Exhaust Question
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Cruiser
Joined: Jul 2011
Posts: 177
Likes: 4
From: Keller, TX
Exhaust Question
So I have a 1995 Heritage Softail with an Andrews EV-3, Mikuni HSR-42, and Vance and Hines Big Shot Longs. I have been contemplating taking the baffles out. I am just curious how much louder this will make the bike and if it will make the bike rack off when I shift or get off the throttle, The pipes do have a build in crossover in them if that changes anything either.
Tourer
Joined: Dec 2013
Posts: 472
Likes: 59
From: farmington ny
Running straight pipes is not good,you need the back pressure that the baffles create.I do not understand how this happens but it does,its called reversion.Its when the exhaust actually goes backwards up the pipe back to the engine.This process will eventually toast the motor.This process defies all logic to me but it does happen so they say.This maybe why texashillcountry's bike ran like ****.
Seasoned HDF Member
Joined: Aug 2007
Posts: 8,198
Likes: 3,087
From: NW AR
When? Dr.L's Sporty has had open drag pipes for the last 45K miles.
If you run open pipes, you have to tune for it. A carb may or may not be adjustable enough for that specific tune on that specific motor. Once we went EFI on the Sporty, any rough spots were just tuned out and it runs great. As Dr.L says, "It's like an automatic transmission. Just put it in a gear and go." I never could get a carb just right on that motor. My pipes are straight through as well and it runs great.
If you run open pipes, you have to tune for it. A carb may or may not be adjustable enough for that specific tune on that specific motor. Once we went EFI on the Sporty, any rough spots were just tuned out and it runs great. As Dr.L says, "It's like an automatic transmission. Just put it in a gear and go." I never could get a carb just right on that motor. My pipes are straight through as well and it runs great.
Seasoned HDF Member
Joined: Jan 2015
Posts: 15,996
Likes: 7,111
From: Sandy Eggo's North County
"Open" exhaust systems allow an easier path way for cooler/wet air to enter after shutdown.
This "cool" air may warp hot exhaust valves over time.
If the ex. valve is in the "open" position, it may allow condensation to enter the cylinder,
forming rust on the cyl walls. This should be removed by the rings at the following start up.
At the expense of the walls & rings...
This "cool" air may warp hot exhaust valves over time.
If the ex. valve is in the "open" position, it may allow condensation to enter the cylinder,
forming rust on the cyl walls. This should be removed by the rings at the following start up.
At the expense of the walls & rings...
Seasoned HDF Member
Joined: Aug 2008
Posts: 5,080
Likes: 2,151
From: Ohio
When running a live AFR reader system you can see reversion in action. When a exhaust is too free flowing, during decel AFR's can climb into the 19.0-1 range which is dangerously lean building cylinder heat, if you don't have your carb over jetted to combat this it will pop out the carb when getting back into the throttle. The dangerous AFR's is caused by the cylinder being filled backwards thru the exhaust with no ability to fill with fuel.
Example: a big cube engine needs a large exhaust to allow gases to exit and i have a 3" full baffle, trade off is something this big will allow reversion so I have to run my idle AFR's on the rich side to keep fuel in the cylinder. Normal Afr's for idle are 13.8 to 14.2, new bikes are 14.5, my engine has to have 12.6 to control decel reversion and also holds heat down at idle, a big cube can eat this much fuel and a different creature but needs the flow at WOT or the banana in the tail pipe effect takes place.
There is a great S&S video somewhere of them using a over sized slinky simulating under throttle the collision of objects on the same plane moving in 2 different directions, reversion in this situation is spent exiting gas pulses colliding with pulses being pulled back to the cylinders from the open exhaust.
On the removing baffle topic, your not going to get any of the salty Evo veterans to back a baffle removal, it is well known a Evo or street Harley engines need some sort of back pressure to keep from pulling spent gases backwards or the result is sluggish bottom end mainly from a lean cylinder condition. The Shovel kackle has been around for ages, sound is great but as efficient as pissing straight into a 50 mph wind. Evo motto is it is your bike do what makes to happy.
Example: a big cube engine needs a large exhaust to allow gases to exit and i have a 3" full baffle, trade off is something this big will allow reversion so I have to run my idle AFR's on the rich side to keep fuel in the cylinder. Normal Afr's for idle are 13.8 to 14.2, new bikes are 14.5, my engine has to have 12.6 to control decel reversion and also holds heat down at idle, a big cube can eat this much fuel and a different creature but needs the flow at WOT or the banana in the tail pipe effect takes place.
