I'm currently installing a RB presilencer on my car, but have no need for the tube that is supposed to direct air back to the actuators on the block. So, I installed a blockoff plate to keep the air from coming out of the tube on the side. My Q is, with this block off plate, will I create unwanted backpressure in the exhaust that could have negative effects on my performance. I could probably thread a screw into the intake side of the pipe to keep air from entering it at all, but is this really necessary. Thanks
Paul

Pic: http://www.racingbeat.com/FRmazda2.htm

 

I don't have a RB exhaust, but I am 99.9% sure it doesn't matter either way.

 

I've installed mine on 87 n/a with the tube connected,and also on a 91 n/a vert with the airpump actuated 5th 6th ports and I blocked mine off and didn't have any problems at all that was three years ago.A friend of mine bought the car from me and he hasen't had a problem with the engine at all.I'd say by removing the main cat you've reduced the backpressure so your cool.

 

Thanks for your input guys. I thought about it and the pressure created will eventually reach a point that no more air could be forced into the tube and it would act as if it were blocked off. So, it really shouldnt matter. Thanks again,
Paul

 

when i've got same stuff you do and racingbeat included this rubber cap that goes over that air tube

did you get the same thing?

 

i got that with mine

 

I don't believe that tube actually gets pressure except maybe at low rpm's. If I understand correctly... the 5th and 6th ports are actually acuated by SUCTION from the split air pipe not backpressure as many believe. The velocity of the gasses passing by the opening at the exhaust end of the pipe actually creates suction that opens the check valve in the split air pipe and actuates the valves.

Then again... I may just be a big idiot.

 

That line goes to the Aux ports and is needed for them to open and will not open without it.

 

I thought the aux ports were controlled by the air pump on S5s?

 

They are, so I dont need it. I got a deal on an S4 presilencer, so i'm using it instead of an S5.

 

No, the backpressure will be almost zero. You're talking about creating a vortex about as wide as that tube, spinning at the same speed as the exhaust. That tiny thing ain't gonna do squat. I mean, even the tail pipe creates more losses with the larger vortices just outside of it (and it's a waste of time to make your tailpipe bigger to lower the velocity, except for looks, b/c those losses are negligible).

 

Whoops! I just dug through the FSM to find this. The Aux ports should open between 1.2 and 2.1 PSI. Meaning, I am in fact a big idiot. LOL