It's a simple proposition. In the case of an engine, what the induction system sucks in, both air and fuel-wise to make power, it must pump out efficiently to make admirable power. If any exhaust gasses remain in the combustion chamber, then less fresh air and fuel is allowed in to burn. Furthermore, if the engine has to struggle to push the spent fumes through the attending exhaust system, then the powerplant will be robbed of ponies as well simply because the engine can't exhale. Think of it like this. Take a coffee stirrer and try and blow air through it. Then do the same thing with a normal soft drink straw. The soft drink straw is easier to blow through, right? That is what an engine has to deal with when equipped with a restrictive exhaust system, as it has to work harder and expend more effort to push the exhaust fumes through said piping.
With that in mind, we set out to improve the exhaust side of this '68 Chevy Nova. While the car isn't equipped with a logjam for an exhaust system, this X-body had a few problems of its own. Originally supposed to be a street/strip car, the little Chevy has spent the last nine years seeing strip duty only in the NHRA's Pro and Street categories.
Thanks to a 406ci small-block topped with Dart Pro 1 heads, a decent camshaft, an Edelbrock intake, and a worked-over Holley 750 cfm carburetor, the Nova has the capability to foray into the low 11-second zone. Thanks to the 11.50-second elapsed time limit for the Street category, ballast and a few other tricks slow the car down to consistent 11.50 runs.
With consistency of the utmost concern, new attention was focused on the exhaust system, which had taken a beating thanks to a broken driveshaft at 5,600 rpm. The ensuing whipping of the 'shaft mangled the exhaust piping, and even broke the flange on the driver-side header right between the numbers one and three cylinders. With the broken flange leading to an serious exhaust leak that would result in a backfire after letting off of the throttle at high rpm, we knew that not only were we taking a chance in burning a valve with the exhaust leak, but the mangled system and said leak were costing power.
To solve our dilemma, we called up a host of suppliers to get our little Nova back to the track in better-than-before condition. We started by ditching the broken headers for a new pair supplied by Hooker. While we made a change from what was on the car, we felt the change would not only help low-end power, but installation as well. Off came the Hooker 1 3/4-inch Super Comp headers, and on went a pair of 1 5/8-inch Competition headers.
"When going from bigger to smaller primary tubes, you will have better torque," says Matt Held, formerly of Holley Performance Group. "If the size of the tube is totally wrong, you will see not only a gain in torque, but in power as well. You will also notice better throttle response."
"The Competition headers are the affordable version from Hooker. The primary tubes are equal in length, and they use 16-gauge material, making them a bit heavier. Super Comp headers will have a different primary tube size and length, and the collector is specifically tailored to the engine's horsepower output and racing needs."
The headers we chose were, which costs a bit more, but add longevity to the headers. "Ceramic coating will help control the amount of heat that radiates from the tube, thus lowering under hood temperatures," Held explains. "The ceramic actually bonds to the metal, and will protect the metal from corrosion and rust. In some harsh environments where the headers might be subjected to road salt or acid rain, the ceramic will only slow the process of corrosion."
Here you can see where the driveshaft flopped around and beat up the exhaust pipe. In spots, the pipe was also starting to rot through. Both the bent pipe and the rotted spots made for some area of impeded flow. It was time for some new pieces for sure.
Here you can see how the driveshaft-induced destruction went all the way up to the header flange, which broke right between the numbers one and three exhaust ports. The broken flange led to a major exhaust leak, resulting in some noticeable backfires on deceleration. The backfire was caused by cold air making its way into the hot engine. Prolonging this problem could have led to burning the exhaust valve.
With the exhaust system all beat up and, in some spots rotted through, there was no way we were going to bolt up our nice new headers to that junk. To solve that problem, we dialed up Summit Racing, which sent out one of its header-back dual exhaust systems. With the car already being equipped with a 3-inch system, we specified the same diameter pipe for our new exhaust kit. The difference between the two came in the fact that the old system was crimped, while the new system is mandrel-bent, meaning a freer-flowing system and more power. The kit came without mufflers, but that was fine with us, as the Borla XR1 race mufflers that were already on the car would be reinstalled with the new system.
While all of this new pipe was great, we asked ourselves the great question--that being, would the car make more power without the mufflers or not. The problem is, to keep the Nova legal for the class it would compete in, we needed to keep mufflers on the car with tailpipes. For those rare occasions when the car would run outside of the Street category, we wanted the option to crack her wide open and make some noise. With that in mind, we gave Barry Adler a call at Quick Time Performance (QTP). Adler listened to our situation, and promptly kicked over a set of QTP's electric exhaust cutout kits. While QTP makes the traditional-style cutouts that require you to get underneath the car and uncork the exhaust, we had to agree with Adler when he said we live in the 21st century. Hence the inclusion of QTP's 3-inch electric cutouts, which operate with the simple press of the included toggle switch.
