Air filters, air filters! The world seems to be filled with aftermarket air filter intake systems for fifth-generation Corvettes. Which one really improves your car’s performance? I am not here to evaluate every aftermarket Corvette air intake system offered. However, when I found one that worked while researching this book, I wanted to share the good news with you. C5s were all fitted with general-purpose, quiet, air intake systems when they left Bowling Green, Kentucky. This factory system flowed 1,120 cubic feet per minute (cfm). Corvette engineers were required to fit a system that made all Corvettes quiet enough to sell in all 50 states. The aftermarket industry quickly found out that adding more air (and noise) to LS1/LS6 engines produced a nice bump in horsepower.
This Tech Tip is From the Full Book “HIGH-PERFORMANCE C5 CORVETTE BUILDER’S GUIDE“. For a comprehensive guide on this entire subject you can visit this link:
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I discovered that Callaway Cars offers an innovative air intake for a C5. I saw impressive horsepower gains when Callaway installed one of their Honker air intake systems on a stock C5. The C5 gained 16 hp and 10 ft-lbs of torque. The Honker directs cool air from outside the engine compartment. The air flows through a well-engineered base, filter, duct housing, and bellow assembly. The last part of this design moves the Mass Air-Flow Sensor (MAFS) close to the throttle body. This integrated design approach is what allows the Honker to achieve maximum efficiency. This system flows at 1,486 cfm, which converts to a big bump in performance. Intrigued, I wanted to see if we could reproduce Callaway’s gains on my car. I ordered a Callaway C5 Honker system for my C5. Callaway Cars sent me a Honker that fits 1997-2000 Corvettes. My system arrived in a well-packed box, with clear instructions and no missing parts. My C5 at the time of this install was equipped with an LS1 engine with an MTI Racing head-and-cam package. The engine also had long-tube headers, performance cats, and a performance aftermarket cat-back exhaust system. The engine produced 408 rwhp. The aftermarket filter system installed on this car was exposed and drew its air from inside the engine compartment. The Honker gets outside air from a hole that is cut in the radiator shroud. Thus, it should not make any difference in power if the hood is open or closed.
To prove the point, two dyno tests were performed with the old system. First, the car was tested with the hood open and again produced 408 rwhp. Next, the hood was closed and retested. The LS1 now dropped to 399.9 hp or a loss of 8.1 hp! So far so good. With the base established, MTI Racing removed the old system and installed the Honker. Installation was straightforward and everything fit. Here are some of my installation observations. Callaway sent detailed instructions, clamps, filter, housing, and parts. The Honker includes a Callaway-designed “green” filter. The green filter is popular in European performance cars. The filter media is combed-cotton cloth for high flow and has excellent filtration, as opposed to other filters. Additionally, stainless-steel wire is used for durability instead of aluminum. After MTI removed the old air filter, they used a #30 Torx to remove the bumper beam air cleaner bolts. A Honker test fitment was made to determine if the car needed to be modified. No changes were necessary.
During the test fit, masking tape was attached to the radiator shroud to mark the filter opening. Next, seven 7-mm shroud bolts were removed from under the car. Two metal retainers were also removed to completely loosen the shroud. Four 10-mm radiator cover bolts were removed, and the cap was taken off the car. Once the radiator cover was off, the shroud was gently pulled from the car. Care should be used during this step to avoid damaging the radiator. I noticed a lot of road debris on the evaporator and radiator, so this was a good time to clean the radiator with a Shop-Vac. Next, the template that Callaway provided was located on the shroud. The opening was cut, and 12 template holes were drilled with the provided #4 drill bit that was part of the kit. The filter base was clamped to the topside of the shroud. The 12 template holes were used as guides to drill into the filter base. Twelve pop rivets secured the filter base to the shroud. The pre-lubricated filter element was attached to the filter base. The other part of the Honker package included the relocation of the MAFS. All C5s have their MAFS located near the filter. When the C6 was introduced in 2005, its MAFS was relocated next to its 90-mm throttle body. This relocation is another reason the Honker produces more power. The completed Honker and MAFS was a perfect fit and looks like a factory installation.
