question abou exhaust port shape
Thread Starter
Joined: Aug 2005
Posts: 2,803
Likes: 1
From: Seminole County, Florida
question abou exhaust port shape i have noticed on heads how the exhaust port is often a squarish, or oblong, or anything but perfectly round, and i only see perfectly round header primaries.
so i imagine that when the exhaust gasses go though the port, the walls of the headers dont match the port walls, doesnt this create unnecesary tubulence? if the two holes were the same shape wouldnt this increas exhaust velocity and there for hp and torque at all rpms, especially lower rpm's
or am i just crazy
so i imagine that when the exhaust gasses go though the port, the walls of the headers dont match the port walls, doesnt this create unnecesary tubulence? if the two holes were the same shape wouldnt this increas exhaust velocity and there for hp and torque at all rpms, especially lower rpm's
or am i just crazy
TECH Fanatic
Joined: Jun 2002
Posts: 1,979
Likes: 3
From: Upstate NY
Originally Posted by camaroextra
i have noticed on heads how the exhaust port is often a squarish, or oblong, or anything but perfectly round, and i only see perfectly round header primaries.
so i imagine that when the exhaust gasses go though the port, the walls of the headers dont match the port walls, doesnt this create unnecesary tubulence? if the two holes were the same shape wouldnt this increas exhaust velocity and there for hp and torque at all rpms, especially lower rpm's
or am i just crazy
so i imagine that when the exhaust gasses go though the port, the walls of the headers dont match the port walls, doesnt this create unnecesary tubulence? if the two holes were the same shape wouldnt this increas exhaust velocity and there for hp and torque at all rpms, especially lower rpm's
or am i just crazy
I'd try to line up the top of the header opening with the top of the port and have the mismatch at the bottom for best anti-reversion. In no case should the header opening project into the port in the head. Minor grinding on the header might be required, especially if the heads were ported.
As to whether you are crazy, that's probably better asked in the Lounge or on www.nutzycoocoo.com.
In one of the old 'Head Tech' threads, one of the head guru's fed answers on the topic. He stated that the top of the port exit and header entry can match, but for reversion purposes (as noted above), the bottom should never match. Reversion is a killer. You want to avoid this if possible.
I had made a set of 1" thick spacers/adapters to bridge the port of the head to the header. The sides of the adapter ports were tapered from being matched at the top to the offset at the bottom to help with reversion. The car pulled noticeably harder from 6500+ Just thought I'd share my experience
I had made a set of 1" thick spacers/adapters to bridge the port of the head to the header. The sides of the adapter ports were tapered from being matched at the top to the offset at the bottom to help with reversion. The car pulled noticeably harder from 6500+ Just thought I'd share my experience
Thread Starter
Joined: Aug 2005
Posts: 2,803
Likes: 1
From: Seminole County, Florida
Originally Posted by NoseUp
In one of the old 'Head Tech' threads, one of the head guru's fed answers on the topic. He stated that the top of the port exit and header entry can match, but for reversion purposes (as noted above), the bottom should never match. Reversion is a killer. You want to avoid this if possible.
I had made a set of 1" thick spacers/adapters to bridge the port of the head to the header. The sides of the adapter ports were tapered from being matched at the top to the offset at the bottom to help with reversion. The car pulled noticeably harder from 6500+ Just thought I'd share my experience
I had made a set of 1" thick spacers/adapters to bridge the port of the head to the header. The sides of the adapter ports were tapered from being matched at the top to the offset at the bottom to help with reversion. The car pulled noticeably harder from 6500+ Just thought I'd share my experience
Take a look at this picture of the LS7 Exhaust Manifold/Header http://vorlon.case.edu/~aap8/gallery.../LS7_Engine_26. Obviously, Chevrolet is addressing this exact issue.
Steve
Steve
We're dealing with less reversion with an OEM cam than we would with a more aggressive after-market grind, so it may not be much of an issue. There are more ways of limiting reversion, but I'm told the port exit to manifold/header entry step is the most effective, as is not 'port-matching' the intake manifold larger than required for optimum flow. A lot of the pro's go as far as designing the intake and exhaust runners in such a way that limits backward flow. Valve angles are part of the equasion. In many cases, a 'stepped' header can also help. Scavanging is very important. Stepped headers, high-velocity merge collectors, x-pipes, and 'boom tubes' all help with this.
Last edited by NoseUp; Jan 19, 2006 at 01:01 PM.
