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Author Topic: The Myth of Backpressure  (Read 12607 times)

geresti

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Re: The Myth of Backpressure
« Reply #60 on: Feb 25, 2013, 08:13:44 PM »
I thought I heard that if you change exhaust you have to add power commander V or something similar. Did ya'll do anything like that with the addition of your new exhaust?


ROADKILL

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Re: The Myth of Backpressure
« Reply #61 on: Feb 25, 2013, 09:01:41 PM »
I thought I heard that if you change exhaust you have to add power commander V or something similar. Did ya'll do anything like that with the addition of your new exhaust?
If you just change the exhaust you don't need to do anything...when you change the air you do.

geresti

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Re: The Myth of Backpressure
« Reply #62 on: Feb 26, 2013, 07:39:25 AM »
I thought I heard that if you change exhaust you have to add power commander V or something similar. Did ya'll do anything like that with the addition of your new exhaust?
If you just change the exhaust you don't need to do anything...when you change the air you do.
the guy that I bought my bike from told me that yamaha told him that he needed to add the power commander after adding the V&H 2-1 big radius to make the bike running correctly and to keep the warranty valid. There is no air kit on my bike.

geresti

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Re: The Myth of Backpressure
« Reply #63 on: Feb 26, 2013, 07:47:34 AM »
I thought I heard that if you change exhaust you have to add power commander V or something similar. Did ya'll do anything like that with the addition of your new exhaust?
If you just change the exhaust you don't need to do anything...when you change the air you do.
I just found this article http://www.motorcyclemart.com/newmustknowexhaust.htm

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Re: The Myth of Backpressure
« Reply #64 on: Feb 26, 2013, 08:15:54 AM »
I thought I heard that if you change exhaust you have to add power commander V or something similar. Did ya'll do anything like that with the addition of your new exhaust?
If you just change the exhaust you don't need to do anything...when you change the air you do.
the guy that I bought my bike from told me that yamaha told him that he needed to add the power commander after adding the V&H 2-1 big radius to make the bike running correctly and to keep the warranty valid. There is no air kit on my bike.

You were misinformed... on both parts.  Needing the power commander and keeping your warranty valid.

You can swap out your pipe and don't need a PC unless/until you also open up your intake (big air kit).
 
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geresti

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Re: The Myth of Backpressure
« Reply #65 on: Feb 26, 2013, 09:34:17 AM »
I thought I heard that if you change exhaust you have to add power commander V or something similar. Did ya'll do anything like that with the addition of your new exhaust?
according to the article that I read you are mistaken. It says you DO need the power commander if changing exhaust. Check out that link in my previous post
If you just change the exhaust you don't need to do anything...when you change the air you do.
the guy that I bought my bike from told me that yamaha told him that he needed to add the power commander after adding the V&H 2-1 big radius to make the bike running correctly and to keep the warranty valid. There is no air kit on my bike.

You were misinformed... on both parts.  Needing the power commander and keeping your warranty valid.

You can swap out your pipe and don't need a PC unless/until you also open up your intake (big air kit).

TRaider_John

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Re: The Myth of Backpressure
« Reply #66 on: Feb 26, 2013, 10:45:16 AM »
Changing the pipes does not mean that you NEED to put in a fuel management system, but you may WANT to.  The Yamaha guy is correct in that he told him "that he needed to add the power commander after adding the V&H 2-1 big radius to make the bike running correctly."  The bike will run without one, but to optimize performance, you will want one.  Read the first post in this thread.  If you change the exhaust, you probably need to tune the engine, too. 

Changing pipes without fuel management does not void the warranty.  My dealer does it all the time. You will find many of our forum members are running that way without a problem.   

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Re: The Myth of Backpressure
« Reply #67 on: Feb 26, 2013, 11:14:01 AM »
I thought I heard that if you change exhaust you have to add power commander V or something similar. Did ya'll do anything like that with the addition of your new exhaust?
If you just change the exhaust you don't need to do anything...when you change the air you do.
the guy that I bought my bike from told me that yamaha told him that he needed to add the power commander after adding the V&H 2-1 big radius to make the bike running correctly and to keep the warranty valid. There is no air kit on my bike.

And this is why we call them "Stealerships"
  

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geresti

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Re: The Myth of Backpressure
« Reply #68 on: Feb 26, 2013, 04:29:21 PM »
Changing the pipes does not mean that you NEED to put in a fuel management system, but you may WANT to.  The Yamaha guy is correct in that he told him "that he needed to add the power commander after adding the V&H 2-1 big radius to make the bike running correctly."  The bike will run without one, but to optimize performance, you will want one.  Read the first post in this thread.  If you change the exhaust, you probably need to tune the engine, too. 

