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remove stock exhaust baffles ok?

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  #11  
Old 09-09-2010, 12:19 PM
Grendel4 Grendel4 is offline
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I can't believe how a "little" information can be turned around!

"removing the baffles could add reversion" THIS IS WRONG

First, removing the baffle "decreases" reversion, it does not increase reversion! Reversion acts to increase low to midrange
torque. Therefore if reversion is reduces ( less backpressure by definition equals less reversion!) you may feel less torque at low to mid throttle.


G:
Might I suggest some interesting reading from Big City Thunder?

http://www.bigcitythunder.com/pages/...ng_exhaust.pdf


When the exhaust valve opens, two things immediately happen. An energy wave, or pulse, is created from the rapidly expanding combustion gases. The wave enters the exhaust pipe traveling outward at a nominal speed of 1,300 - 1,700 feet per second (this speed varies depending on engine design, modifications, etc., and is therefore stated as a "nominal" velocity). This wave is pure energy, similar to a shock wave from an explosion. Simultaneous with the energy wave, the spent combustion gases also enter the exhaust pipe and travel outward more slowly at 150 - 300 feet per second nominal (maximum power is usually made with gas velocities between 240 and 300 feet per second). Since the energy wave is moving about 5 times faster than the exhaust gases, it will get where it is going faster than the gases.

When the outbound energy wave encounters a lower pressure area such as a second or larger diameter section of pipe, the muffler or the ambient atmosphere, a reversion wave (a reversed or mirrored wave) is reflected back toward the exhaust valve without significant loss of velocity.
The reversion wave moves back toward the exhaust valve on a collision course with the exiting gases .........


G:
Also, rbracing goes into the wave reversion phenomenom in nauseating and headache inducing detail here -- http://home.earthlink.net/~mmc1919/venturi.html


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  #12  
Old 09-09-2010, 04:13 PM
FBRR FBRR is offline
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Grendal4,
While I don’t wish to get into an internet pissing contest, I will point out the following:
The “Big City Thunder’s” article (and that is what it is, an article not an engineering nor physics lesson), even states that reversion is a by product of change in velocity. The greater the change in velocity, the greater the reversion pulse generated. The greatest influence, in an exhaust system to changes in velocity is backpressure, whether that decrease in velocity is generated from change in diameter of the pipe, or a baffle. The facts here are that removing the baffle will have an affect on backpressure. And that decrease in backpressure also means a decrease in change in velocity. The delta change in velocities as cited in the article that cause reversions are also LESSONED when backpressure is reduced.

An engine is an air pump. More air in, equals more power and TORQUE out. The beneficial affects of reversion is when tuned correctly in an exhaust system, reversion increases scavenging of the fresh charge of fuel and air into the chamber. It is this scavenging affect, at low and mid engine speeds that bump up the torque curve!
When you open the exhaust and lessen this beneficial affect from reversion, low and midrange torque is reduced.

Big Thunder talks about tuning and timing of the reversion pulses in an exhaust system. He stated that many folks quote the fact that you loose low and mid-range torque when you open the exhaust. He (the author in Big Thunder’s article) then says, even an open exhaust system can be mechanically changed such that you do not necessarily loose low and midrange torque.

What he omitted is those “mechanical changes” are cam timing and overlap! It is possible through variable valve timing to “MECHANICALLY” change that tuning and gain the benefit of reversion pulses with an OPEN EXHAUST system; BUT NOT with a HARLEY fixed camshaft profile and timing! Max. Hp is always a trade off with the torque curve shape at lower engine speeds. The only way around that is with variable cam timing and overlap, as well as variable length intake runners. (All related to TUNING the airflow for maximum cylinder filling.)

Cross over pipes and pipe length in two into one exhaust system are “tuning” features that increase scavenging at the exhaust port. They use the delta pressure generated during reversion to accomplish that “tuning” affect.

With an open exhaust, there will also be less delta pressure ( as well as LESS velocity change) created in the exhaust pipe! That's physics, not opinion.

Last edited by FBRR; 09-09-2010 at 04:18 PM.
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  #13  
Old 09-09-2010, 04:22 PM
Grendel4 Grendel4 is offline
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You lost me at 'backpressure'. There is no such thing.

I'm done here.

