Fourstroke pipes

[evo550]

I am in the process of rejuvinating an old Yamaha fourstroke race bike. I would like to do away with the bulky (and heavy) muffler and install a system similar to the HL yamaha's.
What I need to know is there a formula for working out pipe length/diameter, taper, ect ect and what does that "bomb" thing do, seen on so many fourstroke pipes now days?
It's a dual exhaust port motor, so a gmc pipe won't fit.
All help greatly appreciated and promptly forgotten.

[Tony T]

Good boy! I've been looking forward to this day. 
Oh, I trust we are talking about that gorgeous old 550?
btw I don't know anything about pipes. Sorry.
Maybe talk to Lozza, or GMC could do something custom?

[cyclegod]

I heard that TT600 headers are a bolt on fit, probably the same for racing headers too, muffler might fit too.

[evo550]

Tony
Yes it's the old 550, it has been laying dormant in the shed for close to 2 years now, whilst I have been out flirting with other bikes, but I've seen the error of my ways and have dusted the old warhorse off, given it a face lift and hope to have it back on the track in 08....there is also murmers of a trail ride between Longreach and Birdsville about Easter next year which I'm chomping at the bit to take it on.

Cyclegod,
It currently runs those headers and a modern White bros silencer, but I'm looking for something a little more "period"
I like the way the hl exhausts exit to the side and short (and even more so the bsa pipes that finish with a reverse cone just behind the swingarm pivot) but I notice they also run a longer header than stock with that "expanded" section as the pipe passes past the barrel, so I'm assuming that has something to do with a tuning length . I think if I just plugged a reverse cone on to the stock header it would run like a chinese pit bike and just as long.

[evo550]

Sneek peek Tony

[attachment deleted by admin]

[cyclegod]

Something like this perhaps...

http://cgi.ebay.com/ebaymotors/TT500-TT-500-XT500-XT-500-Megaphone-Exhaust_W0QQcmdZViewItemQQcategoryZ35596QQihZ010QQitemZ200186514063QQrdZ1QQsspagenameZWDVW

[Tony T]

Sneek peek Tony

I really liked it before................. 
Interesting now that I see what you're trying to achieve though. You'll have to cut a heap out of the centre of that tank, won't you?
Have you seen Eddie Hau's 550? I've got a few photo's somewhere.

[Graeme M]

I can't help directly with the formula thing, but I can say that back in the 70s I read an article somewhere that gave a formula for working out the tuned length and ID based on bore/stroke etc. I cannot say how accurate this concept was/is, but I did use it to develop a pipe for my TT500F. If I remember right, to get max power at about 6500 on a TT500, the tuned length for a 1.75" ID pipe was something like 36.5". I found me an old reverse cone megaphone from a system for an earlier XL250 and added that to a 1.5" "tuned" length header using a 1.75" joiner, and the end result was one of the fastest 500s I ever owned. The weird thing was a mate copied the dimensions exactly and made his own pipe and the bike ran like crap... The formula suggested that the longer the header, the lower the power peak, or in effect the less power was developed. I always wondered how well things like Hanco pipes and Peter Allen pipes were, given that they had headers of something like 45" length to wind around the shocks. According to that formula, those engines should have actually lost several HP. That pipe in the ebay advert looks absolutely spot-on just from eyeballing it...

Anyways, what I am trying to say I guess is that yes there's a formula, and I am sure someone knows what that is. Not sure about twin headers tho.

[Lozza]

I went and wallowed in the sandpit of 4T pipe design, and found short fat pipes = top end low torque and long thin pipes the opposite.Couldn't find any formula's but the general consenus was a reverse cone megaphone was the pick with a 60deg included angle on the reverse cone.Shit easy to make.

[oldfart]

interesting reading       http://www.google.com.au/search?hl=en&q=motorcycle+exhausts+design&btnG=Search&meta=

[Graeme M]

By the way, that 'bomb' thing in the header is not at all new. I remember that the hot TT500s that Roberts raced in short track in the 70s used a similar concept. Those things were developing up around 60HP so I guess whoever built them knew what they were doing. I do have one of my old tuning notebooks somewhere which *might* still have the formula in it, I'll see if I can round it up.

[Noel]

hi ,
Yep i picked this one out of that bunch
http://vmaxoutlaw.com/tech/exhaust.htm,
explains reasonably well what is required.
I originally used Phil Irvings "tunning for speed" book which uses the speed of sound within  the exhaust gas
rather than the speed of the gas itself it gives the speed of sound as 1,500 ft/sec for practical purposes.
he uses this in the same way as 2 stroke designers use expansion chambers to not only scavenge the cylinder but also at the right moment create back pressure to force new charge drawn into the pipe back into the cylinder just before the valves close.
Phil Iving also explains the different effects of reverse cones diameters on the pipes, get it wrong and you can have a pipe
thats worse than a straight pipe.
may be able to copy some of the revalent pages if you can't find the book.
Noel

[Lozza]

Problem with using the speed of sound is Sonic Wave Speed(SWS) is the SWS changes with temprature, good news for the dark side is it's relatively stable. The place I would start would be "Tuning for Speed" as that's where everyone else would have started. Interesting to note ALL MotoGp bikes sport variations on megaphones, one would assume they know what it's all about, the reverse cones are very small on those.