Is there a certain degree of inefficiency with low back pressure? Yes. Are your valves toast at this point, not necessarily so, but you are well on your way to serious issues if you don't compensate for the loss of backpressure in other areas of the engine. The blue smoke is a sign or wearing/worn valve guide seals.
Here is a great tech article from Flowmaster on engine building and creating a homeostatic neutrality between increases and decreases in backpressure. I would recommend you read it and consider the ramifications of the loss of backpressure to the life of your engine.
http://www.flowmastermufflers.com/backpressure.html
Good luck.
Is there a certain degree of inefficiency with low back pressure? Yes. Are your valves toast at this point, not necessarily so, but you are well on your way to serious issues if you don't compensate for the loss of backpressure in other areas of the engine. The blue smoke is a sign or wearing/worn valve guide seals.
Here is a great tech article from Flowmaster on engine building and creating a homeostatic neutrality between increases and decreases in backpressure. I would recommend you read it and consider the ramifications of the loss of backpressure to the life of your engine.
http://www.flowmastermufflers.com/backpressure.html
Good luck.
Sorry, gentlemen, but unless an engine builder with a physics background were to walk in here and tell me I am wrong, I am going to have a hard time not standing up on this one.I am not a ASE mechanic, never pretended to be, but one thing I do know is theoretical and mechanical engineering and looking at the "big picture".
A comment was made that NO exhaust system manufactured or available will/can cause premature wear to the valve seals. I strongly disagree in the truest sense of engineering and physics. Sorry. I respect each member here, but you gentlemen need to fundamentally realize that for every action there is a equal reaction.
We live in a world of natural laws and simply believing something is so, does not make it truth. With this said the core issue is aftermarket exhausts have EVERYTHING to do with physics and engineering. In time, ALL uncompensated modifications WILL impact engine performance and longevity.
When we buy that awesome aftermarket exhaust we are looking to: make appearance and sound changes as well as maximize exhaust flow out of the engine.
The inflow of an air/fuel mixture is a separate issue, but it is directly influenced by exhaust flow, particularly during valve overlap (when both valves are open for "X" degrees of crankshaft rotation). Another topic for another issue.
Perhaps the most important aspect of exhaust flow relative to aftermarket products is the issue of flow volume vs. flow velocity and the savaging that occurs during the exhaust stroke.
Ford spends thousands of hours designing a stock engine to maximize each one of these strokes. Even if their idea of maximization is not OUR idea, they have designed and integrated, fully enclosed and self-actuating environment.
A well designed (or modified) engine needs the highest flow velocity possible for quick throttle response and torque throughout the low-to-mid range portion of the power band. The same engine also needs the highest flow volume possible throughout the mid-to-high range portion of the power band for maximum performance. This is where the issue and fundamental conflict arises.
For "X" amount of exhaust pressure at an exhaust valve, a smaller diameter exhaust component will provide higher flow velocity than a larger diameter tube. Unfortunately, the laws of physics will not allow that same small diameter tube to flow sufficient volume to realize maximum potential power at higher RPM. If we install a larger diameter exhaust component at any portion of the exhaust system, we will have enough flow volume for maximum power at mid-to-high RPM, but the flow velocity will decrease and low-to-mid range throttle response and torque will suffer. Yes, this is where the proverbial back pressure myth usually arises. Stay with me, it gets fun.
This is the primary paradox of exhaust flow dynamics and the solution is usually a design compromise that produces an acceptable amount of throttle response, horsepower and torque across the entire power band.
Now we throw in the process of scavenging in the exhaust system and all hell breaks loose.
In physics, we have inertial scavenging and wave scavenging. Different phenomenons, but both impact exhaust system efficiency and engine performance/longevity and affect one another. Scavenging effects are directly influenced by tube diameter, length, shape and the thermal properties of the tube material. As we modify the exhaust system via headers, mufflers, different style and size tube systems, with or without manifolds or cats, we are adversely affecting the original optimal design produced in a controlled environment by Ford engineers.