Removing the radiator shroud was a little tricky and time consuming, but the clear Callaway instructions helped complete the job in less than two hours. The C5 started on the first try, and the LS1 settled to an even idle. Back on the dyno, the first dyno pull, with the hood closed, produced 419.4 hp and 402.1 ft-lbs of torque. Next, with the hood open, we got the same results. This was a gain of 19.5 hp and 15 ft-lbs of torque. We cannot guarantee that your car will gain the same horsepower as mine did, but adding the Honker adds horsepower. The engine response really improved above 3,500 rpm. I learned that systems that draw air from the engine compartment do not make as much power as those that utilize outside air. So, if you are checking the efficiency of your air intake on the dyno, close the hood for real-world results. The Callaway C5 Honker air intake is 50-state legal. Since this installation, I have observed many Honkers being added to C5s with similar results. This is a great way to increase your engine’s air intake.
Throttle Body Change-Out
My C5 had two remaining stock components left in the air intake system: the Throttle Body (TB) and the MAFS. The factory 57-mm throttle body has a butterfly mechanism that opens and closes with the help of a small motor. The motor gets its throttle position signal from the throttle actuator control (TAC)). The TAC receives its signal from the gas pedal electrical actuator. A small amount of radiator water is piped into the underside of the throttle body to help cold-weather performance. Many aftermarket vendors make modified throttle body assemblies. However, since I have had good experiences with Callaway Cars, I ordered a new throttle body from them. I received their CNCmachined, 78-mm, blue-anodized 6061-aluminum BigBoreBillet Throttle Body unit. It has the name “Callaway” machined on its face. The MAFS is assembled as a sandwich of three parts held together with four Torx screws. The center section of the MAFS has small wires built into the part that senses air flow and air temperature. The two outside parts are made of aluminum. MTI makes these outside parts larger with poly, which makes the MAFS run cooler and flow more air. The replacement pieces are a direct bolt-on to the factory centerpiece.
Installation was pretty straightforward. MTI used a 10-mm extension to loosen the two bellows clamps on the air intake. Once the clamps are loose, the factory throttle body and stock mass airflow sensor are removed. Next, a radiator hose tool was used to remove the throttle actuator connector on the left side of the throttle body.
The positive crankcase ventilation (PVC) hose and the throttle position sensor connector on the right side of the unit were removed. The two throttle coolant hoses from under the throttle body were removed and plugged. A small loss of coolant is normal during this step. Next, the three 10-mm bolts were removed from the throttle body, and it was lifted from the car. This car lives in a warm climate, so we elected to bypass the throttle coolant lines. I do not recommend this procedure in cold climates. The removal procedure was reversed to install the new Callaway unit. Next, the car was tuned and dyno-ed, and measured a 5-hp and 8.90-ft-lbs rwhp increase in torque. Then, the lightweight, composite MAFS was modified. The airtemperature sensor and mass airflow connectors were unplugged and the unit was removed. To modify the MAFS, dismantle the factory unit by removing the four Torx screws and place the center section from the factory unit into the two MTI parts.
Reassemble it with the four original screws, and you are finished. The modified MAFS sensor was reinstalled by reversing the removal procedure. When the MAFS installation was complete, the car was tuned and dyno’ed again. We gained 4.9 hp and 6.20 ft-lbs of torque at the rear wheels. These two additions netted us a 9.90-hp and 15.10-ft-lbs of torque increase over the stock units. This bumped our output to 429.30 hp and 417.20 ft-lbs of torque, compared to 419.4 hp and 402.1 ft-lbs of torque rwhp on our base run. Not bad for bolt-on parts!Spark Plug and Spark Plug Wires
The LS1 and LS6 engines were introduced with a new plug wire and coil system, called a coil pack, in which each cylinder has its own individual coil that is attached to a plug wire and connected to a spark plug. This system provides a hotter and more evenly distributed ignition source for each cylinder. Each cylinder head is covered with a plastic fuel rail cover. These covers dress up the engine compartment, but they do not allow heat to escape from the coil packs. I recommend removing these if you are going to run the engine really hard. The wires provided by the factory work well, but I recommend installing aftermarket wires after about 20,000 miles of use. Highquality aftermarket plug wires are thicker and are less prone to power leakage, which reduces engine power.
