On this same thread, I'm looking at buying a Bonez Superflo, but I noticed on the RP site that right under the Bonez Superflo there's a Bonez Dual Cat system for 86-91 NA. Anyone know what the difference is between the two, other than $20? Also, has anyone had any experience with the RP 50mm catback system? I'm wondering if it's significantly louder than stock.

 

the dual cat system has the same config as the OEM ones: pre-cat then main cat.

the superflo is: built-in downpipe then main cat.

 

The double-cat system is just that, it has 2 cats. There is a smaller pre-cat before the main cat. The superflo system has just 1 cat, and a silencer. Honestly I dont see what the point of the double-cat system is, unless you have insanely stringent visual inspection. You can pass emissions wonderfully with the Superflo.

 

I guess unless someone makes a convincing argument for the bonez cat over my 60k mile main cat, I'll just keep it on until the miles get high(er). If the Bonez does indeed flow slightly better, if the gain is only 1 hp, what's the real point?

 

The point is that, at some point, the stock cat will get clogged, and start reducing engine performance, or worse, restrict the exhaust enought for it to overheat and pop a coolant seal. Have you priced stock Mazda cats for our cars?? Try $1100+ for a main cat. The bonez cat is almost 1/4 of that cost, and while I dont have any proof, Id almost bet it does flow more, even if only slightly. I know some 3rd gen guys have done a few tests with high-flow cats vs a stight mid-pipe, and dyno results are within 3-4 HP ususally, compared to the ~10-15 + loss with a stock cat.

 

funny you say this. i know a guy with a suburban that wanted duals which would require two cats. the guy at the muffler shop wouldn't do it because it was illegal to change the emissions setup(i may have worded that wrong, but thats essentially what happened).

 

That's a good point. I guess I will hold onto my bonez cat instead of selling it. It's relatively simple to unbolt the main cat I'm using and do a visual inspection to see if it's getting clogged.

 

i emailed RP about the dual system and its mainly for sound reduction. it doesnt flow as freely, but muffles the tone abit more.

so this would apply to the guy with loud mufflers, headers and cant afford to go any louder for leagl reasons and needs to pass emissions.

 

I bet the OEM cat does better for emissions, since that was what mazda was mainly concerned about when they were introducing these cars to the us. where as RP wants to give ya more power and a cooler sounding exhaust.

 

OK. This thread was fun, but does anyone have any before / after DATA for the high flow cat vs. stock cat?

 

closest i know is this, and i dont think its what youre looking for.
https://www.rx7club.com/showthread.p...hreadid=321221

 

and now OEM cats are what, 800 or so dollars? and people can pass emissions fine on bönez.
i think there was an arguement before about the area between the stock and hi-flows before. i believe someone mentioned the structure of the hi-flow having more "sweep" area than some conventional cats. problem is, i dont know what type of cat our cars came with stock. does anybody know?

 

All right guys, here's the scoop- the internal cat material (hole size, length) is pretty damn close between the Bonez & OEM. The Bonez probably flows more due to the increased diameter down pipe, which, because of an optical illusion, makes the actual cat body look puny compared to the OEM. The Bonez is far lighter (don't have actual weight numbers). I ran with the pre- and second OEM cats gutted for a while before I installed the Bonez, and I couldn't tell one bit of difference on the butt dyno, and I seriously doubt I would have ever clogged up the OEM main cat, if for no other reason, there wasn't anything in front of it to clog it now. My bonez is now itself gutted (thought it too got clogged, and due to bad design you can't see the front of the damn thing from the downpipe). But, due to the fact I've gutted both types, I can verify that the cat materials are the same "stuff"...

 

You’ll need flow numbers. Before you get the cat’s flow numbers, you’ll need to know your flow numbers. An NA 13b, with 95% volumetric efficiency, at 8000 RPM, flows 352 CFM. Your car doesn’t run at 95% VE, but if your cat can meet these requirements, you’re set.

When I was ready for a new cat I contacted RP and asked for flow numbers. They didn’t have any specs, so I bought something else. Something WITH specs. I bought an RT cat with three inch tubing that flows over 500 CFM at 28 inches of water. It's been three or four years and the RT does hold up to the heat.

Does the OEM cat flow more than the Bonez? Without flow numbers, no one knows (regardless as to what the Bonez advertising says). What I can say is besides being a zillion years old, if ATF trick has been repeatedly done, or the oil control rings are toast, or the car runs rich, the OEM cat is probably clogged. If it's clogged, something else would probably be better. There is an article coming up in Mazdasport on rotary engines and cats. You might want to give it a look.

 

Thanks for some solid advice Marcus. Can you point me to that article when it surfaces? Also, how much was that RT (Random Tech?) cat and which model was it?

 

Random Technology cats and exhaust systems are in about every import car magazine i've had. they may be in domestic's, too, i dont know. just speakin from experience. i believe theyre fair priced. maybe look in a mag and get the site url address or just search online.

www.randomtechnology.com

770/554-4242
4430 Tuck rd
Loganville, GA 30052
Fax 770/554-4244

 

Thanks for the post WAYNE, some actual personal experience with both being gutted and whatnot. More data to suggest I should leave the stock main cat in for the time being until it gets clogged or more data in favor of another cat (bonez or otherwise) comes up.

 

Ya, I figured I wasted all that money on the Bonez, since the main stock cat remaining performed the same. What the heck, live & learn...

 

Blah, I'll have quarter mile times and trap speeds before / after for stock cat vs. carsound ebay el cheapo highflow cat in a few weeks. Testimonials are great, but when it comes to performance, when the green flag drops, the bull$hit stops, and the fastest car that trips the laser the earliest has numbers to back it up. That's why internet racing, bench racing, endless forum threads with opinion and not fact, and street racing SUCK.

:banmeplease:

 

You never ever ever want backpressure for torque...you are confusing maximum gas velocity for backpressure. Best flow is the most volume possible (big pipe) as fast as possible (can't be too big of a pipe).

David

 

For that to be really accurate it would have to be the same driver with the same car on the same track with the only difference being the different cat. Also, since there are a lot of factors in that short span of 15 or so secs, it would have to be a comparison of averages. I doubt us forum members will have those conditions readily available, so in the mean time, it's fine to discuss it like this

 

Don't worry, all of those conditions will be met when I get back to the track again in a few weeks. The only difference will be the weather, and it won't change by much. This is Oregon. We're talking mild weather.

Back on topic: What's the deal with that diffuser plate welded in the stock cat's inlet about 2" back? Yikes, that looks restrictive.

 

End3R is right the time slips don’t mean much. I can take the same car out 4 times, back to back, and get four different numbers. I’ve done it. It’s not a matter of technique because I've taken brand new press cars with automatic transmissions - doesn't take much technique to mash the gas when the light turns green. The trap speed is the deciding factor. If you show higher trap speeds you're making more HP.

The diffuser on the front of some cats is to get the exhaust spread over as much of the face of the catalyst material as possible. If you think that's restrictive, cut open a muffler some time.

 

Well, it's stainless steel holding the catalyst in place instead of fiberglass, and it's been holding up on my car for about a month, and theres a few people on the forum that have been using them for a long time, so I can feel somwhat safe in saying yes