So your engine is all apart, and you’ve got containers and boxes of old parts seemingly everywhere. How much of it should you, or can you, reuse? A lot of this has to do with the state of wear your engine parts are in, but it depends even more so on the desired characteristics of your end product. Do you simply want a stock engine with restored stock efficiency and performance, or are you looking to put together a 650-hp high-performance LS? You’ll need to decide this well before you start picking through online catalogs, or loading up parts and heading to a machine shop.
This Tech Tip is From the Full Book, HOW TO REBUILD GM LS-SERIES ENGINES. For a comprehensive guide on this entire subject you can visit this link:
SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. You can copy and paste this link to share: http://www.lsenginediy.com/ls-engine-rebuilds-parts-selection-guide/
This chapter runs the gamut of all the major (and many of the minor) parts that make up a Gen III/IV engine, and is meant to give you as much guidance as possible in selecting the right components for your application. We’ll tell you what to look for when you might want to reuse a part, and also rule out items you cannot. In some cases, we’ll demonstrate how to use tools we discussed in Chapter 2 to help verify the quality of your parts. While many of these tools are by no means mandatory, they can help save you time and aggravation since you’ll have a better idea which parts your machine shop will succeed in refurbishing for you, and thereby avoid phone calls telling you that your parts are no good. We’ll also give advice on what parts you might think about substituting in a high-performance engine. In fact, we’ve scattered information throughout the book (much of it in this very chapter) that focus on parts for making and withstanding high amounts of horsepower!
Parts Selection Words of Wisdom
You probably had a decent idea of what kind of engine you wanted to put together before even beginning to tear your stock LS apart. It’s time to chisel that rough vision into a very clear and precise one. High-performance or not, now is the time to select, and acquire, each and every one of your engine parts. Choosing the combination of components that’s right for you is critical to the success of your rebuild project, and the individual parts need to closely complement one another.
Lack of attention to detail here can not only cause parts mismatch leading to lost power and efficiency, but in severe cases, it can lead to eventual engine failure, or even make your engine impossible to assemble! Imagine spending hundreds or even thousands of dollars on parts and prep, only to discover during pre-assembly that some of your rotating assembly parts simply won’t work together. Being stuck with expensive parts you’ve already had machined (or otherwise have rendered non-returnable) is a nightmare scenario you most assuredly want to avoid.
Be advised, however, that while doing your homework here can assist greatly in avoiding parts compatibility problems, there is always the chance that some additional effort will be required in getting them to fit together. Minor parts fitment issues are a normal part of any engine build. The distinction lies in the key term, “minor.” For example, it’s not unusual for aftermarket rocker arms to require minor modifications be made to factory valve covers to obtain the proper operating clearance. Less significant problems like these are often unavoidable, particularly when combining aftermarket parts made by different companies (and we will deal with many of them in Chapter 7, Pre-Assembly). The type of scenario you would want to avoid right now is purchasing rocker arms that are not physically compatible with your chosen cylinder heads; for example, buying a standard set for later-style heads that require an offset intake rocker. An inattentive choice like this could result in a not-insubstantial headache later on, so putting the time and effort in now will keep the major problems to a bare minimum.
Finally, the blossoming parts market for LS engines continues to expand on a monthly (if not weekly) basis. To keep yourself up-to-date on the latest component availability, it helps to check out LS-oriented websites as well as those of aftermarket parts companies (listed in our source guide). Magazines like GM High-Tech Performance will also help keep you tabbed on the latest trends. Do your research, and you can select a combination of parts that will not only work together in your engine, but will yield the power and reliability you’ve been dreaming of!
The largest part of a Gen III/IV engine is also the one that’s most easily and commonly reused. The vast majority of the time, an engine block can be refurbished by a machine shop and made as good as new, or better! This is particularly true if this is the first time your LS engine has been disassembled (that is, the block has never been used in a rebuild before), as this means there should be plenty of metal left on surfaces that need to be re-machined. We’ll discuss the entire block machining process in Chapter 5.
If you discover (or already know) that the block has been used in a prior rebuild, don’t sweat it yet. Depending on how much material was removed from the bores and other areas in that prior rebuild, you may be able to reuse the block again. Your machine shop may have the final say on this, as they can measure surfaces with precision tools and also have the experience to know “how far you can go” with a given block, and the physical limits of what their machining equipment can accomplish.
