Hello everyone

I am looking to replace my pesky precats and cat with a Racing Beat downpipe and a section of custom made pipe (also 2.5" Stainless). plans are to connect it to the BORLA catback I already have installed. The main reason for this is that I have gone through 2 cats and 2 sets of DP/precats. i am hoping that this wont be excruciatingly difficult. What my main question is. What additional steps will I have to take other than cutting unbolting the STOCK manifold to catback pipework and replacing it with the new RB/Custom straight pipe to the catback?

My main concern is the little tube which extends from the engine to the stock Cat. Will this tube be an issue? also, I have heard much talk about 5/6 ports. And the last thing I read was that I may have to remove the air pump? I got the parts I needed for a steal of a price compared to having a shop delete the precat and running a standard 2" DP to cat to catback.

My RX7 is a 1986 GXL with the original engine at 99,5xx miles. Any help is greatly appreciated.

 

Well, the tube running to the stock cat is the backpressure pickup tube for the 5/6 ports. On S4's that's how they are activated, the tube runs from the cat to the ACV with can send air one of three places.

You won't necessarily need to remove the air pump, my buddy has a custom exhaust and still keeps his air pump so he still has belt coverage on the water pump.

 

So if I remove my cat and do a straight pipe what would you propose doing with that tube?

 

You will need to incorporate a tube into your exhaust for it to bolt to so you can get the needed pressure to activate your 5/6th ports. On my RB presilencer the tube is actually in the exhaust stream to get the pressure.

 

So basically I would have to cut a hole and have little tube coming out?

 

Basically, yes but there are caveats.

The end shape/angle of the tube must be right to get pressure instead of vacuum in that tube.

 

What would happen if I just did not put a hole and plugged the other end?

 

If you plugged it you wouldn't have 5/6 ports, and could just wire those open. You'll be sacrificing a bit of your low end that way.

 

so I know its been awhile since I had a n/a but if I recall when I did my full exhaust I just took out that small pipe and also removed my air pump, never did anything else, and my car ran fine. just saying.....

 

The car will run fine without 5/6 ports working, your just sacrificing quite a bit on the top end if they stay closed, since it won't be able to flow as much, and if they are wired open you lose some of the low end, if I remember right that has something to do with air velocity not being high enough or something.

 

So not touching them looses high end wiring open looses low end. These losses major or something I probably won't notice street driving the car?

 

im going to go on record and say I punched my stock cat out and welded extra pipe on the engine side to connect to an RB header. This way I kept my 5/6 working fine, and my air pump in place.

Granted, I live in a place where emissions do not matter. You could get creative with a "high flow" cat and weld on the stock cat pipe in the same position on the new high flow. just a simple cut, drill, weld job there.

 

Spend a little more money. If you need a cat look at rx7.com. If you don't buy the piece that RB sellers to go after the header. Last thing that you can do is add an electric air pump ran by a switch, I use one when my cut-out is open. Junkyard look for cars with air pumps in the seat.

 

I have no personal experience on keeping them open or closed but from what I hear, if you're strictly dd'ing the car I'd say just leave them shut. The loss of torque from the low end, I'd think, would be a pain dd'ing when you are pulling away from a stop. If you're tracking the car, and regularly sustaining high rpm, keep them open.

Best setup would be to get them properly working, but I know sometimes getting things working can be a pain.

 

On my racing beat presilencer the tube comes through the wall and then makes a 90 degree bend placing the open end of the tube directly in the exhaust stream. I would try to mimic this in your setup.

As to disabling the 5th/6th ports you want them wired open to their high rpm position. From what I have read you lose quiet a bit up top with them shut. Shift at a higher rpm to keep your revs from dropping below 3k to 3.5k rpm and the loss on the bottom can be lived with.

 

See I daily drive in the city. I drive a whopping 2000 miles a year in my 7. so it is no big deal if my high end is loosing a hair of feel. If it was dramatic i would be worry-some but for now I am going to just keep them closed if i notice a major difference i will get another 2 ft piece of pipe and cut the previously described piece from a spare cat and try to make that work.

Thank you to everyone who has pitched in and helped me make my decisions. any further help is always nice but for now it will be straight pipe keeping the pump attached and running.

 

Well, 2k isn't much lol. I hit about 14k in the past 2 years during which probably 6-8 months of that the car was down. So, as much as I dd my 7, having them wired open and having to shift at higher rpm is a no-go. I'm pretty **** about fuel consumption, and that torque is helpful. I'm normally in 5th by the time I hit 35ish, which puts me at about 1350rpm.

 

Yeah that what I figured. right now my car sits comfy at 40 in 4th around 2k rpm a little above it and that's where I want to stay. I don't race or track the car so I don't really need it to have higher end powah

 

i may be chiming in here late. but i guess what you need to do is this tube

https://docs.google.com/file/d/0B6XP...it?usp=sharing

 

Wow ,different driving styles definately determine what is livable and what is not for each person. I didn't shift till 4k or above before I wired them open. I guess That's why I never really missed them. At 35 I'm in 3rd or 4th depending on if I'm in the city and want more immediate power when I press the go pedal or not.

Sounds like disabling them to the high rpm position is not for you guys. Having them functional would be the best way to go. I have my presilencer out of the car right now where I'm getting the car back together after a rebuild so I'll try to get a picture of the tube up for future reference

 

Greatly appreciated. I am going this route because it'll be cheaper (this entire set up <RB Downpipe, 2.5" stainless cat delete, 2.5" stainless borla catback> will total to 325$!) so I cannot complain. But I plan on getting an RB Pre-silencer

 

I'm not saying mine aren't currently working, just saying that putzing around town I'd think having them closed for now would be the best bet.

At one point mine weren't working properly, only intermittently due to a vac leak, and I can tell you it is a noticeable difference between open and close at high rpms, especially when they decide to work and snap open at about 6k. That's all be fixed now and it's quite a smooth transition.

 

Here is a picture of the tube in the presilencer.

 

Any chance you can get me the diameter of that

 

Looks to be 1/2 inch outside dia. Approx 1/16" wall thickness.