Here it is, the September 2006 issue of GMHTP, and our project 2001 Trans Am is eager to have an engine back under its hood--this time with 383 cubic inches of brawn. Having run the gamut of parts selection, block machining and cleaning, preassembly checks and part fitment, and finally the actual bolting-in of our Lunati rotating assembly in Part 1 of this series ("My First Stroker," August 2006), we probably fried a lot of readers' brains with information overload. Completing the short-block was a very time- intensive process, with lots of test fitting and dimension checking; fortunately, the hard stuff is basically over.
Hopefully, eager-to-learn do-it-yourselfers have had enough time to think over and digest all 18 pages of our last issue and are ready for more. If you're up to the challenge, follow along as we continue the assembly--bringing us ever closer to firing and testing our garage-built Gen III.
Like nearly all small-block GM engines produced in the last half century, the LS1 continues the tradition of a cam-in-block, pushrod-actuated valvetrain. While viewed by many techno-freaks as "old school" and dated, this setup yields dividends of increased durability, decreased engine mass, and lower center of gravity over an overhead-cam style engine. It also allows for a lower hoodline and therefore increased aerodynamic efficiency of the vehicle. Arguments of pros and cons of the design aside, what we're really interested in here is how to put such a valvetrain together, and we begin with the heart of it: the camshaft. In the interest of not inadvertently skipping any steps, we're going to continue to follow our GM service manual as closely as possible. Our machine shop had installed new cam bearings for us, and you should insist the same be done for your block. Just prior to installation, clean the cam using mineral spirits and coat all the cam bearings in the block (those you can reach anyway) with SAE 30 oil. Unlike earlier in the install, where too much oil could be a bad thing on some of the smaller engine parts (piston rings, for example), there's no harm in using large amounts of oil from here on out. So as we continue with the build, feel free to lube away!
Degreeing the Cam
We've just gone through what's known as installing the cam "straight up," with the crank keyway in the "0" position and the marking on the camshaft sprocket aligned with the "0" on the crank sprocket. Normally, cam manufacturers design their cams to be installed just this way, and it should yield the proper timing of valve opening and closing events with respect to the position of the piston in the cylinder. However, if you're a professional engine builder with a custom application for a specific cam, you may wish to second-guess the cam designers' choices and have valve events occur sooner, or in the alternative, delay them. By "advancing" or "retarding" the cam in this manner, one can alter characteristics of the engine's powerband. As mentioned earlier, SLP's timing chain makes this adjustment easy.
This author is not a professional engine builder, however, and wants to stick with Lunati's recommendations as to valve events. And theoretically, we've already done that. Nonetheless, it's common practice to degree the cam; that is, double-check that the timing of all valve events with respect to crank (and hence, piston) position match up to the specs provided on the cam manufacturer's cam card. This verifies that all parts have been manufactured correctly (highly unlikely with quality components from Lunati and SLP), but more significantly, the degreeing process ensures that the installers haven't made any errors of their own. This is a far more likely scenario--though we'd like to think not that likely!
We'll need some special tools to degree the cam, but in the interest of showing you how to avoid spending money on duplicate tools, don't be shocked when you see some tools we used earlier in the build in addition to a few new ones.
OILING SYSTEM INSTALLATION & MODIFICATION
The LS1's oiling system is fairly decent from the factory, although the stock oil pump can benefit from some improvement in capacity. To that end, we'll be swapping to a high-volume unit from SLP. Beyond this, minor modifications will be required to adapt the stock oil pickup tube and crankshaft oil deflector to our stroker crank and new pump.
ENGINE COVERS AND OIL PAN INSTALLATION
Older versions of the small-block Chevrolet (many still refer to the Gen III as a Chevy as a nod toward its ancestry, though it has very little in common with the original) had thin, stamped-steel engine covers and oil pan. But with the deep-skirt design of the Gen III, these items are stressed, machined-aluminum members that add to block rigidity. The oil pan also doubles as a mounting point for the clutch housing, so precise alignment of all components is critical for sealing as well as structure of nearly the entire driveline. The steps of installing these covers, while somewhat involved, are quite manageable if you get ahold of the right tools.
