Science Behind Simplicity
OK, so turning a ring filer and sticking a feeler gauge in a ring end gap doesn't take a master machinist. But don't overlook the importance of what you're doing: properly determining and setting piston ring end gap is a crucial part of any engine build, and every engine is unique. Different ring designs and materials respond differently to conditions inside the cylinder, and piston design also factors into how much heat the rings actually see. To further complicate matters, the actual ring gap is not constant even while the engine is running. For example, when the engine is started cold, ring end gap is much wider than it is during full-throttle operation.
It's an exceptionally bad idea to deviate from what the ring manufacturer recommends regarding end gap. Too much gap, and efficiency will be lost; an excess of gases will escape from above the piston--gases that would otherwise have added to cylinder pressure. Too little gap, and with heat expansion under full engine load, the ends of the ring will butt together and destroy the ring, cylinder wall, and piston.
The Pro Series rings we received in our Lunati kit consisted of barrel-faced plasma-moly top rings, ductile iron second rings, and low-tension oil control rings (which do not have to be gapped; they're pre-made and work for a narrow range of cylinder diameters). Lunati specified a minimum of 0.004 inches of ring end gap per inch of cylinder bore diameter for the top ring. So:
3.903 inches bore x 0.004 = 0.015612 inches ring end gap
Rounding up, we get 16 thousandths. However, this number is for a naturally aspirated engine; for this ring set, Lunati recommended adding between 2 and 4 thousandths for an engine that would be seeing a moderate amount of nitrous use. The increased cylinder pressures that come along with nitrous add heat inside the cylinder, which reaches the rings and causes them to expand even more. We chose to err on the side of safety and add the full 4 thousandths, bringing the end gap for the plasma-moly top ring to 0.020 inches. As to the second ring, 0.003 per inch of bore was the suggested minimum:
3.903 inches bore x 0.003 = 0.011709 inches ring end gap
...which rounds up to 12 thousandths. Adding the aforementioned 0.004, the end gap for the ductile iron second ring is 0.016 inches.
Remember, always stick to the recommendations given by the ring manufacturer; don't get cute with "tricks" you heard through the grapevine or found on some online message board. If you have any questions that aren't explained in the instructions, call the manufacturer; they'll be happy to clarify! Remember: screw this step up, and you'll either lose power or end up with a blown motor.
Read Up!
As we hope you're beginning to see, a full motor build requires time, patience, mechanical competence--and most importantly, knowledge. Many resources are available to help you get informed on the parts, tools, and skills you'll need to tackle such a daunting task. Ideally, before even thinking about opening your favorite mail order catalog and perusing for parts, you should get a hold of these resources and get informed about what you are getting into.Start with GM's service manual for your particular vehicle. They are published for GM by Helm and you'll have to contact Helm to get a hold of one. The GM service manual is an absolutely essential reference when it comes time for the actual build (including the preassembly checks we've gone through; they are detailed as well). Do NOT attempt an engine build without it! This book set is a bit pricey--our 2001 F-body service manual, PN GMP01F, came to $135--but it will pay for itself in peace-of-mind, knowing the job has been done right.A couple of bookstore publications we recommend are Will Handzel's "Chevy LS1/LS6 V-8s" and Chris Endres' "Chevy LS1/LS6 Performance." The former is particularly essential as it details easy engine removal and installation for many late-model GM vehicles--procedures beyond the scope of this story. Though each of these publications contain their fair share of typos and gloss over some areas of LS1 engine building, the combination of the two will be a great complement to your GM manual.
The LS1 block: Strong, but how much so?
We spoke at length to Lunati's learned Mark Chacon regarding his opinion on the limits of the stock LS1 block.
"First and foremost, the aluminum LS1 block is the weak link and will probably fail before our Lunati rotating assembly. As to the configuration of the stock LS1 block, the main caps are never going to be a problem on a naturally aspirated application because of the limited cubic inches the stock block can support (with its max 3.905 inch or so bore). When the stock block with stock main caps will start to be a problem is once a power adder is thrown into the equation. Nitrous will put the most stress on the caps due to the large amount of shock it places on the rotating assembly when the system is first engaged. Generally, turbocharged engines will be easiest on the block because of the gradual way they build boost, and supercharged applications will fall in between the two. And of course, you have to look at the amount of power these items are going to add. If it's going to be substantially more than a naturally aspirated LS1 would normally make, then you need to start looking at buying a set of billet main caps."
"But even with the billet caps, the aluminum-block LS1 can start to have problems around the 950 horsepower range. It's hard to say though: these failures I've heard of could be due to assembly error, a poor tune, and so on. It's for this reason that many big-power-adder racers go to iron Gen III blocks at this level because it is perceived as stronger. But this, too, is debatable. The limits of the LS1 might have more to do with bore capability than block strength, and it all depends on who you talk to."
So to sum up, reusing the stock LS1 or LS6 block is not going to be a problem for the typical naturally aspirated or mild-power-adder street/strip ride (ours included). If you're looking to go with really big power and want to stay reliable, you're going to have to blow cash on billet mains and eventually an upgraded block (perhaps even a C5R or Warhawk). In light of our budget-themed, home-grown build, we chose the stock block and mains; but be guided accordingly.
Why Rod Bolt Stretch?
Although it's common to speak of bolt "tightness" when discussing how to properly secure a bolt, what's really happening is better described as "pre-loading" the bolt. Entire volumes can be written on the physics of bolt pre-load, but for our purposes, just know that if a bolt isn't pre-loaded sufficiently, external forces working on the pieces being clamped together will exceed the bolt pre-load, giving the bolt more internal force than usual. When these external forces are periodic in nature--as is especially the case in reciprocating masses like connecting rods--the fastener's internal force itself fluctuates, which under the right conditions will "fatigue" the fastener and eventually break it. So the idea is to give the rod bolts enough pre-load that the external forces on the connecting rod will never affect the internal force pre-loaded into the bolt. Too much pre-load is similarly bad and will cause premature bolt failure or failure of the threads in the connecting rod itself.Connecting rod manufacturers differ in the methods they specify for securing their rod bolts. Some use a torque specification only, others use torque-plus-angle, and some--including Lunati--use the rod bolt stretch method. While it is the most time-consuming of the three, rod bolt stretch gives the most accurate reading of bolt pre-load. Any reliance on torque specification simply gives a reading of how much force is required to turn the head of a bolt, and this "tightness" can be influenced by outside factors like thread and bolt head lubrication. Therefore, torque--and to a lesser extent, torque-plus-angle--won't always accurately correlate to the force the fastener is actually clamping the parts together with.
Bolt stretch directly measures the elastic deformation that the fastener undergoes as it clamps down harder and harder. It's analogous to stretching a rubber band: the more it is stretched, the more force it pulls back with. By measuring this stretch and knowing the physical properties of the bolt and its material composition, we get a direct indication of how much force it is holding the rod together with. See the accompanying diagram and equation for clarification.
Though rod bolt manufacturers obviously design and calculate these things very carefully, as an estimate of our rod bolt preload, let's plug some rough real-world numbers into our equation. Assuming a 30,000,000 psi modulus of elasticity for alloy steel, a 0.150 square inch cross-sectional area for a 7/16 bolt, and a 1.25-inch bolt length (to the middle of the threaded region; the diagram shows it as the overall length for clarity), the Lunati-specified bolt stretch value of 0.0050 inches gives a fastener clamping force (pre-load) in the vicinity of 18,000 pounds. With two bolts per rod, that means the suckers are being clamped together by something on the order of 36,000 pounds!