View Full Version : Closed vs Open Cap

10-10-2008, 09:53 AM
I am new to the forum and am trying to absorb as much information as I can about tuning my 2:1 open cap pipes. I've seen several of the 2:1 systems with closed caps. My question...what's the difference other than the obvious and are there performance advantages to one or the other? If so, can a closed cap be used on an open system.


Downtown Sammy

10-10-2008, 10:38 AM
The open end cap is equivelent to 8-9 discs.

If you have a SuperTrapp 2:1 now with an open end cap, you can install the closed cap but you will also have to add some discs to keep the flow the same.

Better to start with 'what do you have now, and what are you trying to achieve?'

10-11-2008, 04:58 PM
I have a 2004 injected fatboy, Andrews 37G Cams, and a 1550 kit, SE cleaner, PCIII. Bike seemed to be running a bit lean with 20 disks. I just removed 2. I just want to squeeze every bit of performance out of what I have. Bike really pulls in all gears...plenty of torque, but the plugs were really running white. (with 20 disks) I was wondering if there was an advantage to the closed cap from a top end performance standpoint.



10-13-2008, 07:07 AM
In most street applications the only advantage/benefit to an open or closed end cap is going to be sound level.

10-14-2008, 05:41 PM
bschultz - Guru

May sound like the obvious, but I am assuming the closed end cap reduces the noise level of the pipes? When the end is closed, is the exhaust released strictly through the tuning disks?

Downtown Sammy

10-15-2008, 07:04 AM
That's correct.