ESE's works engine tuner

[TZ350]

ok here's one to send people down the garden path with a nice but difficult idea
http://www.muller.net/mullermachine/docs/slippy1.html
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Slippy exhaust pipes

I was having a quick look at some old posts and re-discovered this from F5 Dave about adjustable length expansion chambers. It has to be a good idea, if it could be automated to work by itself even better. Now how to fit it onto my bike?????????????

From an Add for a RC Car exhaust:- The precisely engineered components of the Power Exhaust System use the unique exhaust pressure characteristics of 2-stroke motors to dynamically adjust the tuned length of the exhaust system. This is why Power Exhaust Systems can achieve maximum performance over a much wider RPM range than is possible with a fixed pipe. Changing of the tuned length is accomplished by the movement of the internal Tuned Assembly within the Power Exhaust Body.

While traditional tuned pipes focus on only one RPM range for maximum effect, the Power Exhaust System can boost performance throughout the entire RPM range. It’s (possibly) the world’s only tuned pipe that dynamically adjusts its tuned length during use.

"Tuned length" refers to the total combined length of the exhaust header and tuned pipe from the face of the piston to the end point of the convergent cone. This is the factor that is generally calculated first in pipe design. The tuned length is a function of certain fixed engine parameters and more significantly, a target RPM for maximum performance. Of course, a designer can only choose one target RPM. One RPM equals one best-tuned length. For a maximum benefit over a greater range of RPM you must change the tuned length.

F5 Daves might be better because only the rear cone moves but the RC Car pipe shows how it could be automated.

Pic-1 from F5 Daves post

Pics-2 to 4 is how RC Cars do it.

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[TZ350]

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"Tuned length" refers to the total combined length of the exhaust header and tuned pipe from the face of the piston to some point on the convergent cone. This is the factor that is generally calculated first in pipe design.

Danger Danger Danger There are two common ways that the term "Tuned Length" is used. Some people think tuned length is measured to the end of the convergent cone others measure tuned length to the mean reflective point half way along the cone. Thats half way along the complete cone with its pointy bit still on the end.

When talking about/compairing/calculating tuned lengths you need to know how the "Tuned Length" is being defined. Its an important difference, about 50-80mm or 1,000 to 1,500 RPM and can completly confuse your tuning efforts.

I am indebted to Thomas for pointing this out to me.

He also says that the sum of all the individual stages (cones) in Pic-1 should more correctly be called the overall length, and the overall length is most certinaly not the tuned length given by most/all formulas that you see for calculating the tuned length of an expansion chamber.

Most/all formulas for tuned length based on time and the speed of sound give a value for the length from the piston face to the mean reflective point of the convergent cone (Pic-2) and this is correctly called the "Tuned Length" because this is the mean distance/time the pressure wave travels out and back in the pipe.

Pic-1 Tuned Length. "tuned length measured to the end of the cone"

Pic-2 Tuned Length. "tuned length measured to the mean reflective point of the cone"

Pic-1 is wrong and Pic-2 is right as the "Tuned Length" is the mean distance/time the pressure wave travels out and back in the pipe.

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[speedpro]

It's been done before in bucket racing, Peter Steadman. The end cone was slid back and forth by a servo, possibly a central locking solenoid. It had a cable pulling it in each direction. Remember Peter's bike has the stinger exiting from the centre section. I'm not sure why it wasn't persisted with. His bike was pretty quick without it so maybe it just wasn't worth the added complexity.

[FastFred]

Danger There are two common ways that the term "Tuned Length" is used.

When talking about/compairing/calculating tuned lengths you need to know how the "Tuned Length" is being defined.

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TZ have I got this right??????

Formulas for tuned length based on "time and the speed of sound" give a tuned length measured to the mean reflective point of the cone"

Formulas for tuned length based on "time and the speed of sound plus a mystery bit” give a tuned length measured to the end of the convergent cone.

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[TZ350]

TZ have I got this right??????

Formulas for tuned length based on "time and the speed of sound" give a tuned length measured to the mean reflective point of the cone"

Formulas for tuned length based on "time and the speed of sound plus a mystery bit” give a tuned length measured to the end of the convergent cone.

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Yes you're onto it.

"Time" in the formula is worked out from the Rev's and Ex. Port Timing and the "Speed of Sound" is worked out from the Exhaust Gas Temperature.

Using these fundamental principals, Time X Speed = Length is the way Blair, Jennings Et. all, do it. This gives the "Tuned Length" measured to the mean point of the convergent cone.

Be suspicious of any other so called tuned length and ask how its calculated and where did the "extra bit" come from.

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[pete376403]

Was cleaning out a pile of old magazines in the attics today, found a "Cycle" from January 1973. Has a very interesting article by Gordon Jennings titled "The aspirin-takers guide to port timing".
I could scan and post if anyone is interested

(for those who have never heard of him, Jennings was the guy who "Knew Stuff" before Kevin Cameron)

[bucketracer]

Was cleaning out a pile of old magazines in the attics today, found a "Cycle" from January 1973. Has a very interesting article by Gordon Jennings titled "The aspirin-takers guide to port timing".
I could scan and post if anyone is interested

(for those who have never heard of him, Jennings was the guy who "Knew Stuff" before Kevin Cameron)

Yes, please post it. It will be interesting to see if TZ knows his stuff.

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[Fastborisracer]

Yes, please post it. It will be interesting to see if TZ knows his stuff.

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It has already been posted many weeks back by TZ I think, re-posting is good but ya gotta wonder how well some people are paying attention.

[pete376403]

It has already been posted many weeks back by TZ I think, re-posting is good but ya gotta wonder how well some people are paying attention.

OK that will save me a bit of time. I couldn't get the PDFs under 1 meg anyway. What post (post number or date) I'll have look and see if its the same thing I've got. This one refers to an SAE paper from Yamaha engineers Naitoh and Nomura and the TD3 yamaha race engine. Same one?

[bucketracer]

Yes, Fast Boris, your right and in fact TZ seems to repost his ever increasing collection of interesting links every 10 pages or so, so they don't get to hard to find. I've just searched back and found them on page 70.

[pete376403]

Thanks, found it (post # 1040)
I'm not a bucket racer, just came across the mag article up in the attic and thought it could be useful. Oh well.

On another topic - crank balancing. Anyone suggested using mallory metal for crankshaft slugs? It is a bit heavier than the equivalent size piece of steel (for when you need to add weight)

[bucketracer]

On another topic - crank balancing. Anyone suggested using mallory metal for crankshaft slugs? It is a bit heavier than the equivalent size piece of steel (for when you need to add weight)

Yes, Speedpro has suggested mallory metal. Apparently MM is a bit heaver than lead.

[TZ350]

Thanks, found it (post # 1040)
I'm not a bucket racer, just came across the mag article up in the attic and thought it could be useful. Oh well.

On another topic - crank balancing. Anyone suggested using mallory metal for crankshaft slugs? It is a bit heavier than the equivalent size piece of steel (for when you need to add weight)

"I'm not a bucket racer, just came across the mag article up in the attic and thought it could be useful. Oh well."

Its all good, we need reminding, and often because people don't pay much attention to something untill they need it.

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[pete376403]

Yes, Speedpro has suggested mallory metal. Apparently MM is a bit heaver than lead.

Depleted uranium is heavier again but there are problems getting it (altho there's a quite a bit laying around in Iraq)

[TerraRoot]

what about water injection? the nsr500's used it to cool the pipe which changed the speed of the reflecting wave, think it worked too because they keep it right up until they the 2strokes got ruled out.