There are other issues that can render a block unusable. In some cases, block damage may have occurred during operation due to engine part failure or improper maintenance. The potential for physical harm is particularly high for engines that didn’t run correctly (or at all) prior to disassembly. Depending on the nature and extent of any damage, the block may be beyond hope. For example, internal engine component failure may have caused part of the block casting to crack or be broken completely. Or perhaps the engine was run completely out of oil, overheating the main bearings to the point where the block’s main bearing bores are too far out of shape.
If you and your machine shop determine that your block can’t be reused, it’s not the end of the world. You can likely find a good used block on the relative cheap if you hunt around. If you find yourself in this situation, try to find a block that’s as complete as possible. Engine bolts are optional, but at a minimum, you’ll need a block that still has its original main caps (numbered 1 through 5). Purchasing and machining new caps to fit can be very expensive and will leave you wishing you just bought a whole new block. Also, one of the most important considerations when shopping for a used block is to make sure to find one that hasn’t been sitting exposed to the elements. Dirt and grime will usually wash off, but what you should be most concerned about is moisture. Obviously, iron blocks are most susceptible to corrosion, but parts of an aluminum block can rust too. However, even rustcoated cylinder walls may be OK if it hasn’t eaten its way too deep.
GM also sells brand-new, bare LS engine blocks in several different bore, material, and equipment (ex., AFM-ready) configurations. As we mentioned in Chapter 1, a great thing about the Gen III/IV engine family is that there is so much cross-compatibility of parts, and this is a boon for high-performance. Some blocks offer potential advantages like improved bay-to-bay breathing windows (for reduced pumping losses) over earlier LS castings, but this is only the beginning. Want to swap your iron block for an aluminum one and save some weight on the front end of your vehicle? Or perhaps you’d like to substitute your 3.898-inch bore LS1 block for something with a larger bore, like a 4.000-inch LS2 or 4.065-inch L92? No problem—most engine parts will fit (with the appropriate changes like piston size of course)! We’ll discuss any parts substitutions you might need to make as we proceed along, but by and large, most engine components will work almost across the board.
And if you’re really serious about power, you should know that factory aluminum blocks are generally good for (at a minimum) a couple hundred extra horsepower, while iron ones even more than that. For the ultimate in reliability and power potential, you might even think of stepping up to an aftermarket engine block. Check out our “High-Strength Blocks from GMPP” Workbench Tip for more information.
The term “rotating assembly” generally refers to an engine’s combination of crankshaft, pistons, and connecting rods, but it can also include related paraphernalia like piston rings and bearings. All of these items need to be selected in concert, as each must be compatible with the others in physical dimensions, mass, and material. In addition, once all rotating assembly parts are selected, they’ll need to be balanced (a process we’ll see in Chapter 5).
When selecting each of these components, the money you’ll need to spend will rise with the amount of horsepower you’re looking to make. As we’ll explain below, there are a lot of quality components that GM put into Gen III and IV engines from the factory, and for many stock and moderate rebuilds, you’re often just fine reusing some of them. As we discuss each of the items that make up a rotating assembly below, keep in mind that it’s easy to go overboard and spend a lot of money on parts tougher than you need for your application. Perhaps just as significantly, it’s possible to “cheap out” and buy parts from less reputable companies. There is a difference when it comes to internal engine parts, and it is far better to spend a little extra money on a company with a good name. This way, you can rest easy knowing the parts will stand the test of time—and your lead-weighted right foot!
One of the most expensive parts of an engine is the crankshaft, and the good news is that all Gen III/IV engines were equipped with excellent cranks from the factory. Even the weakest of LS cranks are cast from a nodular iron material, so they are high quality and popular to reuse. Some engines (like the LS7) even had forged steel cranks for high horsepower with even greater reliability. Though Gen III/IV crankshaft stroke, counterweight design, and material varies between engines, all main and rod bearing journals are a common size across the LS engine family (2.558 and 2.099 inches, respectively), enabling one crank to work within virtually any block and with most any connecting rod. If you’re thinking of swapping your crank for a different factory unit, here are a few of the more notable things to keep in mind:
Rear flange width: Most factory cranks use a narrower flange thickness where the rear crank seal rides. However, some early 4.8L and 6.0L Gen III truck engines used a crank with a wider flange. The difference had to do with varying GM transmission dimensions. The short-flange cranks are actually compatible with all transmissions (you can buy a flywheel/ flexplate spacer kit from GM if need be), so you should steer clear of wide-flange cranks in order to avoid a potential incompatibility on this front.