There is a great S&S video somewhere of them using a over sized slinky simulating under throttle the collision of objects on the same plane moving in 2 different directions, reversion in this situation is spent exiting gas pulses colliding with pulses being pulled back to the cylinders from the open exhaust.
On the removing baffle topic, your not going to get any of the salty Evo veterans to back a baffle removal, it is well known a Evo or street Harley engines need some sort of back pressure to keep from pulling spent gases backwards or the result is sluggish bottom end mainly from a lean cylinder condition. The Shovel kackle has been around for ages, sound is great but as efficient as pissing straight into a 50 mph wind. Evo motto is it is your bike do what makes to happy.
Last edited by 1997bagger; Jul 9, 2017 at 01:22 PM.
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Tourer
Joined: Dec 2013
Posts: 472
Likes: 59
From: farmington ny
When running a live AFR reader system you can see reversion in action. When a exhaust is too free flowing, during decel AFR's can climb into the 19.0-1 range which is dangerously lean building cylinder heat, if you don't have your carb over jetted to combat this it will pop out the carb when getting back into the throttle. The dangerous AFR's is caused by the cylinder being filled backwards thru the exhaust with no ability to fill with fuel.
Example: a big cube engine needs a large exhaust to allow gases to exit and i have a 3" full baffle, trade off is something this big will allow reversion so I have to run my idle AFR's on the rich side to keep fuel in the cylinder. Normal Afr's for idle are 13.8 to 14.2, new bikes are 14.5, my engine has to have 12.6 to control decel reversion and also holds heat down at idle, a big cube can eat this much fuel and a different creature but needs the flow at WOT or the banana in the tail pipe effect takes place.
There is a great S&S video somewhere of them using a over sized slinky simulating under throttle the collision of objects on the same plane moving in 2 different directions, reversion in this situation is spent exiting gas pulses colliding with pulses being pulled back to the cylinders from the open exhaust.
On the removing baffle topic, your not going to get any of the salty Evo veterans to back a baffle removal, it is well known a Evo or street Harley engines need some sort of back pressure to keep from pulling spent gases backwards or the result is sluggish bottom end mainly from a lean cylinder condition. The Shovel kackle has been around for ages, sound is great but as efficient as pissing straight into a 50 mph wind. Evo motto is it is your bike do what makes to happy.
Example: a big cube engine needs a large exhaust to allow gases to exit and i have a 3" full baffle, trade off is something this big will allow reversion so I have to run my idle AFR's on the rich side to keep fuel in the cylinder. Normal Afr's for idle are 13.8 to 14.2, new bikes are 14.5, my engine has to have 12.6 to control decel reversion and also holds heat down at idle, a big cube can eat this much fuel and a different creature but needs the flow at WOT or the banana in the tail pipe effect takes place.
There is a great S&S video somewhere of them using a over sized slinky simulating under throttle the collision of objects on the same plane moving in 2 different directions, reversion in this situation is spent exiting gas pulses colliding with pulses being pulled back to the cylinders from the open exhaust.
On the removing baffle topic, your not going to get any of the salty Evo veterans to back a baffle removal, it is well known a Evo or street Harley engines need some sort of back pressure to keep from pulling spent gases backwards or the result is sluggish bottom end mainly from a lean cylinder condition. The Shovel kackle has been around for ages, sound is great but as efficient as pissing straight into a 50 mph wind. Evo motto is it is your bike do what makes to happy.
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Seasoned HDF Member
Joined: Mar 2010
Posts: 21,093
Likes: 7,622
From: Poolville
I've heard back in the day that open pipes without baffles and a good tune will burn the exhaust valves sooner...
Road Master
Joined: Jan 2008
Posts: 1,187
Likes: 8
From: Montgomery, AL
If you want is a little louder I cut the baffles down and put them back in. I ran my standard longshots with no baffles several years. I loved the sound! I put the baffles back in because I was bored. IMHO the short baffles reinstalled I did feel more torque restored due to increase back pressure. As for the reversion it gets worse when the pipes get shorter.The burnt valves from reversion came from the old short drags pipes running open from what I was told.