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Project Shadow - Exhaust
Waiting to Exhale with Exhaust from Edelbrock and Next Generation
Aug 29, 2007
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Project Shadow - Exhaust
For increased access to the driver’s side manifold, we removed the steering shaft. This wasn’t difficult to do, and we made sure the wheels were straight and locked the column in position prior to removing anything. This will ensure our steering wheel alignment stays true.
With access to the engine, this job starts to get easier. Amazingly, we found reaching the exhaust manifold bolts to be best from the top. We left the plugs in place and made sure we labeled the plug boots as we removed them. Once all the bolts were removed, the driver’s side manifold was carefully liberated from above.
The passenger side manifold was likewise pulled out from the top. The only fitting we needed to access from underneath was the rear EGR pipe. This fitting becomes much more important when we begin to reinstall the new headers.
We took a look at both sides for a comparison between the factory manifolds and the new Edelbrock headers. Edelbrock’s representatives told us that while these headers were a good move by themselves, teaming them with complete full-flowing system all the way back would really show their worth. Again, enthusiasts can upgrade the exhaust as a complete system, or one component at a time based on their budget and labor capabilities. The Edelbrock headers carry PN 6602, and are built from 409 stainless steel. The port flanges are 5/16-inch thick, while the collector flange is 1/2-inch thick. All the flanges are laser cut, while the entire header assembly is robotically-welded for consistency and the highest-quality welds.
We also took a moment to compare the all-important Y-pipes to each other. We discovered a few notable differences. The factory Y-pipe relies on mounting the catalytic converters close to the manifolds to encourage quick heating and light-off. Our Random Technology replacement uses a pair of smaller cats designed for use further downstream. Because of the factory cat mounts, the exhaust pipes switch sides on the way to the muffler, the Random Y-pipe keeps the sides dedicated. The left header feeds the left cat; the right feeds the right. While the left side is a bolt-on to the Edelbrock header collector, the right side will require fabricating a small extension pipe to mate correctly. More on that later.
Our factory cats had seen better days, too. It turns out our driver’s side cat was totally shot, as big chunks of honeycomb fell out upon removal. After adding the supercharger, we’re sure the exhaust temps being fed into this cat were much higher than they were from the factory. Combine this with the hard driving we’ve been doing since the blower install, and you end up with a cat like this. It was obviously time for replacement anyway.
Okay, back to the header install. We began on the driver’s side, and found just enough clearance to slip the header in from the top. It’s wise to get the header gasket in place prior to positioning the header itself. Once you get a couple fasteners started, don’t tighten any of them until you get a couple turns on all of them. Then, tighten all the header bolts at once. Note how the header has heat shields integrated into its design; this protects the brake booster from header heat.
The passenger side header wanted to go in from the top, but we needed access to the EGR fitting on the rear of the header. This connection needs to get hooked up prior to the flange bolts, since it’d be almost impossible to do afterwards. Once installed, the header fits right and clears everything.
Edelbrock has engineered their headers to accept all of the factory emissions equipment. Once we had both headers securely bolted to the block and the plug wires back in place, we went ahead and got all the smog stuff hooked up. Access for all of the emissions equipment (except for the previously-mentioned fitting on the rear of the passenger side) is on top of the engine.
The last point to make about the header installation is a tricky issue we can help with. The dipstick is a deceptively-simple unit many enthusiasts have found frustrating in LT1-powered rides. Sure, it should simply slide back into place, but it often doesn’t. The interference fit means the dipstick hole is just about the same diameter as the dipstick tube, which makes installation hard. We found that rounding off the tip of the dipstick tube slightly made installation much easier. Once the tube gets started, a few gentle taps on the butt end of a small screwdriver inserted into the tube will get it in place with minimal hassle.
Okay, onward to the Random Technology Y-pipe. This unit is designed to fit in the stock location and only requires minor mods to fit the Edelbrock headers. We started with the driver’s side adapter pipe, which directs exhaust flow in front of the oil pan and over to the right side of the car. This pipe required no mods and bolted up easily. Remember not to completely tighten the bolts until installation is complete.
We knew we’d have to fabricate a small adapter pipe to mate the passenger-side header to the Y-pipe, so we cut the end of the Y-pipe off so we could better determine where to trim. We decided to cut back into the first bend of the pipe so we could better transition the header to the Y-pipe. The more room we had to work with, the more gentle we could make the transition. The results are great and any competent exhaust shop should be able to duplicate what we’ve done. Edelbrock includes the proper collector fitting with their headers.
With the front of the Y-pipe in place, we moved aft. Random designed this piece to mount up to the stock hangers. It does so well, but access to install and remove the rear oxygen sensor is tricky. We’d recommend installing the sensor prior to bolting the Y-pipe mount bracket in place. We trimmed a bit off the edge of the bracket too; this helped access tremendously.
While we were fabbing up the harness, we took a look at the overall Y-pipe assembly. It fits well and doesn’t droop below the frame- rails. We were hoping for a tight-fitting replacement with more flow potential that would be compatible with our factory computer. We found it in this piece from Random Technology (PN Y524).
After mounting the Y-pipe, we could begin installation of the Edelbrock catalyst-back exhaust system (PN 5675). Designed to bolt up to stock Y-pipes, we’d have to make another minor modification to continue. This minor transition was easy enough to fabricate. Again, any competent exhaust shop could create this.
You can see our fabricated transition pipe in this photo. The new Edelbrock exhaust pipe is a larger-diameter unit than the factory piece (3 inches vs. 2.5 inches), and this diameter continues into the muffler. The pipe has plenty of clearance over the axle, even in our lowered application. The pipe is also aluminized to prevent corrosion.
We chose Edelbrock’s Stainless Steel crossflow muffler with dual tailpipes (PN 5519) to replace our stock unit. Edelbrock also offers a single-exhaust muffler that offers a quieter note and more flow (PN 5676), but we liked the look of the twin pipes with no chrome tips. It closely resembles the design of the factory muffler on the outside.
These before-and-after shots aren’t just to show off our pretty new system. Look at the pipe diameters going in and out of both mufflers. This additional diameter will allow our supercharged LT1 to breathe easier, and the dyno results prove it’s worth power. It’s louder and meaner-sounding than ever, so we might be blowing our “Shadow” cover a bit. Certainly, the pipes don’t hang too low (see the profile shot), and we like that a lot. It makes for a cleaner look, and that’s fine by us.
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