Snout length: Make sure the crank that you’re looking at has the correct snout length for your application. Some examples of particular concern: LS4 engines had a 10mm shorter crank snout to help further alleviate the packaging concerns inherent with FWD applications. Also, dry-sump engines such as the LS7 and LS9 had longer crank snouts to accommodate those engines’ more complex oil pumps.
Reluctor ring type: To aid compatibility with your engine electronics, it makes things easier if you pick up a crank that already has the correct 24X or 58X reluctor ring installed onto the back (even though you may have to replace it anyhow if it’s determined to be out of shape). Also, very early 24X reluctor rings may not work properly with all electronics and should be avoided. Aside from the earlier rings being unrecessed, you can tell them apart because the two ring “halves” are very narrowly spaced. (The crank flange photo on the previous page has an early style 24X ring, while the ring comparison photo below has the updated 24X unit.)
Counterweight design: Even crankshafts of the same stroke used varying-style counterweights to compensate for the pistons and rods used in different engines. Though having a crank with the wrong counterweights probably won’t make balancing your rotating assembly impossible, it could make it substantially more expensive. See Chapter 5 for more information.
Drilled vs. undrilled: Many truck cranks do not have the centerline of the crankshaft drilled out. This makes the car cranks more desirable, as they’re better at evening out crankcase pressure (and are also a little lighter). This drilled hole does not affect strength.
Regardless of whether you’re going to use your own crank or another factory unit, used crankshafts need to be refurbished before they can be incorporated into an engine rebuild project. At a bare minimum, they’ll need to be cleaned and have their journals checked and polished, and we’ll do all of that at the machine shop in Chapter 5 (along with balancing). But for now, look at the photo captions for some tips on what you can do at home to see if your crank is even capable of reuse. The main items to look for are excessive scratching or scoring on any of the surfaces, but you’ll also want to physically measure some critical dimensions of the crank to see what you’re up against as far as machine work.
Perhaps you’re rebuilding for high-performance and have decided your needs (or desires) go beyond what a factory GM crankshaft can handle. Whether you’re looking for reliability at higher amounts of horsepower, or a longer stroke for increased cubic inches, the aftermarket has you covered. A variety of quality cast and forged crankshafts are available for the LS engine family, featuring strokes from stock to well over 4 inches. Again, brand reputation is everything here, so choose wisely! If an aftermarket crankshaft is the route you’re going to take, you should have a look at Chapter 5 before ordering one (in our discussion of balancing the rotating assembly, we mention certain crank-related considerations you should keep in mind).
The factory pistons used in Gen III/IV engines vary in exact aluminum alloy composition, but all are an excellent casting (or, in the case of the LS9, forging). Depending on the use your particular engine saw, its pistons may be in very good condition. In theory, you could even clean them up and reinstall them into your block with new rings (after just a light deglazing of the cylinder walls). In practice, however, this wouldn’t make much sense, and falls more along the category of an engine repair than an actual full-on rebuild. First of all, some amount of wear to your pistons and cylinder walls has inevitably occurred no matter how few miles your stock engine ran, so though acceptable results can sometimes be had with this technique, piston-to-wall clearance will be most optimal if you hone your block and install oversize pistons.
Another reason to install oversize pistons is that most factory LS engine blocks are machined without simulating block-distorting bolt torque, and this means that although the bores of bare factory-machined blocks may spec out just fine when measured, tightening the cylinder heads and main caps in place results in them being out of round during actual operation. Problems here are especially true with aluminum blocks. Since getting the cylinders into the correct shape inevitably requires removal of material from the cylinder walls, this means clearances normally can’t be proper with a standard size piston. All of this translates to the need for an oversize piston for improved efficiency and longer engine life.
