For the past two months, we've taken readers on a detailed ride through a full-on LS1 engine assembly. In Part 1 of this homegrown motor build series ("My First Stroker," Aug. 2006), we prepped our block and installed a Lunati rotating assembly. With a 4-inch stroke and .005 cylinder hone, we came out with a 383 ci short-block. Our second segment ("My First Stroker, Part 2," Sept. 2006) showcased everything from our Lunati Voodoo camshaft installation to compression ratio calculation, and ended with bolting on our 215cc ET Performance cylinder heads. In both of these stories, we'd done our best to highlight all of the tips and tricks needed not only for Gen III engine assembly, but for adapting the stock block under the hood of your late-model ride to accept stroker internals and other high-performance parts. We've kept focus on holding a reasonable budget while upping the fun with a serious but manageable project for the do-it-yourselfer.
And now, the excitement continues: in this segment, we'll finish off the engine assembly and get our big-cube LS1 installed into our project Trans Am, making it ready to fire up!
We start with bolting the rest of the valvetrain atop our garage-built mill. Though it's possible to reuse the stock LS1 rocker arms with our ETP heads, they simply aren't up to the task of handling large spring pressures. Their particular stud-mount design-aside from being non-adjustable-isn't ideal for the prevention of valvetrain deflection and geometry change under engine operation. Even worse, the rocker stud diameter is only 8mm (equivalent to a tad more than 5/16 of an inch)-a far cry from past GM small-block engines, which normally had 3/8- or even 7/16-inch diameter studs. We decided to go with the ultimate in valvetrain stability: shaft mount rocker arms. See the sidebar on the fully adjustable Jesel rockers we chose for this build.
Pushrod Length Determination
Once a rocker arm is chosen for a given engine, the final piece of the valvetrain puzzle that must be ironed out is the pushrod. This item transmits the movement of the valve lifter to the rocker arm, but it needs to be just the right length or else valvetrain geometry will be wrong. This situation will lead to accelerated valvetrain wear, reduced horsepower, and parts breakage; with the length of the pushrod in error more than a few hundredths of an inch in either direction, it will even make the rockers physically impossible to install. Each engine's unique combination of camshaft, lifter, head gasket, block deck height, cylinder head, valve stem length, and rocker dictates a unique pushrod length that needs to be physically measured with extreme care. Therefore, the right pushrod for an engine cannot be accurately known until the engine is nearly fully assembled. The measuring procedure is fairly straightforward, and like we have with the rest of this engine build, we're going to take you through it step by step. We'll show you this process as performed on cylinder number one, but you should repeat these measurements on at least one other cylinder on the opposite cylinder head; you never know when machining tolerances on various parts might create different pushrod needs for different cylinders (though this is uncommon).
Pushrod and Rocker Arm Installation
With our required pushrod length known, it's time to order up a good set of pushrods. Once they are in hand, we can install and adjust the rocker arms to Jesel and Lunati specifications, completing our valvetrain installation.The basic rocker adjustment procedure for each of the LS1's cylinders is the same one hot rodders have used for decades. (Note that the 2-crank-position rocker adjustment procedure outlined in the GM service manual will only safely work for cams with small durations.) First, bolt the rocker assembly on while both valves are closed, i.e., a bit after the intake valve closes. Then, keeping a close watch on the movement of the rockers, rotate the crankshaft until the exhaust rocker just begins to open the exhaust valve. At this point, the intake rocker can be adjusted-since we're at the very beginning of the exhaust stroke, we know the intake valve can't possibly be opening yet. Then, rotate the crank until the intake opens and then almost completely closes. At this point, we can safely adjust the exhaust rocker, as we know the exhaust closes immediately after the beginning of the intake stroke and will stay so for some time.This adjustment procedure is much easier to do on an engine stand than it would be with the motor installed in a car, and happily, it's a one-time-only task for a hydraulic lifter cam. Think about this: a camshaft with solid lifters would not only have to have its rockers periodically readjusted, but it would have to be done while the engine is hot!
TOPPING IT ALL OFF
With the rocker arms on and all valves adjusted, we've completed the last step in the assembly of our engine internals. It's now time to cover up our stroked LS1 and add new items like ignition coils, a higher-flowing intake manifold, and an underdrive crank pulley. Along with modifying a few stock components along the way, this will get us ever-closer to reinstalling the engine into our patiently waiting Ram Air Trans Am.
Valve Cover Modification and Installation
We were all ready to cap off our ET Performance heads by putting the valve covers on, but then we hit a bit of a setback. Despite the added clearance afforded by ETP's raised valve cover rail, we found that our stock valve covers wouldn't go on. Not only did nearly all of the rocker adjuster nuts hit the oil deflectors on the underside of the covers, but the baffling and bracing under the covers also interfered with our Jesel rockers' shaft-mount system.
We immediately ruled out springing for a set of aftermarket valve covers (and their accompanying coil relocation kit) because of cost and packaging concerns. Beyond this option, valve cover spacers are another common solution to the rocker-clearance issue. By lifting the stock valve cover further off of the cylinder head, added space is afforded for the valvetrain. Though readily available from several different manufacturers, we didn't want to use them for a few reasons. First, valve cover spacers are an added expense, costing a couple hundred bucks or more (remember that we're keeping an eye on our budget). More significantly, the geometry of our ignition and nitrous systems would be affected: we simply didn't want to run the risk of plug wires not reaching the spark plugs, direct-port nitrous lines having to be bent at extreme angles, the wiring harness having to be lengthened, and other possible issues associated with raising the valve covers even further than ETP already had. (And as we'd discover later, spacers wouldn't even have worked in our F-body; they wouldn't have allowed our ignition coils to fit between the valve cover and the plastic box surrounding our A/C evaporator!)
With these concerns in mind, we reluctantly decided to ditch the factory PCV system and gut everything under the factory covers in hopes of getting them to fit. Environmental pollution concerns aside, losing this probably isn't a bad thing since the LS1's sub-par PCV system is known to contribute to oil consumption, and excess oil vapor entering the engine can also cause detonation problems. We'll show you how we substituted for the PCV system in a moment; but for now, let's take a look at the factory valve covers and how to mod them up.
The Gen III uses a cast aluminum valley cover that installs into the area atop the engine block between the cylinder heads (traditionally known as the "lifter valley," though the LS1's lifters are not really visible in this area). Unlike past generations of small-block, where hot oil from the valley area would splash onto the underside of the intake manifold, the LS1's valley cover isolates the intake manifold completely from all the hot stuff inside the engine. This contributes to a cooler intake and consequently a denser incoming air charge, as well as improved oil sealing (the front and rear of the intake were notorious locations for leaks on earlier small-blocks).
The higher horsepower numbers that come from a stroker are only possible if one can reliably light the fires that burn over 50 times per second in each cylinder. While the LS1 ignition system is quite good from the factory, we decided it wouldn't hurt to make a few upgrades, especially considering that we'd be throwing some nitrous into the mix down the road. (See the sidebar for more technical information on this topic.) That said, let's show you just how these upgrades are installed.