Insane Thoughts or Siamese Pipes?

[RCUK John]

To save LENGTH in a boat is it possible to SPLIT the exhaust into TWO streams and still have a tuned system? :eek:
Assume any boat with (say) a 90 (15cc) Nitro engine whose exhaust header diverges into two runs. Would it be possible to have two 46 (7½cc) tuned pipes - one port and one starboard - and still have an effective tuned system? :confused:
As I said, "Insane Thoughts or Siamese Pipes" and No I do not have any plans to try such a system!

[Ron Olson]

Aw, come on John, try it! :)
Possibly with a front or rear exhaust engine as you'd want to be able to get each pipe as equal as possible, a side exhaust engine would be much harder to do. How it would or wouldn't work could be interesting. The added weight of the extra pipe might figure in with someone that wanted to give it a shot.
This idea isn't any crazier than some others that I've seen.

[RCUK John]

Aw, come on John, try it! :)
Possibly with a front or rear exhaust engine as you'd want to be able to get each pipe as equal as possible, a side exhaust engine would be much harder to do. How it would or wouldn't work could be interesting. The added weight of the extra pipe might figure in with someone that wanted to give it a shot.
This idea isn't any crazier than some others that I've seen.

I would not have thought that there would be much extra weight.
The size of a 90 pipe is quite large compared to that of a 46 pipe.
Yes, I agree with you that front or rear exhaust stand more chance but what about getting the pipes to peak the engine.

Are there any Tuned Pipe designers out there anywhere to answer that?

[BoatDoc]

they'd each still have to be the length of the original pipe to time the sound wave. as far as i know.

[Burkey1000]

I guess you wouldnt know unless you tried. Might weaken the waves to much but without trying it who knows. whos to say you couldnt have slighlty diff pipe lenth to broaden the band somewhat. Without trying many diff types and ways you will never know. The logic thinking says its a no no, but things have been proved wrong many times. playing with pipe dia, stinger dia and pipe lenth would be the problem. If ya handy with a blowtorch and brazing rods, then a good way to make a temp pipe is use cookie tins. the metal is thin and bends and keeps a nice cone shape, almost like a sprung steel. Braze with low temp rods and you have a very cheap way of making test pipes. Sounds silly but have done it many times on testing pipes as i used to make my own, and have even had pipes better than some of the big names, and then when you have one that works realy well make it outa .6mm steel. And yes i have even raced with a pipe made like that, and won. A great cheap way for a temp pipe. Average cost of test pipe around 6 bucks. :)

PS. Just noticed your from the uk john, bicky tins to us :D
PPS. If all your after is to save pipe lenth then use a two stage divergent cone. A rough guide is 7degree and then 12 degree and with a lenth ratio of 70%/30%. The downfall with this is the pipe dia would increase, the reason for this is to maintain the same pipe volume. Remember that you could easly curve the stinger and cones to work around space etc, changes in angle of the two cones doesnt matter to much, but alot of changes in the header pipe will have a huge affect on performance. Hope this helps a little.

[Ron Olson]

I'd love to see what some experienced people would have to say also. Tuned pipe theory is really close to a black art, kind of like props yet a lot of math involved, stuff that's way over my head as I didn't learn that stuff in school decades ago.

[Burkey1000]

To be honest ron its not that hard, there are a few basic rules you follow then do the math which when you have the basic rules to follow is pretty easy so long as you got calculator. Have you ever read Gorden jennings tunning book. That is my rule book when making pipes and after building a good number and alot of them working aswell and some alot better than the biggger names proves to me it works. IF ya wanna read it ron let me know. It realy does simplify things and he is the guru of 2stroke pipes. :)

[Ron Olson]

I've heard that it is really good. Someone from another forum site has uploaded it in a .pdf version.

I found it! http://edj.net/2stroke/jennings/

[Burkey1000]

I already got it, couldve mailed it to you had you wanted. Read the pipes section, theres some real simple rules to follow which takes alot of the hard work out of it. Anyone who is interested in pipe theory or just knowing a little more i think its a must read. For me its an easy read and i think it will be for most. Let me know what ya think of it. :)

[Fluid]

It's pretty clear form Jenning's book (which I first read 25 years ago) that the pipe length to the middle of the reflecting cone is the determining factor for wave reflection back to the exhaust port and the resulting power increase. With twin pipes the exhaust pulse leaves the cylinder at the same time for identical pipes, and would return at the same time too, just a bit weaker in total so less power. It is possible to make 'shorter' pipes by incorporating more turns as is commonly done with snowmobile pipes, and the stinger does not have to come out at the reflecting cone's point. But for equal performance you'll have to use the 'correct' length as described in Jenning's book.

That said, shorter designs like the old "magic muffler" do seem to work, although how they compare to a full-length tuned system I do not know. :confused:

[RCUK John]

As I said once before to you (and quoting good old Bernard Matthews)

It's BOOTIFUL over here now. :) :)

(Apologies to everyone else - but Burkey seems to be getting forgetful). :confused:

Space can be saved especially with a rear exhaust going foreward and then transferring sideways before reversing the gas flow to the critical point of the pipes - assuming the pipes are almost touching the sides of the hull.

If I do not sell my 4 point hydro I may try it using the CMB 90 from that boat.

[Burkey1000]

Not sure what ya mean by that but oh well. As for the wrap forward headers yes space saved, but the less bends in the header the better. You can shape the cones using the pie method without any great loss, but more bends in the header or far worse than that of the cones.

[Blackmanba]

Hi there, I thought it was OK for heders to have bends as long as its internal shape retains smooth radious. e.x. two stroke motocrossers sometimes have fully twisted headers to save space. It is not good, however, if it has any kink. Loss of power as it was mentioned.
Recently hyper motorcycles started to use conical headers. They are kind of full bends internally. But no kink. The engines we use for boats have no round shape exhausts. Rather squareish. Headers change shape to round without any kink or straight lines thus we've been using kind of conical headers(?). We are ahead of motorcycles... Just kidding, hehe

[BoatDoc]

how about those reverision chambers that the motorcycle crowd started years ago? haven't seen those on our pipes yet. i wonder if that's something to look at.