Not reusing your stock pistons should be a no-brainer, and we’ll discuss the block machining operations needed to accommodate oversize pistons in Chapter 5. However, choosing a set of oversize pistons definitely requires some thought. There are a staggering variety of LS pistons on the market, and the number continues to increase. Start searching around, and you’ll find yourself bombarded with a variety of piston brands in an innumerable array of shapes, sizes, and alloys. After selecting the exact oversize you’re going for, the first choice to make is whether you’ll want a cast or a forged piston. Basically, cast pistons are formed by pouring molten metal into a mold, whereas forged pistons are forced into shape while in a semi-molten state. The latter process yields a more durable part and one much better suited to a high-performance application. (Take note that the cast vs. forged strength argument holds with other metal parts like cranks and rods, too.)
The selection process then turns to the exact aluminum alloy you’d like for your pistons, and this can get tricky. Without getting overly technical, we’ll just say that cast pistons are usually available in eutectic or hypereutectic aluminum alloys, with hypereutectic being the preferred material for most applications. The most common alloys used for forged pistons are 2618 and 4032 aluminum, and it’s 2618 that is considered the stronger (albeit heavier) of the two. Not all castings or forgings are the same, though, even if they are of the same alloy; so for most applications, selecting a manufacturer with a good reputation is more important than anything else!
Keep in mind also that—along with cylinder head combustion chamber size, type of head gasket used, and other factors—the shape of the top of the piston will dictate your engine’s compression ratio. Flat-top pistons (with or without valve reliefs) are the typical choice for standard to high-compression engines, but high-performance engines with aggressive camshafts will definitely want pistons with sufficiently deep valve reliefs to achieve the necessary piston-to-valve clearance. So-called domed pistons should be avoided in most cases, as while they most certainly raise compression ratio substantially, many engine builders feel that their shape tends to interfere with the combustion event (a smaller combustion chamber is considered a much better method of raising compression ratio). See the Appendix for the engine math needed to calculate compression ratio.
A final note on pistons involves wrist pin style. The wrist pin (or simply pin) that connects the piston to the connecting rod can be of either a pressed or floating style. Though we’ll talk more about this in our connecting rod section below, for now we’ll note that almost all pistons you can buy include wrist pins, so you’ll need to make sure the pin type is compatible with the rod you are using (pin diameters can differ, too). Locking rings for floating pins are normally included with pistons as well.
Closely related to the issue of pistons is that of the piston ring set, comprising both compression rings and oil rings. Compression rings seal combustion gases from leaking past the piston into the crankcase, while oil rings prevent excessive engine oil from making its way above the piston and getting burned off. Type and material of piston rings vary nearly as much as pistons themselves, and the reasons for this go beyond the more obvious characteristics like piston diameter and size of ring grooves (and their vertical placement). Changes in intended engine application will dictate alterations to ring sets as well; for example, higher-horsepower applications will want rings made from more heat-resistant materials. Similarly, some high-performance builds may wish to go for a set of lower-tension rings to reduce drag and free up horse-power. Fortunately, piston manufacturers will almost always supply recommendations on rings, so this can help take a lot of guesswork out of this area.
One of the main things to decide when shopping for rings is whether you’d like a pre-fit (“drop-in”) or file-fit ring set. Although oil rings are pre-sized to a given bore no matter which ring set style you choose, file-fit compression rings will be supplied with a narrow gap that must be filed wider prior to engine assembly. We’ll show you how to file fit rings in Chapter 7, Pre-Assembly. If you’d like to avoid this step, drop-in sets already have their compression rings sized to a given bore diameter, but because their endgaps are designed to work in a greater variety of engine environments, they will not be as precisely tailored to your application as would be possible with a file-fit set.
Some of the most commonly (and easily) reused internal LS engine parts are the connecting rods. The vast majority of Gen III/IV rods measured 6.098 inches in center-to-center length, but there were a few exceptions to this. For example, rods used in 4.8L engines were about 0.180-inch longer, while the titanium rods used in LS7 engines measured just 6.067 inches. Keep this in mind if you are thinking about swapping in rods from a different engine.
