tuned muffler calculations?

[one.man.band]

could any of you that use the 'pipe calculator' type software tell me ................?
if the "L" distance:
1. is measured from the edge of piston
2. from nearest edge of exhaust port

i have seen it measured both ways.......

i do not have a software program, and am working the numbers out by hand. either way, it appears to be only a very slight difference between the two, but just want the most accurate #.

 

[trappermike]

I'm not sure which "L" (Length) you are refering to,there are several lengths to calculate but I'm assuming you are looking to calculate the tuned length(Lt) of the pipe. You want to make this calculation from the edge of the piston,as the exhaust port is considered part of your pipe's length,regardless of what program or formula you are using. It is important to be accurate because one mistake can alter your other calculations and make them off.
Generally I find that changing the tuned length,intentionally or by mistake alters the power peak by about 500 rpm's per inch,an inch shorter raises power peak 500 rpm and vice versa.
You will want to consider the exhaust port's length when calculating the length of the lead-in pipe(The pipe from the exhaust port to the first cone). If your formula concludes that the lead pipe be 8" long for instance,and your ex. port is 1.5" long,then the length of the lead pipe you fabricate will be 6.5".
I use 3 different formulas to use to build pipes but the basics are the same.

 

[gink595]

It should be from face of piston as the exhaust port length varies from motor to motor.

 

[one.man.band]

thx trapper.

found what i was looking for. i had to subtract exh. port length after getting my "L".

 

[trappermike]

Great!
I know it can be a little confusing at first,but one mistake can screw up the rest of your calculations!

 

[Stihlmech]

ok, so what is the formula??

 

[poulan thrower]

are you making a pipe or porting the mufflet thats on already

If you are porting the existing muffler you measure exhaust port and measure that and multiply by 0.325 and that should give you maximum port area on the muffler