cat back size ??

Mufflers
Exhaust manufacturers can use a single method or combination of methods to manipulate exhaust noise with mufflers. The main muffler designs are chambered, straight-through, and twin-pass.

Chambered
http://www.team-integra.net/images/B...s/exhaust6.jpg
This is mainly a combination of restriction and reflection methods. The dead end chambers like I mentioned earlier serve to keep sound waves from exiting the system. For sound waves that reach the end of the muffler, the majority are reflected back to destroy any sound waves that may be trying to get through. Very quiet but also somewhat restrictive.

Straight-through
http://www.team-integra.net/images/B...s/exsound2.jpg
Absorption is the name of the game here. The size of the muffler is going to play the most important role in how the exhaust note will sound. A short thin muffler casing will ensure a louder higher pitched note while a long and fat muffler casing will give a deeper and quieter note. Also, exhausts like the Greddy EVO are designed so that the pipe enlarges when entering the muffler. This slows the pulses down and allows more sound to be absorbed. That's how a muffler that is relatively small like the EVO sounds much better than other mufflers it's size. So sometimes you also want to find out what the piping size INSIDE the muffler is, as that can also attribute to how the exhaust will sound.


N1 Straight-through
http://www.apexi-usa.com/graphics/pI...hausts_n11.jpg
A more extreme design of the straight-through systems are the "N1" style mufflers. As you can see, there's little to no sound absorption going on here. Muffler is short and very small. Insulation material is kept at a minimum. This flows no better than a regular large muffler straight through however will sound much louder and high pitched. Couple this type of muffler with no resonator and you'll turn your Honda automobile into a Honda weed trimmer. "Hey my weed trimmer sounds tiiite yo!"



Twin-pass
http://www.team-integra.net/images/B...x/hytechm2.jpg
The method used with this muffler to reduce noise is mainly absorption. The pulses have to travel through the muffler twice, which basically makes the muffler twice as long with twice the sound killing power. Also some acoustical tuning goes into making a muffler like this as well. With brass wind instruments, you change the note by selecting different length tubes for the air to travel. Longer tubes will give a deeper note while shorter tubes give a higher note. This type of muffler basically lengthens the tube, allowing sound waves to spread out and emit a deeper tone once exiting the system. The twin-pass design flows as well as a straight-through but will sound much quieter.


Info taken from www.team-integra.net :)

I had Cat-back exhaust fitted on tuesday.. I had the same dillema..

My current D16Y1 SOHC VTEC will hopefully soon be replaced by DOHC VTEC and I didnt want to get exh system done twice so I opted for mandrel 2.5" in anticipation of the DOHC.

I also went UNDER-AXLE but am amazed by how high the exhaust shop (Genie) managed to keep the system.. it follows the path of the OEM exhaust - AROUND the fuel tank, then ducks under the rear axle and up to the OEM mount points.

so IMO it is much better to go AROUND the fuel tank than UNDER it as yes, you WILL get clearance problems.

FYI, the 2.5" with 1 x hot-dog resonator is FKN loud !!!
Power delivery in low end seems laggy in terms of 'spinning-up' but seems to make good power all the same.. mid and top end is completely different beast, smoothing out my power curve rather than the usual VTEC spike with top end making traction an issue in these damp roads..

The SOHC VTEC's do NOT have VTEC on the Exhaust valves, so I figure any help to get the spent gasses out of the cyllinder would be a great help..

wouold have been VERY interesting to do a before and after dyno comparison on this system.

Basically i'd reccomend 2.25" mandrel for SOHC's..

why did you get 2.5" on a SOHC bede ? thats too big !

Quote:

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Originally Posted by VTEChnique

I had Cat-back exhaust fitted on tuesday.. I had the same dillema..

My current D16Y1 SOHC VTEC will hopefully soon be replaced by DOHC VTEC and I didnt want to get exh system done twice so I opted for mandrel 2.5" in anticipation of the DOHC.

I also went UNDER-AXLE but am amazed by how high the exhaust shop (Genie) managed to keep the system.. it follows the path of the OEM exhaust - AROUND the fuel tank, then ducks under the rear axle and up to the OEM mount points.

so IMO it is much better to go AROUND the fuel tank than UNDER it as yes, you WILL get clearance problems.

FYI, the 2.5" with 1 x hot-dog resonator is FKN loud !!!
Power delivery in low end seems laggy in terms of 'spinning-up' but seems to make good power all the same.. mid and top end is completely different beast, smoothing out my power curve rather than the usual VTEC spike with top end making traction an issue in these damp roads..