Normally, used connecting rods will be in good condition and require very little machine work to get them ready to reinstall into an engine. If you’re going to reuse your rods, about all you can do for now is have a preliminary look at them before taking them to your machine shop. Have a look at the neighboring photo captions for some inspection advice.
High-performance enthusiasts will be happy to know that, like factory crankshafts, GM connecting rods can handle lots of horsepower—so unless you plan on spinning a lot more RPM than stock, these rods probably do not need to be replaced on a naturally aspirated engine. This changes when you’re talking about modifications like increased cubic inches. For example, while stock GM connecting rods could theoretically be used with a stroker crank, a few obstacles stand in the way of this, including compatibility issues with the large-radius journal fillets of many aftermarket cranks (as well as your ability to find a piston whose compression height will match up with a stock-length rod and stroker crank). Stroker or no, aftermarket rods are also the way to go if you’re looking for a piece that will be durable for higher-stress applications like nitrous oxide use.
A few pointers on aftermarket rod selection should help give you some direction. From the standpoint of engine operating characteristics, many readers probably already know that longer rods increase piston dwell time at TDC and also decrease cylinder wall piston skirt loading. On the other hand, shorter rods increase piston speed and pumping action at the expense of some frictional losses. But keep in mind that the length of rod you use is physically intertwined with your crankshaft stroke and the compression height of your piston (as shown in the Appendix). More rod length means less compression height, and for this reason, long rods can have an adverse effect on piston and ring durability in large-stroke engines. More compression height leaves more room for the rings, allowing them to sit lower from the face of the piston. This shields them from the heat of combustion and simultaneously strengthens the top ring land, particularly important in nitrous and forced induction engines. For all of these reasons, it should be clear that a compromise is in order when it comes to choosing the length of rod that’s right for your engine.
Since the LS is a cam-in-block engine, there are three different types of bearings that you’ll need to worry about. They are: main bearings, connecting rod bearings, and camshaft bearings. All of them are wear items, and they must be replaced in any rebuild project.
Often considered part of the rotating assembly, main and rod bearings must be selected to match the connecting rods and crankshaft being used. Probably the most important thing to keep in mind is the shape of the edges of these bearings. While standard-style bearings are compatible with factory crankshafts, the special filleted main and rod journals of many aftermarket cranks require matching chamfered bearings. The manufacturer of your crankshaft can advise you on which bearings to use and will often sell the correct set themselves.
There are a few other factors to consider with main and rod bearings, one of which is the material that makes up the bearing. Here again, you should go by the recommendations of your crankshaft manufacturer, but we’ll just mention that a wide variety of bi- and tri-layer bearings are available, and every manufacturer does things a little differently. Bearing layers may comprise steel, copper-lead, aluminum, Babbitt, and other materials depending on the company you are looking at and the intended application of the bearing (for example, level of horsepower).
A final main/rod bearing consideration is what’s known as oversize or undersize. While factory crankshaft main and rod journal diameters are the same across the LS family, machine work can slightly alter the sizes of these journals (and less commonly, the bores that they ride in). So depending on the machining that must be done to your crank, block, or rods, you may need so-called undersized or oversized bearings to establish the proper running clearances for engine oil. We’ll see more of this when we establish bearing clearances in Chapter 7, but for now, be aware that sometimes the need for a different bearing might not be discovered until you actually pre-assemble your engine.
Cam bearings are a little more straightforward to deal with than main and rod bearings as there are no varying shapes to be concerned with and the required inside diameter of the cam bearing is universal for all Gen III/IV engines using stock-diameter cam journals (which are the same regardless of whether you’re using a factory or aftermarket LS camshaft). Also, because the physical stresses on cam bearings are peanuts compared to those experienced by the main and rod bearings, cam bearing material selection is barely worth worrying about.
The rotating assembly is what makes your engine pump air and fuel, but along with the camshaft, the cylinder heads determine how much of the mix actually enters the engine. High-flow cylinder heads have always been the key to small-block power, and the LS continues that tradition.