Front and Rear Cover
Before installing the front and rear engine covers, the crankshaft oil seals need to be replaced. Though GM designed these seals to last at least twice as long as those of previous generation small-blocks, there's no sense in reusing the stockers--particularly when you've already put thousands of miles on them. They're a press-in design, and as such a bit of care and some specialized tools are required. Their PTFE-coated sealing lips mean the areas of these seals that ride on the crankshaft should not be oiled; GM found that on past engines, oil breakdown would cause the crankshaft seals to become caked with degraded oil and additives over time, destroying the ability of the seals to maintain proper contact with the crank surface. The switch to PTFE coating means no more reliance on oil for lubrication and the elimination of this problem.
Oil Pan: Buttoning Up the Bottom End
The final major item that must be installed down the bottom of the LS1 is the oil pan, which again is a structural part of the LS1 engine. The primary area of loading is at its very rear, where the clutch bellhousing will eventually be secured using two bolts toward the bottom of the pan (along with six others in the engine block above). Therefore, like with the front and rear engine covers, proper installation of the oil pan is a process that dictates the expenditure of time and care.
THE TOP END: CYLINDER HEAD AND VALVETRAIN INSTALLATION
So far as the valvetrain goes, the only item we've installed is the camshaft. Unlike earlier generations of small-blocks, the cylinder heads on the Gen III cover the lifter area; therefore the lifters must be installed before the cylinder heads. (If you think cam swaps are impossible without removing the heads, though, think again: we'll show you how GM's neat lifter guides allow this.) And since we're using head studs instead of bolts, we need to install them before the heads go on.
Valve Lifter Installation
After a thorough external cleaning wipe with mineral spirits (don't submerse them or you'll pull the lube out of the ball bearings), we first soak all 16 lifters in the oil we're going to use at startup (10W-40). While this process pre-oils the interior of the lifters, it also can throw off the adjustment of a hydraulic cam, so we'll have to "bleed them down" later--a simple process you'll see next time. Still, in this author's opinion, it's not a bad thing to get some oil in there for lubrication--even though most of it will be squeezed out prior to startup
Cylinder Head Installation: Setting the Stage
It's possible to re-use the stock cylinder heads on a stroked LS1; their combustion chamber size is compatible with many pistons on the market and, if need be, the heads can be milled to reduce their ccs and get the compression just right. However, even ported castings will only flow so much, leaving a substantial amount of power on the table--especially with the increased cubes of a stroker.
Therefore, we've selected a set of ET Performance 215cc cylinder heads. See the sidebar for a full discussion of the features of these heads and why we chose them. Before we bolt them on, though, we need to install our ARP head studs and lay our head gaskets in place.
Cylinder Head Installation: Checking Piston-to-Valve Clearance
One critically-important step in any engine build is piston-to-valve clearance checking. Imagine the following: at the very end of the exhaust stroke, the exhaust valve is still open and the intake valve is just starting to open. At this same time, the piston is in very close proximity to the cylinder head, creating the potential for the valves to physically contact the face of the piston. If this were to happen, the valves and/or pushrods would be bent and the engine could be severely damaged. The risk is even greater if accidentally high rpms were to be achieved and the valves began to "float" (i.e., the valvetrain being pushed beyond design limits resulting in the lifters beginning to lose contact with the cam lobes).
The exact proximity of the valves to the pistons depends on many factors, including the camshaft profile, cylinder head design, valve diameters, piston valve relief design, and even connecting rod length. A generally accepted value is that the valves should not come within 80 thousandths of an inch of the piston at any time; this distance allows extra breathing room for the possibility of valve float (come on, don't say you've never hit Second when trying to powershift Fourth; accidental engine over-rev can happen to you!)As this clearance must be checked with the head torqued in place and the camshaft actuating the valves, there's no way to get a feeler gauge inside the combustion chamber and measure the distance between the valves and piston. Therefore, we'll need to temporarily assemble the head and valvetrain to the engine and use a very high-tech device inside the engine while we rotate it over. That device, friends, is our childhood pal Play-Doh: a great building material, projectile sibling defense weapon, and--for the truly daring--tasty snack.
We'll quickly note that an alternate method exists to check this clearance, and it involves removing the intake and exhaust valvesprings, installing light-tension checker springs, and using a dial indicator to measure how far down the valves can be pushed (by hand) before they hit the piston. This, too, will be done while the engine is being spun over by hand, and is considered the most accurate method of determining piston-to-valve clearance. But since we didn't feel like taking apart our already-assembled heads, we went with Play-Doh. Also, though a set of aftermarket rockers will be ultimately used, we'll put the stockers on here along with ETP's optional rocker stands to demonstrate that the stock rockers can be reused with the ETP heads for those on a tight budget.
