I'm going to upgrade my catback on my TII and keeping it to 2.5" OD. I'm wondering if I need to replace my y-pipe as well. According to Racing Beat, there is no performance benefit gained from their y-pipe which has the same outer diameter as the stock pipe. Should I just get a pair of mufflers?

 

I am not sure if the RB mufflers bolt into the stock Y pipe, but if they do (looking at the design they should) its really up to you. If your Y pipe doesn't look like crap it would be a good idea, otherwise your not really replacing with a "cat-back" system.

 

I'm not going to use the RB mufflers. I might go with some magnaflow ones. My y-pipe still looks good so if there's no huge gain on replacing it, I'll just keep it stock. My plan is to install the RB downpipe and pre-silencer, keep the y-pipe and install new mufflers.

 

The flange on the cat end of the stock y-pipe is for 2.25" pipe, so you'll have some sealing issues if using RB's 2.5" presilencer. I've mated the two sizes together before, and it always burned up exhaust gaskets. It was a permanent exhaust leak. You may run into the same thing with the flanges for the mufflers depending on what you bolt up.

 

I am having a custom y-pipe made this summer. the y pipes are only 2 inches. Figure 2.25 or 2.5 inch pipes would be worth some HP.

 

you sure about this? was it on a TII? According to RB, their y-pipe has the same O.D. as the TII stock y-pipe.

From Racing Beat's website:
"The Racing Beat Y-pipe for the 1986-92 RX-7 (All Models) is a perfect replacement for a failing stock component. The Racing Beat Y-pipe is slightly larger in diameter than the stock non-turbo Y-pipe, and matches the diameter (2.5" OD) of the stock TURBO II Y-pipe. Therefore, if you are replacing the muffler(s) on a TURBO II application, and unless the original stock Y-pipe is failing, there is no performance benefit to be gained from the addition of this Y-pipe."

 

Well, at one point I took the OEM catback off of my TII, and installed it on my convertible. The flanges matched perfectly, and I had no sealing issues. At that point in time, both cars were almost 100% stock. This was easily 8 years ago, so maybe my memory is a little fuzzy, but that would imply the NA and TII pipes were the same size. I think the simplest way to confirm this would be to take a look on your own car. Measure your Y-pipe inlet.

The S4 parts fiche does list different PNs for TII y-pipes, but then again they also list a separate PN for the convertible y-pipe. It could just be for some subtle reason, or maybe it is a sizing difference.

N319-40-100B N/A Convertible
N326-40-100L N/A Coupe

N326-40-600E Turbo
N319-40-600B Turbo

 

Thanks for all the replies. I just called Racing Beat and I was told that their downpipe/pre-silencer combo will in fact fit on the TII's stock y-pipe. The guy also confirmed that the stock and RB's y-pipe has the same diameter so unless I really need to replace mine (which I don't at this time), then there's no benefit on buying the RB one. The RB part # I'm referring to is #16207.