another exhaust question
Champion
Joined: Feb 2005
Posts: 3,710
Likes: 2
From: Skagit County, WA
RE: another exhaust question
For sure, running single cat/muffler into 2 tips is a far better way to get the look without having to run ~2" pipes the whole way back.
Ok, so as far as removing the exhaust goes, yeah, you could do that and have 0 backpressure, but that would be really bad for low-end, and probably for the valvetrain as well for a couple of reasons.
There would be no way to mount an O2 sensor in order to adjust the a/f mixture, and you could very well have lean burn conditions resulting in burned valves.
The low-rpm scavenging effect would be completely non-existant. At low RPM's you need the gasses to maintain as high of velocity as possible because each "pulse" creates a slight vacuum behind it, effectively pulling the gasses from the other chambers. Without it there is more inert/spent vapor left in the chamber, meaning less oxygen is able to enter the chamber, making for lower power. This isn't nearly as important with boost, as the increased intake pressure will push the exhaust out better.
The scavenging effect and low backpressure is really important when you've got a high overlap cam, as having both the intake and exhaust valves open at the same time can cause the exhaust to actually back up through the intake valves if the backpressure is too high (which one of the links addressed a little when talking about double-loading the fuel mixture in the carb). It's still oxygen-less air and it gets drawn back into the cylinder once the exhaust valve closes. That's why on a lot of high overlap cams the torque doesn't really hit until much higher in the power band. My F303 cam in my 5.0 has a torque peak at about 3200 rpm.
I have to get ready for a class now, so I can't write more. I'm here to learn and share what I've learned, and I'm sorry if I'm tactless and rude sometimes. I just can't tell you how many times I've seen the same threads over and over again in the past 6 years on various forums and I need to be a little more patient.
Ok, so as far as removing the exhaust goes, yeah, you could do that and have 0 backpressure, but that would be really bad for low-end, and probably for the valvetrain as well for a couple of reasons.
There would be no way to mount an O2 sensor in order to adjust the a/f mixture, and you could very well have lean burn conditions resulting in burned valves.
The low-rpm scavenging effect would be completely non-existant. At low RPM's you need the gasses to maintain as high of velocity as possible because each "pulse" creates a slight vacuum behind it, effectively pulling the gasses from the other chambers. Without it there is more inert/spent vapor left in the chamber, meaning less oxygen is able to enter the chamber, making for lower power. This isn't nearly as important with boost, as the increased intake pressure will push the exhaust out better.
The scavenging effect and low backpressure is really important when you've got a high overlap cam, as having both the intake and exhaust valves open at the same time can cause the exhaust to actually back up through the intake valves if the backpressure is too high (which one of the links addressed a little when talking about double-loading the fuel mixture in the carb). It's still oxygen-less air and it gets drawn back into the cylinder once the exhaust valve closes. That's why on a lot of high overlap cams the torque doesn't really hit until much higher in the power band. My F303 cam in my 5.0 has a torque peak at about 3200 rpm.
I have to get ready for a class now, so I can't write more. I'm here to learn and share what I've learned, and I'm sorry if I'm tactless and rude sometimes. I just can't tell you how many times I've seen the same threads over and over again in the past 6 years on various forums and I need to be a little more patient.