One of the few performance modifications that can also be classified as a reliability modification is the addition of a down pipe. One of the main functions of a down pipe besides decrease back pressure is to direct engine heat out of the engine compartment. These cars run hot enough and unfortunately heat is a major enemy of any engine let alone the rotary engine. This is a great opportunity to do some good for your engine. For me, a down pipe was a no brainer!
Cat backs are very subjective performance items. They can range
anywhere from extremely large tips to small inconspicuous looking tips in dual
or single tip designs. What's too loud for some sound great to
others. The most important thing to remember is that just about any
aftermarket cat back will outperform the stock cat back by a wide margin, and
the difference in performance between various manufacturers is small to
none. Choose something that looks and sounds good to you! I chose
the N1 from Apex because I liked the look and the price was reasonable
($400 from RX7 Fashion). I wasn't sure what to expect as far as the
sound went because it was a brand new item, but when I installed it I was
pleasantly surprised. Some people claim it's too loud, but I like
it. It does get loud when the engine is screaming at 7000 rpm's, but I
wouldn't say it was too loud for the street. Apex does make silencers that
screw right into the tip for about $60 a piece. This is one of the few
modifications where I actually felt a gain in HP immediately after
installation. The only problems I've found in the N1 Duals so far is that
it may melt your black plastic piece underneath the bumper a little. Also,
the piping is not stainless steel and will begin to rust especially if the paint
has been scraped off the piping from bottoming out occasionally. Here's
what Apex claims on their website.
I use my mid pipe only when I drag race. The main reason is due to the fact that I'm still using the stock fuel system and I have a problem controlling the boost with my manual boost controller because of the minimal back pressure from the exhaust. The boost will creep up to 16 psi at times and I know I don't have the fuel to support that kind of boost. What I have done to help control the boost is create a restrictor plate, which I install before the cat back. The plate is approximately 2.25" in diameter and restricts the exhaust enough so I can keep the boost at 13 PSI, while keeping a free flowing design, or at least freer flowing than the catalytic converter. Although the 2.25" opening for the exhaust seems small, I am still making a good amount of HP. My 1/4 time best of 11.66 seconds was run using this restrictor plate.
My stainless steel midpipe and downpipe were purchased by N-Tech Engineering. Their pipes are very good quality and their prices are the best I've seen!
Apex N1 silencers
I purchased a set of silencers in an attempt to keep the noise level of my car to an acceptable level. There has been a lot of talk as to how restrictive these silencers are. Apex claims that they do not restrict exhaust flow while others claim they do not receive proper boost with the silencers installed due to the excessive restriction. Here's a direct quote from the Apex website.
I did a few side by side runs with my g tech meter with the silencers installed and removed. My testing was done with the stock catalytic converter in place. After my test runs, the was little to no difference in HP numbers with and without the silencers installed. I also noticed that my boost did not change between runs. It was set at 10 psi with my manual boost controller and was not adjusted while the testing was being done. This is more proof that exhaust flow was not hindered by the addition of the silencers.
When I installed the silencers with my midpipe installed there was a huge difference. My boost was decreased by 2 psi (from 13 psi to 11 psi). This alone told me that the silencers were restricting my exhaust flow.
My testing showed me that the silencers do not restrict exhaust flow as long as the stock main catalytic converter is retained. If a midpipe is used, they will restrict your exhaust quite a bit. The do decrease the noise level of the relatively loud catback system. On a side note, Apex recently changed the design their silencers. I have the newer style. Pictures can be found at the Apex web site.
I purchased a midpipe resonator from Pettit Racing in an attempt to be able to run a free flowing exhaust on the street without any problems with the cops for excessive noise. The resonator is basically a midpipe with a small muffler inserted with baffling to decrease noise. Here's a direct quote from the Pettit website.
"This direct replacement for the stock catalytic converter greatly reduces the droning associated with a midpipe replacement, with no loss of performance. Constructed of flanged T304 stainless steel, this manderal-bent 3 inch straight through pipe includes an 18 inch core of space-age, heat-resistant ceramic packing (not stainless steel!) to take the thermal abuse that the rotary engine can put out. "
When I finally received the resonator in the mail, I went out and bought a sound level meter and did some testing on my own. Here are my results.
Pettit's resonated midpipe VS a standard 3" midpipe
Approximate Performance Gains:
Cat back - 10 -15 HP
Mid pipe - 25 HP
Down pipe - 10 HP