We are most certainly impacting reversion and the physical aspects negatively: in that with the loss of flow velocity not all of the exhaust is able to exit during the stroke time. Some of the reverted exhaust moves back toward the exhaust valve on a happy little collision course with the exiting gases where they then pass through one another like a freight train - with a little less energy and turbulence.
What happens when that reversion wave arrives back at the exhaust valve depends on whether the exhaust valve is still open or closed. This is the most pivotal moment in the exhaust cycle because the reversion wave can be beneficial or detrimental to exhaust flow and mechanical aspects of the valves depending upon its arrival time at the exhaust valve.
If the exhaust valve is closed when the reversion wave arrives, the wave is again reflected toward the exhaust outlet and eventually dissipates its energy in this back and forth motion. If the exhaust valve is open when the wave arrives, its effect upon exhaust gas flow depends on which part of the wave is hitting the open exhaust valve and this can cause physical negative affects on valves and their seals a well.
Since these happy little waves are comprised of two alternating and opposing pressures (one compressed and the other rarefied) each wave contains a compression area called a node at higher pressure and the rarefaction area called a anti-node at lower pressure. HERE IS WHERE LOW PRESSURE BECOMES THE ENEMY.... wait for it...wait for it......
………..A well designed exhaust will place the wave’s anti-node at the exhaust valve at the proper time for its lower pressure to help fill the combustion chamber with fresh incoming charge and to further extract gases from the chamber via vacuum. If it is not well designed and not reciprocating into the engine at the proper time you WILL see premature wear on valves and seals. If the stock engine from the factory is already mis-tuned or suffering a weakness in the system, it will happen. 'Tis a matter or physics, Gentlemen. I don’t make it up for fun. It is what it is.
(puts on rain slicker and hard hat for impending flames...)
Maybe I'm wrong but from that flowmaster article, I gathered that less backpressure can lead to a lean condition in the motor resulting from raw fuel being sucked into the exhaust system before being ignited? Isn't that what these tunes are suppose to take care of?
Not true on the 5" pipe comment.
Ford has known issues with the valve design in the 3V - 4.6L engine. Has for years. I am not saying they are any worse or better than any other mfg. The LS1 has its own set of valvue issues. Nothing is perfect, it is a operating machine.
I do not have to own a 4.6L GT to know how it operates. To think otherwise makes a person who holds that belief closed-minded and defensive. Your issue very well could have been with the CMCV design and oil bypass. My technical contention is concerning this statement, Sir.
"This issue is not related to your exhaust system, none of the exhaust systems available will cause this..."
You are incorrect. Premature valve seal wear and/or failure CAN be caused by incorrect exhaust design and installations, it is compounded with other issues, yes, but your statement is as black and white as they come.
Do not be so quick to come out of the defensive shoot, TGJ, I have my hard hat and kevlar slicker on and am ready for more respectful technical discussions when you are.
Yes, they can. A tune for AF compensations (spark timing, etc.) along with the increased exhaust velocity and flow from the aftermarket system is a perfect example of a compensatory modification to intake and exhaust.
Ruffy's mod list:
"Boy Racer" Wing, Boyd Cottington Junk Yard Dog Wheels, CDC Stars & Stripes Grill Emblem, Hurst Shifter, Redline Hood Quic-Lifts, Sequential Turn Signals, SLP Loud Mouth Exhaust, Steeda Pedal Covers, Steeda G-Trac Brace, Steeda CAI w/ Tune.
So long as the modification order took into account the CAI AND the exhaust, it should run fine and the tune profile should compensate. The trick is to ensure that it is not a canned tune for just a CAI. Once you add the exhaust, then the tune profile should reflect that as well. This is the beauty of modulated modification. There is the mechanical part and the tuning part. They must work hand-in-hand to operate optimally. With Ford's version of variable valve timing added to the mix, it can get a tad tricky.
I miss the days of a carb and a screw driver. lol
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