Many stock and moderate high-performance rebuilds may consider reuse of the factory cylinder heads, as even stock LS heads flow well thanks to their efficient port design. Initially, however, your heads probably will not look the part of a reusable item. They’ll have plenty of carbon and oil residue in the exhaust and intake ports, not to mention all sorts of buildup in the combustion chambers. First impressions can deceive, however, as most Gen III/IV cylinder heads can be reused without much trouble. One of the great things is that nearly all LS heads are cast from aluminum, which is good not just because it makes them lightweight, but because it makes the heads easier to machine. This holds true not only when doing routine rebuild work like replacing valve seats, but when porting them for increased flow and horsepower potential!
Cylinder head porting is a science in and of itself, and there are many high-performance shops that specialize in this service for LS heads. If you’re interested in going this route, you’ll want to do some research into which of these shops are reputable (an incorrect port job translates to reduced port efficiency or even damaged heads). Some shops even offer CNC porting for the ultimate in consistency port-to-port. You should also keep in mind that because there are a number of different head castings used in the Gen III and IV, they vary on suitability as a starting point for this process, so don’t be surprised if a shop recommends swapping your castings for other factory ones.
Though some factory heads offer the potential for excellent flow, moderate to extreme high-performance applications should also consider going with an aftermarket LS cylinder head (i.e., one not based on a GM casting). Besides offering additional flow capability, aftermarket heads typically include strengthening features like thick deck surfaces and steel head bolt hole inserts. The aftermarket is continually bringing new LS-style heads to the market, and there are a lot of quality castings to choose from. Each company offers myriad options like intake port size and configuration. There’s also a huge range of combustion chamber sizes available to fit a wide variety of bore sizes and achieve the compression ratios that different LS customers are looking for. With all of these options to choose from, you should have no problem finding an aftermarket head tailored to your desired application.
For our purposes, the term valvetrain refers to every part of the engine involved in actuating the valves, including the timing chain assembly, camshaft, lifters, pushrods, and rocker arms, along with valvesprings and related hardware. Depending on the goals of your rebuild project, it may be possible to reuse some of these components from your Gen III or IV engine.
One of the items that’s easy to reuse is the LS engine’s hydraulic roller-type camshaft, which probably will have experienced little, if any, wear. Because LS cams are made from steel billet with induction heat treated lobes, any damage generally will only have occurred due to a problem like a failed lifter. If you’re dissatisfied with the surface of your cam’s lobes, consult your machine shop on polishing options. For severely damaged lobes, cams can actually be ground (and the profile even changed if desired), but you’ll need to find a very competent shop to do this and it’s probably more cost-effective just to buy another cam.
To a certain extent, the same reusability goes for the rollerized-trunnion rocker arms that all factory Gen III/IV engines were equipped with. However, other items should never be reused because of their tendency to wear out over time, most significantly the valvesprings and timing chain assembly. You may be thinking, “there are no moving parts sliding against a valvespring; how the heck can it wear out?” The answer is metal fatigue, and valvesprings that had a certain amount of seat pressure when installed will have nowhere near that after tens or hundreds of thousands of miles. Also, though not nearly as much of an issue as it is with some overhead-cam engines, the LS’s timing chain stretches over time, altering and providing less precise cam timing. Though GM eventually introduced timing chain dampeners and even tensioners on many Gen IV engines, this does not alleviate the need to replace the chain.
High-performance rebuilds often require upgrades from stock or stock-style valvetrain components. The main reason for this is that such applications will want to upgrade to a camshaft with increased lift and duration. This in turn requires aftermarket or factory performance valvetrain hardware to hold up to the increased stresses that this will induce, whether due to the more violent valve opening events, the increased engine RPM potential, or both! Stronger valvesprings are mandatory for such an application, and remember that valvesprings must be matched to your cam choice, so ask the cam manufacturer for recommendations on springs that will be a good complement before buying any. You’ll also need aftermarket high-strength pushrods with a stouter cam and springs. As far as the timing set goes, most aftermarket units include additional keyways and sprocket markings to allow alterations in cam timing. Though a compromise compared to GM’s VVT system, this allows some adjustment of the engine’s power curve for those who wish to fine-tune (or even second-guess) a cam manufacturer’s exact timing of valve events, a process that we’ll see in Chapter 7.
