Heads...
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Oval or Rectangular compares the intake port opening in Big Block Chevy heads. It refers to shape.
O port has somewhat smaller intake runner volume than R port and is often preferred for street cars because it tends to produce a snappier low-end throttle response than the larger volume R port.
Intake manifolds also have O or R shape and should be mated to heads accordingly.
O port has somewhat smaller intake runner volume than R port and is often preferred for street cars because it tends to produce a snappier low-end throttle response than the larger volume R port.
Intake manifolds also have O or R shape and should be mated to heads accordingly.
Drifting
Joined: Aug 2004
Posts: 1,883
Likes: 124
From: Lubbock TX
Runners on most production rectangular port heads is around 315/325cc's where ovals are about 255 or so. Don't confuse the ovals with round ports, often called peanut ports. Ovals are taller than they are wide where the round ones are about the same height as width. The peanut ports will be the ones you find most often on 454's built after about 1976 or so. They're excellent for heavy trucks, motor homes, etc. because their small ports promote excellent velocity for cylinder filling, but they run out of air around 4500 - 5000 rpm's. Ovals are great for street machines and will generally take a 454 to about 6500 with some minor bowl blending, etc. and stock valves. They can be ported and have bigger valves installed and will handle a 496 or 502 to about the same rpm range. If you want to buzz something higher or go with bigger cubes, that's where the rectangle ports start to shine. Since the ports are so much bigger, they tend to have low velocity which means that throttle response suffers at the lower rpm's, but they really start to shine at about 6000 and will take an engine will into the 7000 rpm range. When combined with a solid flat or roller cam, they make perfect matches for Corvettes - they kill off a bit of lower end torque which helps a 'vette launch without excessive squat or tire spin, and they'll spin well over 7000, which is where most horsepower junkies tend to spend as much time as possible.
There's a small pic compilation on the Chevelles.com site, you might need to do a search there to see the differences for yourself.
There's a small pic compilation on the Chevelles.com site, you might need to do a search there to see the differences for yourself.
