Exhaust System Upgrade - What A Drag, Part 5

Sucp 1206 001 Improved Exhaust System What A Drag Part 5

Last month, we tuned the 950 Proform carburetor that resides on top of the Dart 509 in our '72 Nova SS. We swapped the fuel jets and air bleeds, added a 1-inch, 4-hole tapered spacer and a taller air cleaner, and switched from a solid lid to a breathable air cleaner lid. All the changes helped us to obtain an optimal air fuel (A/F) mixture ratio of 12.7 to 13.1 during the pull and 13.5 while cruising on the dyno.

Besides maximizing safe engine power output, this also helped to lessen the odds of engine-damaging detonation. That carburetor tuning session resulted in peak gains of 15 horsepower and 18 lb-ft torque to the wheels. At the go pedal, it felt like we gained more--it showed up in the average gains during the dyno pull from 2,500 to 6,400 rpm, where the 509 realized 24 average rwhp improvement.

After success on the induction side, it was time to move on to the exhaust. Our Nova was set up for a big-block when we purchased it, but the exhaust system left a lot to be desired. The dual exhaust on the Nova was 3-inch compression-bent pipes with 3-inch mufflers installed at the typical exhaust shop. Remarkable for this day and age, there was no crossover pipe, neither H- nor X-shaped. It sounded mean and nasty but was giving up power compared to a mandrel-bent exhaust with a crossover. A free-flowing, mandrel-bent exhaust with an X-shaped crossover would help us toward our goal of building a docile, 10-second, pump-gas street machine.

Rather than fab a system from scratch, we turned to the folks at Ground Up Restoration Supply, who supplied us with a Pypes 3-inch X-shape crossover kit, including Pypes' best-flowing Race Pro mufflers. From experience, we knew a mandrel-bent X-pipe exhaust system would deliver added throttle response, fuel efficiency, and power, with lower e.t.'s and decibels. The question was how much.

Once again, Matt Haufe and his crew at Tune Time Performance in Toms River, New Jersey, offered their shop and Mustang chassis dyno to help us get it all done. For our 30-mile ride there, we brought along our trusty decibel meter, carburetor jets, and air bleeds. It's always a good idea to be prepared to retune when making any changes, even an exhaust swap like this. Follow along to see how breathing easier can add more muscle to your super Chevy.

1 Here's a shot of the Nova strapped to Tune Time Performance's dyno. Notice the 3-inch tailpipes. We chose to run downturns after the mufflers due to the mini-tubs taking away clearance for fitment. Down the road we might try adapting the old custom-bent tails to the Pypes exhaust.
1 Here's a shot of the Nova strapped to Tune Time Performance's dyno. Notice the 3-inch t
2 There wasn't a crossover pipe in the muffler shop, compression-bent, 3-inch exhaust. The off-brand, knock-off mufflers probably didn't help either. The pipe diameter was large enough for the old 396 perhaps, but its flow was severely compromised. The mandrel-bent Pypes' system with X-pipe will cure a lot of ills.
2 There wasn't a crossover pipe in the muffler shop, compression-bent, 3-inch exhaust. Th
3a We needed to cut the tailpipes and their hangers since the exhaust shop welded everything together.
3a We needed to cut the tailpipes and their hangers since the exhaust shop welded everyth

3b The front pipes were unbolted from the collectors.
4 The rusty old exhaust was laid next to the new Pypes system to get an idea on length and fitment for the placement of the mufflers and crossover. Not seen are the included clamps and hangers that came with the kit. Up front are optional 3.5- to 3-inch reducers (304 polished stainless (PN PVR13S) that are 12 inches long so they can be cut to length if necessary for X-pipe placement/fitment with the transmission crossmember. The back pipes are also extra long for placement/fitment of the mufflers. This special X-crossover kit (PN XVF 13) will provide additional ground clearance when compared to Pypes' universal X-crossover kit.
4 The rusty old exhaust was laid next to the new Pypes system to get an idea on length an
5a There was a serious loss of diameter and flow in the compression-bent and banged up old exhaust system.
5a There was a serious loss of diameter and flow in the compression-bent and banged up ol