Tougher rocker arms are a good idea to use when employing substantial increases in spring pressure and camshaft lift. Nearly all aftermarket rocker arms are also adjustable, making setting valve lash more foolproof than with the stock nonadjustable, stand-mount rocker arms (which require a change in pushrod length to adjust for too much or too little lash—some aftermarket rockers share this design too). Aside from resisting breakage, a stronger rocker design also yields more precise valve opening events, particularly at high RPM. However, we should note that the adjustable stud-mount design of many aftermarket rockers is actually a bit of a technological step backward even compared to factory rockers, which do not require guide-plates and whose stands are sturdier than any stud. Though choosing an aftermarket stud-mount rocker is usually a more cost-effective solution than going with a shaft-mount rocker system, the inherently more precise geometry of shaft rockers makes them a better choice for all-out performance. On a related note, you may also think of changing your rocker arm ratio to add additional lift at the valve, though most cams are designed to work best with the 1.7:1 ratio typical of most LS engines.
A final note on valvetrain concerns is appropriate for readers thinking of hopping up LS engines equipped with AFM and/or VVT from the factory. The AFM system can only work properly if a cam’s profile has been engineered with cylinder deactivation in mind (just as an example, GM cams that were installed in AFM-equipped engines had different lobe profiles on cylinders that undergo deactivation), so if you’re thinking of changing the cam in such an engine, you will only be able to use an aftermarket LS cam specifically designed for AFM compatibility. (The other option would be to disable the AFM system, of course.) VVT engines will have other cam- related concerns, so you must check with the camshaft manufacturer before using one of its products in a VVT-equipped engine. Aside from the camshaft needing the special oil passage inlet at the second journal from the front, issues arise with cam lobe profile compatibility in such an engine. Similarly, the OEM cam phaser must be upgraded when a sufficiently aggressive cam is used. In either case, there will be additional computer tuning issues to deal with once your rebuild is complete, so we advise speaking to your machine shop and tuning shop (see Chapter 9) in advance to iron out these types of issues before assembling your AFM- or VVT-equipped engine.
The most significant engine gaskets you’ll need to get a hold of are head gaskets. Head gaskets designed for the different bore sizes of various Gen III and IV engines are available from GM and OE suppliers like Federal Mogul’s Fel-Pro division. Factory-style multi-layer steel head gaskets are surprisingly durable, and as such are suitable for stock as well as mild to moderate high-performance rebuilds alike. Though often not required, more extreme high-performance rebuilds that will take on the likes of nitrous oxide or forced induction may want to step up to the extreme sealing abilities of a high-performance aftermarket head gasket. When choosing a head gasket set, keep in mind that adjustments to head gasket compressed thickness should be factored into your compression ratio equation (see the Appendix).
Other more general sealing gaskets are more straightforward to deal with. Though the LS’s carrier gaskets used for the engine covers are durable enough to be reused when parts are removed for service, they should be replaced when performing a full rebuild. New front and rear crank seals to press into the front and rear engine covers are a must as well, and you should also be sure to buy new OE-style intake manifold and throttle body seals. Other miscellaneous seals you will need should have been noted during disassembly, like fuel injector O-rings and the O-ring-style oil gallery seals on the underside of Gen IV valley covers (this applies to AFM and non-AFM engines alike). All of these can be had from your GM dealer or suppliers like Fel-Pro.
Some great news for any rebuild is that many of the factory fasteners can be reused, as there’s a good chance they will be in decent condition. This is because GM used very high-quality bolts through-out the LS engine; take a look and you’ll see metric grade “10.9” stamped onto the heads of many of them. Whether you’re talking about engine cover bolts or main cap bolts, chances are you’ll find minimal corrosion and can reuse these fasteners provided there are no issues with damaged threads.
A notable exception to the reusability rule is the LS’s head bolts. While the ten smaller M8 bolts can be reused, the twenty M11 (or on some engines, M12) bolts must be discarded as they are a torque-to-yield design. This means that the first time they are tightened down, they permanently stretch slightly. Fortunately, new head bolts are inexpensive and even offered as part of a full kit (see Chapter 8 for our “GM Performance Parts” Workbench Tip). The only other LS engine bolt that is impossible to reuse is the one that threads into the crankshaft snout and secures the harmonic balancer/damper, so be sure to pick up a new one of these, too.
