The block sets the stage for the power and performance of your racingengine. As you contin
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."
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."
More on Hot Honing 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."
Materials 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.
Modern cylinder boring machines can provide repeatability and attentionto details.
"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."
Your objective in working on the cylinder bores is to get them round andsquare. It's not a
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.
"It used to be that people didn't use sleeves, thinking a sleeved block was a bad block. Today, they're different sleeves. Some of the sleeves they're running in motorsports are 0.0004 inches, and that's not much of a sleeve.
(above and right) Racing-engine blocks can be composed of various materials. Popularchoice
"There are some significant advantages to running sleeves. Many people don't believe in them and say they're a bad addition, [but] many people have had good luck with them. So we're not going to find anyone saying sleeves are perfect, or they're great, or they're junk. There's still a lot of debate over it. Like anything else, you can build winning engines with or without them, but you have to be careful how you handle each side of it.
"As far as friction reduction by using a nikasil coating, I don't know that I have personally seen power gains just by doing the nikasil. In and of itself, it may not be a power gain, but you may be able to build power you couldn't have without it by using other technologies."
Seeking The Right Bore Jenckes found a possible advantage of using sleeves: They come with bigger bores. "Today, people find that particular bore and stroke combinations are very effective," he adds. "Typically, people are running bigger bores and they find that, no matter what the application, a bigger bore may be helpful. I'd certainly say that's the trend in Nextel Cup. Obviously, if you want to make a block last a long time, you can't go to the big bore size immediately. You'll get one rebuild, and then it's junk and you've just spent all this time building this nice block. A sleeve can allow you to go to your optimal bore size. When you have problems, just replace the sleeves.
Boring for cam bearings is a precision step in which modern enginebuilders rely on high-co
"Some teams in Nextel Cup use sleeves, and some don't. In Nextel Cup, the well is deep money wise, but it's not endless. Consider that you can use a smaller number of pistons and crankshafts, and that means less money tied up in crank and piston inventory. Some teams might approach it from that standpoint."
Power From Bore Center Bigger bores have proven to have better results in most cases. "A larger centerline is preferable because it allows you to have a bigger bore," says Jenckes. "A Ford block has an inherent handicap compared to a Chevrolet or the current Dodge because of the smaller centerline. Having more metal there, other than a weight handicap, means it's more stable and it can allow you to run a bigger bore.
"Most racing has some kind of displacement rule. As long as there's not a bore size rule, you're probably better off running a bigger bore, shorter stroke if engine speed is not limited. If you are limited in engine speed for some reason, say an rpm limit, then always going with a bigger bore may not be the way to go, depending on how low the speed is. At higher shaft speeds, bigger bore engines help the cylinder heads work better. In Nextel Cup, 4.185-inch is the biggest bore size you can have. Even if you have 5 inches between bore centers, it doesn't help you other than the fact you've got more metal there to be stable. Then you have to worry about the weight. The trend has been to bigger bore cylinders. GM is working on a new, next generation Nextel Cup engine with a bigger bore center.
The use of sleeves within the cylinder bores is a matter of personalpreference. Some engin
Cam And Crank Placement There's a design movement to position the camshaft and the crankshaft higher in the block. This begins our look at valvetrain geometry.
"You move the camshaft up to shorten the pushrods," Jenckes explains. "Obviously, with very high spring pressures, a shorter pushrod is a stiffer pushrod, is a lighter pushrod in general. In the valvetrain, you want things stiff and light. There's some kind of optimal stiffness-to-mass ratio that you're going to go after. Having a shorter pushrod that is directionally correct may actually be negatively correct for the valvetrain geometry. You have a shorter distance to go, so you make more angularity in the pushrod. Ultimately, time has proven that the shorter pushrod path is a better path to go down. In very few cases would you find arguments where you want larger pushrods.
"The second thing you'll find is that the camshaft diameter itself goes up. It increases the radius of the cam on the base circle, and the raised curvature goes up, so it is directionally correct for valvetrain dynamics. When you have a larger base circle, you have a lot more room to work, literally, with the cam profile. For the transitions, a larger radius can be smoother than a very sharp one. Having a larger base circle means you can have better valvetrain performance."
The four-bolt main is a preferable way of making long-lasting power. Youcan get power from
Main Strength A final topic of consideration is the number of bolts for the main caps in the block. It's the classic two-bolt versus four-bolt argument.
"A lot of power can be made out of a two-bolt main," Jenckes offers. "If you work in the world of drag racing--stock eliminator stuff--you see this. Drag racing forces people to use production blocks. With the two-bolt main stuff, they make ungodly horsepower. The question is, how long do you make it? In a Nextel Cup engine, in round numbers, you're making 800 hp now and there's a lot of cylinder pressure. Because of that, you have to retain it, and you have to retain it over time. And that's where you get into the two-bolt versus four-bolt.
"A four-bolt is a stronger combination if done properly. Almost all Nextel Cup engines use splayed main caps, which are much more satisfactory than the vertical four-bolt. Again, you're tying in more material. It's all about stability. It's more about peak performance in the long run than it is about the capability of a two-bolt block that can make power for a short period of time. Like I said, the stock eliminator blocks are a perfect example of two bolts that make power--some make as much as a Nextel Cup engine. They just don't make it last as long."