Looks like the sense of humour by pass is working fine.

 

Did not mean it from a purist perspective, more of a realist, not going to put fancy wheels on a minivan.

 

I bet your Mina exhaust is already lower in back pressure. All I can say is that I put Magnaflow style mufflers on my XK and it was a total dog to the point I threw those new mufflers away and went back to stock. On both my Astons, I had/have an active valve controller on the exhaust and if it's open I can feel a slight loss of power at the bottom end. Not enough for me to not have the valve open when I want it...

I don't know if faster or no cats by themselves lowers back pressure, but you need some back pressure is what I am getting at. Are headers available for the XK?

 

*sigh*
There is not an internal combustion engine ever made or conceived of that requires back pressure to run optimally. By its very nature they ABHOR back pressure. WHY WHY WHY would a combustion chamber WANT to have non-burnable gasses (already burnt fuel and oxygen) to remain in the mix?????? WHY WHY WHY????? Why would a piston on the exhaust stroke want MORE resistance to movement while trying to force MORE spent fumes from the cylinder? WHY WHY WHY would it be beneficial to have MORE CRAP to try to force out of the exhaust system??????
NO REASONABLE HUMAN would think that an engine would work BETTER when there is INTENTIONALLY MORE WORK that it is forced to perform.
In an effort to allow some (insert adjective of your choice) people to better correlate to 'perceived' back pressure by some exhaust systems; Exhaust pulses are a finicky bunch... with a poorly designed system there can be eddies created at certain RPMs that can swirl and cause backflow in some instances. Look at a river. Some craggy spots cause stagnant areas and even whirlpools. Not cohesive to flow. Now, introduce a beaver dam to "CREATE BACK PRESSURE". Yep, now the river backs up. Good for River Performance??? Not hardly.
ANY back pressure is Pressure that is Backed up. NOT GOOD. Instead of INTENTIONALLY creating an obstruction via smaller diameter pipes, how about removing ACTUAL obstructions?
NOW we get into Scavenging... and to scavenge correctly velocity is required. BUTTTTTT!!!!!!!!!! Velocity X time X volume is a CONSTANT. Slower exhaust speed in a larger volume over the same time IS EQUAL!!!
Scavenging is a process of headers, not so much exhaust pipes. X-pipes and H-pipes create a FALSE larger volume area to help exhaust escape to a VERY short time period 'Between Pulses' low pressure area in the other side of the X or H pipe. Sometimes there IS a low pressure area on the other side, sometimes there ISN'T. Besides, due to Constantly varying Engine RPM and throttle position, there is ZERO way to create exactly perfect scavenging and exhaust pulse equalization.
Oh! I get it...... 'required' back pressure...... Stick a few bananas up those tail pipes. That'll help.
Now I'll go search for a simple video.

OK, now cue the deniers.............................

 

Here, I found one.

 

What Cambo has discovered is that changes to back pressure without changes to tune results in the engine running sub-optimally from a tuning stand point since the computer is making un-realistic calculations.

I suppose then that dyno-time could get back your lost HP, and yield some gains.

 

Forget rivers and beavers, try this experiment.
Change the hose on your pressure washer from 1/4 to 3/8.
You will lose power.

More air moving through a larger diameter pipe, albeit slower is Not Equal.
You know whats's different, its pressure or 'sucking power'
Google sucking power

 

Another eyeopener, compare Google search for 'sucking power' vs Bing search for the same.

 

May I use an example that everyone is more familiar with to point out the physics. Please, no giggles.
Lets take the god-given tail pipe that we all have.
When expelling air, it doesnt take a rocket scientist to figure out a larger tailpipe would require lot more force and not be as loud.

 

So all search engines aren't created equal!

 

Microsoft has clearly entered a more lucrative business.

 

Another experiment, which will help with a similar misapprehension about the opposite end or intake.
Suck water through a plastic straw, now try the same with a garden hose of the same length.

 

Deleted. You may lose velocity, absolutely not volume. Evidently you 'think' that velocity matters when dealing with volume. Take a sip through a stirstraw, then put your face in front of an eight-inch firehose. YOU tell ME which one flows more.

 

Deleted, a fire hose flows more because there is a massive pump pushing that water. Its not the size of the hose its the power of the pump.
But seriously there is your answer, its not velocity or volume, its about matching both to pump power.

 

Let's try and stay civil please?

 

You are thinking about it arent you.
Experiment #4:
Put a larger diameter attachment on your vacuum than the one supplied with it. You will have less sucking power.
Your engine is also an air pump.

So. There is actually power in the exhaust system that is being wasted.
If you use that wasted power to push air through a restriction, guess what you have just done- turned that exhaust power into sucking power.
Now there is a very fine balance, if the restriction is greater than the power being wasted, than you will have a deleterious effect.

Sooo. when you increase the efficiency of the the exhaust-while simultaneously decreasing the vacuum effect, ie. going to larger pipe, you are only benefiting one side of the equation- throwing more power out the tail pipe.

 

If Q&C says anything, don't tell me. I've finally, after thinking about it for a couple years, blocked him from contact.

 

Be reasonable.
You cant make blanket statements like 'back pressure or restriction is bad'

What are we doing when we add a turbo to the exhaust pipe- we are adding tremendous restriction.
Why is that a good thing, because the power we get from it is a net positive.
We are taking power that was going to be thrown out anyway and used it to do something else.

You are getting worked up about a falsehood you created.
Thats like drawing Casper the friendly ghost and running out of room all scared.

 

Andrew we can meet up later this week or weekend .. my car has high flow cats on it currently , you can hear how it sounds

 

*Sigh*...