5b The new mandrel-bent pipes won't suffer from any loss of diameter and flow through the bends. Better exhaust flow means more power. Check out the restriction in the photo above.
5b The new mandrel-bent pipes won't suffer from any loss of diameter and flow through the
6 The 3-inch Race Pro mufflers (PN SGR13R) are made of 409 stainless to last for years and are a straight-through design claimed to flow 95 percent of a straight pipe.
6 The 3-inch Race Pro mufflers (PN SGR13R) are made of 409 stainless to last for years an
7a It was necessary for us to cut the reducers to uneven lengths because the right-side header collector was longer than the left-side collector. Roughly 7 inches were cut off from the right-side reducer and 3 inches from the left-side reducer. Cutting the reducers was necessary for X-crossover placement and clearance of the transmission crossmember.
7a It was necessary for us to cut the reducers to uneven lengths because the right-side h

7b Notice how the back pipes were tucked up high and straight right alongside of the driveshaft (balanced aluminum, from The Driveshaft Shop) for good ground clearance.
7b Notice how the back pipes were tucked up high and straight right alongside of the driv
8a The back pipes also needed to be cut so the mufflers could be tucked up close in the recessed section of the floor pan for adequate ground clearance.
8a The back pipes also needed to be cut so the mufflers could be tucked up close in the r
8b Both mufflers, along with the downturns, were trial-fitted twice before any cutting began to ensure they were placed in a good position for clearance with the big Currie 9-inch rear axle.
8b Both mufflers, along with the downturns, were trial-fitted twice before any cutting be

9a As you can see the Pypes system fits quite nicely. The downturns (PN PVD13) were faced 30 degrees toward each other to help cancel out some noise. This trick really works.
9a As you can see the Pypes system fits quite nicely. The downturns (PN PVD13) were faced
9b Now, with the X-shaped crossover and the downturns working together, the Dart 509ci sounded much more pleasing to the ears—not obnoxious like before.
9b Now, with the X-shaped crossover and the downturns working together, the Dart 509ci so
10a After the exhaust was in, we strapped the Nova on the dyno to see how much the big-bore (4.500-inch) 454 would enjoy exhaling through the easier-flowing exhaust.
10a After the exhaust was in, we strapped the Nova on the dyno to see how much the big-bo

10b It enjoyed better breathing so much there were gains of 23hp and 20 lb-ft torque realized at the wheels. Peak power was now showing at a lower 5,500 instead of the usual 6,000 rpm.
10b It enjoyed better breathing so much there were gains of 23hp and 20 lb-ft torque real
11 We brought along our old decibel meter for our ride to and from Tune Time Performance. The interior noise level (windows up cruising at 70 mph) on our way to TTP was 96 Ddb. For the ride back home interior was at a more tolerable 90 Dbl. That’s impressive considering the Nova is now missing its tailpipes.
11 We brought along our old decibel meter for our ride to and from Tune Time Performance.
12a Here's a good before and after look of the exhaust with the Nova parked in our home garage.
12a Here's a good before and after look of the exhaust with the Nova parked in our home g

12b The new exhaust was able to be hung close to the transmission tunnel/floor pan without any rubbing issues, helping us gain additional ground clearance over the old exhaust. We're very satisfied with our new Pypes exhaust—great fit, finish, and performance results.
12b The new exhaust was able to be hung close to the transmission tunnel/floor pan withou
13a Looking at the dyno graphs for torque and horsepower, it's easy to see power was gained throughout the pull from 2,500 to 6,400 rpm. Gains of the 20 lb-ft torque and 23 hp should propel the NOVA down the track roughly two-tenths quicker.
13a Looking at the dyno graphs for torque and horsepower, it's easy to see power was gain
13b Luckily we didn't need to reach into our box of jets and air bleeds to make any tunning changes since the air/fuel mixture ratio stayed at 13.1 (12.5 to 13.1 is good) during the peak torque-to-peak hp part of the pull. The new Pypes exhaust improved the average A/F from 12.7 to 12.9 during the duration of the pull (2,500 to 6,400 rpm).
13b Luckily we didn't need to reach into our box of jets and air bleeds to make any tunni

SOURCES
Tune Time Performance 931 Route 166 Toms River NJ 08753 732-349-7800 www.tunetimeperformance.com	Ground Up Restorations 91 Great Hill Road Naugatuck CT 06770 866-358-2277 www.ss396.com