I'm looking to upgrade my main cat to something more flowing. I have about 120k on my stock cat and I'm sure it's in bad shape with 2 apex seals blown into it from my last engine. I don't want to go much louder than it sets now with an Apexi downpipe and RB cat back system. I was looking at the Bönez Performance Converter. RX7.COM makes it sound good and it's a direct bolt, but Damn $420 is rough. Does anybody have an opinion or suggestion on this. I want more performance but the noise is a big issue. Keep in mind this is a daily driver and I do a lot of driving.



Thanks



J

You could go with High flow cat and put resonator. It will definitely lessen the noise.

They are pricey, but materials and construction are first rate, 3" inlet and outlet. It flows very well. I've had one for about 4 years now with no complaints. Rotary exhaust is alot hotter than normal. You could get a cheaper one, but it probably won't last. About a year ago I removed it while working on something unrelated and looked inside. After three years it was still in great shape, inside and out. As for noise, I don't think you'll really see any difference from stock. Plus, when I wrapped the inlet and outlet with header wrap, it seemed to quiet it down a little bit more.

I thought about the resonator but I've been told it would kill performance. If it wasn't for the noise level, I would drop the cat and put a straight mid pipe in so I could spool a little faster.



Thanks



J

I installed one on my 87T2 and liked it. I seemed to allow the turbo to spool a little faster. Did you notice much performance gain between stock and the upgrade?



Thanks



J

It was installed shortly before I bought the car, so I really don't have any baseline. I'm confident it flows well for two reasons. First, because I can get some spike on a cool morning even though the car just has a DP and is otherwise stock. And secondly, because I've ridden in other cars and just felt like mine spooled better, even though they had open intakes etc. I know that's not very scientific, and butt-dyno..ish, but still, I think it's better.

You know the other thing is, IIRC it's a little smaller than the stocker too.

In additon to noise, you'd also have to deal with Boost Creep and smell. No-cat FD's make my eyes water.

A couple of things: I have actually flow tested a number of intake & exhaust components, and I can tell you that the stock cat isn't bad. Of the high flow CATs, get the largest physical sized one you can--although I have not tested the Bonez, it appears to have the best design for flow and is what I would purchase if buying one.



As for noise, add a good stainless packed resonator after the cat (in the pipe to the cat back--it can fit there)!



A properly sized resonator will have NO adverse affect on flow at all and can actually improve flow due to the lower resistance of the perf tubing used inside. There is no merit to the claim that somehow they reduce power, especially in a non-tuned (i.e., turbo) application. You could make the whole exhaust out of resonators and it would work fine! I put a magnaflow in front of my PFS cat back and there was NO measureable decrease in flow; however, the resonance in the exhause was reduced at least 10-20db, depending on RPM. It really helps with noise, and makes it liveable; I cannot overstate this fact.



I also agree with another poster who commented on the value of header wrap. There are benifits to doing this--including a reduction in noise. I recommend wrapping as much of the exhaust as you can.



Attached is a pic of a resonater added to my PFS cat back.



So how much does the whole assy flow? ~970cfm @ 20.3" By comparison, the stocker is about 274cfm. So what does this mean? That you would be hard pressed to produce 1/2# back pressure into the high flow mufflers with any 13B setup under maximum effort. By contrast, you could theoretically produce about 4-1/2# of back pressure into the stocker under equivalent flow conditions, if you could achieve that. Keep in mind that it will always take some pressure to move any mass of gas through a pipe--can't get away from the laws of physics, sorry.



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Interesting data. Maybe I missed it, but are those numbers for the PFS and a midpipe (plus resonator)? Do you have any other flow numbers for different cat-backs?

The numbers are for the PFS with -OR- without the resonator. It resonator made no significant difference--but the flow numbers actually improved a bit with the resonator even though the resonator's ID is less than the 3" tubing feeding it.



The PFS is basically a 3" straight through design that is not unlike many of the other brands. In terms of flow, it's about the same as a straight piece of pipe. I would expect most of the other straight-through cat back mufflers to perform similarly, with no statistically significant difference between them (and I've been testing stuff for over 25 years now). The biggest differences in muffler performance in this class is likely to be sound level damping and tendency to resonate.