Chevy Big Blocks. David Vizard
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The principle job of the top compression ring is to seal against the pressures experienced above it. To do this, it must have some radial load pressing it outward onto the cylinder walls. A relatively high-compressive preload can achieve this, but that means excess frictional losses on the induction or exhaust stroke. You need to increase the rings’ radial cylinder wall loading as the cylinder pressure increases. Gas porting the top ring groove is an attempt to do just that.
If maximum output for a given piston is the goal, gas porting is the way to go and is offered by most piston manufacturers. For drag racing, using a vertical style of gas port through the piston crown is the preferred method. However, in time, these can clog up, so for use other than drag racing, a horizontal gas port in the top ring groove is preferred.
Fig. 2.14. The two notable aspects of this performance JE piston are: the horizontal gas ports (arrows) and the 0.043/0.043/3-mm ring grooves.
Fig. 2.15. Many off-the-shelf budget-oriented pistons do not have gas porting to the top ring. This Goodson tool allows you to gas port your own pistons with little more than a drill.
Fig. 2.16. I typically use Total Seal rings because my dyno tells me I should. The use of thin cross-section rings also pays off. There can be as much as 8 to 11 hp difference between 0.062 and 0.043 compression rings.
Thinner rings are better than thick ones due to reduced friction; Total Seal rings are about as good as it gets because they seal tight. This is not just my opinion but the result of a lot of tests with rings at various gaps all the way down to the zero gap given with a Total Seal ring. Like the bores the piston rings need to have a low-friction prep. The first move is to use a very fine stone to remove the sharp corners from the edges of the rings’ outside diameter (OD). Then polish the rings with a Scotch-Brite pad until they feel really slick.
Connecting rod failure is rarely less than catastrophic. Fortunately, factory rods are fairly stout pieces but carry a lot of excess balance-pad mass. With work, they can be lightened considerably. Also, you can install a set of ARP bolts. But subsequently, your local machine shop needs to cut the caps and resize the big-end bore.
Piston and Rings: Final Specs
Many factors allow a good piston selection to become a great one. Here are the points you need to keep in mind:
• Select a piston and pin with the minimum weight to make an internal crank balance more easily.
• Maximize compression for the fuel octane to be used; first by minimizing cylinder head chamber volume and then by using a piston with a suitable crown.
• Use the thinnest rings your budget allows.
• Be sure the piston crown conforms to the porting specs.
• Deck the block to achieve a net quench clearance of 0.032 to 0.037 inch.
• Do not shroud the spark plug. (For further information see Chapter 11, Ignition Systems.)
• If the cam you intend to use has more than 280 degrees of off-the-seat duration, do a dummy assembly of just the number-1 cylinder with the cam installed to check the valve pocket clearance. (See Chapter 10, Valvetrain Optimization, for more on this subject.)
• If the budget allows for thermal barrier and anti-friction coating, have them applied.
Fig. 2.17. A stock rod can be converted to a fully floating pin by simply honing out the press-fit pin bore to give a 0.0006 to 0.001 clearance on the pin. Here, the pin has had a Tech-Line anti-friction coating applied; it is an option (not a necessity) if the right lubes are used.
Fig. 2.18. Swapping out stock rod bolts for ARP bolts is easy enough, but the big-end bore needs to be resized. The cost for that has to be added to the cost of a rod bolt upgrade.
Fig. 2.19. Before installing any stock-style bolt rods, be sure to put a sleeve over the bolt threads to protect the crank journal from damage during the installation.
Fig. 2.20. This Scat I-beam low-shoulder stroker clearance rod (PN 2-ICR6385) is made of 4340 steel. It’s strong, light, and affordable.
Fig. 2.21. I have used a number of these Callies stroker rods to good effect. The design seeks to minimize the material cut from the block necessary for clearance.
Fig. 2.22. These Scat rods (PN 2-454-6385-2200) look somewhat bulky, but they are, in fact, as light as most other quality rods. I have used them in nitrous engines up to 1,500 hp without failure.
Fig. 2.23. These K1 rods (PN CF6385APRB8) are also a cost-effective buy that is worth checking out. I have limited experience with these rods, but those I have used have held up in high-output builds without problem.
Fig. 2.24. Crower rods are certainly far from the cheapest available, but the quality is almost unbeatable. This billet rod (PN B93911PF-8) has just come out of a 900-hp bracket race engine after three busy seasons of racing. All of the rods look just as they did when they came out of the box.
Fig. 2.25. Manley has a great range of quality rods and is a good source if you are looking for a special lightweight rod for a specific application in which some race-rule-mandated aspect is limiting power, such as the use of a dual-plane intake.
When all of this is done, you will have about half the money into them that a set of good aftermarket rods cost. I use the word “good” here because I have seen failures with one or two brands of “off-shore”–sourced rods. Analysis has shown that the material spec was way off what it was supposed to be. If you stick with the rods I show here, you should be in about as good a shape as can be expected.
The rod I use most (because it has proven time after time to deal with the prolonged dyno sessions my mule engines go through) is Scat’s ICR6385 rod. In addition