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4 into 1 equal restriction ? ? ?

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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Bike exhausts....they like cars in the sense of more flow equal better?
If there is stock 2 into 1 pipes on a 4 banger, why go with 4 into 1 pipes, wouldnt that cause some restriction?
Edumucate me!
 
Logic often does not prevail in the world of tuning.

the reason for a 4 into 1 or a 4 into 2 into 1 is to use the exhaust impulses to create less (or more) backpressure at certian rpms.

That may not make sence. it is 3:15 am. Lets see if I can make something usefull out of it.

While a single pipe per exhaust valve would seem to be the least restrictive you are then treating each cylinder as an individual. When each exahust valve opens it creates a pressure wave down the exhaust pipe. with a long enough pipe, you can actually use the exhaust impulse from one exhaust event to help suck exhaust out on the next exhaust event. OR you can use it to push exhaust back in... (this is usefull for generating more torque at low rpms, but that's another story entirely) Keep in mind that the longer the pipe, the less strong the exhaust pulse benifit will be.

in a two into one exhaust, each exhaust impulse from one cylinder causes the exhaust pipe to temporarily become a low pressure zone, before returning to normal pressure. With a two into one exhaust and 360deg exhaust timing you're looking at pipes that would be half the length as the one into one exhaust. Your goal is to adjust the lengths of the exhaust pipe so the minmum pressure in the exhaust coincides with the exhaust opening of another cylinder. With a three into one, you're now getting into really funny situations. Without getting into the math, the exhaust pulse from cylinder #1 will be at the right time for cylinder number 3, then 2, at different rpms. If you're good at designing an exhaust you can do some real good with that! With a 4 into one, the process repeats more frequently, causing all kinds of benifits across the engines rpm range.

Long story short. while a single large exhaust per exhaust valve would seem to be the least restrictive method for removing exhaust, smaller pipes, with higher velocitys, lower pressures, and tuning as a result of exhaust impulses from other cylinders leads to more efficant extraction of exhaust gasses from the cylinders.
 
The fact that a system is 4 to 2 or 4 to 1 has nothing to do with it's flow rate. They're simply independent things. A really unrestrictive set of pipes, no matter what the combination, will allow more flow, and less backpressure.

And remember, what is good flow to one bike may be strangling to another. My 1100 cylinders are way bigger than 550 cylinders and would have serious problems on an exhaust set made for a 550.
 
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