Port and Polish
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7thgens official a$$hole
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From: St.Louis
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Port and Polish
I was just wonderng if anybody has had a port and polish job done on their 7th gen. I had it done to my old 92z24 and it made pretty nice gains. I was just wondering how a port and polish, and shaving the head down 3mm would do on our cars. i mean its fairly cheap to have done. My machine shop will do it for $200.
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Rep Power: 812 I do as do alot of other members. Mine is milled 1mm and has large exhaust ports (too big actually). You want the ports to be larger, but not too big that it will cause backpressure loss. Also don't polish the intake side. The rough bumps are better for airflow. Getting a 5-angle valve job will also help. With my new head done and a few minor mods like ground wires, and header, I made 100whp on my auto ex. Not bad I guess. Gains on a manual would be better. Just make sure to port match a new header so the holes are as large or larger than the head ports you did.
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Hey guys, consider this...
This thing that some people refer to as "backpressure" is a myth! What you really mean to say is that your ports are too big (in diameter) to support a high exhaust gass velocity at lower rpm. A narrrower port makes the gases flow faster, thereby giving the gasses more inertia, and helping the scavenging effect AT LOW RPM. As you move into the engines higher rpm range, you must consider not only the velocity of gasses, but the volume as well. When you start trying to force more and more volume through the ports, the narrower port becomes more restrictive.
Think of two straws of different diameter. If you blow through the smaller one with light pressure, and then on the larger one with the same pressure, the smaller one will have a faster stream of air coming out of it. Now increase the pressure and blow as hard as you can. The smaller straw will become much more restrictive and require more effort, and the larger one will be comparitavely easier to blow through.
This thing that some people refer to as "backpressure" is a myth! What you really mean to say is that your ports are too big (in diameter) to support a high exhaust gass velocity at lower rpm. A narrrower port makes the gases flow faster, thereby giving the gasses more inertia, and helping the scavenging effect AT LOW RPM. As you move into the engines higher rpm range, you must consider not only the velocity of gasses, but the volume as well. When you start trying to force more and more volume through the ports, the narrower port becomes more restrictive.
Think of two straws of different diameter. If you blow through the smaller one with light pressure, and then on the larger one with the same pressure, the smaller one will have a faster stream of air coming out of it. Now increase the pressure and blow as hard as you can. The smaller straw will become much more restrictive and require more effort, and the larger one will be comparitavely easier to blow through.
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Rep Power: 0 well, if you wanted a high-end power car for track racing, larger exhaust ports would be nice. but for a daily driver, you don't want to go too big or you'll lose all the torque for stop-starts. on a race track you usually only need to stop-start once.
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Originally Posted by skydog
Hey guys, consider this...
This thing that some people refer to as "backpressure" is a myth! What you really mean to say is that your ports are too big (in diameter) to support a high exhaust gass velocity at lower rpm. A narrrower port makes the gases flow faster, thereby giving the gasses more inertia, and helping the scavenging effect AT LOW RPM. As you move into the engines higher rpm range, you must consider not only the velocity of gasses, but the volume as well. When you start trying to force more and more volume through the ports, the narrower port becomes more restrictive.
Think of two straws of different diameter. If you blow through the smaller one with light pressure, and then on the larger one with the same pressure, the smaller one will have a faster stream of air coming out of it. Now increase the pressure and blow as hard as you can. The smaller straw will become much more restrictive and require more effort, and the larger one will be comparitavely easier to blow through.
This thing that some people refer to as "backpressure" is a myth! What you really mean to say is that your ports are too big (in diameter) to support a high exhaust gass velocity at lower rpm. A narrrower port makes the gases flow faster, thereby giving the gasses more inertia, and helping the scavenging effect AT LOW RPM. As you move into the engines higher rpm range, you must consider not only the velocity of gasses, but the volume as well. When you start trying to force more and more volume through the ports, the narrower port becomes more restrictive.
Think of two straws of different diameter. If you blow through the smaller one with light pressure, and then on the larger one with the same pressure, the smaller one will have a faster stream of air coming out of it. Now increase the pressure and blow as hard as you can. The smaller straw will become much more restrictive and require more effort, and the larger one will be comparitavely easier to blow through.
When I installed my OBX header i took a dremmel to my exhaust ports, and slightly enlarged them, but barly the size of 2 pieces of paper, didnt want to messup too much
the stock exhaust ports are only 1" in Diameter, freakin tiny!
the stock exhaust ports are only 1" in Diameter, freakin tiny!
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