Changing pipes without fuel management does not void the warranty.  My dealer does it all the time. You will find many of our forum members are running that way without a problem.
Supposedly he had all of that done but I believe something else needs to be done because mine tends to backfire quite often and I don't think that is right. I will take it to a mechanic for my 1000 mile check-up and see what he has to say. Does your bike pop or back fire any? Mine seems to do it when I shift.

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Re: The Myth of Backpressure
« Reply #69 on: Feb 26, 2013, 06:00:56 PM »
If you are running a PCV, put 30 in the first column of the table and see what happens.  If you don't get popping, try reducing it a bit, if it still pops, try a bigger number. 

That fix comes from the guys at Dynojet and it works on most bikes. 

twinston

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Re: The Myth of Backpressure
« Reply #70 on: Jun 26, 2013, 01:53:56 PM »
Such an interesting topic, and what I don't like to see is people still calling some of this stuff "opinions". It's not...it's exhaust theory and flow facts, and some science-y stuff that can be verified and repeated. What changes is how each system is designed, and how a bike is designed. This Raider, no doubt about it, with better fueling and the Cobra Dragster pipes, is running better.

Interesting point about no baffles, though. My last cruiser (before a couple of FZs) was a VTX 1800 C model, 2005. I ended up having Cobra Speedster Longs on the bike, with and without baffles. I just didn't like them on that bike. So, I put the stock header back on, and had a mammoth 4.5 inch Roadhouse slip-on. I tried a BCT baffle in the header, but then just took it out, along with the slip-on's baffle. Big, open 4.5 inch exhaust. Was not too loud, sounded the best on that bike, and...much to my surprise, when I fueled it right (after a dyno test), or should I say, closer, I did not lose much, if any low end, mid range or top end. I had about 90 ft. lbs. at 2k rpm...and it was a foundation puller all the way to redline. When I sold it, the new owner got it dyno'd again, added a bit more fuel, still, and got even more power and torque from it with a "real" tune, I guess. Thing is, I didn't dyno it with the original baffle from the Shorty pipe in, so I don't have a comparison. All I know is that it was strong from bottom to top, really strong when it was fueled better. Could be the velocity from the stock header was good enough to not notice losses. I just thought it was interesting...as was the original post from TJ...which I agree with, and do get irritated when I still constantly see the words "back pressure" in a sentence with engine performance...because it's used so incorrectly.

SilverStar

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Re: The Myth of Backpressure
« Reply #71 on: Jul 06, 2013, 11:47:47 AM »
Hi TRaider John, thank you for this great posting. I totally agree with your posting. Years ago I use to build road rally cars in Trinidad, and people don't realize how much engineering goes into the design of and exhaust system and how it affects the performance of your bike. That's why I'm being very thoughtful on which exhaust I want on my bike. I prefer to have higher torque in the low and mid rpm range and don't care about the hing rpm range. All of my ride is here in the upstate of South Carolina and the bike is so much power that I really ever run it up to red line. I does agree that the baffles in the after market exhaust not only for sound but to keep the velocity up on the exhaust gases.
When we built 4 cylinder engines for road rally, we used a lot of 4 into 2 into 1 headers because you are using the exhaust velocity of one cylinder to help with the evacuation of the exhaust gases in the others. Also for road rallying low and mid range torque was most important for quick acceleration between one turn and the next.
Great posting, it gives us owners something to think about before spending that precious dollar on our bike mods.

I've been thru this entire thread and find it very frustrating.  I'm a gearhead from way back and there's a ton of knowledge that's completely ignored by exhaust manufacturers.  And that's fine, too.  I just wish people understood how the exhaust fits into the 'tuning' of the whole system of creating horsepower and torque form gasoline.  Hunterman hit on one of the basic concepts of a performance exhaust. 

To make the most power from a naturally aspirated engine the first thing in designing any part of the system is to decide what the rpm range will be.  The engine is basically an air pump, not a compressor, a pump.  Therefore the goal is maximum efficiency at a given rpm to get the most power.  EVERYTHING NOT AIMED AT GAINING THE MOST POWER IS A COMPROMISE.

So once the displacement and hardware of the engine and the operating rpm are established and are constants, it's time to choose intake length and diameter, camshaft lift, duration, and lobe profile, and exhaust length and diameter. Once the cams are chosen the intake and exhaust fine tune the torque curve. Longer intake tracts and exhaust tune the curve down for more torque and shorter ones tune for more horsepower, but the peak torque will stay at the same rpm - IF THERE ARE NO OTHER VARIABLES INTRODUCED.  Larger diameter tubes also increase the rpm range.