The SOHC VTEC's do NOT have VTEC on the Exhaust valves, so I figure any help to get the spent gasses out of the cyllinder would be a great help..

wouold have been VERY interesting to do a before and after dyno comparison on this system.

Basically i'd reccomend 2.25" mandrel for SOHC's..

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It would be good to get a dyno reading for your exhaust, my guess is that you're losing more down low than you think, and not gaining as much up top as you think.

also, the 2.25 and 2.5 exhausts will drone more at cruising speeds

2.5"on a D16y would be detrimental to your backpressure and you WILL lose power and torque.

Please refer to my exhaust write up.

Civic gets exhausted
http://www.dohc-vtec.com.au/pages/li...-exhausted.htm

Quote:

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Originally Posted by Civic Type R

2.5"on a D16y would be detrimental to your backpressure and you WILL lose power and torque.

Please refer to my exhaust write up.

Civic gets exhausted
http://www.dohc-vtec.com.au/pages/li...-exhausted.htm

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hmmm here we go with that nasty "B" word again :D

I explained it in another post (can't remember which) but its nothing to do with backpressure, which is actually bad for power production, but rather its to do with scavanging.
:)

Chris

how could it have nothing to do with backpressure ?

In a nutshell:

basically, its a common misconception that backpressure is good for low end power production in an NA car.

In reality, backpressure is bad for power production.
you want to be able to get max air in and max air out of the engine for it to produce its optimal power.

So why doesn't everyone just whack 3 inch exhausts (which would have very low restriction and backpressure) on their NA civics?

cos with the large pipe diameter, the small displacement NA engine isn't able to produce enough exhaust gases at low to mid (or even high) rpm for it to scavange effectively, so in effect it won't be able to have the exhaust gases exit at a speed at which it possibly can.

Chris

Uh...he said he put on the 2.5 inch exhaust as he was going to go for a DOHC engine, I presume a B16 or B18....

Even though it's still a bit big, at least he thought ahead for his engine swap ;)

IMO anything over stock will be an improvment in power.

What kit says is absolutly true, having back pressure is bad, because if a cylinder can't get all the exhaust out then on the next stroke, the cylinder will only get partial amounts of fresh air in, because there is still crap exhaust gasses in there taking up space.

Although Adam has a point too having a masive exhuast like 3 inch on a civic is bad because exhaust gasses wont travel smoothly through out.

For example, put a straw in your mouth and blow, notice the air comes rushing out the the other end fast.
Now sick you head inside a massive pipe and blow notice the air doesn't rush out the other end, because there isn't enough air inside the pipe to create enough pressure to make it flow, and it just pools in one place.

So ultimatly the trick is finding a size where there is still sufficent back pressure to make exhaust flow, but not so much that it becomes restrictive.

IMO

1.5L SOHC = 2.00 inch cat back
1.6L SOHC = 2.00 inch cat back
1.6L DOHC = 2.25 inch cat back
1.8L DOHC = 2.50 inch cat back


btw Adam, Bede is planning on putting a B18C engine is his hatch, so he was just thinking into the future. But **** it sounds nice though :D

Quote:

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Originally Posted by denaro

Uh...he said he put on the 2.5 inch exhaust as he was going to go for a DOHC engine, I presume a B16 or B18....

Even though it's still a bit big, at least he thought ahead for his engine swap ;)

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thankyou that was my exact point - but has made big gain over stock 1.75" pipes !! Did I not say that IMO 2.5" is too big for SOHC - or I recomended 2.25" for SOHC.

Like I said, it feels to not be losing power, but the ability to get through the revs up till 1,500 RPM.. from then on it's GREAT. but tell me since when do you race with Low RPM ??

is a bit too loud though, but the tone is very nice IMO.. remember I still retain the stock cast exhaust manifold, so basically the stock restrictive header is still there for low-down ; )

yeah I have B18C or worked B16A on the way.. now I just have to weld on the flange at the cat end when I swap.

My car seems to pull better than before - hey Kyle.. if Kyle's NEW civic is a little faster than his old one.. I am pulling harder on kyle's civic than his old one which I could oly JUST beat..

2inch mandrel will give you the best all-round performance, no doubt!

Anything bigger than 2" and you will be sacrificing low end for slightly improved top end.

My BC3 system on my Jazz (remember 1.5) had a diameter of 2.38"! It suffered majorly down low, but absolutely hammered up high. All fine and dandy if you are racing and keeping the revs up all day, but on the street, it could be a b*tch at times...

Don't go 2.25". You said you want all-round performance and 2" will give you just that!