Building Blocks: Engine Block Prep Tips

"There's something called compacted graphite iron, or CGI, that has about 50 percent more tensile strength than gray iron," Jenckes points out. "That material is being used in all levels of motorsports for high-end racing blocks. That's a good foundation.

"There are different types of iron--gray iron, nodular iron. All of these irons have different chemical makeups and different properties. Depending upon where the block was made, what foundry, what metal was used, you can have different performance from them."

Each type, from the CGI down to the gray iron, has its unique properties. "Most of the blocks ordered in Cup today are CGI, and it's harder to machine," says Jenckes. "The big downside for compacted graphite is that you have to tap it. You have to be careful because you'll be breaking taps. It's tough to machine and it's also much more sensitive when you hone it. The honing aspect of it becomes critical. In most Street Stock stuff and Late Model stuff, you're limited in what block you can run."

Bigger Package As the block preparation work continues, the elements to produce power start to come together. As Jenckes emphasizes, good ring seal is critical.

"You have to look at the cylinder kit, which is the bore, piston, rings--those components," he says. "Some of the things that are critical in getting good ring seal are the finish of the bore, what level you hone it, how you hone it, even what you hone it with, and not the least of which is the guy honing it. Machines make a lot of it easier. Back in the day, I can remember a guy standing on top of the block with a 1/2-inch drill motor, and that's how blocks were honed. It worked fine. Part of that was the guy operating it. He was so skilled he could feel a block burnishing just by the increase in the motor speed. When they came out with machines, you could watch a load meter run while you were honing the block. There are a lot of machines out there now that can help the average guy hone a block than ever before."

Coating Sleeves There was some discussion last month about coating bearings. According to Jenckes, there has been some experimentation in applying coatings to cylinder sleeves.

"Nickel silicone carbide is a ceramic that coats either the parent metal of the block, or the sleeves are coated and placed in the block," Jenckes explains. "Coatings are difficult. Whenever you coat something, you have to be very careful that the coating sticks. There's a substrate on the parent metal you're applying a coating to that's an integral part of the chemistry. In a cylinder block, the iron itself is not homogenous. As they pour the iron and it cures, it's not consistent throughout the block. The chemistry of applying a coating to an iron block is problematic at best. A sleeve is easier to coat because the material can be completely homogeneous. It can be a tube that is specially made to be coated. The chemistry is much easier, but even then, you can have coating slips and that can be a problem.