Perfect header length

[Deleted member 12676]

Shortening the header raises the rpm peak, also shifts the powerband higher to match. does not widen it.
Lengthening the header does the opposite.
Now how much higher than the non-EC* you can get away with is unknown to me. On my engines I tune the pipe to peak out at 5-10% higher revs than what the engine does with just a straight header and muffler (standard). I suggest finding out that rpm peak first.

EC: expansion chamber

 

[cRazy_styleR]

Thanks a lot!

I'm alo a bit confused (I don't know much about designing expansion chamber and timings) about pipe curves. For example, if I cut header pipe from yasuni r for about 6" (15cm), and notice that new powerband does not fit very well, or performance is a bit worse, may I weld pipe to old length (with cut piece, as it was before shortening) and get powerband to old "graph" ?

I don't want to make mistake with no posibility to correct it

 

[Deleted member 12676]

of course you can return it to how it was

 

[cRazy_styleR]

I just measured my yasuni r pipe. Pipe looks like this:
http://motor-x.pl/images/800x600_t/image....e923e9d.jpg.jpg

First mesaure is 27cm (10.5 inch), before weld, and after weld is 32cm (12.6 inch). And after second weld, it is 33cm(13 inch) diamter.
Why are there different diameters of the pipe, when (difuzor) cone is way further? How would engine behave if that pipe was the same diameter (width) a whole way to difuzor cone ?
By difuzor cone I mean on cone which is first on expansion chaber.


Also, will performance change if only (without any other modifications) pipe after expansion chamber and before silencer is longer ? And what if that pipe is bigger diameter than stock?

Thanks!

 

[Deleted member 12676]

having the header expand is something useful for high rpm engines. But the increased diameter where the diffuser begins leaves the designer less ability to have a healthy diffuser angle unless the belly diameter is increased.
the questions you ask lead me to believe you haven't read my info on expansion chamber theory. Please read it completely (following all the links) and then get back to me. I charge a small fee to design pipes if you need that done for you.

 

[mikejeffries]

The period of one crank rotation at 6500 rpm is 9.23 milliseconds.

Is this correct?

 

[Deleted member 12676]

1/(rpm/60)=period

yes that's correct

 

[cRazy_styleR]

You're right, I missed your link to book. I saw there was formula for d3 wich is the stinger length.

Somehow, it's confusing to me. Here's my point of view:
Gases back of the exhaust cane, others go through stinger and silencer.. Gasses which went through the stinger are not returning into chamber, they are leaving through silencer, or are they? Don't understand that part - How does the longer stinger affect to higher back pressure?

I want to modify my exhaust, but don't have some strong expirience. That's why I have so much question ..

It would cost a lot of money while that pipe came to me.

 

[Deleted member 12676]

I don't make pipes for people, only consult to help them in their own construction.
smaller diameter stinger and/or longer stinger increases flow resistance which increases back pressure.

 

[cRazy_styleR]

Ok.

So, basically the longer stinger causes bigger back pressure which will then be faster, am I right?

I red that midsection is there to define and set correctly back pressure time to cylinder. So, I'm thinking, if back pressure comes to cylinder earlier than it should be, increasing the midsection would set this timings right, right?