A well-respected and widely-read magazine noted recently that among the top 10 performance enhancements that can be made to an engine, a set of headers ranks as one of the most important for wringing more power out of your engine. Stock exhaust manifolds stifle your engine to the point that they severely limit power output, especially on hotrodded engines. Put it this way: keeping the stock exhaust manifolds on your truck is like having asthma. You can't breathe without difficulty. While there is no total cure for your own breathing problems, fortunately there is a remedy for your truck. And the prescription for this ailment is a set of quality headers.
Choosing a set of headers
With any set of headers you choose, make sure you look for a set that has a good, thick flange for which to mount the headers to the heads. This will aid in keeping heat-related distortion (which causes exhaust gas leakage and noise) to a minimum. Also look for primary tubes that are made of thicker walled pipe. A thicker pipe will also reduce that annoying underhood "pinging" noise, common with cheap headers that are made of thin-walled tubing. A higher gauge number will indicate thinner wall tubing, while a thicker wall will have a lower number (i.e., 14 gauge is thicker than 18 gauge). Consider too how involved you care to be with your header installation. For example, there are long tube headers made for our big block trucks with all the options underhood (A/C, power steering, etc.), but installation of these sets also usually require removal of parts like the starter, steering linkage, and various hoses, lines and so forth, in addition to sometimes cutting on the frame to gain clearance for the big tubes. Shorty headers are much easier to install, and offer maximum ground clearance, whereas most long tube headers hang below the frame rails on many, many cars and trucks. This is important as most typical sport trucks are lowered. Long-tube headers will make more power than shorties if ran open, but most closed-exhaust SS's will not benefit enough from them to make the extra installation trouble worthwhile. Also look for quality welds and cleanliness of the welding area. Poor welds and lots of splatter marks are generally an indication of poor quality and rushed work. Lastly, consider a ceramic coating of some sort. Ceramic coating usually promotes higher gas velocity in addition to looking trick and lowering underhood temps. But a word of advice: if you plan to get them coated on your own, MAKE SURE they fit correctly first! You don't want to receive a set that will not line up right for some odd reason, and make the mistake of coating them at $200 or more, only to find out that they don't line up just right. Take everything apart, fit the headers in, check for a good fit, and then remove and coat them. You are warned…
OK, so I bought them, now what?
Now that you've gotten the prescription for better breathing, it's time to put it to good use. Since the most popular headers for the 454SS appear to be the Thorley tri-y and Edelbrock shorty headers, this article will deal mainly with the installation of these two sets. Your choice may vary, but due to the relative ease of installation and high quality of these sets, and the fact that many more SS's will remain close to stock than will receive wild power modifications that would benefit from huge-primary/long tube headers, I would recommend either set for any year 454SS. The only difference between the 90 and 91-93 SS's regarding exhaust systems is that the later SS's got the factory dual exhaust while the 90's had a single exhaust. Otherwise, headers made for a 90 will fit 91-93's and vice-versa-but the y-pipe will not. This is important if you have swapped the single exhaust on your 90 for the dual exhaust. You must then order a 91-93-specific set to eliminate or minimize cutting and welding of the y/h-pipe. Tip of advice regarding y-pipes: Edelbrock makes great headers, but they do not make a 91-93 dual exhaust-specific set. You'll have to get an exhaust guy to bend up some crossover pipes for you as the 1990-SS-specific-6660 set comes with a single cat y-pipe.
You'll need at least 1 1/2 feet of working space under the truck, so jack it up if you need to, and get a stand/pail/wife's makeup box to boost you up for the underhood work.
The author has also taken for granted that before you do the header installation, you have read the "Fuel Mods for Street Performance" article, and have installed the regulator and tuned the fuel delivery. This will make the power increase of the headers even more apparent under WOT.
Start the truck and warm up the heads to aid in breaking loose the header bolts. You don't need to get the exhaust glowing; just enough to make the outside of the engine pretty warm. This is especially important if you have aluminum heads. If you can, the author highly recommends that you spray some bolt penetrant (such as Rust Buster®) on the header bolts and A.I.R. tube nuts and allowing the penetrant to soak in before attempting to break the fasteners loose. This will aid in loosening and helps prevent breakage of the fasteners, which will be a major job to fix if you break off a header bolt in the head.
