ESE's works engine tuner

[Frits Overmars]

Not sure what Jan did with the Garelli twin Total loss?

Yep, total loss systems for his Jamathi, Piovaticci, Bultaco, Minarelli and Garelli creations. Most of them carried the battery in the fuel tank.

The Exactweld 4 disc tandem Twin no idea how they did the ignition?

Total loss as well.

[Flettner]

Dyno, moved indoors, with the help of Flintstone log rollers.

[JanBros]

as an exhaust pipe does more bad than good at 2/3rd's of rpm of max torque (so before the rpm's the pipe is designed for), is there also such an rpm for the rpm's higher than those the pipe is designed for ?

asking for an idea I have for my moped-MX. standard Honda SKy's are fast to get going from a stand-still/very slow corner's, and I can't seem to keep that good quality while making an engine that's faster once the moped's are moving a bit faster.

So my new idea is : design a pipe that works for a lower rev-range to improve low-speed-acceleration, and since the standard Sky-cylinder has plenty transfer angle area (good enough for over 10.000rpm, rpm's we never reach), and in combination with an 180° exhaust timing, the engine will still (I hope ) outperform standard Sky's in the highr rev's. Unless the pipe does more wrong than good at a certain rpm above it was designed for. (instead of peaking at 8000, I would want to drop it by about 2.000 to 6.000 rpm)

any idea's ?

[wobbly]

The limiting factors for overev power are three fold - tuned length , rear cone angle , and the length % of the header combined with the angle of the first diffuser cone.

Tuned length basically sets in stone where the peak rpm power will fall.
The rear cone angle is a trade off between peak power ( a steeper cone gives a narrower band of useable power with a high peak number ) , and how fast the power will fall off past its peak.
Finally the shorter ( closer to 30% or less ) and the steeper the initial diffuser angle is , this also enables overev capability - always at the expense of front side power.

In your case simply adding a very shallow ( thus longer ) rear cone will drop the peak power rpm , but then allow the pipe to rev on well past the original designs capability.
There are limitless combinations of course , and never any free lunches to be handed out , but heading out along a reasonably well defined tangent using empirical data is always a good start point.

[TZ350]

.

I am pretty lazy and did not want to dick around with dial gauges to center the rotary table and setup the case on center. So I tapered a length of 1" bright and used the taper to force the job on center.

Centering the Rotary Table with the tapered round bar.

Centering the crankcase half.

Starting to cut the pocket. Depth and inner and outer diameters are critical.

Finished the first half. Depths and diameters worked out perfectly. Now to get the cover sorted.

Suzuki RG50 with a GP125 rotary valve assembly. Maybe it will end up a 50 or I could make a 69cc engine and Turbo Charge it. Such exciting possibilities.

[TZ350]

Yep, respirator while working with the Dyno. I understand 2Stroke Stuffings fume problems. I have been using a respirator for a while now as just ordinary fumes from a two stroke can get poisonous after a while. Certainly made me sick.

[Frits Overmars]

as an exhaust pipe does more bad than good at 2/3rd's of rpm of max torque (so before the rpm's the pipe is designed for),
is there also such an rpm for the rpm's higher than those the pipe is designed for?

Yes there is Jan, at least in theory. In practice other problems will probably prevent you from reaching that situation.

[lohring]

There are some ways around this problem;they involve changing the length of the pipe. My favorite as a boat racer is water injection into the header. See below. Another is a sliding pipe. I built one where the baffle cone is the moveable part, but sliding headers are more common.

Lohring Miller



https://www.youtube.com/watch?v=0odVzSgufjk

[Frits Overmars]

There are some ways around this problem;they involve changing the length of the pipe.... I built one where the baffle cone is the moveable part,
but sliding headers are more common.

And more effective.

There are several options in lengthening an exhaust pipe. You can move the end cone, or you can lengthen the header, like a trombone.
The gas pressure generates a force that is proportional to the cross section area of the moving part and proportional to the pressure difference at either side of that area. For a moving end cone this force can be up to 6 times larger than for a sliding header. That is one reason to go for the trombone system rather than the moving cone system.

The second reason: sealing. The circumferential gap that has to be sealed, is three times shorter for the trombone system. That means three times less leakage and three times less friction.