Camshaft Choice: Black Magic, or Informed Decision?
Choice of camshaft is a critical decision that must be made based on a myriad of factors. These include cylinder bore and stroke, compression ratio, desired usable engine rpm range, cylinder head characteristics, and vehicle drivability concerns. For our cam, we once again looked to Lunati, and it just so happens that the company has a new series of camshafts that brings exciting new technology to the Gen III family of engines. Known as the Voodoo line of cams, these bumpsticks utilize an asymmetrical lobe geometry that up-ramps the lifter quickly and aggressively, yet also more gently re-seats the valve, reducing noise, valvetrain harmonics, and the possibility of eventual component failure. This combination results in a cam that's easy on engine parts yet also yields better throttle response, manifold vacuum, and--most importantly--torque and horsepower.
Or at least that's what the marketing folks told us. We wanted some more technical information on this new line of camshafts before making a final choice, one of the most important decisions to make in an engine build. We called up Lunati's Mark Chacon, the company's East Coast Regional Rep., for the skinny on hydraulic roller camshaft design and the new Voodoo cams' advantages. While not an actual camshaft designer, Mark Chacon is an ideas guy with a reputation for thinking outside the box. He contributed to some engineering direction early in the planning stages of the Voodoo line, and can speak about Lunati's Voodoo camshaft design team (then led by Harold Brookshire) and what it has come up with.
"A lot has changed since Ford produced the first OEM hydraulic roller engine back in 1985", says Chacon. "The original intent was to produce a valvetrain that reduced friction and improved gas mileage. Extra power and torque, though not engineering goals, were gained as an end result of both improved area under the curve over a hydraulic flat-tappet camshaft and reduced rotational friction."Now, fast forward ahead 20 years and camshaft technology has grown to a point where it hardly resembles what it started out as. Major lifter intensities (the duration at 0.020 minus the duration at 0.050) have increased dramatically, more area under the curve has been achieved through better overall lobe designs, and greater lobe lifts are now commonplace. When Lunati first looked at launching a new cam line in the summer of 2004, I was brought in as a consultant to set down some engineering guidelines and to explore emerging technologies. Some of the engineering challenges were to find the perfect balance between quiet valvetrain operation and rpm ability versus excellent torque and horsepower production."He continues, "One problem specific to the LS1 engine is that because of the increased 55mm cam journal diameter, the lobe profile will grow if you use a master that was borrowed from another engine family. This will increase both the velocity and acceleration rates and can cause premature valve float.
Larger-than-stock rocker arm ratios only compound this problem. Looking at all these factors, it became clear early in our engineering that lobes would have to be specifically engineered not only to the engine and cylinder head, but also to the specific journal diameter; and that we'd also need to reverse engineer the lobes to better factor in the added affect of a specific rocker ratio used for the engine.
"That said, the main advantage the Voodoo line has over the designs of other manufacturers is the lifter-diameter-specific masters that will hold as-designed acceleration and velocity rates and also account for the working 1.7 rocker ratio that LS1 engines use. This enabled us to design a cam profile that maximizes both area under the curve and engine rpm without premature valve float. The major lifter intensity that I recommended was 28.5 and our new Voodoo hydraulic rollers are made to this major. The major lifter intensities used by some other hydraulic roller cam manufacturers can be as fast as 25.9, which can create excessive valvetrain noise and could limit the engine's ability to rpm very high. A hydraulic roller lifter, which is heavy compared to other types of lifters, has a hard time effectively working with so much acceleration and velocity without trying to valve float the engine. But with the slightly softer 28.5 major lifter intensity, we are able to get both excellent torque and horsepower numbers while also offering increased rpm and lower valvetrain noise than our competitors' camshafts." He adds, "All Voodoo grinds are designed this way and are ground on state-of-the-art, CNC-automated camshaft grinders for unmatched quality and the tightest manufacturing tolerances in the industry."For our larger-than-stock-displacement and big-flowing-cylinder-head motor, we decided to go with Lunati's most aggressive Voodoo profile available for LS1 engines to date, PN 60512 ($310.00 suggested retail). With 232/238 degrees of duration at 0.050-inch tappet lift (282/288 advertised duration) and 0.599/0.601 inches of lift at the valve, this cam is designed for serious street/strip rides with free-flowing exhaust and intake systems--like ours! The advertised powerband of 2,400-6,800 rpm matched perfectly with our intended engine use, and the cam is said to still exhibit decent street manners as well--important for what is, and will continue to be, a street-driven machine. Lunati also included its PN 72432LUN hydraulic roller lifters, sold separately for a suggested $410.00 (set of 16). These are designed to be used with the factory lifter trays and are made from premium heat-treated steel.