Now begin by removing the intake tract and spark plug wires, and lay the wires on top of the intake manifold. This is the time to remove the spark plugs if you are so inclined. Due to the increased difficulty of getting to them once the headers are on, you might want to change them now while you have room. You may also leave them out to aid in the header installation but this is not a necessary step if you are careful in the installation process. Then remove the dipstick. It is a 2-piece unit, secured by a nut to a header bolt on top and by a small c-clip at the oil pan down below.
Also disconnect the two coolant temp sensor (CTS) wires, located on the heads. Be very careful of the CTS during this project; the plastic ends get very brittle after many years and will snap off easily. If the TBI is exposed, cover it with a large lint-free rag to keep crud out of it. While you're up there, you can break loose all of the bolts on the exhaust manifolds. Prepare to spend some serious bonding time with the passenger side bolt, farthest back on the head (This is practice time. On installation, removal will seem like a cakewalk). Now go under the truck, and begin disconnecting the H or y-pipe from the cat(s) and from the manifolds. Finally remove the bolts from the y-pipe and drop it out of the way. Shake the pipe loose in a frenzied back and forth motion to remove your hands from it should you forget to do this with gloves on, and your skin melts to it. Ditto for the manifolds, which weigh about 50 pounds each. Please do not send the author mail asking how he knows this.
If you still have the A.I.R. system in place, remove the plumbing from the manifolds and tuck the piping out of the way. Be careful with the tucking if you plan to have the A.I.R. system operational on the headers. And, replace the small internal pipes (that direct the air onto the exhaust valves) from the exhaust manifold into the header set. You may discard the small pipes that are found in the stock manifolds if you plan not to use the A.I.R. system, or will be installing only the external parts to satisfy your local smog snoopers and uniformed tax collectors.
On the factory dual exhaust setup, the flanged H-pipe will be a little more difficult to remove than the slip-fit cat-to-y-pipe removal. There are 6 bolts to remove in the flange. Without a doubt, you will surely expand your children's vocabulary significantly if you let them in the garage whilst you struggle with these bolts, which have a penchant to break off, and of which are metric thread and conveniently, have been discontinued by GM. If you have the single cat y-pipe and intend to continue using a single y-pipe, or if you have purchased the dual-cat Thorley set, you need to remove the O2 sensor from the stock pipe so as to place it in the new H/y-pipe that should have come with the header set.
The Edelbrock headers are a direct replacement for the stock manifolds in the eyes of the tree huggers, so as long as you don't fiddle with the emissions stuff on them, CARB says it's OK to install them (but take note of who wrote this article and where said author lives…"whirr/bizzz!" goes the die grinder to remove some unneeded metal). First, check out the package contents to make sure you have everything you should. Edelbrock is kind enough to include just about everything you need to install this set, short of tools, bolt anti-seize and paint.
The Edelbrock headers' bolt holes on the rearmost and frontmost of the flange are C-shaped rather than actual holes to permit you to line up the headers by installing one bolt in the head, lining up the flange, and then installing subsequent bolts. So, install one of the provided header bolts, with a lock washer and solid washer, into the rearmost hole on the passenger head, and frontmost hole on the driver head. Slip the passenger header in from the top and line up the header, and install the frontmost bolt with the same washer combo. Move to the driver side and install the header from the bottom, slipping it up between the frame and engine, as the steering linkage will not permit it to be installed from the top. Tip: it helps to have a shop monkey around for this one to grab the header and line it up after you slip it in place. Does it fit just right? Yes? Good. Line up the y-pipe and fit it in place. That fits too? Even with that 5/7 dropped truck sitting on the tires, with 3" of clearance to the frame rails? I didn't think so. Edelbrock y-pipes sit very low. Time for Midas muffler to make you a crossover tube. Take the parts out and if they are to be installed as-is, sandblast and paint them, or have them coated. Sandblasting is an art in itself, and messy too, so you may want to have a buddy do this. Read on and hold off on the ceramic coating if you will modify anything.
