Q. You’ve given me some great advice in the past, and I need your help again. What is best location to install a cross-pipe or crossover pipe in the exhaust system? Is it best to place them forward or to the rear of the system?
A. Glad we can be of service. The best location for exhaust communication between the banks of any V-type engine is as close to the exhaust collector as possible. This is true for either a cast manifold–equipped engine or with headers. The reason that a balance pipe helps performance is the firing order of a 90-degree bank-angle V-8 engine. With any manufacturer’s V-8 engine, you have two cylinders firing back to back on the same bank of the engine. When this happens the exhaust system is overloaded on that bank, and it creates high pressure in the combustion chamber of the first cylinder in the firing order while the exhaust valve is closing. Well, when the exhaust valve is just closing is when the intake valve is opening, and you want the lowest pressure possible (scavenging) in the combustion chamber to aid in pulling the intake charge into the cylinder. On the odd bank of the firing order, the back-to-back firing would be the No. 5 and 7 cylinders. So just as No. 7 cylinder is well into its exhaust stroke, the No. 5 intake and exhaust valves are open during overlap. This causes exhaust gases to rush back up the intake manifold and dilute the incoming charge. On the even bank of the engine, it’s cylinders 8 and 4. If you can eliminate this condition by connecting the two banks of the exhaust system, you have given the excessive exhaust pressure a path to relieve the overpressure condition. With those two cylinders affected during overlap getting full charges of fresh air and fuel, you gain torque and horsepower with the communication.
That said, putting a balance or cross-pipe as close to the collector can be a real challenge. Usually the only things you can do is put the connector as close as possible and take what gains you can get. We worked on one project where we were able to put a balance pipe right between the head pipes, under the oil pan, on a C4 Corvette with an LT1. That engine picked up over 10 hp with no other changes than installing that short communication pipe between the stock head pipes. This was the best packaging of a balance pipe. Usually you have to wait until after the transmission crossmember. Sometimes you can get your communication around the torque converter area on an automatic-equipped vehicle. Give your application a look and get creative. You will love the gains.
Help me Break it in
Q. I have spent a lot of time and money building my first small-block. It’s a 350 0.030-inch-over with a Scat rotating assembly, an Edelbrock billet hydraulic roller, Performer RPM heads, the list goes on. I have filled the oil pan with Royal Purple break-in oil. I have spun the oil pump and have 80-psi oil pressure. After I go buy a battery I am finally going to start the thing. Can you help me out with a good break-in procedure? Thanks! Love the tech.
A. Back in the day engine break-in was much more important. With the quality of our machine work today, the cylinder wall finish, and the high-quality, moly-filled piston rings, it’s a snap to break in an engine. Usually, the rings are quite happy after you have turned the engine over during the assembly process—if you have followed clean assembly techniques. Here is what we would do on a fresh engine today.