The third reason: say you wish to lengthen the total length of the pipe by 10 %. If you do it by moving the end cone, you will also enlarge the pipe volume by a little over 10 %.
But in a good pipe configuration the header length is about 1/3 of total pipe length, so in the trombone system, lengthening the pipe by 10 % will be done by lengthening the header by about 30 %. That gives a far greater variation in the pipe's Helmholtz frequency than a 10 % volume change.

It is true that the length percentages of all pipe components should be in a rather fixed relation to each other. Varying the lengths of all components by the same percentage would be the theoretical optimum, but that is not feasible.
Lengthening the belly will disturb the optimum relations, as will lengthening the header. So the pipe in its lengthened version will not be the optimum for the low resonance rpm dictated by the length. But it will be a hell of a lot better than using an exhaust power valve that spoils the 180° effective exhaust timing, necessary for true resonance.
And a pipe shortened beyond its optimum may not show the optimum length relations between its components either, but it will be a lot more effective in overrev than artificially raising the exhaust gas temperature by retarding the ignition, or by weakening the mixture strength through closing a power jet, which has the disadvantage that not all inhaled air is used for combustion.

Video courtesy of Rimar Motors:
http://www.youtube.com/watch?v=0odVz...ature=youtu.be

[JanBros]

There are some ways around this problem;they involve changing the length of the pipe. My favorite as a boat racer is water injection into the header. See below. Another is a sliding pipe. I built one where the baffle cone is the moveable part, but sliding headers are more common.

I take on a lot of chalenges, but fitting a sliding pipe that survives 4 to 10 hour races on a tiny MX bike (this is for a 50cc moped for MX that cost's about 200 euro race-ready, and that has an engine/transmission combo that is also the swingarm, so the engine moves together with the rear wheel up and down, and the exhaust is entirly curved due to limited space) is a couple of bridges too far


Tnx Frits and Wobbly. I'll built some simple straight pipes and test them on the dyno and see what happens.

[Vannik]

I take on a lot of chalenges, but fitting a sliding pipe that survives 4 to 10 hour races on a tiny MX bike (this is for a 50cc moped for MX that cost's about 200 euro race-ready, and that has an engine/transmission combo that is also the swingarm, so the engine moves together with the rear wheel up and down, and the exhaust is entirly curved due to limited space) is a couple of bridges too far


Tnx Frits and Wobbly. I'll built some simple straight pipes and test them on the dyno and see what happens.

Have you thought of playing with a pipe that has a perforated rear cone as used by karts? It has two tuned lengths which might help, but it is at the expense of peak power?

[husaberg]

Have you thought of playing with a pipe that has a perforated rear cone as used by karts? It has two tuned lengths which might help, but it is at the expense of peak power?

That raises an interesting point or two, multiple outlets controlled by solenoids (pun almost intended)

or variable iris outlets at different points in the stinger, so they rely on different venturis along the stinger to control the length. or even different pipes




it fails on Kiss and likely reality but putting it out there.

but yes the gp rider should be sacked for being out of the powerband, but lesser mortals on Dirtbikes. Are generally less talented and are self employed

[JanBros]

Have you thought of playing with a pipe that has a perforated rear cone as used by karts? It has two tuned lengths which might help, but it is at the expense of peak power?

no, any design rules ?
* same rear cone but perforated ? in a cylindrical chamber ?
* or steeper perforated cone inside a shallower cone ?
* relationship between perforated and non-perforated surface ? 50-50 ? or is it simply a of less perforated = more emphasis on power at high rev's and visa versa ?

[Vannik]

no, any design rules ?
* same rear cone but perforated ? in a cylindrical chamber ?
* or steeper perforated cone inside a shallower cone ?
* relationship between perforated and non-perforated surface ? 50-50 ? or is it simply a of less perforated = more emphasis on power at high rev's and visa versa ?

I do not know. I only recently understood its workings, thanks to a very kind member that supplied me with pressure traces. The hole size, number and positions are prescribed for the karts in a homologated pipe. So you will have to experiment.

The number/size/position of the holes determine the ratio between the two tuned length pulses.

[lohring]

A 50 cc engine is huge by my standards. Below is a sliding pipe on a 7.5 cc model boat. It was connected to the rudder travel so he pipe was lengthened in the turn when increased drag pulled the rpm down. The silicone tube seals the pipe to the movable section. The sliding joint is sealed by a water cooled o-ring.

Water injection in the turns was so effective that one district outlawed it. We used water injection to be able to launch and accelerate with with larger props to set straight line records. We used a simple, servo actuated on/off valve.

Lohring Miller