Performance engines thrive on air—if you add lots of air on the intake side that means you need to reduce or eliminate restriction on the exhaust side. When it is mixed with fuel and burned, it moves out of the heads through the exhaust system and out of the car. Modified engines require higher volumes of air and fuel to make horsepower. Stock exhaust usually robs horsepower from the engine because of excessive backpressure. Headers are designed to minimize backpressure and improve the flow of exiting exhaust gases. Building headers is a science, but if done right, they make a huge performance difference.
High-quality headers are formed out of individual tubes welded to a round collector. In the case of the Corvette, each side of the engine has four tubes, welded to a flange, that come together into a collector. The collector connects the headers to the exhaust system. On street cars, highflow catalytic converters usually come next, and, near the rear wheels, the left and right exhaust pipes are connected with an X-pipe. The X-pipe reduces resonance inside the car and balances exhaust flow. To complete this system, a high-flow cat-back muffler system is attached to allow the exhaust to exit the car.
Aftermarket companies offer three types of headers: short tube, mid tube, and long tube. Tuners select the appropriate length header based on the customer’s driving requirements. The three header types are: shorties—easy to install, small power gain; mid length—not too small, but not so long as to scrape if your car is lowered; and longtube— maximizes power as well as exhaust noise.
What To Look For
Decide which header is right for you. If you want to stay 100% smog legal, stay with shorties only and make sure they have a California Area Research Board (CARB) number. If you have a 2000–2004 car, do not bother with shorties. These cars received a better-designed manifold and flow quite well for what they are. Switching to shorties nets minimal gain, if any. If you have a 1997–1999 car you’ll gain some rwhp from shorties but it won’t be much, either. If you decide on shorties, work your other modifications around your cam’s design aspect, meaning if you decide for a future cam, keep it small (220 duration or smaller).
Headers other than shorties require a new Y-pipe. Mid length versus long tube debates continue to go on, but mid lengths can produce great numbers and are a viable option for most people. Mid lengths are available for 1997–1999 and 2001–2004 cars; if you have a 2000 car, you need the EGR pipes from a 1997–1999 car, or you need to remove your EGR system. When buying long tubes, what you are paying for is fitment, quality, fit, and finish. All LTs are dyno’ed to produce similar net power gains. The 1-3/4-inch primaries are more than adequate for stock cubes. If you have an engine that has been stroked, shop for larger, 1-7/8-inch primary headers. If you have a high-power, stock cubed setup, you might want to look into a 1-3/4 inches stepped to 1-7/8 inches. Buy your headers with some kind of ceramic coating or get stainless steel. If you can’t afford coated headers, hold off until you can. If your car sees a lot of winters (real winters, i.e., East Coast, Midwest, etc.) you might want to seriously consider the stainless-steel headers; they are more expensive than ceramic-coated headers, but the chance of rust is greatly diminished.
Since long tubes are by far the most popular headers, here are some of the more popular choices. Pacesetters: Extremely popular due to price, and they are coated for under $400. Quality is very good for what you’re spending your money on; welds and collectors are good. If you’re on a budget and want long tubes, then Pacesetters should be at the top of your list. Jet Hot/Hookers: The Hooker and Jet Hot long tubes are of the same design; jet hot took the hooker design and improved upon it a bit by moving the O2 bungs on the inside of the headers. They use a thicker tubing and have thicker flanges. Both are great long tubes and cost $500 to $600.
QTP/Kooks: Both Kooks and QTP are made with stainless steel, and are regarded highly. Quality is top notch and they can be polished for that “bling” look, if you’d like. Their only drawback is the price, at $700+, they are not for everyone.
SLP: SLPs make great headers; they are stainless steel and ceramic coated. Their major drawback is price, installation, and lack of ground clearance. If you want to lower your car, pass on the SLPs. They are priced at $700+.
Others available but not reviewed: Flowtech Thunder Racing Headers Dynatech Stainless Works PPC SuperMaxx TTS LG Pro Long Tube Headers MTI Racing
Cat-back Exhaust Systems
Cat-back exhaust systems are used with or without aftermarket headers. If you are adding headers, I strongly recommend adding a highquality, cat-back system to complete your project. Most people do not add headers to their cars; they just bolt on cat-back systems. Owners usually just want to improve their car’s appearance and sound their exhaust makes. Cat-back systems are available from a variety of aftermarket manufacturers. Major companies such as Corsa, B & B, Borla, Bassani, Callaway, etc., all offer specialized cat-back systems for C5 Corvettes.
