![]() ![]() ![]() You can hand port a cylinder head and get really, really close port by port. “You also won’t be as consistent as the CNC machine. “When talking about the time it takes to hand port a set of cylinder heads versus a CNC, you’re probably talking 10 times the time to hand port a set versus a CNC,” Roycroft says. The differences are in repeatability, time and accuracy. However, whether you do it by hand or by CNC, you’re still going after the same results. Some people have always done it by hand and have developed a skill set that is now getting replaced by CNC machines. The bowl transitioning into the throat and into the chamber is a venturi.”Ĭreating that venturi can be done one of two ways – by hand or using a CNC. Then, you have a top angle, which blends into the chamber. As the valve angle changes, you can go to a steeper seat angle. Your most common is a 45-degree for something like a 15-degree head. What I mean by the wrong valve job is if you use the wrong seat angle and top angle. “If you put the wrong valve job on it, you can kill it. That area, your bowl area, your valve job, your throat diameter and your chamber – those are the absolute most important parts of a cylinder head when you’re porting. “The absolute most important part of the cylinder head is from the chamber area on up into the port about 1˝ on each side of the valve. “A valve job is a very, very, very important part of porting a cylinder head,” says Eric Roycroft, an experienced engine builder and the 2019 winner of the Race Engine Challenge. This cut helps reduce valve shrouding of the airflow past the valve (or before the valve on the exhaust side) as the valve starts to lift off of the seat. The third and final cut is called the top cut, which is normally 20-30 degrees and is made immediately after the seat. This is the surface that the valve actually seals against. This helps ease the air’s transition to the seat cut, which is the second cut and is generally done at 45 degrees. Today, a three-angle valve job is standard procedure, and the first angle cut is the throat cut, which is typically around 60-70 degrees. Since the highest speed and longest duration airflow happen within the port at or near the valve seat, optimizing airflow in this area is especially important. In general, the most critical areas when porting a cylinder head are those which pass the most air at the highest speed and for the longest duration. Once a shop has their CNC program dialed in, they can port heads much quicker than someone at a bench with a die grinder, but whether the result offers anything different from a hand-ported head is up for debate. The benefits of the CNC approach are accuracy, repeatability and speed. While plenty of folks still hand port cylinder heads these days, CNC porting is becoming a more affordable option. Specialists are also trying to achieve equal flow through each port so each cylinder experiences a similar air speed. A skilled cylinder head specialist will focus on shaping the port to get the maximum flow with the minimal amount of enlargement so that maximum intake and exhaust air speed is maintained. The actual act of porting or reshaping the ports generally involves a steady hand and a die grinder with an assortment of cutting, grinding and sanding tools attached. Since every cylinder head is different, learning how to improve airflow characteristics involves a lot of trial and error and many hours on the flow bench to determine if port shape changes have made a difference.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |