I have done search upon search with all sorts of different answers. Then I asked Mike T. in the Chips and Programming forum and he just blew me off saying he didn't have time to teach. All I want is to truly know whether having no back pressure on a 4.6 really does hurt the engine and what exactly it hurts. And with the way this "expert in performance" has blown me off about it twice I am beginning to thank that having no back pressure won't hurt them at all and that it is a myth thought up to scare you into thinking that you better not touch anything on your trucks. So please if someone has repetitive proof that it hurts the samethings, i.e. samething happening to two different people, please give me some info. And yes I am talking about no cats and mufflers, but I just want to understand how for my own knowledge.

Sorry I am just a little pissed of how he avoided answering a question that might have probable have taken two whole sentences to answer.

On the post the word should be explain. Broken right ring finger.

 

I will try to help. First, please include more information on your engine.

You COULD HAVE four O2 sensors, two near the cylinder head and two after the catalytic converter. If you remove the cats, you could wreak havoc on the engine control system.

Another hot topic is back pressure. An engine is an "AIR PUMP". If it can exhale more than it can inhale, an imbalance is created (my interpretation). Personal experience with straight pipes decreases the low end and increases the noise. Although at higher RPM's the performance and power seem to increase. Perhaps because the degree of 'imbalance' (as I call it) is lowered due to higher RPM.

there will probably be 100 other interpretations, this is mine.

Good luck

 

Thanks for the reply The Saint. Your interpertation does make some since. But I bet if you used a x pipe it would have keep some more power on the low end because it helps to balance out the pressure on both banks.

I all ready know how you get around with the O2 sensors with simulators or 1/4 ohm resistiors tricking the computer that everything is ok. But just to clarifiy my question, I would like to hear about whether or not it really hurts the engine. Don't want any theroies or cat police, all I want is some hardened proof or someone with extensive knowledge about the 4.6. But the only thing I have picked up from old Mike is that backpressure isn't it, it's the flow velocity and that no matter what backpressure doesn't help you on the low or high end.

 

So, you do not believe that the exhaust and back pressure have a direct impact on volumetric efficiency? Skipped physics did we?

As far as a lack of back pressure hurting an engine, I am aware of no such problem.

 

No, I showed up for physics every day and passed. Have to when my parents are the ones paying my way through college to keep from having to go into debt. Besides it wouldn't be just physics it would involve the courses, fluid mechanics and thermodynamics. Those two classes are mechanical engineering classes, the thing is I am studing to be a civil engineer and they require us to take both of them.

Anyway, believe it or not this past week I argued with my younger brother over the very same interpertation you gave me about exhale and inhale imbalance(I didn't even mention this post to him, ironic). What I have to say is that during the intake stroke both air AND FUEL enter the cylinder. When the gas is burned, the amount of volume it needs to take up is greater(causing higher pressure then initally) as a gas then when it was liquid(also due to the heat that was produced). So here you have more gases then you let enter, therefore you have more gas to expeal. As far as how backpressure effects the power band, have no clue.

 

Too much flow = exhaust gas cools and gets dense within the pipes, requiring energy to expel it out of the system.

Backpressure is bad.
Too much flow is bad.
Proper flow that is matched to your engine is good.