You can buy your exhaust directly from the manufacturer or order them through Corvette supply houses. Some of these suppliers are Mid-America Motorworks, Corvette Central, West Coast Corvettes, etc. Each manufacturer produces its own unique sound and exhaust tip design. Sound and style are really a personal choice. My recommendation is to listen to and look at different exhaust systems before deciding on buying one for your car. If possible, talk to the owners about their experience with installation and quality of their particular system. Most importantly, ask them about cabin noise at cruising speeds. Some systems have so much negative resonance that you cannot hear yourself think on the highway. These cat-back systems are expensive, so it’s best to take your time shopping for the sound and a look that puts a smile on your face. This is exactly what I did before installing a Callaway Double-D catback on my C5. After looking and listening to a number of exhausts, I decided the Callaway was perfect for my car. One of the features of this particular system was how Callaway eliminated interior exhaust resonance without reducing efficiency. Their engineers spent a lot of time eliminating this common exhaust annoyance. I first heard this system on their C5 Z06 development car. From the rear, the exhaust produced a hearty note, but inside it was very quiet. Callaway Cars have been adding their distinctive Double-D tipped exhaust systems to custombuilt Corvettes for many years. The one I selected (PN 208.50.4800) included polished, CNC Mandrel Bent 2.75-inch stainless-steel tubing that flows into their signature Double- D tipped outlets.
My C5 was already equipped with an aftermarket exhaust from another company. I decided to compare the power output of both systems. MTI Racing put the car on their Dynojet for a base run. Again, at the time of this test, the car was equipped with a stock displacement LS1 engine with a head-and-cam package. The engine pulled a respectable 429.30 hp and 417.20 ftlbs of torque at the rear wheels. Next, the car was put on the lift and the old cat-back exhaust was removed in about 15 minutes. Installation took a little more time; still, everything was secured and ready for startup in about 45 minutes. Before installation, we pre-painted the optional Callaway Tip Surround Panel. The new painted panel was secured with screws to the fascia. The panel really finished off the project.
Back on the Dyno, the car was tuned and gained 7.70 hp and 6.10 ft-lbs from the previous system.
The LS1 now produced 437 hp and 423.30 ft-lbs of torque at the rear wheels. I was pleased with the performance gain. From the outside, the car produced an exhaust note with an authoritative rumble; inside, the car was very quiet. Even when we pushed the throttle, we did not experience any annoying resonance inside the car. MTI liked the sound this system produced, compared to the one that was removed. Overall, this installation was a homerun—it sounds better and produces more power!
Tuning one of today’s computerized engines has become a highly technical skill. Tuners use computer software programs to “re-map” the car’s computer. During the installation of our bolt-on products, the car was dyno tuned when each job was completed. Every bolt-on part you add to your engine changes the computer’s air/fuel ratio. Only computer tuning can maximize the performance improvements of each bolt-on part. One of the popular re-mapping programs is LS1 Edit. Power tuning is done on a rear-wheel dyno with the engine running and the tuning computer hooked up to the car’s system.
The car is run up to fourth gear (for a 6-speed) and then accelerated from 20 mph to 140 mph, usually three times. Before any changes are made to the car’s computer, a snapshot is made of the previous settings and saved to a file. That way, they can always come back to the original setting. Next, the tuner begins altering the previous settings in 100-rpm increments, adjusting the fuel and air mixtures all the way across the rev range. Power tuning usually extracts extra horsepower without changing any mechanical part of the engine This is why each time a part was added to the car, MTI owner Reese Cox retuned the engine to maximize each change. He did this after we installed the Honker, throttle body, and cat-back exhaust. I watched as the horsepower and torque started to climb because of our new parts and power tuning. Our final run at the end of our bolt-on project was an impressive 437 hp and 423.30 ft-lbs of torque! We received an overall gain of 32.3 horsepower and 28 ft-lbs of torque with our new parts and power tuning.
The C5 was totally redesigned in 1997, on the outside and the inside. Mechanically, there were very few carryover parts from the fourth-generation Corvette. The C5 was not only lighter, it was stronger, thanks to its new Hydro-formed tube frame rails. Die-hard Corvette fans bemoaned the end of the old, faithful small-block engine that traced its roots back to 1955. A new LS1 engine was all aluminum and displaced 348 cubic inches. Sitting on top of the engine was a high-tech, poly plastic intake manifold.
