4 stroke Exhuast info ?

[bstard]

Hi
I know quite a bit about designing and building pipes for 2 stroke.but I,m in the dark about 4 strokes.
I am going to be building a new megaphone type exhaust for my GS1200SS.This a Japanese model that is nothing like your Bandits.
I'm going to build this pipe as I want to lower the pipe so I can then mod my footpegs...dont ask why I just need to.
So can anyone point me to to some site that will give me a run down on the fundamentals of 4 stroke pipe designing and any programs that could help with the number crunching.
thanks
Richard

[ZenMan]

Bstard... kere is a basic formula that you might be able to use:

ID1 = inlet pipe internal diameter from cylinder head (header pipes)

ID2 = internal diameter of pipe 2 (collector)

ID3 = Internal diameter of pipe 3 (mid-pipe)

P1= Pipe length 1

P2 = Collector pipe length

P3 = Pipe to silencer length

EOP = Exhaust open in degrees befor TDC

cc= one cylinder volume in cubic centimeters

RPM = engine speed

 

So on to the formula:-

P1 = [(2159x(180+EOP))/RPM]-76

ID1 = [cc/((P1+7.6)x25)]-2x8.6

ID3 = [(ccx2)/(P+7.6)x25]-2x8.1

P2 = [0.5x(ID2-ID3)]x[1/TAN (wall declination angle)]

P3 = (P1+7.6)-P2

A little bit of theory now to tie things up shows that if pipe P1 has an increase in diameter then peak torque will occur higher up the rev range, if it is decreased then the reverse will occur. Decreasing the P1 length improves top end performance (power) but decreases low end performance. Whilst increasing its length does the reverse.

When the four main pipes join from the cylinder heads at P2 you need to taper P2 at an angle of between 7-10 degrees for the best performance. You also need to ensure that the pipes (P1) end abruptly i.e cut off at 90o and not finish off at an angle. You can find the length of P2 by using the formula above.

The above should work for you but as with most things in this field testing and experience can show things to be different in practice as against theory. In other words you use this information at your own risk.

I learned a few things from this book:

http://www.amazon.com/Scientific-Exhaust-Systems-Engineering-Performance/dp/0837603099

[Red01]

Good answer Zen!

...my GS1200SS. This a Japanese model that is nothing like your Bandits.

Well, bstard, you know that statement is not exactly true... that's why you're here. For the sake of the newer folks who may not know, here's a pic of the GS1200SS:



It uses a variant of the 1157 engine found in the Bandit and Inazuma. The frame has a very 1G Bandit look to it, but with twin shocks. The bodywork strongly hints at the original GSX-R and the GS1000R factory racer that inspired the Gixxer and that makes it look very different.

[bstard]

Hi
Yes Paul...your right about the engine but what I really meant was that I cannot just go out and by after market things that I need for it.Things like lowering links due to..twin shocks or carb kets...it runs Keihin carbs.
But I'm well impressed by the SS model it looks like a real bike and has helped me win back to back NZ Drag Championships.
Shouldn't really complain should I.
Back to the exhaust.I will most likely just change the pipe from the collector back to the end of the muffler so it appears that there is not too much I will stuff up doing that.
One more thing.If you make a less restrictive exhaust muffler this affects the jetting by making it..Leaner  or  Richer ?
Richard

[Banditmax]

Freer flowing so leaner.

[pmackie]

Thanks for the data and link Zen. Good stuff...

If you make a less restrictive exhaust muffler this affects the jetting by making it..Leaner or Richer ?

yup, since you've improved the breathing on the exhaust side, the whole engine tends to be able to move more air. To deal with more air, you tend to need more fuel. You will want to see if you can improve intake side as well. Airbox mods, freer flowing filter, etc. to allow max performance from the freer flowing exhaust, and then jet.

[Red01]

I take it you're looking to do something like this, exhaust-wise?

[bstard]

Hi
Well sort of.This may sound stupid but as I'm an old fart with dodgy knees I want to lower the foot pegs so that my knees are not so bent up around my ears.This is probably the opposite to what most people do but to be honest I would never come close to scrapping the pegs as I ride so slowly on the road.
I do my racing on the Drag Strip not the road.
So to lower the pegs on the right hand side I need to move the muffler down.Once again I would never scrap it the way I ride.Plus I like the look of those Drag only style pipes.
I'm a Sheetmetal engineer and already have a brand new standard exhaust system that I can put back on if it all goes horribly bad.
Thanks
Richard