i copy this whole chapter down from MIKE KOJIMA's book (how to modify D,B,H series honda /acura)
the key part of your exhaust system is the muffler.the muffler is the can at the end of the exhaust whose job it is to make the exhaust quiet.To do this,a typical stock muffler must have an intricate and labyrinth-like internal flow path to help slow andcool the hot,vibrating exhaust gas.It contains baffles that cause the exhaust flow to reverse direction and mix.these baffles are great for reducing noise but are not good for power.The network of baffles that redirect and intermix this flow are very restrictive,impeding the flow of gasses from the carmwhich directly affects power.
To reduce the most amount of power,an exhaust sytem should restrict exhaust flow as little as posible.Restriction hampers the burned exhaust gasses from exiting the engine,causing some charge dilusion with the incoming fresh air/fuel mixture.This cause a loss of power.Greater restriction also results in backpressure,which makes the engine works harder to pump the exhaust out of the cylinders.This is what I mean by pumping loss discussed previously.
Some stock mufflers produce up to 18 psi of power robbing backpressure.A well designed performance exhaust typically has about 2-6 psi of backpressure.For comparison sake,an UN-MUFFLED straight pipe as found on and off road racecar usually has 1-3 psi of backpressure.Obviously,you wont want to run an un-muffled pipe on the street unless you want to get know your local law enforcement real well..lolx..
To get the least amount of backpressure,most of the good high performance mufflers available today have what is called a straight -through design.There types of mufflers quiet the exhaust by the absorption of high frequency vibrations with a fluffy packing material,usually consisting of stainless stell mesh and heat resistant ceramic fibers.They typically have an inner core that is straight through with no baffling at all,much like a straight pipe with many small holes.The pipe is louvered or perforated when is passes inside the muffler's shell,allowing the radiating sound energy to pass through tbe holes to the packign where it is absorbed and damped.while this is going on ,the exhaust gas flows out of the car unimpeded.You can see straight through there type of mufflers.the louvered or perforated core is usually wrapped with either fiberglass padding,hence the old school term"glass pack" or on the better mufflers,stainless stell mesh andceramic wool to help further absorb the sound.On straight through mufflers the longer the mufflers the queiter it is.the length usually has no effect on the backpressure ,just the noise output.The mufflers work in the same manner as silencers do on guns.if a silencer impeded the bullet's travel ,you would definitely have problems with your gun!
i can't type all of this words man..my finger is Fking tired now...lolx...hope this help u know bout backpressure...will go on with pipe diameter after my finger rest enough..
---------- Post added at 06:36 PM ---------- 6 hour anti-bump limit - Previous post was at 06:12 PM ----------
THE EXHAUST PIPE
to save costs,your stock honda exhaust is make with small diameter crush bend pipe.Crush bend easy and inexpensive to make,which make them ideal for mass production.However ,crush bend can reduce the flow of a pipe by up to 50%.The typical exhaust systemmake by a standard muffler shop is also crush bent.the best exhaust system,like most pre-made exhaust systems,come with mandrel bends.Mandrel bending is donw with a special machine that used a non crushable insert,called a mandrel,that goes into the ppe while bending to prevent it from becoming rushed.The bend is smooth,which helps with exhaust flow.If you are making your own exhaust you can buy pre made mandrels bends from BURNsStainless, Magnaflow,Kinsler or Bassini.
PIPE DIAMETER
Some self proclaimed motor gurus state that you should not run an exhaut pipe that is too large in diameter because he engine need a certain amount of backpressure to run correctly.Although the statement about size is correct,the assumption about the engines needing bckpressure is NOT!! AN engine needs to have the lowest backpressurepossible to produce the maximum power by keeping pumping losses low.AN exhause pipe that is too big cause power loss,especially low end torque,because a big pipe has less exhaust stream velocity than a smaller pipe.Velocity is essential to get the beste scavengin effect from tuned headers which we will discuss in more detail later.To simplify things,if the exhause gas flow is to kept high with good velocity,a vacuum can develop beind the closed exhause valve,allowing even better scavenging when the exhause valve open on the next cycle.Good scavenging is even more critical on valve overlap,the part of the 4 stroke cycle where both intake and exhaust valves are open.
IF the exhause pipe diameter is too large,the flow will be sluggish with low velocity and the scavenging will not be so good.REmembe that a good exhaust has low backpressure and high velocity.The only possible exceptions to this rule are for turbocharged or nitrous motor.It is almost imposible to put an exhaust that is too big on a turbocharged engine,because the turbo depend alot on the pressure differntial across its turbine to make power.A turbo engine can have an exhaust gas volume about 1.5-2 times more than and equivalent displacement,naturally aspirated motor.NOS motors also have pretty high exhaust volume and require a bigger exhaust if they are to be optimized for NOS operation.
Some basic exhaust pipe diameter guideline for HONDA/acura motors are as follows:
D15,D16,B16a,zc-2 inch
B18b,B18c-2.25inch
H22,H23-2.5inch
Add 1/2 inch to the pie diameter to optimized for NOS use.FOr turbo motors ,2.5inch is the minumum size diameter pipe u would wan to run,even for the smaller motors.For the b18 1800cc and bigger H series motors3 inches works well.
IF you dun feel like making ur own system,a reputable company liek DC sport,HKS or Greddy makes well engineered,pre-made exhause system.There systems have a good balance of low backpressure ,roperly sized tubing and low noise..
FOR MORE INFOR BOUT ALL THIS U CAN GO KINOKUNIYA AND LOOK FOR THE BOOK..GUYS SORRY LAH I CANT TYPE ALL ...HOPE THIS ALL HELPS~~~
planning to put the center bullet after this cannot tahan hearing the sound oredi
