Thunder Header Exhaust

[landmanrobert]

I just bought a 2003 screaming eagle (103) Road King. I ordered thunder header slip-ons and USB PClll power commander and new breather. The dealer I ordered from says just by adding the thunder headers, I will see a 15% increase in power. After coming to this site, I am thinking this is not going to be true at all. I am not changing my headers, cause I did not know whether I should and wasn't told by the dealer, anything about changing headers. Please tell me your thoughts. I love the sound of the thunder header, but I do not want to lose power.

[Mike]

The 15% increase is not unrealistic when compared to a totally stock cvo 103 (we would be conservative and suggest 10%). Of course, this is also based on an accurate tune with the PC. Tuning is everthing on EFI bikes. The stock head pipe will not yeild as much power when compared to a true two into one system, but without adding heads and cams the difference is not as great. We do a "Y" pipe mod to remove a restriction where the rear pipe merges with the front. This has proved to be good for 4-6 hp on mild 103's. Last, the typical torque dip between 2 and 3 k RPM will be less noticable with the slip-ons vs. the 2 to 1. Only down side is decel pop may be increased due the more open left side pipe allowing cold air to reach the junction near head the where the left side pipe splits off. Be sure the tuner choosen puts the PC into "advanced mode" and tunes each cylinder independently.
Thanks, Mike