A.Roy, you're trying to compare apples to oranges. I've been around Aunt Martha's to try to get you an answer. All the GM shipping weights have the wooden crate included. Ken Casey at Burt Chevy gave me the shipping weights right off the crates. The LS2 crate engine weighs in at 477 pounds. The ZZ4 has a shipping weight of 478 pounds. Now, you would look at these numbers and say that they weigh just about the same. However, we don't know the specific weight of the two crates (40-45 pounds), and the engines are not outfitted with the same components. The ZZ4 engine comes with a water pump, damper, HEI distributor, flexplate, and inlet manifold. The LS2 engine comes with all that, plus exhaust manifolds, engine side mounts, fuel injectors, fuel rails, and the electronic throttle air valve. I can find no direct comparison between the two engines. Yes, the LS2 engine block is approximately 65-70 pounds lighter than the cast-iron ZZ4 block.
The number we've been using to compare dressed Gen I small-blocks to dressed Gen III small-blocks is around 40 pounds lighter. A final number I found (390 pounds) for the aluminum LS-based engines didn't specify the components on the engine. An aluminum-headed Gen I small-block comes in around 440-450 pounds. We've known this for years. A Gen III at 390-400 pounds sounds very reasonable. Hope this helps.
Ring Gap RangeQPlease address the issue of second piston-ring end gap. I have heard differing opinions, some saying the end gap of the second ring should be larger than the top ring, and others saying the second ring end gap should be smaller than the top ring, as has been common practice. Have there been any dyno tests to confirm one or the other in terms of producing more power/less blow-by? Also, would this vary as to the type of application?Gerry GostenikDearborn, MI
A.Gerry, ring gap is a very touchy subject. Piston-ring end gap isn't something you want to play around with unless you have very good data, or the time and money to spend on a dyno. Then you can tune in the perfect ring end gap for your application. That said, we must use averages and safe assumptions (there is that word). You mentioned the practice of opening up the second ring end gap in relationship to the top ring gap. Back in the mid-'80s, we began to see this trend from the OEs. This is because any leakage of compression gasses from the top ring either from the ring end gap or poor ring seal would create a build-up of pressure between the top and second ring. This build-up of pressure would lift the top ring off the ring land and cause high blow-by of cylinder pressure into the second ring. The second compression ring on the piston is designed as an oil scraper ring. Its primary function is to control the oil on the cylinder wall and prevent oil contamination into the combustion space. Also, with blow-by past the top ring and the lifting of the ring off the land, it allows build-up of deposits on the top ring land, which over time will prevent the top ring from sealing well.
You asked if there have been any dyno tests to confirm one or the other. First, I default to the OE engine designers and their direction to thinner and lighter tension ring packages. By reducing ring tension, you increase power output by decreasing frictional drag. With this reduced tension you must use the combustion pressures to seat the top ring. If the top ring can't seal because of backpressure (second ring gap too tight) or deposits on the ring land, you will have blow-by and lower power. Reher & Morrison also believes that some second-ring compression leakage helps to keep oil in the engine's crankcase. This is very important because oil has poor anti-knock characteristics. Even small amounts of oil in the combustion process cause large power losses. A small amount of compression leakage past the second ring pushes oil back down the cylinder, keeping the air/fuel mixture cleaner.