Custom 2-1 muffler options?
Grand HDF Member
Joined: Sep 2017
Posts: 4,359
Likes: 1,219
From: Dubuque, IA
I can't say a muffler that works well in a 212 system will work the same in a 2in1. The sound waves when they reach the end of the pipe do a 180. Ability to diffuse, length of pipe, cam timing etc. are all key to sound waves not making it back to the intake port and combustion chamber. This is reversion. There's a lot more to making an exhaust system that performs well.
Despite what m8 owners think, back pressure is NEVER a good thing either. Not sure where this myth even started.
You can hear these exhaust waves actually smacking a closed exhaust valve. If it's open and these sound waves make it back into the combustion chamber it can push the incoming charge backwards too.
https://help.summitracing.com/app/an...aust-reversion
Despite what m8 owners think, back pressure is NEVER a good thing either. Not sure where this myth even started.
You can hear these exhaust waves actually smacking a closed exhaust valve. If it's open and these sound waves make it back into the combustion chamber it can push the incoming charge backwards too.
https://help.summitracing.com/app/an...aust-reversion
Last edited by 60Gunner; Oct 2, 2023 at 07:45 PM.
Stellar HDF Member
Joined: Mar 2008
Posts: 2,328
Likes: 2,205
Universal baffles are a dime a dozen. Ones that perform well are not. The ones that have been around for decades are for a reason. They work and they work well.
Very few manufacturers spend the time and R&D money on providing a well performing exhaust. Too many people buy based on looks and sound only. So why should they?
I would say at least 80% of exhaust systems out there are trash when it comes to performance. Something that becomes apparent when used with performance cams. Reversion is a very real and power killing thing when exhaust and cams don't play well together.
Way more important than whether it's a 2in1 or a 212.
True duals are another story altogether. I can only think of two that work well as far as twin cams anyway. When you lose the scavenging effect of a 2in1 and 212, stepped pipes are necessary I think. Just my opinion from what I've seen over the years.
I think 44" is the optimal length as I recall too.
Khrome Werks. A division of Lincoln Industries Ž 600 West E Street. Lincoln, NE 68522. Technical Support. (402) 473-3717. (Toll Free) 1-833-454-1596
Very few manufacturers spend the time and R&D money on providing a well performing exhaust. Too many people buy based on looks and sound only. So why should they?
I would say at least 80% of exhaust systems out there are trash when it comes to performance. Something that becomes apparent when used with performance cams. Reversion is a very real and power killing thing when exhaust and cams don't play well together.
Way more important than whether it's a 2in1 or a 212.
True duals are another story altogether. I can only think of two that work well as far as twin cams anyway. When you lose the scavenging effect of a 2in1 and 212, stepped pipes are necessary I think. Just my opinion from what I've seen over the years.
I think 44" is the optimal length as I recall too.
Khrome Werks. A division of Lincoln Industries Ž 600 West E Street. Lincoln, NE 68522. Technical Support. (402) 473-3717. (Toll Free) 1-833-454-1596
Grand HDF Member
Joined: Sep 2017
Posts: 4,359
Likes: 1,219
From: Dubuque, IA
You're right. They do, in effect, change the length of pipe too. So when using them it's not just a case of using the one that sounds best either.
Khromewerks has a patented Anti Reversion baffle (dogballs) that's been around for decades. It's the same baffle they use in their 3" HP+ muffler. They've been used in straight pipes since the IH days.
Thrashin' Exhaust (Feuling) uses them now. They eliminate or greatly reduce reversion restoring low end torque while not impeding flow and upper rpm power.
https://www.thrashinsupply.com/produ...system-softail
Khromewerks has a patented Anti Reversion baffle (dogballs) that's been around for decades. It's the same baffle they use in their 3" HP+ muffler. They've been used in straight pipes since the IH days.
Thrashin' Exhaust (Feuling) uses them now. They eliminate or greatly reduce reversion restoring low end torque while not impeding flow and upper rpm power.
https://www.thrashinsupply.com/produ...system-softail
Grand HDF Member
Joined: Sep 2017
Posts: 4,359
Likes: 1,219
From: Dubuque, IA
Who says true duals suck at low rpm torque? Not when they're done right. Too bad these are so butt ugly. How they designed their 2in1 might give you some ideas tho.
Ptetty cool video tho. They sound kick *** and perform.
Ptetty cool video tho. They sound kick *** and perform.
Last edited by 60Gunner; Oct 3, 2023 at 10:07 AM.
Stellar HDF Member
Joined: Mar 2008
Posts: 2,328
Likes: 2,205
No it doesn't. Some types of racing require mufflers, that's why they're used. The IDEAL muffler is no muffler. That doesn't mean removing your muffler and leaving everything else the same will necessarily make you more power, either. But the optimal exhaust system for anything is one without a muffler. There are no zero-restriction mufflers, just low restriction and higher restriction designs.
Grand HDF Member
Joined: Sep 2017
Posts: 4,359
Likes: 1,219
From: Dubuque, IA
No it doesn't. Some types of racing require mufflers, that's why they're used. The IDEAL muffler is no muffler. That doesn't mean removing your muffler and leaving everything else the same will necessarily make you more power, either. But the optimal exhaust system for anything is one without a muffler. There are no zero-restriction mufflers, just low restriction and higher restriction designs.
No restriction, i.e. NO back pressure, is the best. Always has been. Always will be.
My 05 sporty build had drag pipes at first. But they used the hidden crossover pipe and had the same AR baffles (dogballs) in the end of the pipes. I've never seen drag pipes like them that used the hidden crossover. They worked amazingly well but I changed them and put the khromewerks mufflers on with the same AR baffles. This opened up the end of the pipes and had less back pressure than the straight pipes with the same baffles.
This puny little 1250cc build with hammer cams that had 52° overlap did 90/90 hp/torque and over 80ft.!bs. torque at 2200rpm.
The trick is to increase low end torque WITHOUT causing restriction/back pressure that kills upper rpm power but by increasing velocity. This is where using wide open stepped pipes come in. It's what Bassani did with the Pro Streets. The 2 1/2 muffler at the end is as open as open can be. The front pipe is also 44" long. The rear is shorter but with the bend is almost equivalent.
3 steps with the muffler body.
Last edited by 60Gunner; Oct 3, 2023 at 11:13 AM.
Seasoned HDF Member
Joined: Oct 2019
Posts: 10,846
Likes: 7,482
From: OH
You both make valid points, but I can tell you that a SOHC Honda 750 with open exhaust ports ( zero exhaust system / zero "back pressure") will not rev past 6000 rpm
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