OK, so we got ourselves a sweet hydraulic roller cam, but I started thinking: I've got a solid roller in my TPI Camaro and it works darn good. Am I leaving anything on the table by not opting to 'go solid' in this stroked LS1? "There will always be a horsepower advantage when using a solid roller camshaft over a hydraulic roller camshaft," says Chacon. "But there are also some drawbacks when using a solid roller camshaft in a street environment. The Voodoo cams close the gap between conventional hydraulic roller cams and solid roller camshafts. If revs are the name of the game and the intended rpm will be above 7,500 rpm, then I would use a solid roller camshaft because the lifter will continue to remain stable at these higher rpms. But in a good street/strip application that will operate at 7,200 rpm or below, I would use a hydraulic roller because the overall long-range drivability and lack of maintenance is much better suited for a good street/strip application." Given the daily driven nature of this Trans Am, Mark really put my mind at ease.
GM Gen III Gasket Technology
The gaskets used to seal the various mating surfaces in the LS1 engine merit a closer look, as they are extremely advanced pieces indeed. Though very high-tech and durable, when performing a full engine rebuild, it's an excellent idea to replace them as per the GM service manual. Though this will require the expenditure of a little extra cash on your stroker build, it'll guarantee a leak-free motor when you're through.
Unlike previous-generation small-blocks, the Gen III does not rely on cork- or fiber-based gaskets and large amounts of RTV silicone to form seals. Anyone who has ever assembled one of these older-style engines knows that this approach results in, for lack of a better term, a friggin' mess. Instead, the major gaskets in the Gen III are carrier-type (more technically, controlled compression aluminum carrier gaskets). The hybrid design means that when sealing surfaces are tightened together, the aluminum portion of the gasket limits how far the silicone portion of the gasket can be compressed. This results in a more reliable, longer-lasting seal and less chance of fastener overtorquing. In addition, the aluminum portion of the gaskets prevents the gasket relaxation associated with traditional materials and also allows them to become structural parts of the engine.
You can see this carrier design primarily in the front and rear cover, oil pan, and valley cover gaskets. Perhaps best of all from the perspective of the do-it-yourselfer, there's no scraping needed when these gaskets are removed for service; and if they don't have many miles on them, they can even be reused. But again, since we're doing a full engine overhaul on a motor that has seen tens of thousands of miles of use, we're replacing everything we can just to be safe.There's a lot more to say on this topic, and we don't have the space to go through the technology that goes into each and every gasket and seal used in the Gen III (you can see more bits and pieces in the photo captions). But now that you've gotten a feel for the kind of careful design and manufacturing that goes into them, hopefully you'll take our advice and spring for fresh gaskets and seals throughout the engine.
|Major LS1 gaskets, with GM part numbers and price:|
|12559271 - Water pump gasket||$4.84|
|12560696 - Valve cover gasket||$19.95|
|12574293 - Rear cover gasket||$21.61|
|12580672 - Oil pan gasket||$33.91|
|12574294 - Front cover gasket||$21.61|
|12585673 - Crankshaft front oil seal||$21.06|
|12585671 - Crankshaft rear oil seal||$18.63|
|12558177 - Knock sensor grommet (set of 5)||$3.41|
|12573460 - Engine block rear oil gallery plug||$5.92|
Compression Ratio: The Big Squeeze
One of the major design parameters to decide on when building any engine is the static compression ratio. The appropriate compression must be designed into the engine early in the planning stages, and numerous factors will affect it. These include desired fuel octane, type and amount of power adder, cylinder head material and design, camshaft profile, and planned engine use (street, drag race, road race, etc.), among others. Here, like many other areas of an engine, entire books can be written on the topic.
Theory aside, the crucial thing from a do-it-yourself perspective is how compression ratio is calculated. Compression ratio is defined as the ratio of the volume of air (actually air/fuel mixture if you want to be technical) inside the cylinder when the piston is at top dead center to the volume inside the cylinder when the piston is at bottom dead center. The volume of the cylinder at top dead center (TDC) consists of the so-called total chamber volume. The volume of the cylinder at bottom dead center (BDC) consists of the total chamber volume plus the swept volume of the cylinder.