Have a nice day.
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  #14  
Old 09-10-2010, 05:01 PM
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Monterey Fat Bob Monterey Fat Bob is offline
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Well FBRR I will have to respectfully disagree and will try and explain without a novel. New Harleys, which is what we are talking about have a closed system, which means with these bikes the O2 sensors, which are a narrow band switch, control the AFR with feed back to the ECM. The O2 sensors are set to only allow an AFR of 14.7:1 to 14.2:1 during idle and cruise or up tp 3/4 throttle. Above three quarter throttle or full throttle the AFR changes to 13.0:1 and actually richens th AFR and swithces to open loop, so even if you change the exhaust or the intake the O2 sensors do not allow the mixture to go outside te narrow band or closed loop of the system which means taking the block off plate will not effect the AFR. As for the reversion or back pressure would be so slight, if any that it will not effect the performance. To change this cams would have to be added or cubes
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Old 09-10-2010, 07:24 PM
FBRR FBRR is offline
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MFB,
You do not understand HOW open loop fuel injection works! From the post you made, it is clear! As OPEN LOOP fueling is affected by closed loop adaptive fuel control,( to a point!) as well as VE's ( volumeteric effiecency).
Just because the software "commands" an A/F ratio in open loop does not mean that is what will be delivered!! If the VE's change as they do when you remove the baffle, the command A/F ratio will not be absolute! That ONLY happens when the VE's are exact!

The VE's will change when you remove the baffle, and yes it is enough to affect different areas of the open loop fuel tables.
( I am a retired calibration engineer that did use very similar software to Harley/Delphi software!) So that answer is not a guess as to how it works.

Additionally MFB, if you would like to KNOW how closed loop fuel control really works, I can explain that too! Those O2 sensors are only one input to "fuel control". As FUEL CONTROL during closed loop is a software function that both adapts and drives the O2 sensor siganl. It is a complex system that is very DEPENDANT on proper VE's. VE's in speed density system, that used by HARLEY software, are THE AIR compontent, just like the output of a MAF sensor is to a MAF system closed loop. When VE's are not correct and ANY CHANGE in the intake or exhaust "backpressure" ( that which Grendel4 thinks doesn't exsist!) will affect VE calibration!
Once again, thiry years of changing hardware and calibrartions allows me to say that "with knowledge" not guessing as to what will or will not affect the VE's. And it always amazes me so many think anything done after the engine, such as exhaust will have no change in flow!! Any change in flow characteristic through an engine will AFFECT VE calibration.

Last edited by FBRR; 09-10-2010 at 07:41 PM.
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  #16  
Old 09-10-2010, 07:29 PM
FBRR FBRR is offline
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Quote:
Originally Posted by Grendel4 View Post
You lost me at 'backpressure'. There is no such thing.

I'm done here.

Have a nice day.
Grendel4,
And that "crack" about there is no backpressure, is pretty funny!
I've had plenty of exhaust systems "instrumented" such that backpressure can be measured across all speed and loads as backpressure in an exhaust system does change with both speed and load!
( Our OEM exhaust engineers are going to be disappointed that all that data for backpressure "does not exist!)

Once again physics takes a back seat to OPINION! Good luck with that!
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  #17  
Old 11-10-2010, 09:36 PM
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I am wondeing if removeing the baffles will cause an extream lose of torque,or realy make my bike run very bad or not hurt to much,and would it help it sound like a bike should and not so stock
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  #18  
Old 11-10-2010, 09:54 PM
Artlee Artlee is offline
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Get the slip-ons, keep the stock mufflers unmolested. The EPA is cracking down everywhere more and more. Put the stockers on for inspections ( which is or MAY come ) and put the slip ons on afterwards.
Believe me, I am having a helluva time getting stock mufflers for my bike. Nice stockers for an FXR are rare and, now, expensive. JMO
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  #19  
Old 11-10-2010, 10:31 PM
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performance wise knocking the baffles out of your stock pipes is no differant then performance mufflers, low restriction is low restriction no mater how you sugar coat it...the only differance is sound tune..on my 01 i took the baffle plugs out and it sounded like crap.. king of like a rusted out exhaust on an old car..your bike has a cat converter so it already has the back preasure it needs..wont really make much differance eather way..you wont get good sound with out a full exhaust and a tuner
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  #20  
Old 11-11-2010, 06:03 AM
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I drilled out the rivets, removed the baffles, and threw away the fiberglass packing.

I went to Lowes and got a metal cutting hole saw with an OD the same as the ID of the exhaust outlet. I also purchased a drill bit extension. I put the hole saw on the drill extension and put this assembly in my drill motor and ran it into the outlet on the muffler and cut the entire plug out, because that is all it is. Just a sheet metal plug. Nothing to it. Repeated the process on the other baffle and reassembled both mufflers with pop rivets. Slight improvement in the tone, nothing noticible as far as how it ran good or bad. I wasn't satisfied and threw away good money on Rush Mufflers w/2 inch baffles that everyone here just raved about. They were only marginally better than my Frankenstein mufflers. Ultimately I got a Fat Cat 2 into 1 with the quiet baffle and I love it. Great sound, great perfomance.
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