:icon_lolsign :
why does 2 into 1 exhaust giver better performance?
Ultimate HDF Member
Joined: May 2008
Posts: 6,642
Likes: 48
From: Ogden, UT
Hmmm...personally never heard that before, but I do get your point....
Road Master
Joined: Jul 2008
Posts: 1,063
Likes: 5
From: Flatlander
Thanks
Road Warrior
Joined: Nov 2010
Posts: 1,251
Likes: 30
From: Ashburn, VA
You may actually see a higher peak HP with the big shots, but no one drives at 5500 rpms were it happens. I know everyone will add there 2 cents on rider variables and 600 hp Mustangs, but the Mustang is not running 8 individual pipes and I've seen plenty of guys run consistent times to the tenth. I used to so a lot of bracket racing. So I know both. The torque is where a 2-1 shines. Everywhere from a stage 1 to a 120R. Ask any engine builder and they will let you know how much difference pipes make. I would guarantee same stage 1 bike with same rider a thunderheader, supertrapp or pro pipe will open up 3+ bike lengths on big shots, short shots or drag pipes and do it every time. Go ask this on the engine tech section and see the answers you get.
As for scooting around town, I am not disagreeing with you on the mid-range hp and torque being usable but the difference is nothing to lose sleep over, especially on a stage 1 bike.
I don't need to post this for the engine guys. And I purposely left out built motors so let's not twist what I said. There is only 1 known way to settle this.... we need to run'em at the track.
Road Warrior
Joined: Apr 2010
Posts: 1,739
Likes: 10
From: Suffolk, England
Not seen too much behind the claims made here. Here's a few thunks on the subject...
For big engines you need big fat exhausts for best higher RPM performance. Optimally you want a can 10 times bigger than the cylinder size. If you have a 2-2 skinny exhaust system then each cylinder has its own small skinny exhaust. However, a 2-1 has a single fat can shared by the cylinders (one using it at a time) in the space of the two mufflers of a 2-2 system. The touring models achieve good results with large exhausts cross-linked to give an even bigger exhaust as seen by each cylinder.
Some 2-1 systems, like Supertrapp, offer the feature of tuning the exhaust with adjustable baffles. This gets over the one-size-fits-all issue of 2-2 systems.
Open, straight 2-2 systems can out-perform 2-1 systems at higher RPMs, at the risk of loss of lower speed performance.
Most exhaust systems are designed firstly for looks/noise and only secondly for performance. Those with this reversed tend to look relatively ugly and/or like racing cans. This is true whether its a 2-2, 2-1-2 or 2-1 system, so it's definitely not possible to say something as simple as, "Its a 2-1 system so performs better".
For big engines you need big fat exhausts for best higher RPM performance. Optimally you want a can 10 times bigger than the cylinder size. If you have a 2-2 skinny exhaust system then each cylinder has its own small skinny exhaust. However, a 2-1 has a single fat can shared by the cylinders (one using it at a time) in the space of the two mufflers of a 2-2 system. The touring models achieve good results with large exhausts cross-linked to give an even bigger exhaust as seen by each cylinder.
Some 2-1 systems, like Supertrapp, offer the feature of tuning the exhaust with adjustable baffles. This gets over the one-size-fits-all issue of 2-2 systems.
Open, straight 2-2 systems can out-perform 2-1 systems at higher RPMs, at the risk of loss of lower speed performance.
Most exhaust systems are designed firstly for looks/noise and only secondly for performance. Those with this reversed tend to look relatively ugly and/or like racing cans. This is true whether its a 2-2, 2-1-2 or 2-1 system, so it's definitely not possible to say something as simple as, "Its a 2-1 system so performs better".
Road Master
Joined: Jul 2011
Posts: 1,016
Likes: 3
From: West New york, NJ
Again, in an all-out drag race, you will only see the upper rpm range. That was my point. The mid-range hp and torque don't mean anything in a drag race. So unless you are putting a rev-limit of 4500 rpms on both bikes, I don't see how the 2-1 is gonna run 3+ bike lengths on a 2-2. Pretty sure most Stage 1 bikes, at least my PowerVision, is set to 6200 rpms.
As for scooting around town, I am not disagreeing with you on the mid-range hp and torque being usable but the difference is nothing to lose sleep over, especially on a stage 1 bike.
I don't need to post this for the engine guys. And I purposely left out built motors so let's not twist what I said. There is only 1 known way to settle this.... we need to run'em at the track.
As for scooting around town, I am not disagreeing with you on the mid-range hp and torque being usable but the difference is nothing to lose sleep over, especially on a stage 1 bike.
I don't need to post this for the engine guys. And I purposely left out built motors so let's not twist what I said. There is only 1 known way to settle this.... we need to run'em at the track.
A Harley isn't going to be in the upper rpms in a drag race either. I'm pretty sure when you shift, you will be right at that torque peak. When you are down 7-10 ft.lbs., you will be struggling to get back up to your HP peak. Even launching at 5500 rpms is going to drop down to your mid range rpms when the tire grabs. Harleys are not screamers, they are torque monsters. To put it into car terms, think of a big block like the Buick 455 GSX. 510 lbs. From the factory, but barely made it over 5,000 rpms. It was one of the quickest muscle cars of its day due to this. No bogging when you drop the clutch just pure torque to accelerate you. I had an old Firebird that was the same way. A smaller displacement over square engine is a different story, but that is not what a Harley is. I'll run it down the track, but I'd be at a disadvantage against yours. Another 88" though. It would be a lot of fun. I wouldn't mind seeing how close to a 96" I could run though. I miss the days of drag racing with the car. I had a '69 Firebird with a 400. Ported 350 heads and cast iron intake with a worked quadrajet. It was a sleeper. Looked like a stock 350, but it ran a best of 12.12 at 116 mph. I miss that car.
Last edited by JohnC FXDX; Feb 29, 2012 at 10:06 AM.
Road Warrior
Joined: Nov 2010
Posts: 1,251
Likes: 30
From: Ashburn, VA
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