DIY Exhaust Mod – Gain of 10+ HP!!!

[particlewave]

This one is a bit clearer

[chipmunk]

I did look when my box was off but didn't pay that much attention. I am pretty sure though that the inlet pipe (from the left and rights sides) goes right through i.e. no blockages - maybe someone with a box off can confirm this.

If so, then by drilling a hole on the bend you are allowing gas that diffuses out in the middle chamber to exit directly, rather than first being routed to the 5th chamber and then out. Wouldn't make a huge difference to anything but enough to change the exhaust note.