How To Calculate Muffler Size and Exhaust Pipe Diameter
If you’re a math wiz and/or an engineer, you’re probably going to like this article and the resources we’ve linked to. However, if you find yourself getting stuck (or bored) with the info below, here are the key take-aways:1. The factory exhaust pipe diameter is usually a good choice for most vehicles.
2. The muffler manufacturers are doing all the math for us – no need to reinvent the wheel. If they say it will work for your vehicle, it will probably work for your vehicle.
3. We’ve got an easy-to-read exhaust system size table that is good for quick calculations.
Breaking Down The Problem
While we’re not going to go through and list out all the formulas and calculations you need to figure this exactly, we will break down the problem, explain how you would go about figuring things out scientifically, and then leave you with some good quick-and-dirty exhaust system math as well as some interesting links.The science goes like this…
1) Mass of air that the engine breathes in + mass of fuel = mass of exhaust gases
Conservation of mass, right?
2) To calculate the volume of air the engine takes in, we multiply the displacement of the engine by the engine RPM and then divide by two (it takes two full revolutions for the engine to exhaust it’s entire air volume). We then convert that to volume to mass.
3) To make the calculations easy, you want to assume that combustion is perfect, i.e. there aren’t any byproducts, any unburned fuel, etc. It’s easier to assume perfect combustion and then “back in” to the actual numbers using an estimate after the fact.
4) Since you’re assuming perfect combustion, it’s easy to figure out how much fuel mass is added to the exhaust.
5) Once you know the mass of the exhaust gas, you just figure out how much volume that mass would occupy. Of course, you have to adjust for expansion due to the high exhaust gas temperature.
That’s it! Of course, when you sit down to figure it, you’ll find that getting a good scientific estimate takes a lot of work (which is why we don’t bother with it here).
#more on http://www.exhaustvideos.com/faq/how-to-calculate-muffler-size-pipe-diameter/
Calculate Exhaust Header Length
Maximum Horsepower Output
Tuning the exhaust system can be an important component in achieving maximum power when optimizing the performance of an engine for racing or dyno shootouts. While not recommended for street bikes, the use of drag or straight pipes can maximize the horsepower produced by any specific engine combination. The RPM range that the straight pipes produce their maximum power is very narrow. The best ways improve the performance of straight pipes is to "tune" the exhaust length to the required power band.
Determining Exhaust Pipe Length
Opinions differ as to the best exhaust pipe lengths for any engine. There appears to be two major "schools" of thought on the best exhaust system length. The "short" pipe and "long" pipe calculations performed below present both views. Short pipes seem to win from an esthetics point of view, but the longer pipes seem to produce a better power curve. The decision of which to use is up to you.
Any formula that calculates header pipe lengths must take into account conditions such as exhaust temperature, gas speed, exhaust valve duration and the RPM the engine is running at. Each formulae makes different assumptions about these items resulting in different results from the same basic input parameters. The formulas used here result in short and long pipe length being calculated.
For serious performance efforts, the pipe lengths are calculated for a 3-step drag pipe. This 3-step design has generally proven to give the highest horsepower results over any other design. 3-step pipes are generally a custom build pipe.
#more on http://www.nightrider.com/biketech/calc_exhaustlength.htm
INTAKE PIPES AND EXHAUST PIPES SIZING CALCULATOR
The Intake Pipes
You've read it all before, the intake pipe diameter and length is very important because it affects volumetric efficiency, impinges on pumping losses, mean effective pressures, etc, etc. You have also heard of rarefaction waves, reversion pulses, syphoning, blah, blah, blah. Well guess what we actually incorporated a lot of this stuff in the calculator to make out we know what we are doing. This will also hold truw for the exhaust side of things where we claim a proper sized exhaust will suck harder than the piston itself.
Alrighty heres what we have thrown into the soup to come up with the intake pipe sizer:
Long inlet pipes increase volumetric efficieny at low speed, but decrease VE at high speed (VE is volumetric efficiency);
Mean effective pressure increases proportionally with volumetric efficiency;
The amplitude of pressure waves increase as pipe length increases;
Pressure peaks occuring around the inlet closing occur later as the pipe length increases;
Cylinder vacuum comes on later in the stroke as the pipe length increases, until the number (frequency) of pressure waves per engine cycle changes and it reverts back to the original angle and starts coming on later as the pipe continues to be extended.
Later inlet valve closing is better with long pipes and earlier with short pipes. This is because the arrival of the pressure wave is later with long pipes
Which when translated means you install long small bore pipes when you want power and torque at low to medium revs, long large bore pipes for midrange torque and short pipes when you want performance at higher revs (at the expense of losing some of your low end performance).
So what about all this pressure waves stuff you ask? Well that's simple too, because some else spent a load of some government's money when dinosaurs walked the earth and came up with some observations that you can get a whopping 15%-20% increase in mean effective pressure by just making the pipe a length that encourages a third harmonic based on the speed of sound and engine rpm. And better than that the fourth and fifth harmonic suck too!
The Exhaust Pipes
Learn a lot from the previous section? Probably not, but we aren't here to study for you. So onto the exhaust pipes. What do we know about exhausts you ask. Well we know that there lots of guys who swear by their own secret sizing method and guess what, we probably have it as an option here too!.
The object of sizing the exhaust is similar to the inlet, but in this exercise we want the exhaust pipes to scavenge as much waste gas as possiblel and also induce fuel mixture into the cylinder. If we are clever we can create enough vacuum on the exhaust port to pull extra fuel/air mixture in. We know that the piston is going to pull nearly it's own displacement into the cylinder, but with some extra help from the exhaust escaping we should be able to fill the clearance volume as well.
So the same principles apply to the exhaust as the inlet, longer pipes suit low and midrange performance and short pipes are good for high end performance. We know that a vacuum does appear on the exhaust port if the system is designed well, otherwise car makers have wasted a lot of money on PAIR systems and the like.
Once again sonic waves, pressure drop, gas velocity, etc come into play. And before you start getting cute about our pipe sizes, consider that there are dedicated engineers out there who spend most of their time imperically testing the best fit for particular engines with more equipment than the average enthuisiast. We don't have that luxury.
#more on http://dairally.net/daihard/chas/MiscCalculators/DaiPipes.htm
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