Once you get the parts finished the way you want, installation time comes. Throw a large, thick blanket in the engine compartment, one on each side of the engine, to cover the inner fenderwells, frame parts, and so forth. This will keep the headers' fresh finish in good shape during installation. Again slip in the passenger header from the top and align it with the rearmost bolt you installed earlier. Install the front bolt. Then slip in the gasket between the head and header and install the rest of the bolts, which will align the ensemble. Tighten all bolts and, starting with the middle bolts and working out toward the ends of the flanges, torque them to 40 ft/lb if you have an iron head. Torque specs for aluminum heads are slightly different. Consult your paperwork that came with the heads. That rearmost bolt will take more time to tighten than the rest of the 15 header bolts due to its extremely difficult position. Use some anti-seize on all the bolts to prevent them from getting stuck in the heads. You'll also need to use the OEM dipstick-header bolt on the passenger side so as to secure the dipstick in place.
Onto the driver side, get your shop monkey and slip in the header. The procedure for tightening is the same as the passenger side. Reconnect the A.I.R. tubes and grottings (if applicable), plug wires on the driver side, and CTS connectors, if you were skilled enough not to break the CTS. On the passenger side, you will need to replace the stock straight boots on the plug wires for 120* angled ones, also provided with the headers, to keep them off of the primaries. Read the Custom Plug Wire article by this author for more information on how to do this.
Now move onto the y-pipe. Smear a little conductive anti-seize on the threads (DON'T get it onto the sensor fins!) and install it in the H/y-pipe that you'll be installing. It is important to use electrically conductive anti-seize as the O2 sensor grounds through the threads. Fit the pieces of the y-pipe together (provided with Edelbrock's set, if you used it). Then fit the y-pipe (H pipe for you dual exhaust users) into place, and bolt everything together from the underside. Installation is now complete.
The installation procedure with the Thorley headers is very similar to the Edelbrock header installation. The tubes of the Thorleys are 1 5/8" while the Edelbrock tubes are 1 ¾", so slipping the Thorley headers in is no more trouble than the Edelbrock headers. The A.I.R. tubes mount in the same manner as well. However, the driver's side header does not come furnished with a steering-linkage heat shield as the Edelbrock headers do, so slipping it in from underneath will prove a little easier. Also, with a dual exhaust setup, you need only remove the H pipe and replace it with Thorley's provided pipe, which offers about the same amount of ground clearance as the stock setup. This means that if you have any more than a 2/4 drop, it would probably be a very good idea to have your local muffler ace weld up a new crossover pipe from the driver side of the engine. Thorley does offer a special "lowered" H/y-pipe for use on lowered trucks; however, the author has no experience with these specialty pipes.
On these 2 sets in particular, there tends to be a healthy amount of splatter inside the header primaries from welding on the flanges. Also, if you desire to remove you're A.I.R. system and do not want to drill out/weld the bungs over, you may grind the excess off of the inside of the primaries, making the tubes smooth again. The same techniques described in the author's TBI porting article apply here. This should take about 2 hours for each set of headers. Just grind away the metal that protrudes into the header tubes and smooth the metal into the tubes. This is not difficult as the welds are on the outside, and cutting off this excess material inside the tubes should not cause the welds to fail. Once the A.I.R. bungs are generally cut off inside, switch to a small stone and hone the bungs down to make the tube-to-bung transition smooth. Then address the splatter marks, some of which are down to the first bend in the primary. You will save much frustration and do a very good job if you own a Dremel tool with the flex bit extension. Cap off the bungs on the outside with some black pipe plugs. These are available at your local plumbing supply store. They are ½", standard tapered pipe thread. Don't use Teflon® tape; just install them with a little oil and tighten to 40 ft/lb. Lastly if you do not drive in colder temperatures then you may remove the heat stove on the passenger side header. This does nothing for performance, but makes the header look a little cleaner, especially when used in conjunction with a more traditional air cleaner assembly. Use a cut-off wheel and be very careful not to damage the header tube while you knock off the weld and cut both sides of the heat stove pipe (cut it in half) in order to remove it.
Finally, with the turn of the last wrench the prescription has been taken, and your SS's breathing problem is remedied. With your header installation completed, re-tune your fuel delivery to maximize your power output at WOT. Now that's a breath of fresh air.