This past weekend I finally replaced my stock cat that had 117k miles on it, with a Bonez hi-flow from RX-7.com. The old one was rattling horribly at idle, so I'm assuming it was toast. I was amazed at how heavy it was in comparison with the new one. I'd say it probably weighed 50 pounds and the Bonez maybe 10. The Bonez appears to be very good quality, and even comes with all the hoses, pipes, and clamps you need to reattach your old air pump. Which leads me to question one: The (rather poor) instructions seem to indicate getting rid of the metal pipe with a flange that's right next to the old cat. The best I can tell, it's a one-way valve, so I sawed the flange off and reattached it. That sound like the correct thing to do?

The volume and tone changed quite considerably from the swap. I really liked the deep throaty sound that I used to have with the stock cat and PFS exhaust, but unfortunately that's been replaced with a louder, more civic-with-a-coffee-can tone. I'm a little unhappy about this but with all I've invested in the swap I'm afraid it's here to stay. The other surprising thing is that the car actually feels a hair slower now. Granted when I had the stock cat off to check it for rattles, some of the pellets "might" have fallen out, so the old may have actually been flowing better. But then the temperature increased about 20-30 degrees the day I changed it, too, so that's probably the real culprit. The other change is that my once subtle backfires now sound like a full-fledged cherry bomb. Drive through the hood and people hit the deck.....

The installation wasn't too bad. Using jackstands, it only took about 2 hours for me to do alone. The only things that prevented it from going smoother was getting the rusty bolts off and trying to figure out whether to reattach the air pump valve (and then cutting it).

Just thought I'd share my experiences for those others who are looking to do the same....

 

Is the Bonez hi-flow cat a true 3" I.D. or a smaller diameter?

 

damn, anyone else want to mention what hi-flo cat they are running and the sound involved?
I don't like the sounds of what you described

 

It is a deeper sound, but the "canny" sound will come from the catback. So depending on the catback you might have the more canny sound of the cannister catback or you could go with something like a N1 or Racing Beat.

It won't be as loud as a midpipe (thank goodness), but it will be quite a bit louder than stock.

I don't know about your lose of speed. I noticed quite a bit more power, but then again I replaced the entire exhaust all at once. I didn't do the install myself though...

 

damm 2 hours to installed a drop in cat? what went wrong dude?

 

Want loud? Try a dp, mp, and N1 cb with non-seq setup - LOUD!!!!!!!!!!!! Deafening! A hi-flo cat should yield about 8-12 rwhp over the stock cat. My car is somewhat loud but there is no substitute for the beautiful exhaust note my FD's exhaust note when WOT - not loud, just downright mean sounding and sporty. To me a dp, hi-flo cat, N1 cb is the perfect sound for a FD. Shouldn't be many backfires - when I changed to a Power FC I lost all my backfires.

 

As far as I know, it's a true 3" system, but I didn't actually do any measuring. The tubes seemed to match the 3" downpipe and catback, though.

I don't know about the sound. When the stock cat was in place, the PFS catback really had a nice low growl. Seems like a good exhaust, though, so I doubt I'll go replacing it. Give it a week and I'm sure the new sound will start seeming normal to me. And I don't mean to imply that it's AS bad as your typical ricer, it's just moving more in that direction. I'm probably just overly sensitive about that.

Basically it took 2 hours because I did it at the end of the day after changing diff mounts and the fuel filter. So I was tired. On top of that I'm new at doing my own work and I was being careful. Plus the little things like stuck bolts and the air pump hose.

Yeah, I feel sure the backfires are the result of my ECU. It's definitely running rich, so anytime I abruptly let off the gas and occasionaly when shifting I get a nice pop. I was just saying that it's considerably more of a bang with the hi-flow than the old stocker. No biggie, I kinda like it.

So anybody have any idea what the valve looking thing I modified is? Was it good that I left it on there?

 

yeah when I got my n tech hi flow cat I got those "pops" all the time and was like WTF!!! hehehe Now I love it when it pops

 

I think the valve you are talking about is a one way valve that routes to the air pump to pump extra air into the cat to make it more efficient and last longer.
-Jedon

 

Good, sounds like the valve should have stayed on there then.

Just wanted to add that I've spent a couple more days with the install and want to change the power statement I made earlier. The temps dropped back off so conditions are more similar to when I installed it. I'm now thinking I may have gained a little power, but the delivery is different and contrary to what I would have expected. With the (probably clogged) stock cat, I would get a good drive on the primary, a spike into the secondary, then a little lag, and then afterburners at around 6k due to my street port. Now the power feels extremely linear...no lag, but no spike at 6k. And I think lower RPMs have improved. I would have expected a higher flowing system to have increased top end at the expense of low end grunt. But unfortunately I don't have any dyno proof so this is all seat of the pants. Feels like the end result is still faster, though.

One thing that's definitely changed is that in 1st gear at 3/4 throttle I now totally break the tires loose at 4k rpm. That used to only happen higher up in the rpm range, so that seems to imply more grunt.

 

which is also why it seems slower in the lower rpm range.... that's the one lousy thing about improving your exhaust's air flow. oh well.

 

Actually, I was implying that it felt like I had more low end power at the expense of top end, instead of vice-versa. I always thought opening up the exhaust added top end and killed low end.

Another thing I haven't taken into account is that I also changed the fuel filter at the same time. It's no telling how long it had been in there, but the gas that poured out of it looked like coffee (not _quite_ that bad). That may have made some noticable differences.

Anyway, I consider 4k to still be "lower rpm range" in this car!

 

I had a Greddy SP Sport catback for about a year before swaping out the stock precat and cat with a bonez stainless downpipe and freeflow cat. My boost went way up so I installed a Profec-B to bring boost back to stock levels. I noticed way more power from 3000 up.

If you still have the precat that may be the problem. I pass Maryland emmissions with just the single cat. I recommend the stainless steel downpipe if you haven't already done the swap. BTW - All the above are 3".

 

I recently installed a high flow cat with the PFS catback & I concur about the noise. Not pleased. Tone & volume changed significantly. And talk about "pops". I like the PFS so I think I am going back to a stock cat.

 

How about smell? Do you guys get the fume smells that mid pipe people talk about?

 

Nope, not with a hi-flo cat. That's a midpipe only feature.