Aftermarket companies attempted to improve on this part, but mostly failed. When the LS6 engine was introduced in 2001, it featured a revised intake manifold, which produced about 10 to 15 more horsepower if bolted onto an LS1. The most favored aftermarket LS1 and LS6 is the FAST intake offered by the COMP Performance Group. The FAST is priced around $900 and usually produces around 20 extra horsepower on a car with a head-and-cam and headers.
All three manifolds are tricky to replace. The C5 engine sits partially under the dash, with little room to maneuver the units off the engine. Removal process starts by removing the fuel rail and the injectors. All of the electrical leads and vacuum lines are unhooked. The vacuum lines are mostly located, unseen, at the rear of the manifold. The manifold includes many small parts that need to be carefully stored and reinstalled in the correct order. A quality shop can usually complete this job in about 30 to 45 minutes; a weekend mechanic might take 3 hours. It is not a job for the faint hearted, but the FAST does produce power and allows you to bolt on a 90-mm throttle body to your engine.
Nitrous oxide, also known as dinitrogen oxide, is a chemical formula, N2O. Under room conditions, it is an odorless, non-flammable gas with a pleasant, slightly sweet odor. It is commonly known as laughing gas, because when inhaled it can cause spontaneous laughter in people. Nitrous is used in racing applications because it increases a car’s horsepower. Nitrous oxide is injected into the intake manifold to increase power. The gas delivers more oxygen, allowing the engine to burn more fuel and oxygen. Additionally, since nitrous is stored as a liquid, the evaporation of nitrous in the intake manifold causes a large drop in intake charge temperature. This results in a smaller, denser charge, and increases power to the engine.
One of the major problems using nitrous in a reciprocating engine is that it can produce enough power to destroy it. Power increases of 100 to 300% are possible. Unless the mechanical structure of the engine is reinforced, most engines do not survive this kind of operation. Nitrous can be introduced into a motor in several different ways. Nitrous kits such as BOSS, NOS, Nitrous Express, and Nitrous Direct all offer nitrous kits. Dry kits, wet kits, and direct port kits are available from aftermarket suppliers. Again, talk with people using these systems to determine which one is right for your application. It is very important when using nitrous in your engine to maintain proper water temperatures and fuel levels to avoid pre-ignition or detonation. This condition destroys your engine. Nitrous is a compressed, liquefied gas. While normally inert in storage and fairly safe to handle, nitrous can detonate under the wrong applications. Contamination with fuels has been implicated in a handful of accidents. Carefully follow your manufacturer’s safety guidelines when using nitrous. Nitrous is brought into the engine via an electric solenoid and can be designed as a single-shot or multiple-stage system. A three-shot system, for example, can introduce power to your engine in 50-hp gains, for a total boost of 150 hp. Each system can be custom tailored to fit your needs. Nitrous bottles are usually stored in your luggage compartment, and braided lines are run to your engine. It’s a cheap way to get horsepower, but an easy way to destroy your engine. So be careful and have fun.
Do Bolt-on Products Really Work?
Now that we have reviewed some of the available bolt-on products you can put on a C5, I want to take a minute to share a secret experiment that GM performed on C5s in 1998. This experiment was actually part of the Z06 and SCCA T-1 showroom stock-racing development program. Its primary purpose was to determine what changes were required to make the Corvette competitive with its chief rivals, Viper and Porsche. GM noticed that after owners purchased their Corvettes, they began non-factory modifications aimed at better handling or quicker acceleration. So, GM conducted their own tests to determine the most effective ways to improve the C5 Corvette. They wanted to accomplish this by using aftermarket parts and established hot-rodding procedures. Corvette engineering developed the Corvette’s engine, suspension, and structure with ample potential for higher performance.
These engineering experiments provided enterprising owners with a menu of sure-fire modifications they could do to their cars. They also offered a realistic look at the types of improvements GM was required to make for the T-1 and Z06 programs. Chevrolet’s Specialty Vehicles Department used test methods that were very familiar to car magazine journalists. Standard 1998 coupes equipped with F45 (adjustable ride control) and Z51 (performance handling package) suspensions were hot lapped on the 2.25-mile road course at Moroso Motorsports Park in Palm Beach, Florida. To set appropriate performance benchmarks, test driver Andy Pilgrim flogged a Dodge Viper GTS and Porsche 911 Turbo.