The swept volume of the cylinder is easy to calculate. It's simply the displacement of one cylinder and is computed as bore area times stroke. The total chamber volume is a bit more difficult to deal with as there are a few different volumes involved, which we've attempted to show pictorially in Figure 2.
The combustion chamber volume, shown in yellow, is the familiar "combustion chamber cc" that cylinder head manufacturers quote. The stock LS1 cylinder head, for example, has a 67cc combustion chamber volume. This is the main volume involved when the piston is at TDC, but there are other smaller volumes that come into play.
The head gasket volume, shown in light blue, is equal to the compressed thickness of the head gasket multiplied by the circular area cut out in the head gasket. Typically, this area is of slightly larger bore than the engine's cylinder. Head gasket manufacturers do things this way primarily so that a single gasket will work for a range of finished cylinder sizes.
The deck clearance volume, shown in orange, comes into play because almost without exception, the face of the piston does not sit exactly flush with the engine block deck surface when at TDC. While in the graphic we've shown a piston sitting slightly down into the cylinder, in reality nearly all LS1 pistons actually protrude above the engine deck surface, giving these engines a so-called negative deck clearance. The calculation is the same, but we'll just be adding in a negative number instead of the positive number we'd use if the LS1 was a positive deck clearance engine.
The piston valve relief pocket volume, shown in purple, is the valve relief cc discussed by piston manufacturers. We've actually shown it pictorially as a full dish for clarity. This is one of the main specifications one looks at when shopping for pistons.
Finally, an oft-overlooked volume is that which exists above the piston's top compression ring, which we've shown in light green. As pistons are always slightly smaller in diameter than the cylinders they occupy, a very small ring-shaped volume of air exists encircling the very top portion of the piston. This volume is often very hard to figure out, too, as when the engine is actually running, the piston can expand with heat to close this area up further--not to mention that piston manufacturers rarely quote the vertical distance between the face of the piston and the top compression ring. Therefore, this volume, sometimes called crevice volume, is often simply assumed to be 1 cc.
By looking up specifications for the cylinder heads, head gaskets, and pistons you're shopping for, as well as knowing whether your block will be decked or not, you can mix and match these parts to come up with the desired compression ratio for your engine. In our case, we wanted to stay below a static compression ratio of 11 to 1. This decision was based on our goals of a naturally aspirated engine that would be able to run on pump gas, but also have a moderate amount of nitrous injected into it at some point in the future when the yearning for even more horses hit us. As the factory LS1's compression ratio is only 10.1 to 1, we knew a compression increase like this would pay excellent dividends in efficiency and, hence, power production.
That said, here's how our compression ratio was calculated. We'll perform all of our calculations in English units and do the appropriate conversions from metric. The simplest calculation is the swept volume of one cylinder, and its equation can be seen in Figure 1. It's simply 1/8 the total displacement of the engine, and in our case is calculated as:
Swept volume = 3.14159 x (3.903 / 2) x (3.903 / 2) x 4.000 = 47.85713 cubic inches
Moving up top, let's take a look at our deck clearance. To find out how far the face of our piston is protruding from the cylinder bore, we'll need to sum up the distances between the centerline of the crankshaft main bearing and the piston face. These distances are half the crankshaft stroke, the connecting rod length, and the piston's compression height (the distance from the centerline of the piston pin to the face of the piston).
This gives us:
Height of piston face = (4.000 / 2) + 6.125 + 1.123 = 9.248 inches
As stated in the last issue of GMHTP, we chose not to perform any decking of the block, therefore our block retains the stock LS1 deck height (the distance from the centerline of the crankshaft main bearing bore to the block deck surface) of 9.240 inches. Subtracting the height of our piston face from this:
Deck clearance = 9.240 - 9.248 = -0.008 inches
We see that our piston protrudes 0.008 inches from the cylinder bore, giving us the negative deck clearance typical of Gen III engines. To get the deck clearance volume, we simply multiply this number by circular area of the cylinder bore as per the equation shown in Figure 3:
Deck clearance volume = 3.14159 x (3.903 / 2) x (3.903 / 2) x (-0.008) = -0.095714 c.i.
