The block sets the stage for the power and performance of your racing engine. As you conti
[Editor's Note: Last month we talked to DEI engine specialist Chuck Jenckes about procedures in preparing a block for an engine build. Jenckes continues his thoughts on matters like mains, honing, and sleeving.]
We have lightened the block, cleaned it up, and done a thorough inspection. Where do we go next?
"Basically, after you have the fundamentals done, you can talk about the bore itself," Jenckes says. "There's a lot to be said about bores. The most important design element is, at operating temperature, to have a round and square bore or have a bore that [is as close to cylindrical] as possible. The piston runs up and down, and if the bore is round and straight, you can run tighter piston-to-wall clearances. Your rings are going to perform better. You're going to have less friction. This whole interaction between the block and the piston and the rings has a lot of performance that can be left on the table. The entire combustion process has to be sealed by the rings. If the rings aren't working properly, you're going to be losing power. Having good sealing is critically important to making the engine work."
Modern cylinder boring machines can provide repeatability and attention to details.
Jenckes points out that great strides have been made to make bores cylindrical. "You find pretty quickly that these hot honing techniques people are talking about, even used at the Street Stock level, are going to get you power. You need to hone the block at operating temperatures, and you need to have the honing oil hot, not just putting water through the water jacket. The oil needs to be heated to anywhere between 150 and 190 degrees. Getting the block up over 120 is probably a good area to be operating, but if you can get it to 150, it's better. You have to have hot honing oil. If you heat the block up and douse cold honing oil on it and then hone, localized cooling is going to distort the bore. With a production block, you have all these residual stresses built up in the block, and the bore distorts tremendously. We're talking about multiple thousandths of an inch, like five thousandths. When you have piston-to-wall clearance of eight thousandths and a distortion of five, that's a huge percentage."
The goal is the perfect circle, actually a perfect cylinder. While being round and square may sound like a contradiction, it's the ideal objective. "The cross section is a perfect circle," Jenckes states, "and it's perfectly square because the cross sections are true, so it's round and square. It's a perfect cylinder."
Jenckes believes the hot honing, when done properly, can be beneficial. "It is certainly a technique that has been proven fundamentally sound at all levels," he adds. "Is there one brand of hot hone that's better? No. It's not to say a guy at a machine shop can't build his own hot honing apparatus. If they buy one, there are many on the market and people need to evaluate them. It is absolutely a technique that is good at all levels because it provides the foundation for what is going to come later, which is how the rings are going to perform and how the pistons are going to work. The trend is toward lighter pistons and higher shaft speed."
Your objective in working on the cylinder bores is to get them round and square. It's not
Today's engine block can be one of a number of possible materials. While many of the racers are dealing with simple gray iron, the composition of the block must be taken into consideration.
"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."