4.9l headers
Thread Starter
Senior Member
Joined: Mar 2009
Posts: 765
Likes: 8
From: Green Bay Wisconsin
i get what you guys are saying but with the 300 having a lot of low end torque could a high flow cat work like stock to keep that low end torque or will i loose some torque?
Hi-Rev Motorsports
Joined: Aug 2009
Posts: 4,898
Likes: 65
From: Northern Indiana
no you wont lose any torque....
I actually still have the factory exhaust on my truck and I modded the cat myself and I actually picked up a little power...
Next I am going to remove the exhaust right after the cat and replace it....
I pull the exhaust off the truck and drove it with just the modded cat and it was TONS peppier....so it goes without saying the factory exhaust is VERY restrictive....
I was going to pull the O2 sensor and put a pressure gauge in it to see just how restrive it is but I could just guess and be safe...
I'll bet with headers and just collectors these things would rip pretty good considering these are low compression engines...mine was not loud at all considering the high flow cat I know have...
I actually still have the factory exhaust on my truck and I modded the cat myself and I actually picked up a little power...
Next I am going to remove the exhaust right after the cat and replace it....
I pull the exhaust off the truck and drove it with just the modded cat and it was TONS peppier....so it goes without saying the factory exhaust is VERY restrictive....
I was going to pull the O2 sensor and put a pressure gauge in it to see just how restrive it is but I could just guess and be safe...
I'll bet with headers and just collectors these things would rip pretty good considering these are low compression engines...mine was not loud at all considering the high flow cat I know have...
Never Learns
Joined: Sep 2009
Posts: 3
Likes: 0
From: Vermont
Backpressure / torque
Hey guys... At the risk of putting my foot in the soup on my first post here, the attached is taken from a BMW guys site and talks about backpressure, torque and all that good stuff. If you click on the question below, it will take you to the source.
Some say that "an engine needs backpressure to work correctly." Is this true?
No.
It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.
The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below. (more by clicking hyperlink).
Some say that "an engine needs backpressure to work correctly." Is this true?
No.
It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.
The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below. (more by clicking hyperlink).