Head gasket volume is found in a nearly identical manner. All we need to know is the compressed thickness of the head gasket and its bore. For our Cometic MLS gasket, these values are 0.051 inches and 3.910 inches respectively. Therefore, as per the equation shown in Figure 3:
Head gasket volume = 3.14159 x (3.910 / 2) x (3.910 / 2) x 0.051 = 0.612369 c.i.
Our Lunati pistons have a valve relief pocket volume of 8 cc, which converts to 0.488190 cubic inches. Our ET Performance cylinder heads' combustion chamber volume is 62 cc or 3.783472 cubes. Assuming a 1 cc (0.061024 cubic inch) crevice volume, we can now sum up the total chamber volume as per the Equation shown in Figure 1:
Total chamber volume = 3.783472 + 0.488190 + 0.612369 - 0.095714 + 0.061024 = 4.849341 c.i.
Using our compression ratio equation seen in Figure 1, our static compression ratio is then computed as:
CR = (4.849341 + 47.85713)/(4.849341) = 10.869 to 1
This meets our stated goal exactly: a compression ratio of just below 11 to 1! Of course, when actually going through the process of selecting pistons, cylinder heads, and head gaskets, you'll have to rearrange these equations and solve for the unknowns you're interested in; but hopefully, we've pointed you in the right direction.
Cylinder Heads: The Heart of Horsepower
The single part of the engine that has the most influence on horsepower production is the cylinder head. After all, it's where the air/fuel mixture flows in, gets compressed, burns, and flows out. The shape of the intake and exhaust ports, the angle and sizing of the valves, and the contours of the combustion chamber all have a huge effect on the way in which the mix travels and is burned and, hence, the kind of cylinder pressures you end up with.
There are a whole lot of cylinder heads on the market for the Gen III (see our "Gen III/Gen IV Cylinder Head Buyers' Guide," January 2006) and a lot of them are very good. The choice wasn't easy, but we went with a company that has a reputation for very high quality and exceptional power production: ET Performance.
ETP offers several different styles of cylinder head for LS1-based engines--a line it refers to as ETP G III--with intake port sizes ranging from 215 cc all the way up to 265 cc. As we're putting together what is essentially a street motor that we'll be having some fun with on racetracks, we needed something that would be very driving-friendly. This put us in the lower range of ETP's offerings, and the guys at the company recommended their 215cc heads, which they said work well for "bolt-on 346 to 383 cubic-inch combinations for daily driving." While we had an eye on the 225cc versions, designed for more radical 346-383-cube engines as well as even higher displacements, we were told that for our streetable application the 215s would give us better torque and horsepower across the rpm range. "There is a lot that comes into play when picking a cylinder head, such as what the engine will be used for and the personal opinion of what is streetable and what is not," says ETP's Craig Thibeau. "Camshaft choice and compression ratio also play a big part in selecting the correct head. About the worst thing to do is to have no 'plan of attack' and just buy a product because you are told it is the best on the market. This is a common thing that people don't think of; many overlook the overall combination and how every piece falls together." That said, we trusted ETP was giving us the right head for our ride: an assembled, ready-to-bolt-on head featuring 2.04-inch intake and 1.57 exhaust valves. This particular head is advertised as flowing 320 cfm on the intake and 211 on the exhaust at 0.600-inch lift (3.900-inch test bore, pressure of 28 inches of water). Flow numbers, while always fun to quote, don't always tell the whole story, and there's a whole lot going on with these heads that sets them apart from others on the market.
As these heads are a proprietary casting, ETP was able to fine-tune many areas that couldn't otherwise be altered on a factory or factory-style head casting. The most major change is that the valve angle has been changed from 15 degrees to 11 degrees, which helps promote better low- to mid-lift flow. It also improves piston-to-valve clearance, allowing the use of more aggressive camshafts. The intake valve is moved toward the center of the cylinder bore, decreasing valve spacing to 1.880 inches, and the spark plug relocated. The cylinder head deck is a full 0.800-inch thick, double that of the factory, spreading the load for better head gasket retention. In addition, the head's coolant passages are C5R-style, decreasing the chance of blowing a head gasket into a water passage. The exhaust ports are raised 0.100-inch to improve flow; as with the intake ports, they are an extremely efficient, high-velocity design with increased wall thickness. A raised valve cover rail provides more space for aftermarket rocker arms.
Even with all these changes, the great part is that these heads still bolt right up to factory intake manifolds, valve covers, and headers. Many options are available including various valvespring types, titanium valves, copper seats, Inconel exhaust valves, titanium retainers and locks, and much more.