Bigger Headers on 2.5

[Tal]

As we know the biggest restrictions on these and the previous Rockets are the headers...the way they turn at right angles as they exit the head ports.
Problem is the extra header pipe diameter is putting them closer to your legs...it's been a problem with the 2,3's and it is a problem with the 2.5's as well.
I too look forward to seeing some gorgeous 2 inch headers...as in like Paul Bryant type headers...I wouldnt feel happy with headers that work well but look bloody awful.
Some magican will come up with something i'm sure.

 

[Mongler07]

Restriction vs added power. Big difference. It's all about cost over perc

Can't make more power without being able to get it out, and after changing exhaust a trip to a good dyno man is necessary, he will adjust fuel and timing required.

That's not how exhaust works. Your engine is a 2500 cc air pump. When the intake throttle is open 100% it will make no difference what the exhaust is, it will still pump the same volume. The velocity and sound pressure waves however are tuned to the right frequency to maximize power. Once you add more fuel you change that and thus a tune and exhaust are needed due to the brute force of just being able to add more fuel and suck more air in. Air filters and exhaust will never change the volume that the Air pump will move. It's a very complicated system

 

[Gerald]

Restriction vs added power. Big difference. It's all about cost over perc

That's not how exhaust works. Your engine is a 2500 cc air pump. When the intake throttle is open 100% it will make no difference what the exhaust is, it will still pump the same volume. The velocity and sound pressure waves however are tuned to the right frequency to maximize power. Once you add more fuel you change that and thus a tune and exhaust are needed due to the brute force of just being able to add more fuel and suck more air in. Air filters and exhaust will never change the volume that the Air pump will move. It's a very complicated system

If you have restrictions in the exhaust, there is no way to get the spent gases out and full intake charge in. All air filters don't flow the same cfm's and all exhausts don't flow the same.

 

[Mongler07]

If you have restrictions in the exhaust, there is no way to get the spent gases out and full intake charge in. All air filters don't flow the same cfm's and all exhausts don't flow the same.

You would think that.
It's been proven many times. Motor trend did a test where they crimped the exhaust headers on a small block v8 from small dents all the way down to nearly pinching off the pipes at the manifolds bends. Lost hardly any power at all. Egts shot though the roof.
There are 3 things in fluid dynamics we only care about. Temperature, velocity and pressure and the shape of the vessel. Increase one and you increase the others . The key here about power gains is not at WOT but ultimately area under the curve. Many times you only see on the Dyno a little bit of increase of power at peak and this is where torque and HP cross . This is the maximum "air pumping" that yields the most explosion force seel from the crank. You are always pumping the same volume of air at all rpms the difference is how much more pressure you add to the system in burning fuel. Thus the velocity increases.
I know it's simantics and it's easier to say that the exhaust is a restriction but it's not fair to look at the exhaust system that way.
Think of it this way. The volume basically never changed but the times it is moved over time due to rpm and the density of the air that is moved changes.

 

[Mongler07]

Changing the exhaust does not technically add power. If you change the exhaust on a carburetor engine it runs worse until you tune the carb. Same with the ecu it must be tuned. The ecu however does it automatically to accommodate the AFR this adding fuel to the system. If you left the fuel and the air the the same but "upgrades the exhaust you will run lean. When you add a tune it ads fuel to max out the capacity of the exhaust improves pressure and sound shockwave dynamic and a slight improvement over restrictions that make heat. Nearly nothing to do with having a bigger pipe that moves more air.

 

[dougl]

Physics aside. The rear wheel max hp and tq of a stock 2005 Rocket III with the cat installed and stock mufflers was about 127 and 145, respectively.

For my 2005 RIII with cat removed and Triumph off road mufflers, the numbers were 139 and 150. This was with a custom dyno tune for this configuration by Wayne MacDonald (Tuneboy).

For my 2007 RIII with full Jardine Rumbler exhaust and individual K&an filters on the throttle bodies, the numbers with a stock tune were 146 and 153. After a dyno tune, the numbers were 152 and 162. Dyno charts attached.

 

[Gerald]

Changing the exhaust does not technically add power. If you change the exhaust on a carburetor engine it runs worse until you tune the carb. Same with the ecu it must be tuned. The ecu however does it automatically to accommodate the AFR this adding fuel to the system. If you left the fuel and the air the the same but "upgrades the exhaust you will run lean. When you add a tune it ads fuel to max out the capacity of the exhaust improves pressure and sound shockwave dynamic and a slight improvement over restrictions that make heat. Nearly nothing to do with having a bigger pipe that moves more air.

I remember an episode or two on Engine Masters where they were comparing factory exhaust against several header mfgs. on dyno tests, and factory results were well below all the headers. On our bikes I agree that with a header the heat goes up against the right leg, but it's a small price to pay for increased performance. I'm extremely happy with my LMS header,.