So since the goal for this discussion is to maximize efficiency and power then we need to look at how these parts interact and affect each other.  The 2-1 works because: at the merge of the two pipes, the collector in header terms, when an exhaust impulse goes through, it creates a low pressure in the adjacent tube.  Depending on length and diameter, at some rpm, this vacuum will hit the other exhaust valve just as it opens and suck the exhaust from that cylinder, and, due to overlap designed into the cam, the fresh intake through the intake valve.  That's how a naturally aspirated race engine can achieve efficiency above 100%.  It also explains why more fuel has to be added.  With a restricted exhaust there is still burnt exhaust in the cylinder.  Gas won't burn without oxygen.  With a purer intake charge the oxygen won't burn without more fuel. Simple concept but the fine tuning is the hard part.

So larger diameter pipes slow the velocity of these pulses so will function better at higher rpm.  So the ideal pipe for a 1900 is too large for a 750, unless the 750 rpm range is a lot higher.  That also explains why bigger pipes might kill low end and increase top end power.

The stock pipe is a compromise of power, durability, noise, emissions, and fit.  The smaller diameter gives the pulses the velocity to give it low end torque so it's responsive on the street, but it and the other factors limit the top end power. The EXUP is a good way to broaden the power band, but for a race engine or maximum peak power it's considered a Band-Aid or crutch to some.

So the 2-2 exhaust has to overcome the disadvantage of not having a collector. You can put a crossover H-tube in that helps a little but not nearly as much as a collector.  The 2-2 works because it ELMINATES BACK PRESSURE.  So it will always make, at best, slightly less power than a PROPERLY DESIGNED 2-1.  Obviously, a good 2-2 can make more power than a poorly designed 2-1.

The whole back pressure issue came up in the late 70's or early 80's.  Till then it was obvious that headers and no mufflers made more power because the factory systems on cars since the first flathead V8 were so restrictive that anything changed would relieve back pressure.  Any real drag car had open headers.  Then some cities in the Northwest placed noise restrictions on the drag strips, so they had to run mufflers.  Lo and Behold, most of the naturally aspirated door slammers went quicker and faster, some as much as 2/10s of a second quicker.  So the concept that back pressure is necessary was born.

I maintain the cars that went faster had headers and collectors that were designed for too high an rpm.  By adding a muffler on each collector they lengthened the exhaust tract which would cause the rpm range of the power band to be lower.  The extra length increased efficiency more than the restriction decreased efficiency.  They DID NOT HAVE WELL MATCHED PARTS prior to adding the mufflers.  But that's just my opinion, for what it's worth.

So where does that leave us?  If you like the 2-2 run one!  If you like stock keep it!  If you want every last bit of power the 2-1 may be the way to go.  It's all about individual preference. Only YOU have to like your bike.  Nobody else does.  But I hope this helps at least one person make an informed decision instead of hoping for the best guess, or just doing what someone else did without knowing why.  We don't have tons of options unless we can fabricate and chrome our own exhaust.  Personally, for what pipes cost, I want to get it right the first time.  My philosophy is form follows function.  I can paint so if I want pretty I'll custom paint it.  If I'm going to spend money on mods, I want the biggest performance bang for the buck.  I'd run a Warrior muffler if it made my bike the fastest (thank God it won't it's way ugly).  I'm not a chrome whore or billet whore at all.  If I had a choice I'd have chosen a Raider over the Raider S.  It'll be a while till I make any changes but I'm leaning towards the V&H 2-1.  For pure aesthetics I'd go with Cobra Dragsters.

I know this is a long post, sorry about that.  I just hope it helps somebody.

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Re: The Myth of Backpressure
« Reply #72 on: Jul 06, 2013, 01:22:27 PM »
I think you said the same thing in a more practical way.  Whether you call it tuning the exhaust to the engine or "backpressure" it is still getting the most out of the engine by scavenging the exhaust gases.  I'm just opposed to calling it "backpressure".  Our engines don't need backpressure, thy need and exhaust that is sized for the displacement and rpm of the engine  they are connected to.  There are a dozen threads that say the torque improved when they put the baffles back in.  To me, that affected the tuning of the exhaust (volume and velocity).  To you, it added backpressure. 

PantherMaw

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Re: The Myth of Backpressure
« Reply #73 on: Oct 03, 2013, 08:13:43 AM »
Guys,

Many thanks for posting this thread. I was actually a little confused about this subject while doing research for a new exhaust... it took a while to get through all the posts but I'm sure glad I did.

TRaider_John excellent write-up, and to all those that contributed, I really appreciate it.

I've got some great ideas.  8)
~J


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TRaider_John

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Re: The Myth of Backpressure
« Reply #74 on: Oct 03, 2013, 08:37:34 AM »
from all of us, you are welcome.