Generically speaking, there are 3 exhaust designs:
1. chambered
chambered muffler
2. 2 pass, twin loop, or sound-cancellation design
- twinloop muffler
3. straight-through
straight-through muffler
The straight-through design is when you look through the tip opening, you can see straight through to the other side of the muffler…no bends, or staggered pipes, or chambers.
The majority of popular 60mm diameter aftermarket exhausts are straight-through designs like Apex N1, Tanabe Racing Medallion or G-Power, Greddy EVO, 5 Zigen Fireball, HKS Drager or HP or SE, etc.
A twin- pass or sound cancellation exhaust has a second pipe beside the muffler tip that loops back to the front of the muffler. Mugen and HyTech make very good twin-pass exhausts.
Most stock exhausts (like the ITR exhaust) are chambered exhausts. In a chambered exhaust, the muffler pipe goes into separate chambers and an outlet pipe is staggered and not inline with the inlet pipe into the muffler.Straight-through and twin-pass designs flow much better than chambered designs. But acctualy many people think chambered design is the best muffler type for the stock cars.
A. Design Characteristics to Look For When Shopping for an Exhaust
We may want to look at what exhaust characteristics makes power:
1. Diameter is King:
The most important factor about an exhaust is the B pipe and inlet muffler tube diameters needed for your flywheel hp goal. These outer diameter sizes are suggested by SMSP. The suggested diameters assumes that the thickness of the exhaust tube is 16 gauge steel:
Most Integra owners have 1.8L engines with “bolt-ons only”. You may want to look for a 2 1/4 in. diameter exhaust to start off with. If you begin to think about big lift-long duration cams, bigger 2.5 in. collector headers, headwork, or boring out to get 2 L displacement, then go up to the next levels in diameter as determined by your power goal.
2-1/4″ up to 210HP @ the flywheel (about 180-185 whp)
2-3/8″ (60mm) up to 235HP @ the flywheel (about 200-207 whp)
2-1/2″ up to 265HP @ the flywheel (about 225-235 whp)
2-3/4″ up to 325HP @ the flywheel (about 275-285 whp)
3″ big for big HP (Forced Induction: > 275 whp)
The general rule here for sizing an exhaust is: for every 60 flywheel hp, you need 1 square inch of exhaust cross-sectional area (i.e. 60hp/square in.), in order to achieve the exhaust flow speed required for adequate exhaust gas scavenging out of the cylinder.
All aftermarket exhausts are mandrel bent these days and so this isn’t as important an issue when you compare exhausts. However, many of you prefer to have custom exhausts made for yourselves. To show you how important diameter is, a 2.8 in. crush bent exhaust will outperform a 2.25 in. mandrel bent exhaust, if the header collector and cat are 2.5 in. diameter as well and you are aiming for power above 210 whp. Don’t get me wrong, if you can get a 2.5 in. mandrel bent system, it’s the way to go. This is just to show the importance of diameter and sizing for the entire exhaust system together.
[ Aside: If you don't know what cross sectional area is, I have defined it in the article entitled "Ideas: flow velocity, flow capacity, and flow quality" in the Performance, Engine External section . If you can't be bothered to look at that thread, then use these outer diameters as a guideline for selecting the proper exhaust for you. ]
Please be careful: The diameter just behind the exhaust flange that connects the Bpipe to the catalytic converter on many aftermarket exhausts bottlenecks down to a smaller diameter, compared to the rest of the B-pipe. So check that out when you look at exhaust diameters before purchasing an exhaust. (Please see the my article on how to remove this and get better exhaust flow performance in the Performance, Engine External section).
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Other exhaust characteristics you may want to look at (but aren’t as critical as diameter) are:
2. Insulator Material in the Muffler:
Pay attention to what is used as a sound absorbing insulator in the muffler. Stay away from fiberglass or what’s called a “glass pack”. Fiberglass melts with heat over time and guess what? you become loud as shit and it’s not due to more power..it’s due to a failed muffler.
3. The Rust Factor: Stainless Steel versus Aluminized Steel versus Mild Steel
Pay attention to materials, if you live in a snowbelt area that uses road salt: get aluminised mild steel or better yet, stainless steel, so you don’t rust out your exhaust.
4. Gauge Thickness of the Tubing:
Pay attention to the gauge thickness of steel. A 16 gauge steel thickness (0.65 in.) is thicker than 18 gauge steel. The 18 gauge steels saves you about 20 lb. on an exhaust which is great for racing but can dent easily and is not as durable for the street as 16 gauge.
The same goes for titanium exhausts over stainless steel or aluminised steel. Titanium is lighter but less durable.
5. Hardware Provided
Pay attention to fitment and hardware provided like gaskets and areas for the hangers to hook on to.
Please don’t obsess over an exhaust because it makes around 2-4 whp in “bolt-on only” engine combinations. If you plan to make over 185 whp then the size of the exhaust becomes very important.
