Can I get an easy to understand straight answer?
#21
Join Date: Oct 2007
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I've already owned #7,#6 and #5 on that list of bikes. Put four into one pipes on all of them. I know bikes, I don't know cars. Having fun getting educated though. Just a little challenging due to the amount of douche' comments like, wind down your windows etc...
Stuart, thank you for your feedback regarding cut outs. I'll start getting educated on them now!
Stuart, thank you for your feedback regarding cut outs. I'll start getting educated on them now!
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Queen and Country (07-16-2018)
#22
Did not mean it from a purist perspective, more of a realist, not going to put fancy wheels on a minivan.
#23
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?
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Andrew 07 XKR (07-16-2018)
#24
*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.............................
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.............................
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XJ8JR (07-16-2018)
#25
#26
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.
I suppose then that dyno-time could get back your lost HP, and yield some gains.
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Andrew 07 XKR (07-16-2018)
#27
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
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
#28
#29
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.
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.
#30
Join Date: Oct 2007
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#31
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Ranchero50 (07-16-2018)
#32
#33
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
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
Last edited by Norri; 07-16-2018 at 02:36 PM. Reason: Derogatory Language
#34
But seriously there is your answer, its not velocity or volume, its about matching both to pump power.
Last edited by Norri; 07-16-2018 at 02:37 PM. Reason: Derogatory Language
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moronthethrottle (07-17-2018)
#35
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Location: PHX some of the time
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#36
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.
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.
#37
#38
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.
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.
#39
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
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Andrew 07 XKR (07-16-2018)
#40