High-performance applications may wish to upgrade some of the more highly-stressed factory engine bolts with aftermarket ones. ARP is by far the best source for super-strong engine bolt and stud kits, and the stock main bolts should be replaced if you plan on making a lot of horsepower. To a lesser extent, the same goes for the factory head bolts, which generally will only require upgrade if you’re making lots of boost or throwing a bunch of nitrous into your LS. ARP also offers stainless fasteners for those seeking a cosmetic upgrade for bolts that will be visible under the hood.
Other Engine Parts
Putting together an LS engine requires more than just the major parts we’ve gone through above. Here are some pointers on some other not-insignificant parts you’ll either need to get a hold of for your rebuild project or may think about upgrading for a high-performance application.
There were a few different styles of oil pump the factory used in Gen III/IV engines. While all were of a gerotor design, the differences between them primarily had to do with capacity, as some engines (like AFM-equipped Gen IVs) had greater oil flow needs than others. The LS7 and LS9 pumps are also different because of their dry-sump oiling system. While it’s theoretically possible to rebuild an LS oil pump by replacing and/or refurbishing its internal parts, even GM does not recommend this. Besides, all engines can benefit from increased oil flow capacity, so it makes more sense to just buy a new high-flow unit. This is particularly true on early LS engines, some which were known to include less-than-adequate pumps from the factory.
It’s possible to reuse the stock harmonic damper (or “balancer,” if you will) from an engine that didn’t see an excessive number of miles. However, these items use elastomer-type material that will eventually wear out and reduce this item’s ability to cancel out harmful torsional vibration frequencies—a bad thing for your crank and bearings. (Some aftermarket dampers use other damping methods such as gels or pendulum-like internals, to varying degrees of effectiveness.) Also, any damper reuse will require it to be involved in the rotating assembly balancing process—see Chapter 5 for more information on balancing and the role of the harmonic damper.
Intake manifold and throttle body
Unless your factory composite intake has been dropped or has otherwise somehow been cracked, there’s no need to get yourself a new one, that is, unless you’re looking for increased horse-power! Some factory intakes are better-flowing than others, so you might consider swapping yours out for a different GM one. For example, it’s popular to ditch earlier-style LS1 intakes in favor of the LS6 intake used both on LS6 and later LS1 engines. (You’ll just have to keep in mind that some GM intakes were designed for Gen III-style heads, while other intakes only work with Gen IV-style heads. Even then, not all Gen IV intakes fit all Gen IV-style heads; the LS7 is a good example of an oddball manifold with limited cross-compatibility.) Even higher flow potential is available from the aftermarket, though. The best aftermarket intakes are also made from composite, but others are made from aluminum. The disadvantage to the latter is not only added weight, but the potential for heat soak affecting the density of your intake charge (and hence, robbing you of power and efficiency). On a similar note, factory throttle bodies can be swapped for aftermarket units that are larger in diameter, providing increased flow potential—though Gen IV throttle bodies were often fairly large to begin with. Changing between earlier-style, cable-actuated throttle bodies and later electronic throttle bodies is not uncommon and often fairly simple with the help of the aftermarket (and the correct ECM/PCM to enable electronic throttle actuation if needed).
We hope that this chapter has provided you with enough information to get you started with your LS parts selection process. Whether you’re in this for high-performance or just for a stock rebuild, it’s all about putting together the engine that’s right for you, and doing so with the best information you have at hand. We hope that we’ve been able to show that because Gen III and IV engines include so much high-performance technology from the factory, you can still make a lot of power reliably on a budget; but the huge aftermarket scene also means that you can forego factory performance and build the baddest LS on the block!
Truth be told, the process of parts selection can be a very daunting one, and mentally speaking, it is easily the most trying part of any engine rebuild. It’s easy to get discouraged when shopping around because there are a lot of Gen III/IV parts out there to choose from. Remember this: the final outcome hinges on your making the effort to inform yourself, set realistic goals (and a budget), and stick with your decisions throughout the stages of selecting, purchasing, and assembling your engine. Do your homework, and you’ll find the parts selection process to be a very rewarding one that will pay off big time in the end.
Once you’re satisfied with the parts you’ve selected, it’s time to head to the machine shop, so read on to Chapter 5.
Written by Chris Werner and Posted with Permission of CarTechBooks