BONEZ HIGH FLOW CAT

Difficulty: Easy

Time: Depends on the rust factor…

Discussion:

This is another one of those things that I’ve been meaning to do for a long time…

I’ve never done anything to the catalytic converters on this car since the day I bought it in 1991.  They’ve always been solid and never leaked, so if it wasn’t broken, I didn’t fix it.  Then back in the summer of 1997, I was driving along and all of a sudden the car had no power what so ever.  I thought there was something seriously wrong with the engine, but it turned out that the first pre-cat disintegrated and clogged the second pre-cat and the main cat.

At this point in time, I took everything off and punched out the guts from my clogged cats.  (When you do this you definitely want to make sure that you do not breath any of the dust particles that come flying out, this stuff is toxic!)  I put it all back together and took it for a test.  WOW, was all I could say!  I don’t know what kind of HP numbers I gained, but there was definitely a difference in the “seat of your pants dyno”!

The only thing I didn’t like was in the summer with the windows open, you get a pretty rich exhaust smell in the car.  It started making me sick so I decided to get a new cat installed… Even if this meant loosing some power. 

TAKE #1:

I went to Midas and had them weld in a new “generic” main cat for me.  It cost about $200 bucks for the install and the rich smell was gone.  But the first thing I did notice was that the car was a little more sluggish again.  I knew why, but I was happy that I could cruise around with the windows down and not be gasping for oxygen.

This lasted for about 18 months when I noticed a “rattle” from under the car.  It was coming from the exhaust.  I started bumping the exhaust and found that it was coming from the main cat.  Turns out that the internals of the thing were falling apart due to the high exhaust temps from the rotary engine.  I heard about this before on a couple web sites, but I didn’t know about the problem until after I went to Midas…

TAKE #2:

This time I went to the Rotary Performance web site and bought a “Bonez High Flow Cat”.  They claimed that it was designed for rotary engines and can take the heat.  Since I didn’t want to do this again, I paid the $300 plus shipping because I could not find another product that claimed to work with a rotary.

The construction of the Bonez product is pretty decent.  The 2.5” pipe is galvinized for rust protection, as well as the converter itself.  The flanges on the end are 3/8” thick, and are slotted to allow better fit.  

Installation was a snap.  The only thing I noticed is that the 2.5” pipe is a little bigger than the engine exhaust manifold 2” outlet.  The flange was big enough to cover the size difference, but I was a little concerned that I might have an exhaust leak here.  Other than that, everything else went in as planned.

RESULTS?

Compared to the clogged, melted, rattling piece of crap Midas cat that I just took off, the Bonez product is great.  Power was up, but this was probably due to the fact that the Midas cat was about dead, and I had a couple exhaust leaks from the original gutted pre-cats. 

Another benefit I noticed is the fact that the Bonez pipe is a strait pipe with only one ~45 degree bend.  Compared to the original twisty pre-cats, the strait pipe probably also helps with the velocity of the exhaust gases.

MY ONLY GRIPE?

The bend in the Bonez cat was not mandrel bent.  This means the pipe is crimped where the bend is.  This is very easy to spot in the picture that I took.  I’m sure this doesn’t make much difference in performance, but I was expecting a quality part for $300 bucks and the bend in this pipe is crap.  I guess I’m a perfectionist when it comes to my car…  Do you blame me?

FINAL THOUGHT…

I would definitely recommend this product to anyone who is looking to gain a little power and stay environmentally friendly.  However, if your looking for PEAK performance and you can put up with the smell, you can save yourself the money and just punch out the guts from the existing cats.  (Note:  I am not recommending that you remove your catalytic converters since it is a crime to do so!) 

The only other thing to remember here is BACKPRESSURE!  You can't see the return tube in the picture, but it is there and you DO NEED it if you have an 86-88 RX-7 because the backpressure from the exhaust is what opens the "six ports".  Without 2 PSI of backpressure, your secondary's will not open and you will loose more power than you gain. 

If you do decide that you want max power and go with gutted cats or a strait pipe then you will have to find a different way to supply pressure to the six port actuators.  There are several thoughts on this, including an electronic method that works off engine RPM like this example here...

Of course if you have an 89-91 RX-7 or any year Turbo, then you can just ignore the need for backpressure and run strait pipes all the way to the rear bumper!