"With these cutouts, you don't burn your hands or have to get underneath the car," Adler explains. "The cutouts come in 2 1/4-, 2 1/2-, 3-, 3 1/2-, and 4-inch sizes. We also have 2 1/4 to-3-inch diameter oval-shaped cutouts for cars that are lowered or have ground clearance problems."
Before we rolled the Nova into the installation bay for the parts install and subsequent dyno testing, we quizzed Barry on the advantages of running the cutouts, along with the ideal location. "The gains are seen everywhere," he comments. "With the ultimate exhaust system, gains of three to five horsepower are seen. With other systems that are not as free flowing, you will see more. It all depends on how restrictive the system is. The gains are seen because you are reducing exhaust restrictions. A muffler not only lowers sound, but also creates backpressure and slows down exhaust velocity. Open headers have very little to no restriction, but it also has no velocity or backpressure. Backpressure creates velocity, which helps pull the exhaust fumes out, but you don't want too much of it either."
When it came to mounting the cutouts, not only was performance a concern, but clearance was as well. "Ideally, you want the cutouts to be mounted 12 to 18 inches off of the header collector, as that is the general rule of thumb," Adler explains. "The old school method is to paint or draw a chalk line along the length of the exhaust pipe. Take the car for a couple of rips, and then check the line. At the point where the line reappears, this is where you want to put the cutout, as this is the best place in terms of flow. Of course, clearance is an issue, so keep that in mind."
In a sense, this install was a three-part deal, as we had Gil Davis of Davis Race Engines install the headers (and the killer looking Dart valve covers). Crazy Horse Racing then installed the new exhaust pipes a few weeks later, followed by W&W Auto & Truck Repair taking the time to install and wire up the QTP cutouts. The headers were easy to install when compared to the Super Comps, and the new exhaust fit perfectly, even though the mufflers, which were previously located four inches behind the headers, were moved rearward to the stock location.
The mufflers were originally bolted to a flange on a collector extension. The kit called for relocating the mufflers to the stock position, so we had to cut the flanges off of the mufflers so we could reuse them.
As for the QTP cutouts, well that install was as easy as pie. It took us a little over four hours at W&W Auto and Truck Repair in Bound Brook, New Jersey, to get the job done, but that's only because we were extra careful in measuring, cutting, and welding. The cutouts fit along the first portion of the mid-pipe, with the electric solenoids that operate the cutout blades being hidden between the cutout itself and the inner portion of the subframe connector. The only gripe we had was we should have gotten a larger diameter cutout, as we had to open up the exhaust pipe opening to slip the cutout inside slightly. Without performing that task, we would have had to flush weld the cutout to the pipe, which would have been messy and nasty looking.
The wiring was also simple. Once the Weatherpak connectors were linked up, we had to drill a hole in the firewall and run the wires into the cabin of the car. After the toggle switch was mounted to the shifter pedestal, we ran the power lead to a key-on power source, cranked the big 406 Mouse up, and depressed the toggle switch. A few seconds later, we were rewarded with that open header cackle we all love so much, without having to go under the car and undo a few bolts to get it. Ah, the beauty of technology!
While track data wasn't available to gather since the install was performed in the middle of winter here in wonderful northeast, we were able to strap the Nova to the dyno to see just what it made with the new pipe on and the cutouts both open and closed. We cruised down to Crazy Horse Racing in South Amboy, NJ, where the car was tightened down to the rollers, fired up, and beat in anger. With the new exhaust on and the cutouts closed, the Nova cranked out 355 rear wheel horsepower. After a short cool down period, we depressed the toggle switch, allowing the solenoids to cycle the butterflies on the cutouts into the open position.
The muffled sound emanating from the tailpipes quickly changed to a nasty, angry cackle with a slight hint of NASCAR Cup car to it. The loud pedal was planted, the small-block screamed, and the open cutouts allowed the Nova to crank out 366 rear wheel horsepower, an 11 horsepower increase. We would have loved to compare the torque curves but a glitch in the dyno prevented us from doing that.
Either way, the little Chevy II made a noticeable increase in power with the cutouts open, with the air/fuel ratio remaining nearly the same both open and closed. The A/F ran between 12.1-12.3 closed, with a slight jump at 4,000 rpm to 12.5 when the cutouts were open. Other than that, the A/F ratio both open and closed were nearly identical. While the car could stand a jet change to lean it out and make some more power, we decided to leave things well enough alone and do a honest-to-goodness A to B comparison. Timing was set at a conservative 34 degrees.