I've spent several hours with search and still have not found definitive information regarding what to do with automatic convertibles and a catalytic converter replacement. I haven't fiddled with exhaust before and need some help.

My car has 95K miles and is ready for a new catalytic converter. I understand there are fitment problems with this particular tranny/body type combo and the regular aftermarket parts.

I live in California and am due to smog this year, so I must have street legal and emissions passable equipment. I drive top down always - it rarely drops below 50 degrees here, so the system must be quiet. Right now my stock exhaust is nearly silent, and I like it that way. I'm not looking for an "aggressive tone".

I have an automatic convertible - so no matter what my performance will still suck. This is just a fact of the auto. That said, if I can squeak a few hp by excluding the pre-cats and adding a high-flow, then sign me up. Maybe someday I'll get a manual tranny and it will be of use.

Question 1: Can a high flow direct drop in be fitted to the automatic convertible? This would leave the pre-cats in place etc. I have found Random Tech and Bonez for this part. Are there other catalytic converters I should consider (or locate)?

Question 2: Is there a Bonez superflow system (replaces pre-cats with presilencers) that fits my car? The websites are inconclusive. If this system fits, what kind of sound level increase would result.

Question 3: Assuming someday I decide to get a cat-back (maybe when the stock mufflers die), what can I do now to make that upgrade easier?

Question 4: Can I replace the pre-cats with a pipe? Does this cause me emission troubles? Can I buy a pipe (ie, does the RB pipe fit my car?) Does this increase sound a lot when combined with only 1 high flow cat and the stock cat-back?

Any convertible owners that have replaced the entire system and achieved stock type sound levels, can you please tell me what you did?

Thanks in advance.

 

i have the bonez single cat system for my vert, it was put on by a rotary shop here in houston to pass emmisions and houston emmisions are about as tough as california, but it seems to fit well. the car is a bit louder at wide open throttle but at idle its about as silent as it gets with the stock cat-back. its been on for a few years and is good quality so i recomend, it definitly gave the car more power, nothing special but it helped.

 

Thanks for the reply. It is good to know that the sound in the cabin doesn't go up much with the high-flow cat.

Was the bonez a "drop-in" replacement? Did you get the "Super-flow" system?

 

I just bought the bonez main cat replacement (superflow i believe) You get the gaskets and the cat with it... since the rest of my exaust system looks ok.

Im trying to see if its legal for me to remove the pre-cat or not, I doubt it is.. but wondering more is there a replacement pre-cat to put there? Im worried it might be bad... after 15 years of rotary heat who knows right?

The guy at the place where I ordered the bonez cat from said it was a bolt in setup, will bolt right to where the old one is, and I had my car on a rack yesterday it looks pretty easy, as long as the bolts come out They offered a gasket set for an extra 10 or 20.. so I picked it up to.. might as well get it done right..

I researched it first and it WILL pass our crappy CA emission laws. While the people in the rest of the states make up for our emission reduction.

 

I researched this a few years ago for my auto '90 GTU. Here are some findings:

1. The Bonez Superflo system with a downpipe and presilencer attached to the cat won't fit an S5 auto. The S5 tranny is wider than the S4 auto tranny.

2. The Racing Beat downpipe is designed to be used without a cat. When I called Racing Beat they told me it wouldn't fit.

3. The Bonez Powerflo cat only replacement is a direct bolt-in. I've had mine on for 2.5 years, and it seems very durable.

4. I'm sure it is illegal to remove the pre-cats, but if you don't you run the risk that they will fail/clog due to their age.

My solution was to have a muffler shop custom make a stainless downpipe to go with the Bonez Powerflo cat. There was a definite noise increase in my car, but it has mellowed somewhat with age. There is a bit of a drone at 3100 RPM.

My first exhaust mod was a Borla cat back that increased noise levels only slightly. Later I had my engine rebuilt with a mild streetport which also increased sound levels a little.

This single cat Bonez setup passed Pennsylvania emissions, and supposedly will pass CA. The guys at Rotary Performance will be happy to talk to you about the various options. I found them very helpful.

http://www.rx7.com/

Good luck!

 

Does that Bonez cat have the stuff to stand the rotary heat? I got my vert with a terrible custom exhaust. I have a vert and I think my exhaust is too quiet. Mine didn't pass emissions so I'm trying to get the parts to pass, like a stock exhaust setup. I would definatly prefer a cheaper solution.

-Max

 

Yes, the Bonez can withstand rotary heat quite well. According to Rotary Performance, it was designed for use with rotaries:

http://www.rx7.com/cgi-local/2catalog.cgi?cat=4&part=1

 

Thanks David
-Max

 

Just got my email back from rx7.com regarding the bonez superflow pre-silencer and cat. It doesn't fit the s5's, which matches with Daviddeep's observations above (Sent them a query before you weighed in DD)

A stand-alone cat will fit - looks like a custom dp (or RB dp) is in order if a standalone cat is the only solution. However, I'd rather have a presilencer. Esp. since Dd indicates sound hum at 75-80 mph (3100 rpm in 4th)

Anyone seen any presilencer's that will fit the S5 auto convertible? I can get a shop to fab up the connecting bits I guess.

 

Still looking for recommendations on a pre-silencer.
Thanks.