ESE's works engine tuner

[ApolloMotoMoto]

I tested the two differing approaches in a KZ race engine, where I lowered a stock normal stagger engine , then ground up all the ports to replicate the Aprilia regime.
In EngMod and then on the dyno it showed a loss of around 3 Hp at 10,000 ( the usual lowest rpm on track ) and then gained around 2 Hp ( in 50 ) at the peak of 13800.
But it made an amazing 8 Hp more at 14600 - close to the max the rpm down the shute.
This setup went from 140 Km/Hr at our fastest track to an easy 145, but the serious lack of acceleration off the two slowest 2nd gear corners meant an average drop in lap time of 3/10 sec
even with shorter gearing ratios.
With a PV and a digital ignition if allowed , this reverse stagger setup would have been way faster.

This sounds quite familiar to me...

I feel like I read the same story from Frits Overmars, although the engine in question is not directly referenced...

Direct-drive engines are a very special case. When I first encountered such an engine, I thought it was horrible and I was convinced I could do better. The first thing I did was make a new exhaust pipe for it. With this pipe, with a much narrower, tapered header, 'my' kart could overtake two or three competitors every time it went onto the main straight.
Small problem: it would be overtaken by two or three competitors at every corner exit. And all circuits have more corners than straights...

(...)

Below is the power graph of a world champion direct-drive kart engine. You can see that it is willing to rev to the moon, which allows the rider to fit a short gearing that will help with accelerating out of the corners. The maximum power is nothing special, but the power range is.

Conclusion: I hesitate to give any advice regarding your exhaust. You may think, as did I, that the exhaust systems of these direct-drive engines are not very effective, but bear in mind that they are the result of many fine technicians trying everything to improve them over many years.

PS: if the rulebook allows it, you can gain a lot with a programmable ignition.....

The reason this piques my interest so much is my own Single-Speed Direct-Drive application wherin I DO NOT have access to power-valve cylinders (yet....), but I do have access to programmable ignition curves.

I am also currently in the position where I am not YET ready to start making pipes, so we are simply "stealing" pipes from other engines and using what gets the best results so far, which happens to be literally any manufacturers 80-85cc "motocross" pipes. No one has yet tried -ANY- 100cc Kart pipes on our engines.

The "feature" of Frits' world champion direct drive kart engine that interests me DEEPLY is the "plateau" of power in the over-rev after an initial drop-off of power from the peak.

Attached is Frits' dyno chart as well as a much more modern reed valved 100cc single-speed direct-drive karting engine, the IAME KA100, which also exhibits this over-rev power-plateau effect. (along with screenshots from the KA100 homologation fische)

How do you create this plateau?
-I have read from Wayne that part of it is the internally perforated baffle cone that is not clearly visibly until you cut one of their pipes open, or examine the homologation fische
-I further understand that this is being achieved with a FLAT ignition curve as mandated by all top-level Karting series

Given the imposed limitation of my case of "no powervalve" and also considering the availablity of fully programmable digital ignition;

What features of the engine would be required in order to achieve this over-rev power-plateau without negatively impacting the net-net "power range" by hurting the 'front side' part of the power curve?

As noted, I have a suspicion that its mostly the pipe; and I would like to hear anything anyone has to share about what needs to happen to the pipe in order to achieve this effect....

But, I am also very curious how the other elements of the engines design must be tailored to suite this goal.

[wobbly]

The answer to your question regarding power range in the direct drive kart engine application is surprisingly simple.
Its the perforated rear cone surrounded by a resonant volume, ending in a flat plate end that also just happens to have the stinger in it.
Neels finally nailed down the sim operating mechanism, after alot of email back and forth and hair tearing out.

I discovered the effectiveness of each element in the design many years ago, after doing nothing but build and dyno testing pipes for our classes of the KT100 Yamaha.
This was a solid 6 months of doing nothing else by trial and error.

The mechanism is straight forward, at low rpms the perforated rear cone, and the non resonance of the " muffler " volume, allows most of the advancing wave front
from the diffuser to pass thru almost unhindered.
This wave is then bounced off the end plate, at a much longer tuned length than that of the rear cones.
As rpm increases, the rear volume gradually begins to resonate , and eventually the " holes" almost disappear and the rear cone starts to work in its effective tuned length range.

I tested every single 100cc direct drive pipe available on the planet , as the pipe and header was open in our KT100 classes.
The pipe I finally developed was far superior in every part of the powerband, from around 6000 to 16,000 rpm
It had a fully tapered header, with 3 diffuser cones ( the first being the steepest ) and a two part rear cone , the first one had no perforations.
I hand cut and built around 2000 of those things , winning every class title available for over 10 years.

The Yamaha class is redundant now , so there will be pipes lying around doing nothing under benches - I dont have the .dxf pattern files I eventually drew up, long gone on an old Win 7 hard drive.
I am sure the laser guys will still have the files , but getting a sample should be easy.

Edit - re the intake length , there is no such thing as too short - the 30mm carb on the TM125 KZ has the manifold recessed into the reed block , just to loose 3mm.

[ApolloMotoMoto]

(...)

I discovered the effectiveness of each element in the design many years ago, after doing nothing but build and dyno testing pipes for our classes of the KT100 Yamaha.
This was a solid 6 months of doing nothing else by trial and error.

(...)

I tested every single 100cc direct drive pipe available on the planet , as the pipe and header was open in our KT100 classes.
The pipe I finally developed was far superior in every part of the powerband, from around 6000 to 16,000 rpm
It had a fully tapered header, with 3 diffuser cones ( the first being the steepest ) and a two part rear cone , the first one had no perforations.
I hand cut and built around 2000 of those things , winning every class title available for over 10 years.

The Yamaha class is redundant now , so there will be pipes lying around doing nothing under benches - I dont have the .dxf pattern files I eventually drew up, long gone on an old Win 7 hard drive.
I am sure the laser guys will still have the files , but getting a sample should be easy.

I dont suppose you had a "name designation" for this pipe you came up with so I can search for it?

I just started looking around at KT100 pipes, and well, damn. There are a LOT of them.

I have been thinking about it for a while, but the itch to slap a KT100 pipe on our Motorized Bicycle engines is getting stronger.

At some point in the not-to-distant future I will begin using EngMod2T to develop this package even further. When that time comes I will have a lot of technical questions about how to design a pipe to achieve this effect.

Until that day comes, I would love to try the pipe you came up with

[wobbly]

The pipe was sold world wide thru my Wobblypipes company name , but mostly in NZ.
The name for it became " Wobbly 3 Cone".
You have to be careful as many classes used centrifugal clutches - a very different animal altogether.
I will ask around the kart guys and see if I can find one hiding in a corner.

[crbbt]

I am guessing there too many other approaches available on a GP bike to use a perforated rear cone?