Corvette Web forums, my own conversations with knowledgeable ZR-1 enthusiasts confirmed that none had never been performed. The fact that no one had overcome this challenge was a big motivating factor for me.

The Project
After extensively researching various supercharger brands and models, I chose a Rotrex unit based on the following criteria: physical size, output (flow), step-up ratio, and oiling-system design (having a self-contained oil system was essential, as I didn't want to tap into the LT5's existing oil supply).


Thanks to a conservative 4 psi of supercharged boost, the original "King of the Hill" can now perform on par with its C6 successor.

In January 2008, with a Rotrex supercharger head unit in hand, I set out to make my vision a reality. It quickly became evident, however, that many hurdles existed. First was the difficulty I'd face in establishing a drive pulley for the supercharger. Supercharger-drive pulleys are normally installed on the harmonic balancer and are an extension of the engine accessories' drive pulley. However, on the LT5, the rack-and-pinion unit resides directly in front of the balancer, and no room exists for an add-on pulley. Therefore, the supercharger needed to be driven inline with the engine accessories.

Second, the location most suitable for installing the head unit (the driver side) was where the power-steering pump's fluid reservoir and the traction-control adjuster assembly resided. As a result, we'd need to figure out a way to relocate these items. Third was the issue of interference caused by the AC lines and the left-side engine-coolant outlet tube. Overcoming this hurdle required the development of adapters, the fabrication of new lines, and the re-routing of the associated hoses.

Once the supercharger head unit was in place, we needed to figure out how to route and install the air filter and discharge hoses. Initially, we simply attached the filter directly to the supercharger head unit, but that positioned it directly above the driver-side exhaust manifold-not the best location for picking up cool, dense air. As for the discharge side, a collection of 90-degree aluminum pipes and silicone hoses was assembled as a temporary solution.


If the telltale whine of the supercharger doesn't give the car away, a pair of personalized fender badges surely will.

The car was fired up for the first time in May 2008, albeit minus the remote intake system, the intercooler, and any fuel-management unit or ECU manipulation for fuel enrichment. We literally got the car running the night before leaving for Bowling Green to attend the annual C4/ZR-1 event. The idea was to show the ZR-1 community our work-in-progress prototype.

Once back from this trip, the next phase of the development got underway. It took an additional 12 months to work through what seemed to be the more complex elements of the build. These included the following:
* Designing and fabricating an intercooler
* Routing the discharge hoses
* Selecting the correct blow-off valve (based on the intercooler's output volume and displacement of air)
* Determining a remote location for the air-intake system
* Fabricating the air-intake system
* Relocating the battery to accommodate the new air-filter placement
* Selecting and installing a mechanical fuel-management unit
* Installing and calibrating a data-logging system to obtain real-time information on fuel enrichment, boost, inlet temperature, impeller rpm, engine rpm, fuel pressure, and so on

The Result
The project is now nearing completion, and we'll be getting dyno and track times soon. During our around-town test runs, there's no mistaking that this ZR-1 is supercharged. The whine that emanates from the Rotrex's drive unit, magnified by the intake-system tubing, lets passersby know this isn't a stock ZR-1.

Throttle response is clean, and the timing of the vacuum-to-boost transition point seems to coordinate effectively with the car's vacuum-actuated throttle secondaries. Both "come in" at the same time, providing a feeling of throwing a switch and instantly having a substantial amount of additional horsepower at your disposal.

Although boost levels are being kept low for now (less than 4 psi due to the stock 11.0:1 compression ratio), we expect an increase of 80-100 hp at the rear wheels. Our test vehicle has already dyno'd at just less than 410 rwhp, so with the addition of the supercharger, 500 rwhp should be possible. And of course, more horsepower is on tap if we lower the compression and increase the boost.

While we won't be installing these kits in customers' cars ourselves, we're negotiating with some reputable LT5 specialty shops that have expressed interest in becoming authorized installers. If all goes as planned, we hope to offer these supercharger systems to the ZR-1 community in the near future.


Specialized Racing Products (SRP)



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