Baseline tests placed the Corvette about five seconds per lap behind the Viper and four seconds behind the Porsche. The challenge faced by the Specialty Vehicles Department was to close that gap as affordably as possible, without reinventing the Corvette. In other words, make the Corvette run harder and faster, using parts and procedures that could be duplicated by a clever tuner at home. Phase I focused on handling improvements. Goodyear supplied some of the stickiest original-equipment rubber in its inventory—Eagle F1 Fiorano tires in sizes appropriate for the Corvette. Fikse 18-inch aftermarket wheels were used all around, with a 9.5-inch rim width in front and a 10.5-inch rim in back. With even a modest increase in section width (to P295/35ZR-18 size radials), the Z51- equipped Corvette jumped a significant 0.10g in skid pad cornering tests—from 0.90 g to over 1.00 g. Various sway bars were also evaluated to balance the car and achieve best results, not only on the skid pad, but also in flat-out, roadcourse lapping. The best combination of skid-pad stick, road-course speed and open-road tractability came from a combination of P265/35ZR-18 tires in front, and P295/35ZR-18 rubber in back. Upsizing the stock front sway bar with an aftermarket part available from Hotchkiss Performance helped dial in the optimum handling balance. With the Corvette’s adjustable suspension set in the Performance mode, the Viper’s lap-time advantage was chopped in half. The beauty of simple wheel, tire and sway-bar modifications is that there’s no loss of ride quality. Switching the adjustable suspension to the Tour position yielded a comfortable ride perfect for everyday commuting or cross-country excursions.
Phase II addressed the power disparity between Corvette and the Moroso pace setters. Specialty Vehicles technicians began with a standard hot-rodding trick: cylinder-head modifications. Milling 0.030 inch from the head’s deck surface delivered a nominal increase in compression ratio—from the stock configuration’s 10.1:1 to 10.9:1. The second step was what tuners call “pocket porting,” improved airflow through intake and exhaust ports by opening up the bowl areas just below the valve seats. The required hand grinding isn’t difficult, but expertise is required. So, these head modifications were assigned to an established machine shop and performance engine builder. The final step was swapping the factory camshaft for one with longer duration and higher lift. Three external alterations helped the engine’s volumetric efficiency. In lieu of the factory air cleaner, Chevrolet Specialty Vehicles fitted Nitrous oxide systems are an inexpensive way to bolt on horsepower. This photo shows the parts of a typical, 150-horsepower, electronic-fuelinjected, nitrous-oxide system. Remember, the power only lasts as long as you have nitrous in the bottle. CHAPTER 7 dual K&N conical-type filters (keeping the standard throttle body, mass-airflow sensor, and intake air duct). The stock, double-wall exhaust manifolds were replaced with single-wall designs fabricated from larger-diameter, stainless- steel tubing. A low-restriction Corsa tail pipe and muffler assembly was added downstream of the standard Corvette catalytic converter.
Dyno tests revealed a healthy 105-hp boost in output. The torque peak climbed by 69 ft-lbs, yet the curve was still flat; there’s an energetic response when the throttle is nailed at any RPM. More than 100 extra horsepower is a very worthwhile improvement. The reasonable cost of the modifications that Corvette owners could make without removing the block from their car was a huge plus. The stopwatch told the most convincing story: the combination of extra power with improved handling was more than enough to advance the Corvette to pole position at Moroso, ahead of both the $68,000 Viper and the $106,000 Porsche.
Jim Campbell, former Corvette Brand Manager, was quoted after the test, “Our Corvette Super-car test demonstrated that there was plenty of potential untapped in the Corvette that allowed it to take on true super-cars. What was also amazing was the modest investment required to reach those performance improvements. Specialty Vehicles’ menu of bolt-on modifications provided Corvette owners ample inspiration for tuning their own cars.”This test confirmed that the T-1 and Z06 program was on track. They were right; GM development engineer John Heinricy won the SCCA National T-1 championship four years in a row driving a Z06.
Written by Walt Thurn and Posted with Permission of CarTechBooks